Bypass question

I’ve only see the formula solve for needed HP so I’ve broken it down for GPM & PSI…

GPM x PSI / 1100 = HP
HP x 1100 / GPM = PSI
HP x 1100 / PSI = GPM

I’m about to order a fancy Udor 5 gpm gear drive but in the meantime, my General EZ4040G / GX390 is pulling the load & we are handlin bidniss! This should be an easy one for you guys that bypass to buffer tanks…

11.7 x 1100 / 4gpm = 3217.5
11.7 x 1100 / 4000psi = 3.2175

My gauge is set at 3950 psi. Does this mean I am bypassing the extra GPM while on the trigger? If so, am I also loosing the same amount of flow with soap nozzles? Should I set my unloader for 3217ish PSI to increase flow across the board?

You folks have been so awesome! Every question I’ve ever had has been answered by the search bar in the past until I ran into this one. Another odd observation, I originally had this EZ4040G on a Kohler 14hp (13.4). When I swapped the pump over to the GX390, I put the gauge on to readjust the unloader - low & behold it was dead on: 3950 PSI. Just trying to wrap my head how this thing works.

Thanks in advance dudes!!!

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So first off: the PSI * GPM / 1100 formula is not set in stone. It’s more a rule of thumb so you don’t overwork your motor.

The unloader will only bypass partially when using high pressure tips. It has to reach the set point of 3950 psi before it opens the bypass to divert some of the flow and keep it at 3950. That’s way more pressure than you need to be using, so in practical terms, you’ll never lose flow with your setup.


I appreciate it kind sir! You explain things very well.