Extending the flowmeters calibrated range – an expert view

It’s not an uncommon request.  When the enquiry comes in the client thinks the required range will be 1 to 10 but, once installed, it’s clear that he should have stated 2 to 20.  Then, the question is: what do we do?

First: it’s unlikely that the range can be extended beyond the meter maximum rated flow rate.  Some flowmeter principles can cope with excessive flow rates, probably at the expense of pressure drop, but most can’t.

Second: Consider the magnitude of change and the expectation of accuracy. If it’s a change from 1 to 10 to 1 to 11 with a 5% accuracy requirement when the maximum rate is 12 then that’s an easy one – check with the factory on how the range can be changed within the instrumentation but the range extension will be OK. On the other hand, if it’s a ±0.2% meter then it’s unlikely that any range extension will be within that value without a return to the factory for recalibration.

Here’s an example:

The client had purchased an LF03 VFF positive displacement meter for the measurement and control of corrosion inhibitor.  The viscosity was 55cP and, although the meter is capable of 18 litres per hour, had specified an operational range of 0.2 to 2.3 l/h which we calibrated over.

A year later we had a request for a range change – could they up the calibration range to 5.6 l/hr? Of course, yes. Could we provide a statement to this?  See below:

VFF Flowmeter Extended Range Accuracy – 50cP viscosity

The original calibration for meter VFF5112 was up to 2.3 l/hr on 55cP. Litre Meter have analysed the last 17 LF03s calibrated at or around 50cP and can confirm that re-ranging to 5.6 l/hr will have only a minor effect to system accuracy.

VFF Analysis:

It can be seen from the aggregated performance curves above that extending the flow rate above 2.3 l/hr up to 7 l/hr produces little change in the meter linearity. We would suggest that, in the absence of any higher flow rate information above 2.3 litre per hour, that the meter is unlikely to be outside of ±2% of the 2.3 l/hr pulses per litre value up to 7 litres per hour. Increased confidence and accuracy can be obtained by recalibration.

Linearisation:

Litre Meter produce a document LM0688 “Technical Description – Linearisation” that explains the linearization process and the flow rate versus pulses per litre table. Also here.

KEM Küppers flowmeters include the ZHM round gear PD meter

Litre Meter are the exclusive UK distributors for KEM Küppers.  These include the ZHM, SRZ positive displacement, HM turbine and the Tricor coriolis series. Sign up for FlowSight, the Litre Meter newsletter.

KEM ZHM01/3 gear meter
KEM ZHM01/3 gear meter

The ZHM series is highly engineered round gear PD flowmeter suitable for a slew of different applications such as hydraulic oil, automotive paint and chemical dispense measurement.

  • From 0.002 to 1 LPM to 1,000 LPM
  • Ratings to 315, 414, 690 bar and higher
  • Accuracy: ±0.5% of reading or better
  • Repeatability: ±0.05% of reading
  • Can be installed in any orientation
  • Cartridge, compact & aluminium options.

All of these units are manufactured in Germany by Litre Meter’s sister company, KEM Kueppers GmbH.

 

 

Low Flow Calibration – limits

The accuracy of the flowmeter can be determined by the change in the pulses per litre value over a flow rate range selected from the calibration certificate.  This document is also available for download from litremeter.com.

  • Repeatability is better than ±0.1% of reading over the top 99% of range.
  • Accuracy with linearisation is better than ±0.5% of reading.

The minimum flow rate achievable depends on many variables but can be reduced to two factors:

  • the viscosity of the fluid. The higher the viscosity, the lower the low flow rate ability
  • the perfection of the meter dimensions and components
  1. Standard (STD) calibration rates can be achieved 99 times out of a 100. No special selection required
  2. Low Flow (LF) calibration requires matched parts and more calibration time
  3. Ultra Low Flow (ULF) calibration requires the best parts and the most patience by our
    calibration engineers. It is highly unlikely we can provide a batch of ULF meters due to their scarcity.

In particular, for LF03, LF05 and LF15, we can compare the low flow limits both on a linear scale and, secondly, on a logarithmic scale, as well as in a traditional table:

VFF flowmeter LF15 – flow range on various viscosities STD vs. LF vs. ULF
VFF flowmeter LF05 – flow range on various viscosities STD vs. LF vs. ULF
VFF flowmeter LF03 – flow range on various viscosities STD vs. LF vs. ULF

Reverse flow measurement – an expert view

Most flowmeters are setup for forward flow measurement. That is, they have a preferred direction for operation and that is adopted by the manufacturer/designer and advised to the customer.

Some flowmeters are symmetrical in the forward and reverse direction and will work in the reverse direction, too. Some are symmetrical and may not function or function well, due to meter design or principle, in reverse.

Finally, some meters may detect that the flow is in reverse and, better still, measure in either direction to the same accuracy.

We use the term flowmeter generically. When discussing flow direction and measurement we should consider the instrumentation as well as the flow sensor itself.

Distinctions:

Type A – not designed for Reverse flow, may cause damage:
Type B – can accept reverse flow, no detection
Type C – can accept reverse flow, detects direction of flow
Type D – Can accept reverse flow, measures accurately but doesn’t output direction
Type E – Accepts reverse flow and provides flow velocity and direction

B, C, D, E may need special instrumentation to extract the desired information.  The type designation just helps us understand the designs – it isn’t used outside of this article.

Flowmeter element Type
Orifice plate B, C, D or E
Wedge B, C, D or E
Venturi tube B, C, D or E
Flow Nozzle B or C
Pitot tube B
Elbow meter B, C, D or E
Target meter B or C
VA A or E (E with a special meter)
Positive Displacement A, B, C, D or E depends on design and sensing
Turbine A, B, C, D or E depends on design and sensing
Pelton A, B, C, D or E depends on design and sensing
Vortex A or B
Electromagnetic B, C, D or E – most units would be E
Ultrasonic(Doppler) B, C, D or E – most units would be E
Ultrasonic(Time-of-travel) B, C, D or E – most units would be E
Mass Coriolis B, C, D or E – most units would be E
Thermal Mass Insertion B
Thermal Mass Capillary B
Weir A
Flume B

 

Litre Meter flowmeters

Pelton Wheel

The LM range have a jet (apart from the LM220 and LM330). With a jet concentrating the flow onto the rotor, a reverse flow is very inefficient and the rate of rotation is much reduced for the same flow. The 220 and 330 are broadly symmetrical in some models and have different pipe layouts in most versions. These have never been fitted with technology to provide direction.

The same can be said of the larger, orifice plate based, MM meter. The inlet and outlet holes to the pelton wheel chamber are much different in size, so function poorly in reverse. A sole MM was manufactured with two pelton wheels and two sensors facing in different directions. By comparing the magnitude of the signals it was simple to tell which direction was active.

VFF

All VFF (rotary piston positive displacement) meters are perfectly symmetrical in design with rotors able to rotate clockwise or anticlockwise. There are small differences in machining so there are small differences in meter performance forward and reverse. There is a prescribed forward direction (purely for consistency) but the client can select the other direction as forward.

With a standard sensor the output is the same whether the flow is forward or reverse – just a series of pulses. When two sensors are fitted then the direction and magnitude of flow can be determined if the right instrumentation is used.

There are two suitable instruments used by Litre Meter and at least one system used by clients with varying degrees of sophistication. Sometimes two sensors are fitted for redundancy purposes. The instrument monitors one sensor. After a certain time period, if there isn’t a pulse attention is switched to the other sensor. The period is set to be a few seconds longer than the frequency for lowest flow achievable or the clients lowest expected flow.

Litre Meter use two sensor setups both based on reed switch sensing of the magnet in the VFF rotor. Litre Meter are developing a 3-D magnetometer based field sensor that can determine the position of the rotor in the chamber for finer pulse output.

If reed A switches before reed B then direction is forward. If B before A then direction is reverse.

The two reed switch setups are similar in concept but packaged differently. The original reed switch is situated in a sensor hole. When two reeds are used there are two parallel holes generally situated along the radius of gyration of the magnet. They are spaced to produce a clear lead or lag depending on rotor direction. The Fluidwell F115 is designed to interpret the lead/lag to produce a display with directionality.

With the introduction in 2015 of the CIFM versions of the VFF and the Litre Meter FlowPod the sensor was repackaged, with two reeds as standard, in an M8 stainless sensor body. Only one sensor hole is required as the reeds are side by side. The F115 and FlowPod can both interpret the CIFM sensor output.

F115

Fluidwell manufacture a wide range of instrumentation which Litre Meter have used since 2002. The F115 version is specifically designed for directionality. It does not have linearisation.

Description

The flow rate / totalizer model F115-P is a microprocessor driven instrument designed to show the flow rate, the total and the accumulated total. This model is able to detect the flow direction and to show a positive or negative flow rate, the totals for both directions and the cumulative totals.
This product has been designed with a focus on:

  1. ultra-low power consumption to allow long-life battery powered applications (type PB/PC),
  2. intrinsic safety for use in hazardous applications (type XI);
  3. several mounting possibilities with aluminum or GRP enclosures for harsh industrial surroundings;
  4. ability to process all types of flowmeter signals;
  5. transmitting possibilities with analog / pulse and communication outputs.
Flowmeter input

Two sensors with a phase difference of 90 or 270 degrees, can be connected to the F115-P.

Standard outputs
  1. Pulse output to transmit a pulse that represents a totalized quantity as programmed.
  2. Negative / positive pulse output indication – i.e. a flag.
  3. Linear 4-20mA analog output to represent the actual flow rate as programmed. The 4-20mA signal limits can be tuned.

FlowPod

Description

The FlowPod was designed from the outset with the CIFM sensor which is fitted with two closely positioned reed switches in one M8 stainless steel package. They are positioned in the flowmeter to provide a two separate pulses along the path of the spinning rotor. They are fairly close together such that there is a distinct time difference between reed A and B depending on direction.

In most installations the second reed is for redundancy purposes. The FlowPod monitors reed A. After a certain time period, if there isn’t a pulse, attention is switched to reed B. The period is set to be a few seconds longer than the frequency for lowest flow achievable or the lowest expected flow.

For directionality the FlowPod monitors reed A and B and interprets lead and lag to determine flow direction. Within the software forward direction can be set as ‘A before B’ or vice versa. Redundancy is still offered, although, of course, without direction.

Linearisation is standard on the FlowPod. The curve of flow rate versus frequency is similar in forward and reverse.

 

Litre Meter – who are we?

1. Can we start with some background on yourself and a brief history of Litre Meter?

Litre Meter was founded in 1975 by Sandy Wemyss. It originally designed and manufactured a Pelton wheel turbine flowmeter – still on sale today – along with a comprehensive selection of flow instrumentation. After Sandy’s death in 1978 his son, Charles Wemyss joined in 1982 and has been there ever since.

2. What inspired you to establish Litre Meter?

It was spun out of a development company looking at many types of flowmeter technologies for a variety of clients. One particular design was not used by that customer and was the genesis of the LM Pelton Wheel line. The MM soon followed and so a wide range of applications could be solved and Litre Meter Limited was established.

3. Given the massive proliferation of marketing technology, how do you see the Litre Meter market evolving over the next few years?

Litre Meter will always find a market for flowmeters at the margins. We are famous for providing flow solutions that are out of the ordinary, perhaps at low flow, with special materials, high pressures, or with specific pressure drop requirements. Whilst everyone one of our meters can measure the ordinary we will always aim for the niches.

4. Could you tell us about a standout business campaign to supply flow meters?

Our best campaigns come through word-of-mouth. Our two largest orders were as a direct result of providing, successfully, similar systems to original clients. They were impressed and those teams, when the time came, placed orders for similar equipment.

5. One word that best describes how you work.

Dynamically

6. Something you do better than others – the secret of your success? 

We still feel like a small family company. Staff turnover is very low, our longest employee has been here 31 years.

7. You did a thesis on ‘Weight reduction in the car with particular reference to the Wankel rotary engine’ in your Mechanical Engineering (The University of Sheffield). Can you brief the major points on it?

Even back in 1981, we were looking forward. Fuel consumption and efficiency were still drivers in car design but not as much as they are today. The thesis explored weight reduction in all aspects of the car but especially in the engine. There are great challenges to non-metallic materials in the engine bay relating to temperature and pressure. Various materials were explored, and simple components identified for evolving into composite construction. The Wankel engine has since fallen by the wayside, limited in its combustion efficiency with its awkwardly shaped combustion chamber. However, it now finds a role in UAVs where it’s relatively light weight and low vibration characteristics are close to ideal.

8. Litre Meter had received a Queen’s Award for Enterprise, which is an outstanding achievement to be recognized at the highest levels for your success. Can you please elucidate on this?

Litre Meter awarded Queen’s Award for International Trade

Specifically, this was an award for Export, reflecting our global success. Traditionally Litre Meter finds its markets overseas, not only in the USA but also in South East Asia and Europe. For a period of several years, our export orders increased culminating in over 70% in 2015.

9. Can you please address the challenges of low-flow measurement?

The term ‘low flow’ has different values to different people. The VFF can easily measure down to 200 milliliters per hour. For other meters, this will be considered impossibly low. For some, 200 ml per day is achievable but not necessarily with the right combination of other specifics such as viscosity or pressure. For Litre Meter, the challenge is to achieve these low flows in a package suitable for some of the most arduous conditions on the planet. We select appropriate materials, backed up by ISO9001:2015 quality management, with high specification testing procedures, high-pressure ratings and high resistance coatings for longevity.

10. How do Litre Meter’s flow meters meet the demands of your customers and transform their business in the new digital economy?

Litre Meter’s Mission Statement is very simple: Our purpose is to provide flow measurement solutions to enable our customers to control their usage of fluids, materials ultimately to reduce costs and environmental impact. The digital economy has the same focus as most economies: to drive down costs and reduce the ecological footprint. High-performance measurement.

11. What are some of the primary end user drivers and requirements in the market that impact the flow meter productivity, and which are the primary market sectors represented by your major customers?

Flowmeter performance is king in our main market which is Oil & Gas. Clients drove the design of the VFF meter to what it is today. The components have been optimized to be as compact and lightweight as possible whilst retaining the flow performance and instrumentation specification. The adoption of our CIFM philosophy has produced a number of crucial advances in meter and instrument design. CIFM is an abbreviation of Chemical Injection Flow Meter. The first and most obvious is that the meters are more compact. Underneath the skin though there are important advancements in components, reliability, Exd philosophy and instrumentation. Standardisation has been a keyword and Litre Meter expect 80% of future orders to be from a standard (but wide) range rather than 20% with 80% bespoke. Over 800,000 variations are possible and every drawing including GA and lifting is available at the time of inquiry.

12. We understand that Litre Meter will enlarge market sales to drive further expansion. Can you share with us in which geographic and technology areas this will cover and do you anticipate further growth via acquisition?

Litre Meter has a 5-year plan and this involves organic growth within our current markets plus expansion into other markets and acquisition. Our geography is driven by our customers and therefore currently covers many of the oil and gas hotspots and includes multiple areas worldwide where skids are built. Our technology platform is stable but we continuously push the operating boundaries to measure lower flows with or without higher pressures.

About: Charles Wemyss – CEO
Charles Wemyss

Charles Wemyss is the CEO of Litre Meter Limited, the flowmeter experts in supplying Mass, Water, and Chemical Injection Flowmeters worldwide. He holds the Bachelor of Engineering (BEng) degree from The University of Sheffield. His area of expertise lies in Oil & gas flow measurement and especially chemical injection measurement for positive displacement meters and Coriolis mass meters, over the last twenty- five years. Charles Wemyss plays a key role in launching a bespoke range of customisable flowmeters, growing the organization’s reach worldwide.

 

Originally published in PlantAutomation.

 

A history of subsea flowmetering – Litre Meter experts

Here is a short history of deploying flowmeters, of various technologies, subsea
France, 1985:
The first custom design involved the LM pelton wheel. A compact product was required for installation on a submarine.  The pelton wheel is a radial turbine meter type suitable for low viscosity liquids and, in this incarnation, with a stainless steel body rated to 20 bar internal pressure and capable of 0.1 to 28 l/min. Sign up for FlowSight, the Litre Meter newsletter.
Challenger Oceanic, 1992:
Litre Meter contributed a plastic bodied LM pelton wheel.  The internal and external pressures were identical so the plastic housing was quite strong enough with simple hose connections. The electronics, however, was inside a submersible pod where the pressure was 1 bar. To withstand the pressure differential (300bar, 3000m) the sensor wall, thin for good signal acceptance, was constructed in a titanium alloy, previously purposed for the nose cone of a Harrier Jump Jet. The meter was installed on Alvin and used as part of a sampling system in subsea fumaroles, in places such as the Marianas Trench. Particles were collected and the volume of water measurement helped determine the percentage of solids.
North Sea, 1993:
For a simple solution to the flotation and righting of an offshore vessel two VFF 4 flowmeters were designed with subsea totaliser displays.  The VFF4 was the original VFF flowmeter size capable of measurement, at that time, of 4 l/minute as they were fitted with carbon graphite rotors.  A simple reed switch sensor was used.  With a battery powered LCD display mounted behind a clear acrylic window the diver were able to assess the amount of hydraulic fluid being used and thereby the angle of the platform as it slowly rotated from it’s horizontal transport position.  The challenge was to design a compact subsea display against a tight cost restraint.
Heron and Egret, 1996:
As Litre Meter extended it’s capability with increased design freedom internal pressures increased to 690bar. The application required a very low flow of chemical to be measured and the smallest meter at the time, the MF15, was selected, again with a carbon graphite rotor.  The next problem was designing for 300 bar external pressure and provide a loop powered 4-20mA output with a customer specified Tronic connector.  Two sensors were utilised with a well designed electronic board that provided redundancy by continuous monitoring each sensor.  Typically, scale inhibitor was measured at 0.5 to 2.5 litres per hour. A stainless steel housing was constructed incorporating the connector and fully O-ring sealed.  The housing was tested by Sira at 300bar.
VFF MF15 for subsea duty with 4-20mA loop powered output
Subsea visual rate display, 2005 onwards
By upgrading an existing turbine design Litre Meter engineers were able to add a submersible battery powered display for use by an ROV mounted camera.  Starting with a standard ‘topsides’ meter a subsea collar was welded on. Then a stainless steel canister was constructed with a heavy duty acrylic window to withstand the pressure at 800m external depth. A large height LCD rate and total instrument was incorporated.  As the turbine used a magnetic sensor requiring no power, a simple battery powered solution was provided to the client. Flow rates were typically 5 to 90 l/min of water but the design has been incorporated in to different size turbines since.
Turbine flow meter for subsea duty with battery powered LCD totaliser
Galley Tieback, 2006:
Hydraulics measurement was needed, in a very specific envelope. The fluid was Castrol Brayco running at a wide ranging 1 to 50 litres per hour. Internal pressure was up to 414bar and the external pressure was 20bar.  A 4-20mA loop powered electronics was integrated within a cylindrical housing and utilised a Tronic connector.
MF30 VFF flowmeter developed for subsea use, mounted
Thunderhorse, 2006
When hydraulic fluid is measured valve position can be interpreted.  When subsea this is considerably more difficult as the measurement has to be compact and resist high pressures inside and out.  With an innovative manifold base little of the VFF MF30 meter remained. The sensor was standard but all other aspects of the design were optimised to use least space, maintain a pressure rating in and out and incorporate a custom electronics interface. Forward and return lines were monitored with pressures at 760bar and 345bar respectively. External pressures could be up to 300bar. Glass to metal seals for the sensor outputs were utilised together with the redundant sensor design used before.
MF30 VFF flowmeter developed for subsea use, with manifold mounting
Subsea valve, 2006 onwards:
The VFF meter in it’s various sizes were becoming more and more popular for chemical injection particularly at high pressures and low flows.  The MF15 was redesigned as the LF15. This enabled a higher accuracy, lower flow ability and crucially a smaller chamber diameter.  This, in turn, allowed a more compact meter design at the same pressure or, usefully, a higher pressure rating for a specific cap diameter.  The design brief was simple: Could we design a 1,035 bar meter for 90 litres per hour and 345 bar external rating in the same envelope as a can of Guinness? – we’re still working on this! What we did end up with is a fairly compact device (100mm diameter and 125mm long) where we  supply just the chamber and cap and the customer integrates these parts into a subsea module.  The unique chamber design allows pressure independent measurement whether at 1 bar or 1,000 bar.
With an expected lifetime of 30 years all efforts were made to increase the ability of the rotor and chamber.  Extensive testing on various bearings and coatings refined the design, retaining it’s simplicity but greatly improving resistance to high flow shocks and significantly improving low flow performance.  A full 2.5 years continuous running at twice the previous maximum flow demonstrated it’s durability. Careful calibration showed that low flow measurement at the start and the end of the 30 months were identical thereby proving that 90 litres per hour was the new maximum with that design and coating.
Hundreds are in service subsea around the world. The meter is used to provide feedback on the flow rate of chemical.  The pulse output (with a redundant sensor) requires no power and the meter has excellent particle size acceptance.
North Sea, 2012
The VFF4, when specified with a PVD coated Nitronic rotor and chamber, can measure up to 8 litres per minute. With a pressure rating of 300 bar (external and internal) a compact 3 wire 4-20mA meter was designed with 1/2″NPT connections. Hydraulics footprinting was then possible subsea. A Seacon Micro Wet-Con 4 pin connector was utilised with dual reed switches for redundancy. Field not known.
VFF4 VFF flowmeter developed for high pressure subsea use on hydraulics
North Sea, 2013
Apart from the Pelton Wheel, turbine and VFF rotary piston flowmeter designs there are other meter types that an provide a significant design benefit to subsea modification.  The ZHM gear meter offers a wide range and high pulse output rate. A SubConn subsea connector was incorporated and a high pressure 690bar design modified for 0.3 to 6 litres per minute.  The application was again chemical injection and 409 bar was the external rating.
ZHM positive displacement gear meter for subsea use
North Sea, 2015 onwards
When a clean sheet of paper is used then a streamlined solution can result.  The subsea turbine flow meter developed for hydraulics measurement from 3 to 33 l/min (HM009) is typical of this approach.  The turbine blades are standard whilst the sensor and Canbus electronics board are encapsulated by welding into the integral stainless steel housing. The customer specified subsea connector provides easy integration electronically. Internally, the meter can withstand 1,035 bar (tested to 1550 bar, 22,500 psi) and externally the specification allows for 300 bar.
HM turbine flowmeter for subsea use in two common configurations

The drive to save weight from the flowmeter experts

There was a very interesting article about Shell in last months Fortune. It explains how Shell were approaching the next decade and building 4 different scenarios of oil price and availability and their investment reactions to those.  I’ve included the link at the end of this article.  Sign up for FlowSight, the Litre Meter newsletter.

It also detailed the effect on their platform design when the oil price suddenly reduced.  The most striking image is of two platforms designed in different eras.  Appomattox will soon be active in the Gulf of Mexico so would have been designed in 2013 with a Final Investment Decision (FID) in July 2015.  Vito was designed in early 2014, when oil was at $100.  By 2015, when the price had slipped, Vito was looking bulky. In early 2016 it was decided to slim it down to be profitable at $40.

A radical design overhaul slashed the top weight over the next year, from 40,000 tons to 8,900 tons. The shell team right-sized Vito, for a world of ‘peaking oil demand’.

The similarities with Litre Meter developing the FlowPod instrument seem tenuous – and we don’t have meters on either platform, which is unusual. But, the FlowPod was developed over 12 months from the original FPod Exd flow display.  The prime motive was size reduction and improved performance.  With that, and unclear at the start of the process, was a beneficial reduction in meter size and weight into the bargain.

The original purpose of the redesign was two-fold: firstly, to reduce the size of the instrument enclosure – mounting them remotely from the meter produced some unexpected challenges for our clients from time-to-time; secondly, to replace on obsolescent internal electronic component. It transpired that the new component was even bigger than the old one so a thorough instrumentation re-design was discussed, eliminating the large isolator and taking the benefit of a reduced enclosure size. This wasn’t an easy task and soon we were down the road of a ground-up redesign encompassing the traditional sensor which now had to be part of an Exd system.

With a new sensor every cap was also redesigned and there was a knock-on effect to the VFF body. We coupled this refinement with a desire to provide our customers with more standard meters ‘off-the-shelf’ shifting our traditional 80% bespoke/20% standard to 80/20 standard design vs custom, offering better availability.
When the dust had settled the new VFF, although having the same flow rate ranges, had a standardised Pressure Balanced Chamber design with a redesigned sensor, a compact display dubbed FlowPod certified Exd and over 114,000 different standard designs.
Litre Meter have analysed our customer’s requirements which has resulted in the various meter sizes being available in most appropriate connection sizes and styles. For example:

VFF flowmeter sizes and selected threaded connections

The sheer range of choice, which also encompasses body & cap materials, seal materials and instrumentation has effectively designed out the need for customization. Drawings are available for over 114,000 different VFF configurations – including

  • General Arrangement,
  • Parts List and
  • Lifting Diagrams, together with a
  • STEP file, allowing instant modelling.

Lead times are reduced, enabling customers to bring their projects to fruition earlier. There is a dedicated program that enables Litre Meter and their distributors to select and configure flowmeter solutions quicker and more accurately.

All the VFF range are designed around the Pressure Balance Chamber.  Cap and body sizes have been rationalised and minimum pressure ratings increased. For example, the most popular 1/2″NPT female body is now rated to 530 bar rather than 414 bar previously, increasing it’s usability just by varying bolting material.

Here are two identically ranged meters with 1/2″NPT female connections:

The older FPod on the left dwarfs the more compact FlowPod and rationalised body and cap.

Instrument weight plummets from 5 kg to 1.2 kg and display enclosure diameter reduces from 6.5 to 3.5 inches.  Stainless steel is now standard.   Here’s a quick comparison:

FlowPod benefits

We think this clearly demonstrates Litre Meter’s commitment to continuous improvement, matching Shell’s dramatic reductions on the Vito project. Fortune article.

 Sign up for FlowSight, the Litre Meter newsletter.

Upgrading your FPod to FlowPod – a simple guide

Litre Meter ships biggest ever VFF flowmeter!

At the end of 2017 there was more activity than usual at Litre Meter as some of the largest VFF meters were gathered together for assembly and calibration. A complex project involving 7 different VFF sizes including the largest ever VFF was nearing completion.  The V400 weighs a hefty 600kg and measures a suitably massive flow rate of 330 l/min and is designed for 19m³/h normal flow. The liquid is lean MEG (monoethylene glycol) which is used as an antifreeze in offshore production platforms, amongst others.  The VFF series normally tops out at 2″ connections so 6″ was quite an engineering and logistical task.  Sign up for FlowSight, the Litre Meter newsletter.

The pressure rating of 260+bar and the customer’s 6″ line dictated the use of 6″ANSI2500 connections and a 316L body.  On top of this is the standard chemical injection instrument, the FlowPod, which provides a clear display, 2 wire operation and HART all in a 316 Exd enclosure.

6" VFF V400 with 6" ANSI2500 flanges for measurement of Lean MEG, ready for final testing.
6″ VFF V400 with 6″ ANSI2500 flanges for measurement of Lean MEG, ready for final testing.
6" VFF V400 with 6" ANSI2500 flanges for measurement of Lean MEG.
6″ VFF V400 with 6″ ANSI2500 flanges for measurement of Lean MEG.

Other meter sizes included a V270 for methanol measurement, several HF60s also for methanol and an LF03 measuring just 0.5 litres per hour of antifoam (40,000 to one range from the smallest to the largest, in case you’re wondering). They all use the VFF rotary piston technology with pressure balanced chambers to ensure accurate measurement independent of operating pressure.  The range of displacements is from 0.4ml up to around 860 ml.

Connection ratings were equally disparate, ranging from ANSI150 to API6A, matching pressure ratings from 16.5 to 690bar.

Litre Meter CEO Charles Wemyss said: “Many new technologies provide superb measurement at various pressures, flow rates and operating conditions but lack the ability to provide measurement when the going gets tough, the pressures get high and the rates get low, or in this case when the rate gets high.  For super low flows at challenging pressures, or when pulsing flow can’t be tamed, the VFF comes out on top.

“Hydrate, scale and corrosion prevention strategies provide protection during normal operation, start-up and shutdown.

“Litre Meter’s VFF flowmeter is ideally suited for use in the oil and gas industry and in particular for low flow / high pressure applications.

“Years of experience in chemical injection applications onshore and offshore have confirmed the instrument’s capability to reliably measure fluids under extreme conditions of both flow and pressure.”

What’s in a typical flow meter datasheet?

First, let’s have a look at what might land on your desk.  Later, we’ll review it line by line. Sign up for FlowSight, the Litre Meter newsletter.

A typical datasheet relating to a flowmeter is given as below – this one is based on a NORSOK format:

Flowmeter datasheet – Norsok layout.

This one is for the same meter but based on an ISA format (a version used by Litre Meter which uses S20.25 as it’s base):

Flowmeter datasheet – ISA layout, describing the same flowmeter.

Norsok:

This is an approximate layout, typified by NORSOK.

1 General

1.01 Type – a description of the flowmeter, by trade name and basic principle

1.02 Manufacturer – manufacturer’s name.

1.03 Design Temperature Limits – maximum and minimum design temperatures in suitable temperature units (°C)

1.04 Design Pressure Limits – maximum and minimum design pressures in suitable pressure units (bar gauge)

1.05 Estimated Pressure Loss – pressure drop at a specific flow such as maximum in suitable units (millibar)

1.07 Face to face dimension – complete assembly length in millimetres, with a tolerance

1.08 Mounting – type of mounting, in this case, In-Line but could be insertion, clamp-on etc.

1.09 Weight – dry, without fluids – in kilogrammes

2 Instrument Characteristics

2.01 Calibrated Range – flow rate range that the unit will be calibrated over – and units

2.02 Characteristic – an appreciation that not all meters are necessarily linear – some are non-linear such as orifice plates where the pressure drop is related to the flow rate by a square law, in this case linear – and linearised.

2.03 Meter factor – an estimated value of the number of pulses per litre – or other volume or mass unit

2.04 Accuracy – with percentage bounds and either proportional to the actual reading or FSD (Full Scale Deflection)

2.05 Linearity – with percentage bounds and either proportional to the actual reading or FSD (Full Scale Deflection)

2.06 Repeatability – with percentage bounds and proportional to the actual reading

2.07 Max Range limit – not necessarily the same as the maximum calibrated flow – describes the capabilities of the flowmeter

3 Meter Body

3.01 Nominal Size – normally relating the meter body size to the pipe size

3.02 Manufacturer model number – to precisely define the scope of supply

3.03 Process connection size and type – Size and flange or thread type, for example

3.04 Pressure rating – the rating of the flowmeter body in comparable units to 1.04

3.05 Face to face dimension – will match 1.07 in most cases

3.06 Body inner diameter – where appropriate

3.07 Sour service specification – nominated when appropriate – ISO or NACE in this example

3.08 Material, body – A specification for the material of the flowmeter body i.e. the main part of the meter

3.09 Material, Raised –

3.10 Protective coating/color

3.11 Other

4 INTERNAL

4.01 Type – such as rotor and chamber or another description of the flowmeter internals and principle

4.02 Material, shaft – if any

4.03 Material, support – if any – this might refer to a turbine flowmeter part

4.04 Material, rotor

4.05 Material, bearing – if any, may include material and type

4.06 Material, Seal – not just the materials but may include seal type

4.07 Material, pick-up – i.e. sensor material, wetted, or not

4.08 No of pick-ups

4.09 Other

5 FLOW STRAIGHTENER

5.01 Type

5.02 Material

5.03 Connection

5.04 Other

6 METER TUBE

6.01 Material

6.02 Connection up/downstr.

6.03 Up/downstream length

6.04 Tube inner diameter

6.05 Other

7 STRAINER

7.01 Type

7.02 Body/mesh material

7.03 Connection

7.04 Other

8              TRANSMITTER

8.01        Manufacturer model no

8.02        Mounting

8.03        Max distance meter/trans

8.04        Cable connection

8.05        Cable entry

8.06        Dimension

8.07        Material

8.08        Enclosure protection

8.09        Ex. classification

8.10        Protective coating

8.11        Indicator

8.12        Tamb

8.13        Totalizer

8.14        Output signal (note 9.02)

8.15        Communication

8.16        Recommended loop voltage

8.17        Transmitter loop voltage drop

8.18        Max loop current (fault condition)

8.19        Other – in this case describes more of the hazardous area ratings and standards – CSA, IECEx and ATEX

Measuring Sodium Hypochlorite in Hazardous Areas

Sodium Hypochlorite

Sodium hypochlorite is a green/yellow liquid with the characteristic smell of chlorine. It was first used as a bleaching agent and was then discovered to be effective in controlling wound infections. Subsequently, it is most commonly known as household bleach. The solution exhibits broad spectrum anti‐microbial activity and is widely used in healthcare facilities in a variety of settings. It is usually diluted in water depending on its intended use. Sign up for FlowSight, the Litre Meter newsletter.
In the chemical injection arena, it is common to inject sodium hypochlorite into sea water. Sea water can contain dissolved oxygen, bacteria and solids. These can affect an oil reservoirs life. Hypo is used as a bactericide whilst filters take care of the solids. Hypo is aggressive before it is diluted in the sea water and therefore requires some specialized devices in terms of wetted materials. Litre Meter have been manufacturing flowmeters since 1975.
We’ve always concentrated on the harder margins of metering typically at low flows and/or at high pressure. For this application note Litre Meter illustrate two solutions to this application based on <20 % solution. Download brochure.

Sodium Hypochlorite Flowmeters ‐ Applications and Rates ‐ VFF

The VFF has successfully metered fluids such as oils, hydraulic fluids, corrosion / wax / demulsifier / pour point dispenser /scale / hydrate inhibitors, biocides, oxygen scavengers, etc. for over 30 years. Meter bodies are produced in a variety of high grade materials which offer good chemical and environmental resistance. For sodium hypochlorite, Litre Meter recommend Titanium for the body and chamber with carbon graphite for the actual rotary piston. This ensures maximum compatibility, life and accurate response. The magnet is either encapsulated in titanium or PTFE.

VFF Flowmeter Sizes and Connections.

Applications for flow‐rates as low as 0.5 litres per hour have been supplied. Normal minimum flow rates depend on operating viscosity. In this case, viscosity is assumed to be between 1 and 2.5cP. Using the smallest VFF with carbon graphite rotor (LF15) and calibrating on water, which has a lower viscosity than NaOCl, a range of 0.5 to 40 L/hr is achieved. The meters range in size from the smallest titanium body, LF15 – 40 L/hr, to the largest V270 ‐ 270 L/min max. Higher flow‐rate meters are available to special order. The table at the end of this article assists in the selection of the best technology.

Sodium Hypochlorite Flowmeters ‐ Applications and Rates ‐ Pelton Wheel

Litre Meter started manufacturing the Pelton Wheel turbine in 1975. These usually had some stainless steel components together with a plastic rotor, elastomer seals and sapphire bearings. All plastic versions soon followed, including all Polypropylene, all PFA, all PVC and all PVDF. The other wetted parts are still sapphire with a suitable elastomer such as FKM or FFKM for the single O ring seal. The normal specification for Sodium Hypochlorite compatible Pelton Wheel flow meters is now PVC for the main body and cap with PVC or titanium internals, sapphire bearings, an FKM O‐ring and PFA rotor.

Pelton Wheel Flowmeter for Sodium Hypochlorite

The Pelton Wheel is an economical device with low pressure ratings and needs to have relatively steady state non‐pulsing flows.
The table at the end of this article assists in the selection of the best technology.

Compatible Materials

Due to the nature of Sodium Hypochlorite only a select group of tested materials is recommended by Litre Meter. We tailor our meters using three key materials, developed over 30 years of measuring Sodium Hypochlorite:

PVC, Hastelloy and titanium
The PVC design can be used up to 15 bar pressure maximum. Hastelloy (UNS N10276) up to 1035 bar. For the ultimate select titanium (UNS R50400) designed for 1380 bar (20,000psi, 20 ksi)

These material make up the body and the cap of the meter. The seals between the meter body and cap are normally FKM. Other seal materials include FFKM and PTFE. All seals within the meter are fully compatible with Sodium Hypochlorite.

Flow ranges and references

All Litre Meter manufactured flowmeters are custom calibrated across the customer specified minimum to maximum flow conditions and working viscosity. The minimum flow rates achievable are dependent on fluid viscosity. With sodium hypochlorite, in most normal concentrations, water is used as the calibration medium as this proves to be the best for accurate calibration representation. The table below assists in selecting which technology is preferred.
Normal engineering materials like 304 and 316 stainless steel, aluminium, brass and steel are unsuitable due to the aggressive nature of the free chlorine in the Sodium Hypochlorite. Plastics such as PVC and PTFE are suitable together with Hastelloy C and purer grades of Titanium.

Comparison table:
Table showing selection criteria for Sodium Hypochlorite meters in two different flow technologies.

Why should I measure Scale Inhibitor (and how)?

Money, money, money – or, as we now call it, Flow Assurance, coupled with a low flow meter

Allowing scale to build up on the inside of the pipeline may seem fairly inconsequential. However, when the amount of scale is considered, (and referencing the image) it is immediately obvious that the expensive crude will slow down and pumping costs will soar. Sign up for FlowSight, the Litre Meter newsletter.
Scaling reduces the area of a pipe if scale inhibitor is not used
Scaling reduces the area of a pipe if scale inhibitor is not used – Stock image
Chemists will analyse the crude oil as it comes out of the well, sometimes years before production starts. From geotechnical surveys other technicians will determine the rate of oil output through the anticipated life of the field.  With this data the chemist will recommend what the concentration of the scale inhibitor should be.  The pressure of the well will determine at which pressure the inhibitor needs to be injected at. Day to day the temperature will vary according to the seasons, the weather and location of the measurement.
The analysis of the crude, unrefined oil will tell the chemist whether the pipe will start to scale up as a result of pumping the oil through a pipe to the ship or refinery.  Certain chemicals are then formulated to optimise and negate the scale.  There will be compromises between concentration of the fluid, application flow rates and storage availability.  If the concentration can be increased so that the tanks only need filling up once per month then that is preferred to once per fortnight. Inevitably this means that the flow rate is lower, and probably, the viscosity increases. Measurement range will also vary through the life of the field. It may start slow, then plateau a few years later and then tail off as the field winds down.  Additionally to this, the consistency of the unrefined oil will probably change from start to finish.  All of these variables can lead to a range of viscosities and a range of flow rates.
In summary, selection of the meter philosophy and specification is critical to successful measurement of scale inhibitor and future condition of the oil pipeline.

The VFF rotary piston flowmeter has been used for many years to measure scale inhibitor at a variety of flow rates, pressures and viscosities.

VFF flowmeter for chemical injection service, with FlowPod display

Flowmeters for Sodium Hypochlorite – Hazardous Area, too

Sodium hypochlorite

Sodium hypochlorite is a green/yellow liquid with the characteristic smell of chlorine. It was first used as a bleaching agent and was then discovered to be effective in controlling wound infections. Subsequently, it is most commonly known as household bleach. The solution exhibits broad spectrum anti‐microbial activity and is widely used in healthcare facilities in a variety of settings. It is usually diluted in water depending on its intended use.
In the chemical injection arena, it is common to inject sodium hypochlorite into sea water. Sea water can contain dissolved oxygen, bacteria and solids. These can affect an oil reservoirs life. Hypo is used as a bactericide whilst filters take care of the solids. Hypo is aggressive before it is diluted in the sea water and therefore requires some specialized devices in terms of wetted materials.
Litre Meter have been manufacturing flowmeters since 1975.
We’ve always concentrated on the harder margins of metering typically at low flows and/or at high pressure. For this application note Litre Meter illustrate two solutions to this application based on <20 % solution.

Sodium Hypochlorite Flowmeters ‐ Applications and Rates ‐ VFF

The VFF has successfully metered fluids such as oils, hydraulic fluids, corrosion / wax / demulsifier / pour point dispenser /scale / hydrate inhibitors, biocides, oxygen scavengers, etc. for over 30 years. Meter bodies are produced in a variety of high grade materials which offer good chemical and environmental resistance. For sodium hypochlorite, Litre Meter recommend Titanium for the body and chamber with carbon graphite for the actual rotary piston. This ensures maximum compatibility, life and accurate response. The magnet is either encapsulated in titanium or PTFE.
Applications for flow‐rates as low as 0.5 litres per hour have been supplied. Normal minimum flow rates depend on operating viscosity. In this case, viscosity is assumed to be between 1 and 2.5cP. Using the smallest VFF with carbon graphite rotor (LF15) and calibrating on water, which has a lower viscosity than NaOCl, a range of 0.5 to 40 L/hr is achieved.
The meters range in size from the smallest titanium body, LF15 – 40 L/hr, to the largest V270 ‐ 270 L/min max. Higher flow‐rate meters are available to special order. The table on the last page assists in the selection of the best technology.

Sodium Hypochlorite Flowmeters ‐ Applications and Rates ‐ Pelton Wheel

Pelton Wheel Flowmeter for Sodium Hypochlorite

Litre Meter started manufacturing the Pelton Wheel turbine in 1975. These usually had some stainless steel components together with a plastic rotor, elastomer seals and sapphire bearings. All plastic versions soon followed, including all Polypropylene, all PFA, all PVC and all PVDF. The other wetted parts are still sapphire with a suitable elastomer such as FKM or FFKM for the single O ring seal.
The normal specification for Sodium Hypochlorite compatible Pelton Wheel flow meters is now PVC for the main body and cap with PVC or titanium internals, sapphire bearings, an FKM O‐ring and PFA rotor.
The Pelton Wheel is an economical device with low pressure ratings and needs to have relatively steady state non‐pulsing flows.
The table on the last page assists in the selection of the best technology.

Compatible Materials

Due to the nature of Sodium Hypochlorite only a select group of tested materials is recommended by Litre Meter. We tailor our meters using three key materials, developed over 30 years of measuring Sodium Hypochlorite:

These material make up the body and the cap of the meter. The seals between the meter body and cap are normally FKM. Other seal materials include FFKM and PTFE. All Seals within the meter are fully compatible with Sodium Hypochlorite.

Flow ranges and references

All Litre Meter manufactured flowmeters are custom calibrated across the customer specified minimum to maximum flow conditions and working viscosity. The minimum flow rates achievable are dependent on fluid viscosity. With sodium hypochlorite, in most normal concentrations, water is used as the calibration medium as this proves to be the best for accurate calibration representation. The table below assists in selecting which technology is preferred.
Normal engineering materials like 304 and 316 stainless steel, aluminium, brass and steel are unsuitable due to the aggressive nature of the free chlorine in the Sodium Hypochlorite. Plastics such as PVC and PTFE are suitable together with Hastelloy C and purer grades of Titanium.

Comparison Table:

Table showing selection criteria for Sodium Hypochlorite meters in two different flow technologies.

Litre Meter can provide optimum solutions for a wide range of flow rates of Sodium Hypochlorite. Using a variety of materials, a flowmeter can be constructed that handles any specific concentration of NaOCl and provide a display and/or output for measurement and control. For references etc please download our brochure.

What’s the best chemical injection flow meter? An expert explains:

Litre Meter VFF rotary piston positive displacement flowmeters have proven to be the foremost solution for chemical injection flow metering applications. They are able to handle the wide range of flows at pressures from a few bar up to 10,000 and 20,000 psi (690, 1,380 bar) and higher. The FlowPod instrument has been developed after feedback from many clients in the chemical injection arena, focussing on ease-of-use, compactness and functionality. Sign up for FlowSight, the Litre Meter newsletter.

In many chemical injection applications the VFF is the sole answer because of it’s unique capabilities at the ‘margins of measurement’. This might include super low flow rates and low viscosity or awkward chemical compatibility and material requirements. The standard range of VFF meters, available from 2015, was also designed in response to user feedback. It provides a number of bespoke chemical injection features that are no longer specials.  Since then, 80% of meters supplied have been from stock designs as opposed to 20% before.  This also means that drawings are immediately available including STEP files, lifting diagrams and parts lists.

Since 2013, as standard, all VFF meters have a URL given on the name plate and a QR code that links to a website with specific calibration certificates, manuals, hydrostatic test certificates and material certificates.

  • VFF positive displacement meters can measure accurately at any pressure and with a pulsing pump.  The measurement accuracy is unaffected by working pressure or change due to the unique construction.
  • VFF positive displacement meters can measure a range of chemicals at extreme low flows such as less than 100 ml per hour and at low or high viscosity.  Particle size limits are a generous 40 or 100 microns.
  • VFF positive displacement meters can measure a variety of chemicals requiring alternatives to 316L.  Titanium rotors are standard with titanium, super duplex and Hastelloy options for body and cap.
  • VFF positive displacement meters can be constructed using exotic materials and/or exotic material specifications. Litre Meter have developed their own material specification for 316L, duplex and super duplex. We have built meters from highly specified materials with extensive testing regimes to tight delivery times.

Call us now with your chemical injection metering requirements for probably the best flowmeter.  (it’s why LITRE METER RECEIVES A QUEEN’S AWARD FOR ENTERPRISE)

VFF Flowmeter Sizes and Connections.

Electronic documentation – leading the way

Litre Meter now provides all documentation electronically for it’s manufactured flowmeters.  That’s not just a manual emailed to the client, either.  Each meter has a product label and includes a QR code and URL. At the website location there’s a minimum of a calibration certificate, quick start instructions and a full Installation and Operation Manual (IOM). Most will also have material certificates, hydrostatic test certificates, wiring diagrams and a function test cert. Sign up for FlowSight, the Litre Meter newsletter.

The product label is comprehensive, providing all calibration data.  The URL provides everything else the installation engineer might need. Using a smart phone and scanning the QR code is even more convenient.

Charles Wemyss, CEO of Litre Meter, says:”If a client needs any information emailed we just send the link. For larger projects with a number of flowmeters and larger documentation packages we include a single zip file for ease of downloading.  We’ve been providing this as part of our service since 2013 and our customers love it! This is a project dear to our hearts that cuts waste right down and provides our clients with a very quick and easy access point.  As far as we know, there is no other instrumentation company providing this level of data direct to their clients.”.
Litre Meter QR code allows remote access to documentation

KEM Küppers Subsea flowmeter solutions

Litre Meter are now the exclusive distributors for KEM Küppers. In addition to their standard ranges of positive displacement and turbine flowmeters KEM offer a customisation service that encompasses the necessary modifications and approvals for subsea service. Both the ZHM gear meter and HM turbine meter have versions that are designed to rigorous subsea specifications. The subsea versions have encapsulated electronics, a welded stainless steel cover and an FEA designed housing that remains stable at high external pressures. All of these are manufactured by Litre Meter’s sister company KEM Küppers in Germany. Sign up for FlowSight, the Litre Meter newsletter.

Two Subsea Applications:

Production – Blow Out Preventers (BOPs) are large subsea control valves used to prevent uncontrolled release of pressure or flow of fluid during well drilling operations or production. The hydraulic valve can be remotely controlled to close or open to avoid a “blow out”, and are typically installed multiple times in stacks as a precaution. Maintenance of BOPs and regularly testing is a very high priority for both the oil company and drilling rigs. Subsea turbine flow meters are used on the hydraulic fluid to monitor the valves to ensure that they are functioning correctly when needed.

ZHM: Positive displacement gear meter with wide flow range. Image shows subsea cover and connector.

Subsea chemical injection – As oil is pumped from the subsea well, many chemicals and additives are injected to ensure maximum productivity. In many cases, oil companies install subsea flow meters to measure these chemicals at the point of entry, which is often far below the surface, instead of topside where the liquid has to travel a great distance before entering the flow stream. Often this is more cost effective. Subsea Positive Displacement (PD) flow meters are used to inject additives such as mono ethylene glycol (MEG), methanol, and low-dose inhibitors (LDIs).

HM: Axial turbine flowmeter, redesigned for subsea duty, with subsea electrical connectors.

Call Litre Meter now for further information. 01296 670200. www.litremeter.com

What is linearisation – what is it and why do I need it? An expert explains:

Linearisation is a process that enhances the accuracy of any repeatable flowmeter. Sign up for FlowSight, the Litre Meter newsletter.

This article will show the amount of accuracy increase that can be expected from optimising linearisation points in terms of number and position.

A standard calibration of a VFF flowmeter will involve 10 calibration points. These are always spread out along the customer’s operating flow range. They will be distributed in favour of lower flow rates – where changes in raw meter accuracy are higher.

Below is an example of a flowmeter calibration curve. The results of a calibration are a table of flow rates and the corresponding pulses per litre.  In an ideal world, there would be a hundred or a thousand such points so that the complete curve could be plotted and for any given flow rate the pulses per litre would be known. In practice, there are usually 10 to 20, distributed as shown.

A plot of flow rate against frequency would be an apparently straight line relationship.  The angle of the straight line would be the ‘meter factor’ or the average number of pulses per litre.

Flowmeter linearisation. Flow rate versus frequency.

Flowmeter linearisation. Flow rate versus frequency.

To make this more visual, it’s common to plot the flow rate against the ‘pulses per litre’. This emphasises the changes as the flow rate increases.

Flowmeter meter factor or 'k' factor plotted against flow rate.
Flowmeter meter factor or ‘k’ factor plotted against flow rate.

Better still is a plot of flow rate against accuracy using the ‘meter factor’ as a zero.  The biggest positive excursion defines the positive error and the biggest negative excursion is the negative error.

Flowmeter linearity expressed as percentage error versus flow rate
Flowmeter linearity expressed as percentage error versus flow rate.

If the flowmeter is repeatable then we can use a technique called linearization.  In other words, if the curve (i.e. the relationship between flow rate and pulses per litre) is the same the next time around, then the flow rate can be calculated from the frequency output using the specific pulses per litre value rather than an average pulses per litre value.  If the flow rate is identical to one of the original calibration points there is no adjustment. At other flow rates a calculation is required.  In between the points most linearization systems use simple linear interpolation. For example, if the flow rate is halfway between two original calibration points then an average of the pulses per litre for those two points is used.

The error is represented here by the length of the red arrow.

Linearisation is normally linear interpolation between two points. The difference between the brown linear interpolation and the blue real value is the subsequent error.
Linearisation is normally linear interpolation between two points. The difference between the (brown) linear interpolation and the (blue) real value is the subsequent error.

Now the measurement error is no longer compared to a single meter factor from min to max but a linearity curve built into the meter.

By carefully selecting the calibration flow rates along the range the remaining error can be minimised.  In the example below, the actual curve (in blue) is shown plus the linear approximation (in brown).

The meter character and the linear interpolation between linearisation points for the whole range of the meter
The meter character and the linear interpolation between linearisation points for the whole range of the meter.

Magnified in scale:Here is how this linearization improves the accuracy, on the same scale:

Results of the linearisation.
Results of the linearisation.

Magnified in scale:

The result of linearisation. Now between +0.19% and -0.28%.
The result of linearisation. Now between +0.19% and -0.28%.

And here is the result, if there are 4 calibration points at the lowest flow rates rather than 2.

Concentrating the calibration and linearisation points at low flows, in this example, has a further impressive improvement to overall linearity.
Concentrating the calibration and linearisation points at low flows, in this example, has a further impressive improvement to overall linearity.

As a result of linearization, the overall error has been reduced from max error: 1.19%, min error: -3.98% to max error: +0.19%, min error: -0.28% representing an 11x improvement.  Selecting the calibration points carefully improves this further.  Every calibration point has a cost so there are diminishing returns. If the repeatability is +/- 0.25% then 10 points overall are normally enough.

If enough calibration time is available and the repeatability of the system is considerable then more points can be selected for the linearisation table.  In this extension of the example above 21 points are used rather than just 10.  Arranged carefully throughout the flow range, the net effect is to reduce the max/min to 0.08%, a 64x improvement over the non-linearised version.  If the repeatability of the system was ±0.1% then no more points are required.The flowmeter response (blue) is almost perfectly matched by 21 carefully selected calibration points (brown).

The flowmeter response (blue) is almost perfectly matched by 21 carefully selected calibration points (brown).
The flowmeter response (blue) is almost perfectly matched by 21 carefully selected calibration points (brown).
The final analysis. Total non-linearity reduced from 5.17% to 0.08%.
The final analysis. Total non-linearity reduced from 5.17% to 0.08%.

This article shows that linearisation with a flowmeter instrument can significantly improve the linearity of the flowmeter system.  In this example, if the meter is repeatable, then 6 to 60 times improvements are possible.

Next article: Is there good and bad linearisation?

Sign up for FlowSight, the Litre Meter newsletter.

VFF FilterPro filter protects VFF meters from contamination

Litre Meter introduces the VFF FilterPro Filter that maximizes the efficiency of its flow meters by eliminating contaminants that cause reduced flow, damage to internal construction as well as a blockage.  As 96% of flow meter failures are associated with contamination issues, the FilterPro protects flow measurement instrumentation, assuring optimal flow in liquid injection, batch processing, and lubrication systems. Sign up for FlowSight, the Litre Meter newsletter.

VFF FilterPro - a filter to match your VFF Flowmeter
VFF FilterPro – a filter to match your VFF Flowmeter

Featuring a four-layer wire woven mesh filtration design, the FilterPro uses a proven surface filtration principle that filters elements from 10 to 100 microns (depending upon unit option) by trapping particulates between its layers.  Available in three key filter sizes, the FilterPro pairs perfectly with the company’s positive displacement, rotary piston, and turbine flow meters with connection sizes from ¼” up to 9/16” in multiple thread types.   Offered in 316 stainless steel or exotic materials, the FilterPro is available in the same materials as VFF flow measurement instrumentation to avoid compatibility and performance variances.

Units are suitable for use in low and high viscosity liquids at pressures up to 20,000 psi (1,380 bar) and can withstand a pressure drop of 870 psi (60 bar) with a burst pressure drop of 2,175 psi (150 bar).  Simple to install, the FilterPro is easily cleaned by unscrewing 8 bolts and replacing the filter insert.  The company is currently developing larger filters to accommodate larger meters while incorporating a filter maintenance indicator and greater resistance to burst pressure. Sign up for FlowSight, the Litre Meter newsletter.

VFF FilterPro pressure drops for viscosity and flow rate values - 30 micron
VFF FilterPro pressure drops for viscosity and flow rate values – 30 micron
Exploded view of VFF FilterPro with annotation
Exploded view of VFF FilterPro showing simplicity of design and disassembly
VFF FilterPro with filter cartridges
VFF FilterPro with filter cartridges, available in 10, 30 and 100 micron sizes
VFF FilterPro Dimensions - threaded body
VFF FilterPro Dimensions – threaded body – NPT or Autoclave Medium Pressure. Other connections on request.
VFF FilterPro typical materials and pressure ratings
VFF FilterPro typical materials and pressure ratings

 

VFF FilterPro typical connections and pressure ratings
VFF FilterPro typical connections and pressure ratings

20k meters – brochure available

Litre Meter have been making meters for higher pressures for over 3 decades. Our first 1,380bar unit was shipped in 1997.  We’ve now produced a brochure to cover these ratings.

Download the 20k VFF datasheet
20,000 psi rated VFF flowmeters – brochure

Litre Meter have been manufacturing flowmeters since 1975. We’ve always concentrated on the harder margins of metering typically at low flows and/or at high pressure. The VFF range has many uses in the oil and gas industry and meets the high specifications required. Outside of oil and gas we have manufactured these to 2,500 bar. We have recently noticed a trend towards 20,000 psi ratings and this brochure is in response to that.

Since 1997 Litre Meter has made numerous VFF meters for 1,380 bar in Oil and Gas applications and a reference list is provided at the end of this article.
The same design can be used on 22.5ksi (1,550 bar) with little modification.
The breakthrough in our design philosophy came in 2005 when we separated the measurement of the fluid from the pressure containment. We designed a measurement chamber that floats in the pressure vessel. This ensures accurate, pressure independent flow metering from 10 psi to 20,000 psi. The Pressure Balance Chamber is explained below.

Key Features

  • Rotary Piston/ Oscillating Piston type flow meter with a single moving part provides robust and low maintenance technology.
  • Suitable for low & high viscosity liquids at pressure ratings up to 4,000 bar (60,000 psi). 20,000 psi designs as standard.
  • Available materials of construction: 316L (UNS S31603), Duplex F51(UNS S31803), Super Duplex F53(UNS S32750)/F55(UNS S32760), 6Mo F44(UNS S31254), Hastelloy (UNS N10276) & Titanium (UNS R56400).
  • Connections: Autoclave, Grayloc Hubs, Galperti Hubs, Techlok hubs. More on request.
  • Communications: 4‐20mA HART, Pulse, MODBUS, Foundation Fieldbus, dependent on electronics and certification requirements.
  • Compact
  • Very Low Flow Measurement
  • Tolerant of particulate up to 100+ microns
  • Low pressure drop (<0.1 bar typical)

20K Flowmeters ‐ Applications and Rates

The VFF has successfully metered fluids such as oils, hydraulic fluids, corrosion / wax / asphaltene / demulsifier / pour point depressant (PPDs) /scale / hydrate inhibitors, biocides, oxygen scavengers, etc. for over 30 years. Meter bodies are produced in a variety of high grade materials which offer good chemical and environmental resistance.
Applications for flow‐rates as low 0.00013 litres/min (0.19 litres/day) have been metered within the offshore oil industry. The VFF flow meter provides exceptional rangeability with potential turndowns of up to 3000:1, dependent on operating viscosity.
The meters range in size from the smallest standard stock size, LF03 ‐ 18 L/Hr max, to the largest V270 ‐ 270 L/min max. Higher flow‐rate meters are available to special order.
An extensive range of meter designs and materials offers pressure ratings to 20,000 psi (1,380 bar). Higher pressure rating designs are manufactured up to 4,000 bar (60,000 psi). 20,000 psi designs available, as standard, up to HF60 and special designs can measure higher flow rates.

20K Flowmeters ‐ Meter Sizes

The VFF meter is not just one size, one specification. It’s a comprehensive range of carefully engineered devices to meet today’s standards in the most demanding oil & gas arenas. It’s truly a Versatile Fluids Flowmeter.

In the illustration below the smallest meter is typically housing an LF05 or LF15 rotor and chamber with FlowPod instrument and Autoclave Engineers MP connections.

The middle unit is a medium size meter, say, VFF4 with hub connections and FlowPod display.

The right‐hand meter also has hubbed connection sizes, FlowPod display but is larger to accommodates the HF60 rotor and chamber.

VFF Flowmeter Sizes and Connections.
VFF Flowmeter Sizes and Connections.

Pressure Balance Chamber

What Is a Pressure Balance Chamber?
Extensive testing by Litre Meter in 2005 proved that leaks occur over the top of the rotor at higher pressures. This is due to minute distortions of the cap. For example, at 700 bar the cap moves by just 0.02mm in the centre. Increasing the bulk of the cap still produces this movement. The effect on meter performance was the creation of a leak path for fluid that avoided the positive displacement of the rotor. This was equivalent to about a 3% inaccuracy at 700 bar. As a result, of this Litre Meter designed a pressure balance chamber for its VFF flowmeters so it could operate at extreme pressure and at low flow rates. The pressure balance chamber acts as a barrier, protecting the internal measurement components of the instrument from the high pressure conditions, preventing them from expanding and contracting under the immense pressure. NO DISTORTION MEANS ACCURATE MEASUREMENT AT ANY PRESSURE. All VFFs over 414 bar are fitted with this technology. It is identified by the letters PBC in the calibration certificate.
Key Benefits:

  • No distortion of the chamber at higher pressures.
  • Enables selection of optimal materials for the chamber to match the rotor i.e. PVD coated stainless steel or titanium.
  • Enables selection of optimal materials for the pressure vessel.
  • Enables construction of a duplex bodied flowmeter.
  • Swappable PBC for simplified sparing.

Flow ranges and references

All VFF flowmeters are custom calibrated across the customer specified min – max flow conditions and working viscosity. The minimum flow rates achievable are dependent on fluid viscosity. To see the achievable calibration ranges for each meter size please consult the table below. We can offer meters that range from 0.005 L/hr to 3,600 L/hr at 20K pressures to best suit your applications and with exceptional turndowns.

20K flow ranges

Areas of key significance:

  • Extended experience in measuring 20,000 psi in Oil & Gas applications.
  • World leaders in low flow and high pressure measurement.
  • High or low viscosity fluids flow measurement.
  • The Chemical Injection Specialists.
20,000 psi reference list
20,000 psi reference list VFF meters

Future developments

Litre Meter have already provided meters for 2,500bar. Offshore models at 22.5k & 25k are designed and 30k, 40k and 50k will be produced.
Litre Meter continues to innovate in the field of flow measurement. Recent successes include the LF05 and LF03 size meters, a new sensor, the FlowPod instrument and the FlowLabPro calibrator series. In the near term, expect to see lower flow capabilities, more calibrators and a low flow meter for any liquid type.

Offshore Corrosion Inhibitor Measurement at 20,000psi

APPLICATION: Various chemicals are injected into a deep water well to prevent corrosion, paraffins, hydrates, and scale. The flow rates for the injection are generally very low and need to be metered precisely to prevent under or over-dosing a well.

PRODUCTS SUPPLIED: • VFF series LF03, LF05, and LF15 • HM turbines HM-007 and HM-009/TC-AC/S-EX

CHALLENGE: As oil exploration goes into deeper and deeper water and deeper reservoirs, new challenges arise that put current technology to the test. The newest development is reservoirs that are reaching pressures of up to 20,000 psi. The chemicals need to be injected at a pressure that will overcome the force of the oil flowing up the umbilical.

SOLUTION: By utilizing different technologies available through the TASI Flow portfolio, we were able to offer a solution for this unique chemical injection challenge.
Positive displacement meters from Litre Meter were used for their ability to measure ultra-low flows and their flexible materials of construction that allows for high tensile strength steels exceeding the 20,000 psi pressure requirement. For the higher flow methanol and LDHI applications, the high pressure HM turbine line from AW was used for their ability to measure very non-lubricating fluids while also achieving the desired pressures.
The hazardous area location of these meters also require that all electrical components be hazardous area certified. Because of the close cooperation in development between AW and Litre Meter, as well as all other TASI Flow brands, we were able to offer a single type of user interface for all the meters. Using Litre Meter’s FlowPod transmitter in conjunction with the AW HUB-40EX pickup added a uniformity to the installation of all the meters on the chemical skid.

Corrosion Inhibitor measured at 20,000 psi 1380bar
Corrosion Inhibitor measured at 20,000 psi 1380bar

RESULTS: This is simply one of the first projects heading to locations with reservoirs up to 20,000 psi. In the near future equipment manufacturers in this segment of the market are going to need to produce technology that can keep up with industry needs. TASI Flow’s continuing innovations and ability to customize will allow them to keep pace with the constant change in the O&G production environment. Sign up for FlowSight, the Litre Meter newsletter.

Fuel and fuel additive test system uses Tricor for final testing of Formula 1 gasoline pumps

APPLICATION: Fuel and fuel additives test system for final testing of gasoline pumps at Parker Hannifin Manufacturing Germany GmbH & Co. KG in Mainz-Kastel. The pumps are used by Formula 1 racing teams. Every single gasoline pump is tested and qualified on the test system under completely different operating parameters before they are delivered to the racing customers.

CHALLENGE: A test system of high technical complexity was being designed and modelled for unlimited final testing of gasoline pumps for Formula 1 racing customers. To meet the very high demands for quality, the test must cover the entire performance spectrum and provide the optimum testing conditions for the final test. In the area of flow measurement, the task was to specify a highly accurate sensor for the most varied operating parameters. The flow conditions comprised a large spread in temperature and process pressure. This resulted in a change in the viscosity of the fuel. In the first design, turbine flow meters and TRICOR Coriolis mass flow meters were considered. The solution with turbine flow meters required a cascading of several devices to cover the required flow measurement range. Furthermore, different calibration curves needed to be used in order to meet the accuracy requirements.

TCM 0650-FA-HGSS-CSDS Tricor Coriolis for fuel measurement
TCM 0650-FA-HGSS-CSDS Tricor Coriolis for fuel measurement

SOLUTION: TRICOR Coriolis mass flow meters, by contrast, provide multiple technical advantages for this test bed. Flow meters using the Coriolis principle are significantly more accurate, faster and are almost completely independent from the medium properties like viscosity, temperature and pressure – in contrast to some other flow meters. The TCM 0650 covers the entire testing measurement range. With the TRICOR Coriolis solution, Parker Hannifin can cover the required temperature and process pressure range on the fuel test bed with one device. There are no restrictions in regards to fluid, viscosity or accuracy of measurement. Additional components for a cascading measurement (such as needed with the turbine flow meter option) and the associated added expense are eliminated.

CUSTOMER ADVANTAGE: All requirements are met by the broad measurement range of a single TCM 0650. It reduces not only the purchasing costs but also the costs for having replacement devices. Using analogue output signals and modbus TRU interfaces, mass flow, volume flow, temperature and medium density can be read out at the same time on the local display – remote optional. The TCM 0650 is the optimal solution for Parker Hannifin in order to master this challenging measuring task.

 

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