From PSI to GPM: Understanding Pressure Measurement
The pressure output of a pressure washer is measured in pounds per square inch (PSI). The PSI indicates how much force the sprayed water has – a higher PSI means the water is sprayed with more force.
The right PSI setting depends on the cleaning job. Higher PSI is needed for tough tasks like removing paint or grease, while lower PSI works for rinsing surfaces or washing vehicles.
In addition to pressure, the flow rate – measured in gallons per minute (GPM) – also influences cleaning performance. Higher GPM sprays more water per minute, allowing faster coverage of large areas. But it uses more water.
When adjusting the pressure on a pressure washer, make small changes and test the results. Increase pressure gradually to avoid damaging surfaces or causing injury. Decreasing pressure too much will reduce cleaning effectiveness.
Other factors to consider:
Nozzle size: Larger nozzles have lower PSI; smaller nozzles produce higher PSI. Swapping nozzles is an easy way to change the pressure.
Unloader valve/pump regulator: Fine-tune the pressure within a given nozzle's range by adjusting these controls.
Temperature: Warmer water has better cleaning ability, but cold water won't hurt most machines.
How To Adjust Pressure – Pressure Adjustment Methods
1. Adjusting The Unloader Valve
The unloader valve is an important safety feature on a pressure washer. Its main purpose is to relieve excess pressure when needed to prevent damage to the machine. When you start the pressure washer pump, water is pressurized to a high level. But if you do not start spraying, the pressure will continue to build up. This is where the unloader valve kicks in.
To adjust the unloader valve, you typically rotate the handle or knob.
Turning it clockwise closes the valve slightly, allowing more pressure to build up.
Turning it counterclockwise opens the valve more, lowering the maximum pressure
If you want to learn carefully, we already have an article about how to adjust the pressure washer unloader valve, go there to see the details.
Tip: Using a pressure gauge is recommended so you know the actual pressure setting as you adjust the unloader valve.
2. Adjusting The Pump Itself
Some pressure washers have an adjustable regulator on the pump or an adjustment valve on its main body. It is usually a knob attached to the water output port, and you can control it by simply rotating it clockwise or anticlockwise.
You can increase the pressure by turning it clockwise and reduce it by turning the regulator on the pump anticlockwise.
3. Changing Nozzle Sizes
The nozzle at the end of your pressure washer spray gun plays an important role in determining the output pressure and water flow rate.
Larger nozzle sizes have wider openings that allow more water to pass through, resulting in lower pressure.
Smaller nozzle sizes have narrower openings, restricting the water flow and producing higher pressure.
Color | Degree | Pressure Level | Recommended Use |
| Red | 0 | High | Removing tough stains, paint stripping, concrete etching |
| Yellow | 15 | Medium-High | Heavy-duty cleaning of concrete, brick, and masonry |
| Green | 25 | Medium | General-purpose cleaning of siding, decks, and driveways |
| White | 40 | Low | Delicate surfaces such as cars, boats, and outdoor furniture |
| Black | – | – | Soap application or low-pressure rinsing |
Note: The black nozzle is not associated with any degree or pressure level as it is typically used for soap application to washing cars.
4. Adjusting The Throttle
The simplest way to adjust the pressure on a gas-powered pressure washer is by adjusting the engine throttle. As the engine spins faster, the pump spins faster which increases the water pressure output.
Start with the throttle in the slowest position for the lowest pressure. Turn on the pressure washer and allow it to warm up. Attach the spray nozzle you want to use. Point the spray gun in a safe direction and squeeze the trigger to start the flow.
Slowly push the throttle lever forward to increase the engine speed. You will hear the engine RPM rise which speeds up the pump. This will increase the water pressure, making the spray feel and look more forceful.
5. Regulator On The Wand
The regulator on your pressure washer spray wand provides an easy and convenient way to adjust the water pressure as needed for different cleaning tasks. Pressure washer pumps output a fixed maximum pressure, so the wand regulator allows you to fine-tune the actual pressure at the nozzle.
Regulators work by partially or fully closing a valve in the wand. When the valve is closed, it restricts the water flow, lowering the output pressure. When the valve is more open, water flows with less resistance, producing higher pressure.
