Ex-Cell EXPRO2530 w/Cat Pump. Pressure builds and stalls engine.

Frank, either the unloader valve is out of adjustment(try loosening it off) or it is faulty and needs rebuilt or replaced as most people do.
Check the attached vids,instruction and guides, Good luck
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It is true the pump could have been damaged but equally the unloader valve might be stuck wide open. When the lance trigger is released and the high pressure flow stops one of two things would happen without the unloader valve - either the pressure would rise until something broke or burst or the motor would stall so to prevent this an unloader valve is fitted that opens at a preset pressure that is higher than the working pressure but lower than needed for something to break.

When the valve opens to prevent the pressure building to unsafe levels the "surplus" water is generally dumped into the pump intake so the same water is circulated to some extent and it is likely to become warm under those conditions.

An air leak into the pump intake will almost completely rob the output of both pressure and volume. There is often a facility provided where detergent can be added to the intake controlled by a simple valve which if left open with an empty detergent container will be an effective intake air leak.

In the old days all the pumps were made of bronze or bronze and cast iron but these days pumps and components are made of a variety of materials and now unless pressure washers are in continuous use corrosion can be a big problem.

I suggest you run the pump with the hose disconnected to ensure a good volume of water is being moved and if not work backwards...

Greetings, I read your question and I think Reliable-Store can help you in this. Here's the site link -

Best Manuals

Make sure the injector is turned on. Clean the nozzle or the strainer if either are clogged or blocked. There may also be dried chemicals in the injector; dissolve them by running warm water through the injection tube.
Check to see that the faucet is open if the engine is running but the pump is not building maximum pressure. If the unit has been stored in freezing temperatures, you'll need to thaw it out completely, including the gun, wand and hose. There may also be air in the pump. Allow the engine to run with the gun open and the wand removed until a steady stream of water is released. In addition, make sure the adjustable pressure knob is set to the maximum position,
Clean the nozzle if the engine is overloaded, as the nozzle may be partially blocked. Reduce excessive pressure by using the pressure adjustment knob.

hi
there is an unloader fitted it sounds like it is not working
check it out

I have a similar problem and diagnosed it to be a problem with the gun. I spoke to a technician that services this pressure washer and he walked me through all the diagnostic steps. The pump is working because there is pressure being built up and the gun sort of works because you can get water out before the washer is started. The technician said that the mechanism inside the gun is either clogged or broken. I am going to Home Depot or Lowes to purchase a new gun and will try it tonight. Guns are only about $30-40. He said generic is fine as long as the thread matches and PSI is in range. Good luck!

common for not starting unless trigger engaged as you are turning the pump as well as engine creating pressure,as for stalling pump has unloader valve which is probably in need of grease(use good silicone grease)this allows water to ciculate when trigger released.

sounds like you have either a sticky unloader valve or a blockage causing back pressure to pump causing excess load to engine,a possibility is to check the nozzle at end of wand incase there is a piece of grit there since engine runs okay with no load,another solution is to check venturi that is located beside outlet of pump that you connect hose for wand to for possible wear or blockage,hope this helps

1999 campbell hausfield 1800 psi--2.2gpm. weak pressure at the nozzle. water sprays out, but with the pressure of a garden hose.

Sounds like the unloader is not working. try replacing it and see if that helps.