I have a Pressure Washer with a Comet ZWD 4040 Pump. It recently had a new Unloader Valve fitted.
It has suddenly developed a problem, the pressure goes up to 3000psi and then drops back to 2000psi. I...
Derek, Hi and welcome to FixYa. I am Kelly.
I just now happened across your post and note it is 3 months old. Hopefully you already have the problem solved.
If not.. looking at the pump history of having the un-loader valve replaced it sure seems that the current un-loader valve is sticking. When an un-loader valve is removed the internal housing is sanded smooth and everything about the un-loader valve is coated with Lubriplate #105 White Grease. I get the feeling that who ever did the un-loader valve repair failed to sand / clean the housing and use White Grease for the final assembly.
You should remove the valve... Sand the housing and get some Lubriplate #105 white grease (auto parts store) in a tube. Lubricate it liberally and reassemble it. If should work fine after that.
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