Accumulator Tank


Active member
I know I'm just missing the physics of it,..but,..why,..when a 5850 rated at 5 GPM or a Fatboy rated at 7 GPM,...what is the reason why the seemingly correct nozzle size 5 GPM or 7 GPM will make the pump cycle. At face value to me, seems that you shouldn't have to go up to a 30 or 40 GPM nozzle to make a 5 GPM pump work properly.

And after 200' of half inch hose the 5850 is down to around 3 GPM and 40 or 50 PSI,..and the pump will cycle with a 10 GPM nozzle?

Can someone explain to me the physics behind this?

Thank You,
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New member
I see what your asking. The problem with running what would seem to be the correct gpm nozzle for your pump is, You would be running a nozzle which is right at the same output of the pump. This would make the pump cycle constantly. The nozzle needs to be so much larger than the gpm of the pump so you basically create an "open" flow for the pump. With the what seems to be so much larger flow gpm nozzle, The system simply goes into an "open" flow system however, You have so much volume in the hose which is then constricted at the nozzle, It gives the 50, 60 or so psi at the nozzle.

Another example is when the bladder in a accumulator on a "well" fed water system ruptures, Water will start filling more and more of the expansion tank. As the volume of water in the expansion tank increases, The volume of compressed air decreases. Once this condition nears the point of the expansion tank being "water logged", The well pump will cycle on and off very quick. You would be able to see the needle on the low pressure gauge spike up and down as the pump cycles on and off very rapid. The system has entered the point at which the pump can overcome the flow and in turn makes the pump cycle rapidly. The pump wouldn't last very long with this condition.

The spray tip on a roof pump has to be so much larger than the flow of the pump so the pumps flow output can't keep up with the rated flow of the tip but the tip has to have just enough restriction so the pump can build pressure.