Question

[everybodyin]

Someone please help.

How many GPM's can a 2 1/2" discharge flow on a 2,000 GPM pumper?

I heard once that all of 2 1/2" discharges on a pumper, flowing at same time, should pump total GPM's of pumper's rating.

Is this true?

If this is the case, then a 2,000 GPM pumper with (3) 2 1/2" discharges would flow 666 GPM per discharge?

Thanks

[firepundit]

Someone please help.

How many GPM's can a 2 1/2" discharge flow on a 2,000 GPM pumper?

I heard once that all of 2 1/2" discharges on a pumper, flowing at same time, should pump total GPM's of pumper's rating.

Is this true?

If this is the case, then a 2,000 GPM pumper with (3) 2 1/2" discharges would flow 666 GPM per discharge?

Thanks

In olden times one 2-1/2" discharge was required for each 250 GPM of rated capacity. Not so today. Times have changed.

If you just open up a 2-1/2" discharge and start flowing with nothing on it the flow will depend on how must pressure you run. A simple flow chart in the back of any good brass catalog will answer that question. Theoretically, if you can get a pitot reading of 200 PSI at the opening it will discharge 2626 GPM.

On a practical level, however, tell us what will be attached to it and we can tell you what you will get. Do not forget to include the size and length of hose as well as what will be on the end of it.

[BoxAlarm187]

In olden times one 2-1/2" discharge was required for each 250 GPM of rated capacity. Not so today. Times have changed.

Pundit has it. You used to divide the pump gpm by 250 to determine how many 2.5" discharges you needed. There was never an expectation that one discharge could flow 666gpm or other high figure.

[plumb25]

I don't know if this is correct but I was taught that for pump testing purposes you should count on approx. 450 gpm out of a 50' 2 1/2" run into a tri-gun with a pitot set on the end. If this in wrong, I would love a better number.

[everybodyin]

Thanks for the help.

I guess I am just looking for a max GPM number that a 2 1/2" can flow with nothing attached.

Am I correct to assume that the max GPM would occur at 150 psi?

Thanks

[kuh shise]

everybodyin: That's a sort of "DEPENDS" question. Depends upon what the piping looks like behind the panel. Depends upon the size of the valve. (2 1/2" with 3" valve, 2 1/2" outlet with 2 1/2" valve, or a 2 1/2" with a 2" ball valve opening) Stick your head in the inspection door or crawl under with a creeper and look at the plumbing inside the pump housing. For every 90 degree elbow it effectively adds about 15 feet of pipe to the system. This is why the "Pony Suction" inlets usually perform very poorly. Trying to feed 1200 to 1500 gpm out of a 2 1/2" outlet with no elbows and a full flow 2 1/2" valve will need between 50 and 80 psi loss in the engine. Add an elbow or two and it is twice as difficult. Some manufacturers simply go by the 250 gpm rule, and put in 2 1/2" valves with 2" openings. It takes 80 psi to get 1,067 gpm out of a 2" SS nozzle, so it takes 80 psi to get the 1,000 gpm through the small valve. Friction loss changes (gets smaller) by the 5th power of the diameter of the hose or pipe. Doubling the size of the pipe reduces the friction loss (exact same flow) by a factor of 32 : 1. Of course we immediately try to stuff more water through the bigger hose. Compare the friction loss numbers for 2 1/2" hose with 5" hose at the same flow. There is no real upper limit to the flow, but the engine rpm and discharge pressure limits will stop you. Suppose that at 250 gpm you have a 10 psi loss in the valve and piping. Wishing to increase the flow to 500 gpm, you need to increase engine pressure to 40 psi. pipe friction loss plus velocity head (nozzle pressure) of 7 psi or Eng. Press = 47 psi. Trying to reach 1,000 gpm will require 160 psi friction loss plus velocity head of 29 psi or an engine pressure of 189 psi. You will probably need a 1500 gpm pump to reach this flow. (70% at 200 psi = 1050) For arguments sake lets try a flow of 1250 gpm. Friction loss from the outlet would be 250 psi and a velocity head of 45 psi or a pump pressure of 295 psi. Clearly beyond the design for a standard fire pump at 250 psi, and also would need a 2,500 gpm pump just to hit the 1250 gpm at 250 psi.

[kuh shise]

I don't know if this is correct but I was taught that for pump testing purposes you should count on approx. 450 gpm out of a 50' 2 1/2" run into a tri-gun with a pitot set on the end. If this in wrong, I would love a better number.

plumb25: A 50' section of 2 1/2" hose at 450 gpm would have a loss of about 25 psi. Assuming you were feeding a 2 inlet deck gun with a 1 3/4" nozzle with dual 2 1/2" lines, then nozzle pressure would need to be 96 psi. Most master stream devices have about a 20 psi internal loss at 1,000 gpm, and assume a piping / valve loss in the engine of 10 psi. So 96 + 20 + 10 + 25 = 151 psi. The designed flow of a fire engine at 150 psi. Your mentor is correct for a 1,000 gpm pump.