Water hammer when water is running

[Gary Yang]

Greeting All.
I googled some water hammer posts. They either happen when people shut off water, or happen to specific faucets. My problem seems different from most of them.

When I turn on a faucet, water seems flowing "normally" at first, but the flow gradually slows down, then I hear the hammer sound. At the same moment, water flow increases back to norm. All take about 7 seconds from the time I turn on the faucet. When someone else uses water, I can hear a few-second noisy water flow, followed by the hammer sound. After the hammer sound, the noise from water flow decreases obviously.

This is not specific to any faucets.

Additionally, a few months or a year ago, I used to hear a periodic sound when water was NOT running. The sound was not very loud. If I turned on a faucet, the sound would stop, but it would resume few seconds after I shut off water.

Hope some exports tell me the reason and solutions. Much appreciate your advice.

 

[FullySprinklered]

Start with a pressure gauge and make sure your water pressure is below 80#. Check it over several days. Any great inconsistency may indicate a bad PRV. If it's bad, the expansion tank is probably gone also.

You may have more than one issue, but that would be a good place to start. Attach the gauge to the water heater drain, not on an outside spigot.

Report back.

 

[Sponsor]

 

[LLigetfa]

It does sound like a bad PRV.

 

[Gary Yang]

Thank you both! I will buy a pressure gauge, measure it and report back.

Bye the way, there is no expansion tank installed in my home.

Update: I just bought a pressure gauge from HD and measured the pressure at the water heater drain. The pressure is 72 to 73 when all faucets are shut off. My additional observation is when the faucet in the basement open to its maximum, there are periodic hammer sounds, once in less than 2 sec, and the pressure changes between 20 and 40 along with the hammer sounds. If the faucet open half way, I normally hear hammer only once.

Please advise. Thank you.

Gary.

 

[Gary Yang]

I monitored the pressure gauge for a couple of days. If no one in my home is using water, the pressure is between 72 to 75 in the evening; but it's around 82 in the morning. Apparently, this difference is caused by water usage in my neighborhood. If anyone in my home uses water, the pressure would go down significantly to 40 or 20 depending on how widely the faucet is turned on.
So is the fluctuation of pressure normal? Do I have a bad PRV?
Appreciate your advice.

Gary

 

[Reach4]

Normal. During the night they fill the water tower higher. Higher water in the water tower adds to the pressure. The neighbors using water is also a factor.

What you next want to check is the pressure after you use a lot of hot water, such as after a hot shower, and you stop using all water. No sink. No flush. No water from the refrigerator dispenser. See how much the pressure climbs as the water heater heats more water.

 

[LLigetfa]

Spot checking the pressure is not going to nail down the source of the banging. You need to have your eye on the needle at the time of the water hammer and correlate that to what the needle is doing. Getting a pressure gauge in and of itself won't diagnose the problem. It is just a tool the results of which you need to interpret.

 

[FullySprinklered]

You can wait for a fairy to come riding in on her unicorn and sprinkle stardust on it, or you can replace the PRV.

 

[Gary Yang]

Spot checking the pressure is not going to nail down the source of the banging. You need to have your eye on the needle at the time of the water hammer and correlate that to what the needle is doing. Getting a pressure gauge in and of itself won't diagnose the problem. It is just a tool the results of which you need to interpret.

Thank you for replying to my question. I already mentioned that , but it might not be clear. If a faucet is widely open, the needle turns from around 80 to almost 10, then a hammer sound is heard, at the same time or immediately following the hammer, the needle quickly jump to 40. If a faucet is fully open, there could be repeating hammers, then the needle would jump between 10 and 40.

 

[MACPLUMB]

These are all symptoms of a BAD PRV ! change it or call a plumber to do it and see the change,
I have seen this many times over the years

 

[Gary Yang]

Normal. During the night they fill the water tower higher. Higher water in the water tower adds to the pressure. The neighbors using water is also a factor.

What you next want to check is the pressure after you use a lot of hot water, such as after a hot shower, and you stop using all water. No sink. No flush. No water from the refrigerator dispenser. See how much the pressure climbs as the water heater heats more water.

After using hot water, the pressure seems a little (2~3 psi) higher than before using hot water. I am not quite sure if this is the effect of using hot water because I did see fluctuation before.

 

[Gary Yang]

These are all symptoms of a BAD PRV ! change it or call a plumber to do it and see the change,
I have seen this many times over the years

Thank you for the advice. Appreciate it.

 

[Gary Yang]

You can wait for a fairy to come riding in on her unicorn and sprinkle stardust on it, or you can replace the PRV.

The fairy hasn't come yet . I plan to replace the PRV before she comes. Thank you!

 

[Gary Yang]

Report back: I adjusted the PRV to lower pressure. I can tell that the pressure is MUCH lower per water flow from faucets. The hammer sound stopped. However, when no one is using water, the pressure gauge still shows almost 80. I cannot tell the difference by pressure gauge. It makes me think that the pressure gauge is not functioning correctly.

 

[Reach4]

Report back: I adjusted the PRV to lower pressure. I can tell that the pressure is MUCH lower per water flow from faucets. The hammer sound stopped. However, when no one is using water, the pressure gauge still shows almost 80. I cannot tell the difference by pressure gauge. It makes me think that the pressure gauge is not functioning correctly.

See #3, #8, and #10.

 

[Gary Yang]

See #3, #8, and #10.

Thank you for reassuring me. I had already bought a new PRV and only needed additional supplies to replace it. I was just curious for an explanation why the pressure seems reduced a lot but the pressure gauge still has the same reading, wanting to learn a bit more.

I really appreciate everyone's help!!!

 

[Reach4]

I was just curious for an explanation why the pressure seems reduced a lot but the pressure gauge still has the same reading, wanting to learn a bit more.

I presumed you were looking at the pressure gauge while you were not running the water.

Usually with a PRV you want a thermal expansion tank. You probably have one, but it might need replacing also.