PSI vs GPM. What is more important?
When it comes to power washing, PSI and GPM are similarly important. In general, the PSI (pounds per square inch) refers to the amount of pressure generated and the GPM (gallons per minute) refers to the volume of water flow.
Think of PSI being a erasing action to blast off dirt or contaminates with force on the surface you are cleaning. While GPM would be the volume of water used to rinse away that dirt.
Cleaning Units
The combination of PSI and GPM is what we in the pressure washing industry call Cleaning Units or CU. Think of Cleaning Units as a gauge on how efficient a pressure washer operates.
How to calculate Cleaning Units
To calculate your machines Cleaning Units (CU), you will need to multiply the PSI by the GPM.
Example:
- Power Washer #1 has 2000 PSI x 3.0 GPM = 6000 CU
- Power Washer #2 has 3000 PSI x 2.0 GPM = 6000 CU
One might think these machines are equal but that is not the case. Because PW1 has a higher GPM rating, it is the superior machine in this comparison.
The Deception of PSI
Generally, when we think of power washing our homes, the amount of PSI dominates our decision on what pressure washer we might buy. We say to ourselves, ‘I’ll just buy the power washer with the most PSI and I’ll be able to clean way better’. The answer? False. Pressure washing manufacturers can cheaply increase there PSI rating. Even changing your nozzle sizes can easily manipulate PSI. Meanwhile if the GPM rating is only about 1.0 GPM, depending on your type of use, you are most likely using a inefficient pressure washing machine. When buying a pressure washer, focus on the GPM rating if you want to work more efficiently. This rating cannot be cheaply manipulated by a manufacturer.
A professional power washing contractor will usually prefer a higher GPM (gallons per minute) over a higher PSI (pounds per square inch). The reason for this is because a professional will lean more on their expertise of using quality chemicals and products to complete a job more efficiently.