Can Flow be measured accurately by Pressure Transmitter

[Watro]

Helow

Please advise, if a discharge Pressure transmitter (not differential) downstream a Centrifugal pump can be used to measure an accurate corresponding flow? Is this normally acceptable in Industry?

Thanks, Niss

 

[GHartmann]

It might give a general idea of where the pump is running (as long as you are not in the flat region) along its pump curve. However, after some time and the pump clearances are not "new" then the pump curve is going to decrease slightly.

It is by no means an accurate measure of the flow.

 

[moltenmetal]

If you validate the pump curve using a flowmeter once the pump is installed, the pressure gauge can give you an idea what part of the pump curve you're on. But by no means would that be considered an "accurate" method of flow measurement- rather it's just a crude way of inferring flow.

 

[LittleInch]

Unless you have a FIXED inlet pressure AND a fairly steep and constantly rising head flow curve that you can extrapolate the flow based on pressure, the answer is no. It is not normally acceptable. There are many cheap flow meters which can give you accuracy of +/- 5%, but this isn't one of them.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[DubMac]

No.

 

[1gibson]

As stated, no. If you have differential pressure across the pump, and the pump curve is fairly steep then the answer is maybe, for a brand new pump. After it's been running a few years and loses a little efficiency, the answer is again no.

Is it acceptable? As with anything, it depends on how you are using the information. Differential pressure along with motor amps can get you a pretty good idea, again for a new pump with a steep curve.

 

[1gibson]

I should elaborate on my comment about checking motor amps.

Flow is on the X axis. Head and horsepower are on they Y. If you mark the head (based on measured differential pressure) and the horsepower (based on measured motor amps) and draw vertical lines, they should be very close to each other and you can determine an approximate flow.

Let's assume the pump is a little less efficient than when it was new. This means your power is higher, and your pressure is lower, for a given flowrate. All that does is put the two lines farther apart, but the actual flow is still somewhere in between.

 

[bimr]

You cannot measure flow with just a pressure gauge. Measuring flow in this manner is not accepted in the industry either.

 

[GPRnD]

I'm not sure if it helps you but:

ITT Goulds does offer a VFD (PumpSmart) that will achieve flow control to a claimed accuracy of +/- 5% using the measured power. Obviously this would require neither a pressure sensor or a flowmeter. The main drawback is that it won't work in applications that handle different densities of fluid.

The link for it is below

[URL unfurl="true"]https://www.ittproservices.com/ittgp/medialibrary/ITTPROServices/website/Literature/Brochures/PRO%20Services/PSmartbulletin.pdf?ext=.pdf[/url]

 

[Watro]

Dear All

Thank you for feed back.

Best Regards
Niss