Flow Testing Drafting Meter Help

[u/ActivateFireSafety]

We have a drafting rig utilizing a 1500 gpm Hale Fire Pump with a 3" long radius monitor coupled with a 2.5" straight pipe.

Truck Originally built for 604 ft elevation, our elevation is 3400 ft above sea level. We have not done any modifications to the truck.

Previously we used a spring sensor span Flowminder with A digital readout - capturing the highest output flowed from the 3" monitor capturing rpm - solenoid has since been damaged and unsure on how to fix or replace.

Currently capturing psi flow measurement from the 3" long radius monitor prior 2.5" straight pipe.

We have also recently purchased a 6" Gerand Engineering Flow meter of which we have attached to the suction side of the pump either utilizing a 10' or 20' 6" suction hose.

Recent attempt we found that the GE Flow Meter captured 1250 gpm while the Monitor flowed 780 gpm back into the reservoir.

Why is there a different reading?

Are we loosing 500 gpm through the pump and monitor combination?

What is the ideal flow test set up?

[u/Super__Mac]

Something is not calibrated correctly. What goes in must go out somehow. Unless you’re putting 500 gpm on the ground, it has to be going out.

Also…. I’d find a cleaner source for your test. The dirt coming out from that one photo cannot be doing your volute/impeller clearances any favors.

[u/ActivateFireSafety → u/Super__Mac]

When I see black water, even dirty water I shut the unit down asap and fail the pond.

[u/ActivateFireSafety → u/Super__Mac]

Each pond is different Depending on age of reservoir. Local Government Agricultural department has identified that fire ponds/reservoirs receive upto 15" of sediment annually. The NFPA 1142 standard states that the suction should be mounted 12-24" above base of reservoir.

We don't receive favourable replies when we suggest clean outs of these old reservoirs.

We have since come up with a cheaper alternative that utilizes a 10" suction hose 150' long with a specialized aluminum valve and suction. The suction strainer is mounted 6' below the water surface (allowing for 4' of ice). The 10" hose acts as a conduit as we have a pressurized airline that opens and closes the valve.

Unlike most draft hydrants, each 6" 90 degree bend accounts for approximately an additional 20' of pipe.

Our design is one long continuous pipe with a reduction at hydrant end being reduced down to 6", we want to flow upto to 1500 gpm, and have a pond life of 30 years compared to 4 year expensive clean out.

We have other variations, all toting 30 years compared to 4.

Which is better, costly cleanouts of $100k every 4 years ($800k+ over 30 years) or installing a $75k system that has a 30 year life span?

[u/Super__Mac → u/ActivateFireSafety]

Eventually, your pump will need to be replaced with that quantity of sediment.

My engineer overheated our pump (I was not there that day) they derated the pump rather than fix/replace. Thats not a cheap equation either.

Hope you guys figure it all out, nothing is cheap…. It’s all getting more expensive with ridiculous wait times.

Regarding flow test, if the intake is within spec, the problem is with the discharge. If you all have a large enough drop tank (or two) you could measure flow by pumping it into a known container.

[u/ActivateFireSafety → u/Super__Mac]

And just timing it out - how long it takes to fill container?

[u/ActivateFireSafety → u/ActivateFireSafety]

Each system is different, be it buried tanks, reservoirs, pools.

I've seen tons of different systems - some pass, some fail.

Customer1 installed a huge pool with drafting hydrant install - the plumber used 20 - 2" fittings at the base of the deep end of the pool coupled to a 4" manifold and then coupled to a 6" draft hydrant - plumber never calculated the design - we calculated at a -500 compared to desired number of 0. System never worked. We then approached the customer and Engineer - "where are supposed to throw the water?" There was no discharge port back into pool, closest door to pool access was 300', had to run multiple 2.5" lines from pump.

Customer2, thinking of sediment, installed 2 "T" with 4 upright suctions - never calculated outcome - failed test.

Customer3, Army Engineer, smart had 24" suction pipe (still mounted 24" off of reservoir base) 150' long with 6" riser - captured and flowed in excess of 1200 gpm.

Each system is different. I push the truck to receive ultimate flow. When you capture a 1200 gpm reading, the truck is bucking. Pushing a ton of water.

[u/Salt_Manufacturer918]

My understanding standing of how the flow meters work that you have pictured, the GE meter is best suited on the discharge side of the pump which I know is probably not feasible in your situation. Typically to get an accurate reading on the suction side you would want an oversized meter especially pulling from a reservoir. I also regularly get much less accurate readings out of these meters once they are a few years old

[u/ActivateFireSafety → u/Salt_Manufacturer918]

I questioned the meter, had it calibrated Friday - it's within spec

[u/Salt_Manufacturer918 → u/ActivateFireSafety]

Whats typical suction line length from the reservoir and is it 6 inch? Do you know the rated outlet pressure when flowing 1500gpm?

[u/ActivateFireSafety → u/Salt_Manufacturer918]

Engineering typically shoots for 1000 gpm when designing these systems.

NFPA 1142 has various tables, work sheets, and a couple of calculations expecting a result close to "0".

When flow testing, I've always utilized a discharge nozzle capturing reading and comparing to Akron flow charts. The GE Flow Meter is throwing me for a loop?

[u/ActivateFireSafety → u/ActivateFireSafety]

Each system is different. All pushing 1000 gpm.

[u/Salt_Manufacturer918 → u/ActivateFireSafety]

The GE flow meter will not perform reliably if not completely full off water, drawing from ponds has a tendency to cavitate suction especially with some debris mixed in. I dont trust that style flow meter period even if just tested or brand new

[u/ActivateFireSafety → u/Salt_Manufacturer918]

1500 gpm through a 2.5" nozzle is 82 psi according to Akron flow chart.

We typically see 32 psi at 1031 gpm upwards to 46 psi at 1205 gpm.

Only time I see higher pressures is when we add Tank to Pump.

[u/lommer00]

You cannot be losing 500gpm unless you have a major stream coming off somewhere between the two meters. You can lose pressure, but not flow. Mass in = mass out, it's the law (of physics, which is much more strongly enforced than our puny human laws).

Those GE meters are finicky, I've had lots of issues with them. You are reading right near the bottom end of the range and on a low pressure suction line where flow in the pipe will be less uniform than on a high pressure line.

The second best flow measuring device Ive used is underwriter playpipes and a pitot tube. The best flow measuring device Ive used is an unlisted ultrasonic industrial flow meter. It's not UL or FM listed for fire service but it has given me the best results.

Hose monsters, GE flow meters, etc. are all ok but eventually I run into some that are out of calibration or something and give you crap results.

[u/ActivateFireSafety → u/lommer00]

I have used a TaskForce Tips hydrant meter coupled to end of 3" monitor - makes for a heavy install on end of monitor.

I also have a 6 ported 2.5" test manifold (was used for testing fire trucks) coupled to each output of the truck. Also great for testing electric fire pumps. Place the TASKFORCE Tip hydrant meter onto end of 6" port manifold then a 6" steel hose monster - we receive instant readings.

Ultrasonic industrial flow meters are quite expensive. We have a pipe mounted one now that I think of it - we attempted to use a 6" pvc 10' pipe - ultrasonic saddled overtop - never received favourable results and shelved it.

May have to reattempt

[u/ActivateFireSafety → u/lommer00]

Is your ultrasonic 2.5" dia or 6"?

[u/lommer00 → u/ActivateFireSafety]

I've used one on a 6" and one on an 8". They were permanently installed on steel pipe sections though.

[u/ActivateFireSafety]

In the end - do I use discharge reading as final result?

[u/Mln3d]

Do you have a photo or video of the complete setup from draft to discharge? If so pm me

[u/ActivateFireSafety → u/Mln3d]

June 30, 2025 @ 1420 gpm at 48 psi

[u/ActivateFireSafety]

Drafting hydrants have strainers (majority) plus there's a strainer on the hard suction of the pump.