Can Flow Meter Be Installed in Test Header Feed?

2/21/2024

Can a flow meter be installed in test header piping?

This is the first time I've ever seen this installation. Thanks.

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9 Comments

Dan Wilder

2/21/2024 07:02:01 am

Is it against NFPA, no, however it defeats the purpose of having one to avoid flowing water annually if it only feeds to the test header. It "could" be used to just flow from the test header without the use of any pitot readings however they still need to be calibrated so it's not a 100% resolution and an expensive alternate with no real added value (IMO).

Ideally, it will go (with appropriate clearances)
Pump discharge->check->bullhead Tee->butterfly (NC)->flow meter->bullhead tee to test header/tee run side back to supply side->butterfly (NC)->pump suction.
This would allow using the flow meter yearly (no water discharge), use the test header every 3 years (water discharge), and the ability to calibrate the flow meter without removing it and sending it off.

Jesse

2/21/2024 10:36:49 am

Yep it can indeed. Just think of it a really expensive pitot tube in that arrangement though.

WES

2/21/2024 10:44:07 am

While it seems like a logical idea - we've been told from the flowmeter manufacturer themselves (the #1 brand) that a flowmeter will NOT accurately read when flow happens out through the test header.

We found this out by repeatedly running tests out through the test header and measuring the flow with calibrated pitot gauges, and the flowmeter consistently read far too low of a flow to match.

We had calibrated flowmeters and ended up swapping with two additional calibrated flowmeters with the same result.

The flowmeter manufacturer wrote a letter and stated the flowmeters will not test accurately when flow is out to the test header (and not circulated back to suction), because of the difference in back-pressure between the two methods.

Perhaps it's possible to have a flowmeter piped both ways and get it to accurately read on the outside discharge, but we have not had success in doing so and have the letter from the manufacturer stating it is not built nor will work for that scenario.

Don't mean to throw anyone under the bus, otherwise I'd share the letter/who the flowmeter manufacturer is.

Franck

2/21/2024 11:46:53 am

Looks pretty strange to me.
In Europe we have flowmeters installed on test lines (no test headers), with water flowing back to the top of the water tank (not back to the suction side of the pump).
It looks similar to having a flowmeter on a test header, except that in that case you will flow top the outside (and grow the grass around the pumphouse).
The only limitation is to have sufficient length between the flowmeter and the valve upstream (min. 5 times the diameter of the test line) and between the flowmeter and the valve downstream (min. 2 times the diameter of the test line).

The valve upstream needs to be fully open and then regulate the flow by opening the valve downstream (or the valves from the test headers in your case).

Maybe the issue you had was related to a too small distance with turbulences preventing a good reading ?

To my experience, flowmeters are far more accurate than using a pitot tube and test headers (too many variables) and much more practical.

Thomas Duross

9/8/2024 03:35:40 pm

Whenever I've been involved in installing, replacing or repiping, I've always advocated for a flowmeter. FM is 5 diameters (min) after the test valve (between pump check and discharge valve) but I valve it 2 ways. 1 to the header and 1 back to suction. This way I always flow through the meter to check, even though it has to be calibrated yearly and be within 1%. Closed loop FM numbers are good, but open loop FM goes awry. I'm told due to backpressure or the lack thereof. I really learned my lesson this year as I installed the digital version along with a new FPC/TS with the modbus communication to read suction, system and flow, and plot a curve on the FPC screen. Things are still a mess.

Glenn Berger

2/21/2024 11:46:59 am

I have been asked by clients to include the flow meter, whether the flow goes to exterior hose valves, back to a storage tank, or a return to suction side of fire pump with no objections except by contractors that failed to follow the design documents.

Jack G

2/21/2024 11:55:30 am

Basically the above is correct. I disagree with putting 2 hose valves in a valve room and running the hoses to the exterior. Hoses burst or leak.
I would make a straight header, weld 2.5 ipt inch outlets on it. Run a nipple thru wall ( ipt x nst nipple) put a plate on it that says “ test “ ( or sign)
Cleaner test.

Mark Harris

2/21/2024 04:04:01 pm

Some great comments about being expensive pitot. But as Glenn notes routing to a ground suction storage tank is common and saves water verses hose valve test. But sounds like Wes has documentation that is not right with the flow test meter manufacturer?

Megan Asbrock

3/21/2024 06:50:37 pm

sure can. the meter and pipng arrangement can be found in NFPA 20.

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Can Flow Meter Be Installed in Test Header Feed?

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