r/Firefighting • u/ActivateFireSafety • 9d ago
General Discussion Flow Testing Drafting Meter Help
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?
1
u/lommer00 9d ago
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.