- When specifying flowmeters how does size affect meter selection?
- Can you specify the available pipe length? Some installations are very limited on installation length and meter selection can be pivotal. Assume that the number straight lengths before and after the meter (but, see below) isn’t relevant for the moment and all meters are available: If there’s only 1 diameter of straight pipe then the PD meter is probably the Number 1 choice. There’s likely very little room so larger meters like the Coriolis, which is a ‘bulky’ technology, are too long, even if they, too, need no straight lengths: that’s not strictly true but that’s another story entirely.
- Width: Does the unit have to fit in a narrow space? Perhaps there’s a wall one side -the meter can’t overhang that side, but is it then facing the right way?
- Does the installation space enable the unit to be provided with a local display – which is facing the right way? or will it need to be a remote mounted version?
- Is there access for maintenance? Is that all important termination panel just in front of you or is it tucked beyond a stem in a dingy corner of the installation. How good are you at holding a mirror?
- If it’s remote mounted – how far away can the display be? ie. what’s limit on the length of cable?
- If it’s remote mounted – is that panel mount, wall mount or post mount? Any special mounting considerations like weight, panel size, panel thickness?
- Height If it’s not a length or width then height might be an issue. Perhaps the meter can be/ needs to be installed upside down? Maybe there’s a bunch of pipe in close proximity.
- Are there weight limitations? On vehicle and aerospace installations the weight can be an overriding factor in meter selection. Are there weight reduction regimes? Changing the connection type or reducing a flow meter size or changing to a lightweight material can have significant effects on weight. A threaded turbine meter can be a tenth of the weight of a flanged coriolis.
- Does the meter type require straight lengths before (and after) the meter? Some meters are better than others. Some are much worse than others. A turbine meter needs a minimum 10 lengths before the meter and 5 lengths after. Orifice plates are meant to have more before depending on prior pipe configuration to ensure swirl is minimised.
- What comes before the straight lengths? If its two bends in 2 different planes then that’s a great recipe for swirl. Up to 100 lengths of pipe after that will be required to eliminate the swirl.
- What methods can reduce pipe lengths? One valid suggestion is to use flow straighteners or plates. These can be as little as 1 diameter long, but with a pressure loss, knock out some flow profile imperfections. They aren’t necessarily commercially available nor cheap. Perhaps, have a look at another measurement technique?
All in all consult the specialists.
Ten top tips for flowmeter selection