Initial high pressure and water hammer

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Old 02-07-20, 04:56 PM
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Initial high pressure and water hammer

I have noticed this mostly with my washing machine, but when it initially fills, it sends water to it in spurts (on-off-on-off) for a few seconds at a time and the first two shots of water really rattle the pipes. If I run some water in the sink while it is filling, it doesn't do that. Anyways, I mentioned this to someone in the plumbing section at the hardware store and he suggested I get a pressure gauge to test the pressure. I hooked it up to the washing machine connector and it registered 55 but the directions on the gauge said to leave it for awhile. I came back later and it was up to 115 which is as high as it has gone. I do have a pressure regulator but shouldn't that keep it at 55 all the time? Does that mean it is bad?
 
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Old 02-07-20, 05:48 PM
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Welcome to the forums.

I do have a pressure regulator but shouldn't that keep it at 55 all the time?
Yes it should.

Does that mean it is bad?
Most likely...... yes.
 
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Old 02-07-20, 06:03 PM
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Ok thank you. I thought that is how they work. I imagine they could have less pressure, but if working properly, the pressure should never be higher than what it is set at, right?
 
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Old 02-07-20, 06:16 PM
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They can creep up a little. Almost double indicates a defective valve.
 
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Old 02-08-20, 06:58 AM
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How long does it take to creep up? Was any hot water used before or during that time?
It could also be your expansion tank, or lack of one. As water heats in your water heater, it expands. Many PRVs include a check valve which means the expanding water doesn't have anywhere to go - and the pressure increases.

Easy way to test is do the same test for a few hours with the water heater off or set to low.
 
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Old 02-08-20, 08:53 AM
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I hooked it up to the washing machine connector and it registered 55 but the directions on the gauge said to leave it for awhile. I came back later and it was up to 115 which is as high as it has gone. I do have a pressure regulator but shouldn't that keep it at 55 all the time? Does that mean it is bad?
Before I condemned and replaced the pressure regulating valve, I'd try the pressure test again with the water heater turned off or set back to pilot if it's a gas heater.
 
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Old 02-08-20, 01:00 PM
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Do you still get the spurting if you open a faucet for several seconds and then turn it off and then start the washing machine almost immediately thereafter?
 
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Old 02-09-20, 01:22 PM
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I will try the pressure test again later when the hot water has not been used for awhile and turn it back so the tank doesn't go on.

I just ran some laundry now and ran the faucet for a bit and turned it off and then started up the washer. It does not get the hard hammer effect like it does if the water has not been running. That must release some of the built up pressure.
 
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Old 02-10-20, 12:06 PM
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I just turned the hot water tank down and tried his again. It was initially 55 and 15 minutes later it was up to 85. Then 15 minutes after that it was up to 100. Thoughts?
 
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Old 02-11-20, 01:20 PM
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I am not the expert here but this sounds very similar to what is happening to mine and the guys on here said it is bad.
 
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Old 02-13-20, 08:11 PM
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I just turned the hot water tank down and tried his again.
Sounds like a bad PRV. With the water heater off (or practically off), it isn't heating the water enough to cause that much of a pressure change that quickly.

I'd recommend a setup sort of like this if you need to do more reconfiguration than just pulling the old PRV and replacing it. The gauges will make it easier to test issues in the future.
 
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