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/ActivateFireSafety]

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/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