Psi vs HP - Contractor Talk - Professional Construction and Remodeling Forum

ShaneWarne · 11-10-2008, 10:12 PM

My old man used to own a 3000psi, 15hp, 4 gpm water blaster. I am currently looking at purchasing a 4350psi, 13hp, 4gpm water blaster. He was arguing that his past machine would be more powerful than the one I'm looking at because of the bigger motor. However, I pointed out that what it lacked in HP it more than made up for in Psi. Could somebody please shed some light on this?? Which machine, assuming they were both Honda engines, and assuming they were both the same make, would be more powerful????

Pearce Services · 11-11-2008, 05:16 AM

A pump requires a certain amount of HP to work to it's capacity. if both are running 4 gpm, and one is a higher psi, then the motor should be larger for the higher psi. since that is not the case, the smaller motor that is pushing more psi, is working harder that the other unit.

The 15 HP unit has the capacity to run a bigger pump, so the unit is limited by the capacity of the pump, it would not matter if the motor was 25 HP, you have maxed out the pump.

Assuming that the 13 HP unit is truly capable of driving the pump to it's capacity, then that is the more powerful unit.

Install a 8-10,000 psi Pressure gauge on the line before your gun to verify pressure, if it is higher than 3000 psi, with the trigger pulled, then you have your answer, if the pressure drops below, then your motor can not handle the pump. try different sized orifices. verify gpm with a calibrated bucket and a stop watch.

You may find 4300 psi at lower gpm, scaling down on pressure as you increase tip size.

MALCO.New.York · 11-11-2008, 08:07 AM

There is also the possibility of Horse Power rating "fudging". Your Dads old machine may have been "Over stated" on the H/P.

Either way it makes no real difference as long as what you buy delivers what it promises. But even more importantly that it delivers what you NEED!

johnisimpson · 11-14-2008, 06:46 PM

most washers tend to look at gallons per minute more than psi or hp, though greater hp means you can run a larger pump with more gpm.