Occasional Thump or Thud when running water - PRV failure?

[Ethan Hubler]

Hello. My wife and I moved into our current home about 5 years ago. The home is now 18 years old. Our water supply lines are all copper, with PVC waste and drain pipes. Over the last 1-2 months, we've noticed a slight thump when flushing toilets, or turning on a faucet full blast. Not every time, but usually the first time we run water after nothing has been in use for awhile. At first, I thought the sound might indicate some kind of drain blockage, but I opened up the maintenance in the front yard while water was running, and it sounded like things were moving fine. Then the other day I noticed the thump while filling a bucket - this was the only faucet or spigot that was on, and nothing was going down the drain. Interestingly, it's only 1 thump, about 1 second after the water turns on. Our water pressure at the both outside spigots measure 45 PSI, but the meter on the PRV off the main line is too dirty to read at this point - and that SEEMS like where the noise comes from when we run the water. Could this be a sign of the valve failing? I think it came with the house, and it did not occur to me to clean it or anything because this is the first time we have had one of these. Just curious if anyone has thoughts. I had a plumber out, but we could not duplicate the sounds. He noted that the PRV is old, could not find any leaks yet. Any thoughts would be appreciated! Thanks...

 

[Valveman]

Could be too much or not enough air charge in the expansion tank.

 

[Sponsor]

 

[WorthFlorida]

You're probably hearing a very slight water hammer. The cause could be almost anything. At full blast of water drops the pressure and when the water is rapidly turned off it's like it hits a wall. A PRV may have been added years ago to eliminate the problem but now the PRV is perhaps failing.
If you can duplicate the problem place your hand on the PRV and you may feel it when it makes the thump. A PRV uses a spring and a diaphragm (washer) to regulate the pressure and it could be the valve is closing when the pressure increases when the water is turned off. A possible reason why it's about a second delay.

 

[Ethan Hubler]

Thank you for the responses! I am going to try and monitor with my hand on the PRV, and see if I can feel it.

 

[Ethan Hubler]

Just to update, I ended up replacing the PRV and a check valve, and the sound seems to be gone, and the overall system is quieter. So thanks - seems to have worked...