How to Set the Unloader Valve or Pressure Regulator

There are many steps to properly set the pressure regulator / unloader valve on a pressure washer. We will attempt to cover the proper procedure for a few of the most common unloader valves. Before we begin the step by step procedure, we will go over the basic concept.

There is an ideal spring tension for each unloader valve on a given pressure washer that will result in maximum pressure when the pressure washer trigger gun is engaged, and minimum spike in pressure when the trigger gun is released. Your goal is to find this ideal setting. Some pressure regulators will also let you adjust the pressure to less than this maximum setting to safely wash cars, screens, or wood to name a few things and then return to the maximum setting without going over that point where releasing this gun trigger would result in a dangerous pressure spike.

Step 1

  • Make sure the engine or motor is spinning at the proper rpm. 3700 before a load or 3400 when under a load.

Step 2

Step 3

  • Remove the nylock nut off the top of the unloader valve and spin the black plastic pressure adjusting knob off.
  • Also remove the thin washer and the spring. What you now see should be a threaded piston rod with two locking nuts.

Step 4

  • Lock the two nuts together with wrenches at 3 threads off the bottom and put the spring washer and black adjusting knob back on.
  • Clip a pressure gauge assembly in between the Pump and high pressure hose in such a way you can see it while triggering the gun and tightening the adjusting knob.
  • Turn the water on, before you start the machine trigger the gun until all the air is out of the pump and just water is coming out.
  • While watching the gauge, trigger the gun and begin to tighten down on the spring. If the nuts are set a bit too low, while tightening down on the spring you will reach a point where you will reach maximum pressure with the gun engaged, and when you let go of the gun trigger the pressure will only spike up about 6 to 9%. This is the spot you want the nuts to stop the adjusting knob. If you crank down more on the spring you won't get any more working pressure with the trigger engaged but when you let go of the trigger you will get a high spike pressure that is dangerous and could damage your pump.
  • You never want more than a 10% spike in pressure when you let go of the trigger. For example, if you're setting the working pressure to 3500 PSI when you let go of the trigger the pressure should not exceed 3850 PSI.

Step 5

  • To help break in the unloader engage the gun trigger and let go about 20 times. This will help so the unloader valve won't hang up.

Step 6

  • With the machine running, continue to take the adjusting knob, washer, and spring off and move the nuts higher or lower on the piston rod until you find the spot where when you bottom out the adjusting knob on the 2 nuts you get maximum pressure with the gun engaged, and minimum spike when you let go of the trigger. When you find this spot, take off the adjusting knob, washer, and spring and tighten the two nuts firmly together with a set of wrenches and replace the spring, washer and adjusting knob.
  • Crank down the spring until it bottoms out on the two nuts and re-check the pressure and spike pressure. If all is still well screw the nylock nut onto the top of the piston rod until the rod is just through the nylon and pop the cap on top of the adjusting knob.
  • Now while the gun is engaged you can adjust the pressure by turning the adjusting knob between the two nuts and the nylock on top. If you adjust the unloader without the gun engaged, when you do engage the trigger parts in the unloader move rather violently and could damage the unloader.