PSI and GPM are both equally important when choosing a pressure washer. The PSI refers to the amount of pressure and GPM refers to the flow. You must have the correct combination of PSI and GPM to have the most ideal pressure washing system for your needs.
To clean effectively, a pressure washer must provide a "stripping" action to scrub off the dirt and "flow" to move the dirt away. Think of the pressure (PSI) as the stripping force that is applied to the surface you are cleaning and the flow (GPM) as the rinsing power that carries the dirt away.
- PSI (Pounds per Square Inch) refers to the amount of cleaning pressure that the unit can produce.
- GPM (Gallons per Minute) is the amount of water that is coming from the unit.
- Cleaning Units (CU) is the result of multiplying the PSI by the GPM. Cleaning units gives the customer a measure of unit performance (efficiency) to compare one unit to another. Cleaning units is calculated by multiplying PSI and GPM.
A pressure washer with 3000 PSI and 2.0 GPM has 6000 Cleaning Units
A pressure washer with 2000 PSI and 3.0 GPM also has 6000 Cleaning Units but the rinsing power is greater than the stripping power.
GPM is usually more important to contractors than PSI. Since most contractors use cleaning chemicals to do all of the cleaning, their job becomes one primarily of rinsing the dirt away.