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I have a simpson 3000 belt drive w/ a honda moter.runs great and well taken care of. delivers good pressure, but when not holding the trigger a small burst of air/water shoots out from thehigh pressure overload about every 15 sec. i changed the springs on the system and it checked out o.k. is there an adjustment on the bottom of this overload valve? please return a.s.a.p. Thanks, Pettke deco. Raymond

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  • fauxray Sep 05, 2010

    Thanks but I need to know how to fix this...I know what the problem is as you described but this is not helping me with the problem. Can water be heating past safety limits within 15 seconds? There is a screw on the bottom of this unit does this suggest an adjustment can be made? Thank-you

  • fauxray Sep 05, 2010

    This is an addendum to last message. The specific part on this pressure washer is a unloader valve UV760 series. Please refer to a manual to see what I'm talking about


  • fauxray Sep 10, 2010

    ok,the effective part i am refering to is the unloader valve,on a simpson 3000 washer,uv760 series if that helps.when under pressure,[trigger on washer not engaged],water shoots out @the unloader valve every 10 to 15 sec and reacts like i am starting to pull the trigger;[moter under load.i had referred to the high press overload but that is not where the water is coming from.can i rebuild or replace the unloader valve if this is the problem,andif so how do i detect what unit to replace it with?

    sorry about my terminology

    thanks R.

  • Doug Gobeille Oct 21, 2012

    Some washers do have a high pressure relief...a lot like the thermal relief that J Trevino speaks of, but either way, your problem is that the "unloader valve", is not unloading properly. This Simpson unloader was a rare OEM piece only made by the original Simpson Co. switch is no longer in business. I saw a replacement New old stock on line for $400 dollars. Several differant manufacturers make similar and wholely adequate replacements that will U-Bolt to the same spot. General Pump and Giant Pump come to mind. Grainger, Northern Tool, Watercannon all sell this part. Match the pressure, the Gallon per minute, and the size and position of the inlet, the bypass, and the outlet for the easiest installation. Call 513-242-4500 if you would like futher help. Midwest Spray


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I worked at a tool rental store during my college days and rented a similar unit quite often. I am puzzled about the high pressure valve that you describe. If I recall correctly, the units that we rented had a high temp relief valve. The springs were obtained in temperature incriments. Most likely water is heating past safety limits and releasing to allow fresh cooler water to enter loop. Do not leave the unit on bypass too long because water is looping thru unloader and heating up with every pass. Good Luck with your projects.

Posted on Sep 04, 2010

  • John Trevino Sep 07, 2010

    At the rental store, the pressure washers would get very high usage compared to yours for example, thus would get several years of use in very short time period. The mechanic was constantly replacing unloaders and thermal /pressure valves. The pressure /thermal valve has a seat that would be cut just like faucet seat. The valve is adjusted just a bit higher than unloader setting to help protect unloader. Best to lower pressure of unit to maybe 75-80 percent of max to preserve life of parts. Look here for universal eplacement parts, not expensive:

    If water was released due to high temp limit, you would see steam or just measure water temp and compare to temp marked on valve. If your valve has adjustment I would not increase pressure, but instead lower pressure of unit at regulator to temp solve problem.


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