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There's a pressure regulator on our garden hose spigot. When the valve is opened with the hose nozzle closed, it reads 60psi.

I attach the garden hose to a 2700psi electric pressure washer. After using the pressure washer for several minutes, I release the wand handle, which turns the washer motor off.

If I take a couple of minutes to examine the thing I've been washing, and then walk over to the spigot, the pressure regulator has jumped up to 135psi.

Does that 135psi reading indicate that there is a pressure leak in the pressure washer? Its seals are allowing some of the unit's internal pressure to back up into the mains?

The manufacturer specifically cautions against putting a one-way valve between the mains and the pressure washer. Why would the manufacturer want to allow backflow?

Tim
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  • Does that 135psi reading indicate that there is a pressure leak in the pressure washer? Its seals are allowing some of the unit's internal pressure to back up into the mains? Yes. Just pull the handle to release the pressure after you turn it off. But some people are untrainable. We have a couple electric units that get cycled a couple hundred times per day, 7 days a week. I make sure they are dripping a little every time I go by them for just this reason. – Phil Sweet Sep 27 '22 at 01:35
  • I do release all pressure when I'm done working. The issue is, if I take a two-minute break to examine what I've been washing, the backpressure situation occurs. I'm wondering if 135PSI is going to cause problems for the 1940s-era copper pipe in the house. Also, is the unit defective? Or is this standard behavior? – Tim Sep 27 '22 at 10:02
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    I don't think the pipe itself will be in harm's way for brief exposures to 135 psig unless the pipe size is large (e.g. >2" type M tubing). Joints exposed to that pressure are another story, especially given the age. The only reason I can see to not have an additional check valve outside the limit of the washer would be to make sure there isn't a trapped volume of liquid somewhere not designed for high pressure that could expand when heated. What does the owner's manual say regarding this? – J. Ari Sep 27 '22 at 14:25
  • @J.Ari The manual doesn't offer any rationale but merely issues a warning: "DO NOT use a one-way valve, vacuum breaker, or check valve in any part of the water supply." [the upper case is in the manual] – Tim Sep 27 '22 at 14:58
  • It's got to be that, or water hammer. – Drew Sep 29 '22 at 05:23

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