Flow meter @ suction of the Pump
Flow meter @ suction of the Pump
(OP)
All,
Is it ok in the engineering design concept?
gladkenn
Is it ok in the engineering design concept?
gladkenn
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Flow meter @ suction of the Pump
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RE: Flow meter @ suction of the Pump
In fact it is easier to get your before and after straight pipe distances on the suction side for mag meters which typically recomend 3d to 5d up and 1d down. You will need that short spool piece between (at the least) due to the high swirling action of the impellor.
But if the meter is a high pressure drop mechanical device (such as a disk or piston at high flow) it is not recomended unless available NPSH can cover the pressure drop
Hydrae
RE: Flow meter @ suction of the Pump
RE: Flow meter @ suction of the Pump
RE: Flow meter @ suction of the Pump
As the pump discharge velocities are always higher than that of suction, the meter size becomes inherently lower. It all depends upon what is the acceptable pressure drop.
Regards,
RE: Flow meter @ suction of the Pump
You can use low headloss meters such as mag meters, ultra sonic meter (depending on your liquid) to measure at the suction but, depending on your accuracy requirements, remember the run lengths before and after the meter.
RE: Flow meter @ suction of the Pump
In tests I performed in the 80's with suction viewports, to supress cavitation took NPSH levels 3 times that at head fall-off.
Further, in the discussion of flow straightening, without agressive flow straightening techniques (honeycombs, etc.) typical length requirements are closer to 40 diameters of upstream pipe. I have performed tests with flow-traversing pitot tubes, where agressive flow straightening vanes and honeycombs were used (.18 in cells in a 12 inch inlet), and it 5D was nowhere near enough to smooth out the velocity profile.
So, in short, if you can avoid it, put the meter at the discharge where fluid energy is high instead of at the suction where energy is in short supply -- the risk of less than satisfactory suction performance and/or cavitation damage is greater there. But simply doing some pressure drop calcs and assuming that because NPSHA is greater than NPSHR, everything is OK could give you a nasty surprise.
RE: Flow meter @ suction of the Pump
In the suction line there can be fluid rotation coaused by the pump particulalry at start up, but even after.
Another consideration is that the larger meter to suit the suction conditions not only costs more but is operated in the lower part of its range. The meter may not be a s accurate at the % of its span.