Adjust pressure washer pump pressure?

[92saturnsl2]

Pump on this pressure washer is a consumer grade axial cam pump (see photos). Is it possible to adjust pump pressure? There is a gizmo (unloader valve?) that appears adjustable, is this possible or even wise to adjust? Looking to lower pressure, not raise it.

Would reducing engine RPM be an acceptable alternative method?

Also, anyone know what the plastic hose is at the bottom of the pump? It's not the soap hose, that's above the pump. The hose in question just hangs down and goes nowhere to my knowledge.

 

[Wrenchturner44]

What brand or make and model is this pressure washer?

 

[Tman220]

Pressure at the tip/nozzle is based on orifice size and gallons per minute of the pump.

Assuming rpm of the engine/motor remains the same you can only increase pressure at the nozzle by decreasing the orifice size. If at that time you are running into the blowoff pressure of the unloader valve then increasing the blowoff pressure of the unloader valve to get continuous operation will get a higher outlet pressure at the nozzle.

Short story, if you are currently getting continuous operation of the pump while opening the valve on the wand, then increasing the blowoff pressure at the unloader will do nothing besides adjusting the static pressure of the water in the hose when not opening the valve on the wand.

 

[Tman220]

Nozzle Size for Pressure Washer

choose and find the right nozzle for your pressure washer unit as well as surface cleaner nozzle recommendations.

www.ultimatewasher.com

Here is a link that should give you a ballpark pressure figure based on gallons per minutes and orifice size.

 

[Tman220]

I just re-read and realize you are trying to decrease pressure.

take a look at my link. Lets assume your pump is capable of 2.5 gallons per minute. If you have a 3.0 orifice on your wand you'll have about 2750 PSI at the tip.

going to a 3.5 sized orifice will give you about 2000 psi at the tip

going to a 4.0 sized orifice will give you about 1500 psi at the tip

You can then adjust the un-loader valve to decrease the cut off pressure to somewhere above your desired pressure, but it's not a requirement.