# Thread: Gallons per minute

1. ## Gallons per minute

I work for a fire protection co. where we work on fire pumps that are rated by gallons of water per minute.I was wondering if anyone knew how many gallons per minute a RXT could possibly pump at WOT.The reason for the question is an argument with a co worker. thanks for any help.
Doug

2. enough to make your balls burn if you fall off the back

3. LOL

4. definitely alot.... but i'm bad at estimating... ... hmmm...

i dont think ANYONE will have this specification for you, but i'll go out on a limb and guess 325 gpm

what gpm are the fire hose pumps rated at that you deal with?

5. actually.... someone must know... i remember coming across a device used by the fire department on jetskis where they could hook up a directional nozzle to the jet pump on the jetski and extinguish fires from the water... i bet that company would have the specs... forget the name of it tho.

it threw a sick rooster tail tho!!

6. It is somewhere betweene 6000 and 7000 GPM.

7. ## Water horsepower for flow in gal/min

Water horsepower for flow in gal/min can be expressed as:
Pwhp = SG Qgal h / 3960
where
Q = volume flow rate (gpm)
SG = specific gravity
SG for water is 1.001 at 32oF and 0.948 at 240oF.

So, if we say that the actual efficiency of the pump and motor is a little over 50% in transfering the power to the water, we could estimate that 110 hp actually gets transferred to the water. And, I believe someone hooked up a gauge and noticed that the pump is producing around 45 psi which equates to approxmately 99 feet of head. Using 1.0 for the Specific Gravity of water and doing some quick algebra the equation becomes:

Qgal = Pwhp * 3960 / (SG * h )

= 110 *3960 / (1 * 99)

= 4400 gpm

8. At 40 psi which I think is around what the ski's pump has at full speed a 4" pump has to move 2148 gpm. That is my guess!

9. Originally Posted by stvdrag225
It is somewhere betweene 6000 and 7000 GPM.

I'm declaring bolchit.

This is why you don't mix math and drugs...
(a 2.5" discharge on a fire pump puts out approx 250-300 gpm at 100+ psi. And IF I remember, a 5" was 1250-1500gpm)

JP

10. At 40 PSI you would only have 335 pounds of thrust the PSI is much higher.