How to Adjust a Safety Pop-Off Valve:

That Pop off Valve is rated for 6000PSI. It is very easy to adjust the Pop Off Valve to the pressure of you unit:

1. Screw the Allen head plug on the end of the Pop Off valve all the way in (clockwise) till it stops.

2. Install the part on your machine.

3. Turn on the water, Start up your unit, and run it up to full pressure.

5. Slowly unscrew (counter clockwise) the Allen head plug until it Pops off.

6. Shut off the unit and turn off the water

7. Turn the Allen head plug back in (clockwise) 1/2 an turn

Now it should be set for the pressure of your unit. If it Pops again you might have to give at an extra 1/4 turn (clockwise).

http://www.watercannon.com/p-2229-safety-relief-valve-38-mpt-whb-outlet-1000-6000-psi.aspx