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I was using my pressure washer yesterday and left it running for a few minutes while I hosed off the area that I had just cleaned. After five to ten minutes, the engine stopped. I checked to see if it had run out of gas, but it hadn't. After a few pulls it started again, but would die the second that I pulled the trigger to begin spraying. I have been reading about the "unloader" and am guessing that this may be the problem. Any suggestions beside buying a new pump?
 

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good news: The owners manual will tell you the unit can be run without spraying water for xx minutes without harm.
bad news: the owners manual will tell you it's not recommended you run the unit without spraying water for xx minutes.
Translation: Pressure pumps get really hot. Water that flows through the pump while pumping is the primary cooling source to keep it from damage.

(the following is not an exacting explanation. But the concept is close enough)

Some pressure washer pumps have a feature that will dump water if the pump gets too hot. Some pumps, for instance, have a valve or a seal that opens if the pump's internal temp becomes too hot. It's possible this is what happened. If so, you'll have to determine if the pump has been permanently damaged.

The next suspect is the unloader. The unloader allows the pump to reach, and maintain, a certain (adjustable) pressure when the engine is running at speed. When that pressure is met the unloader will bypass a portion of the water to recirculate within the pump.

Note that the unloader retains water that has been pressurized to the setpoint level. That existing pressure head is usually easily overcome by engine power when the washer gun is triggered.

I suppose it's possible that if the pump or unloader is stressed long enough -whether by prolonged heat or by too high pressure- it could re-adjust itself to set a much higher pressure; a pressure so high the engine cannot pump it.

There is one other possible scenario, although your write-up doesn't suggest this. I'll detail it anyway:
A condition can be set where the engine is running at a low a power setting (i.e. low rpm) so that when the trigger is toggled there isn't enough engine torque to pump against the (already) pressurized water, or 'head pressure' if you will.

Unloaders are relatively inexpensive. Be aware some manufacturers, like Briggs & Stratton, would purchase a certain brand of pump. Let's say, for example, a Annovi Reverberi pump. They then either used some other brand of unloader valve, or modified the included one to meet specific Briggs spec.
So, if you purchased, for example, an unloader from Annovi Reverberi they'd send you an unloader that would fit but wouldn't work properly.

Just make sure of the correct part #, which would be, or, should be, listed in your service manual.

Good luck.
 
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