What Is This ? Water Shock Arrestor ?

What is this device ? A water shock arrestor ? Sister is having problems with water pipes viberating when you turn on the water , especially the shower / House was built in the 1970's and has pvc pipes . This device is located inline with the main incoming water line It is in the basement almost directly above the hot water heater . This just started recently like within the last month . They have a three knob bathtub / shower . Water shuts off and dosen't drip when you turn it off except from the shower head unless you turn the middle knob to tub spighot then the shower head stops dripping and water then runs out the tub spighot until it drains the line going to shower head . But no matter where you turn the middle knob to tub side or shower head it will eventually stop dripping . They think it's leaking and air is apparently getting into the water lines . Oldest kid work in a nearby city doing building maintaince and he said that it might be the tub faucets especially since an older guy told him that it could be that too . I say no it's not because water dosen't keep dripping . It will eventually quit . And how could air get into the lines if it's apparently sealing and not dripping plus with the water in the lines as well as the water pressure ? What causes pipe viberation and how can you fix it ? What is the devise in the pics ? It has a tag on top but I didn't have a way to reach it at the moment . Is it a shock / viberation arrestor for water lines ? Who do you think is right ? Me or them ? By the way , the bath tub facuect is a older model out of the 1970's! I forget the name but it has the stem with the rubber washer screwed on the end and the seat behind it in the faucet body . If that tells you anything ! Thanks for any and all help and please excuse my spelling . Thanks !

Whizkid

P.S. Looks like it double posted the pics . Was only four of them . Sorry

Didn't do it just now after flushing the toilet . Mostly seen it do it while using the shower ! At least to me from what I've noticed ? Saw the main water inlet pipe from the road to this device in the pic viberating the other day when someone I believe was showering . The first three to four feet of the main water line from this device back towards the road was viberating ! Did it on me a few minutes ago while I was showering !

Whizkid

Looks like a pressure regulator. Reduces the water pressure coming in from the street.
Gerrit

As others have said your device looks like a pressure reducing valve. Fine Homebuilding magazine had an interesting article about how the expansion caused by a water heater could cause vibration if the water system had a pressure reducing valve.
Vibration caused by water heater

Put your phone in selfie mode and stick it up there over the valve to read the tag.

Is there a screw on top? Some pressure regulators are not adjustable, others are. There are lots of different manufacturers of pressure reducing valves. Many utilities also require a back flow preventer.

That valve looks to me like it was recently installed. It has nothing to do with dripping faucets.

What she is experiencing is water hammer. See the attached article on how to fix.
water hammer

It's not water hammer which is just one bang when a solenoid valve as on a dishwasher or laundry washer closes. It is not air getting into the lines because her water lines have pressure in them. Water shoots out any opening. No air can get in. My experience with vibrating pipes is the old type of hard rubber washer in a stop and waste valve used everywhere at that time. The bib screw that holds the washer in place gets eroded away allowing the washer to move as water flows past it. sometimes it will be in just the right position to open and close the valve very rapidly as the water flows through, setting up a vibration. Stop and waste valves can be readily opened up with a fairly large wrench just under the packing nut, but they will be stubborn of course with age. Be prepared to replace them probably with ball valves.

Sounds like the pressure regulator is getting fouled/binding and slower to move.. thus its now vibrates as it trys to open and shut again due to it binding and then over the increased out of balance causes it to over react... It will do it more at a certain flow rates of water. Time for a new one.

I have no idea what is happening in your instance but here is my experience. I was taught to be stingy with water use growing up so I do not blast the shower wide open. My home was built in the 70s and what happened was the stem valve cartridges became worn and loose. When I ..throttled.. the water flow the inner stem the handle is mounted on would vibrate causing noise through the pipes. I could slightly adjust the flow and it would stop, but sometimes I would have to shut it off and reopen it. My wife who as most people do blast the water nearly wide open so the valve never made the noise or vibration for her. So I could not investigate what the plumbing was doing because it only happened with me in the shower. I replaced the the stem cartridges and the problem went away.

(quoted from post at 12:45:34 11/19/23) I have no idea what is happening in your instance but here is my experience. I was taught to be stingy with water use growing up so I do not blast the shower wide open. My home was built in the 70s and what happened was the stem valve cartridges became worn and loose. When I ..throttled.. the water flow the inner stem the handle is mounted on would vibrate causing noise through the pipes. I could slightly adjust the flow and it would stop, but sometimes I would have to shut it off and reopen it. My wife who as most people do blast the water nearly wide open so the valve never made the noise or vibration for her. So I could not investigate what the plumbing was doing because it only happened with me in the shower. I replaced the the stem cartridges and the problem went away.

Click to expand...

Same idea as my experience.