Pressure Washer Pump Theory

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Basic pressure washer pump theory

If you are not technically inclined or intensely curious feel free to skip this page.
But if you are then read on to gain an appreciation of the dynamics involved in pump engineering.

Crankshaft Bearing Life is a function of lubrication, speed, and load.
This last factor (load) is calculated as follows:

Plunger Area (in square inches) x Pressure (psi) = Plunger Load (in pounds)

OR

((½ Plunger Diameter in inches)2 x p) x Pressure (psi) = Plunger Load (in pounds)

Volumetric Efficiency compares the pump’s actual output to its theoretical output. If there were no losses in the pumping system, its flow would equal:

Area x Stroke x Number of Cylinders x Crankshaft Speed ___________________________________________

(231 in3) /gallon = gpm

Dividing the actual flow by the theoretical value calculated above will yield a value which, taken as a percent, indicates volumetric efficiency.

Valve timing is a major factor in achieving good volumetric efficiency. This timing is affected by the relationship among poppet weight, spring rate, poppet travel distance, plunger speed, and plunger diameter.

In most top tier commercial pumps a volumetric efficiency of roughly 85% is about the norm.
Inlet Flow Curve relates volumetric efficiency to specific inlet pressures. General Pump provides inlet flow curve charts for all of their pumps, on request.

Horsepower Requirements
Because different types of prime movers vary in their pumping performance capabilities, the horsepower required to achieve a given output depends on the energy source.

Hydraulic power is more efficient than either electric power or internal combustion.

Various requirements may be calculated using these relationships:

Hydraulic horsepower required =
Pressure x Flow / 1714

Brake horsepower (electric) required =
Pressure x Flow / 1457

Gas engine horsepower required =
Pressure x Flow / 1100

Thanks to General Pump for this resource about basic pressure washer pump theory.

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