Water Hammer

J Van Lund

We are on a community water system. There is a 3/4" cold water feed (approx. 45 ft of straight pipe and supported by wire hangers) to the water heater with a 1/2" branch loop off the same feed line. The branch has a grundfos ciculating pump, which pushes water into the water heater, and a brass pressure reducer with set screw. There are ball valves on each side of the pressure reducer and circulator. Water pressure to all fixtures is very good. Whenever we close a faucet or the toilet completes filling, we get an annoying water hammer in the wall 12" downsteam from the reducer. Whenever my neighbor 400 ft. downstream shuts a faucet, we get the same water hammer noise at the same location. however, there is no water hammer noise if we close one or both of the ball valves on each side of the circulator in the branch loop. Here are my questions: (1) What is causing this? (2) Would a pressure reducer or expansion tank located where the cold water inlet enters the house eliminate the noise? (3) What is the purpose of the set screw on the pressure reducer and which way do you turn it to reduce the noise? (4) I will call my plumber and discuss this with him. I wanted to understand the cause(s) and possible fixes before doing so. Many thanks for your help.

Ken_8

I have more questions than answers...

Please give more detail about the recirc. pump and define what exactly a "community water system" is.

Any check valves in the recirc. line? Or is it just 'there'?

How many fixtures hooked up to this "community" system?

Assume the recirc is for d/h/w only? Or is it for somestic cold too?

How many apartments/cabins/ homes on this "system"?

If a well is involved, the likely culprit is the expansion tank (Welltrol) being undercharged. If the bladder pressure is at or below the system low normal operating pressure, the hammer can be very pronounced!

There is a way to test the bladder pressure with a tire gage - but the system must be a zero psi to see the expansion tank's charge.

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hr

What's the pressure?

by far the biggest cause of hammer is excessive pressure. 45psi is plenty for most homes and is the "suggested pressure" found in many plumbing code books. It's also the precharge found in most DHW expansion tanks, and the preset on most PRV valves.

If yours is higher (check with a lazy hand gauge for several days) a prv may be needed.

hot rod

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jackchips_2

I agree with

Hotrod about the high pressure.

What is the size of your piping?

High pressure in small piping = banging pipes. That water can be moving through those pipes very fast and any quick closing valve or faucet stopping it will cause a hammer.

J Van Lund

Water Hammer Question Continued

It isn't a really loud hammer, but what I can't figure out is when we shut off one or both ball valves on each side of the prv and circ pump, there is no hammer noise. One would think the problem is with one or both of these or because of the smaller 1/2" pipe with at least four to five 90 degree bends where the branch line comes off the 3/4" feed line. I thought of having my plumber install an arrestor in the 3/4" line just before the 1/2" branch and a pressure reducer just inside the house where the 3/4" line comes in. Would the arrestor absorb the pressure wave from the hammer? As to adding the prv on the inlet, there is some sludge in the water and I was worried that the prv valve would get clogged. Right know we use a whole house filter to remove the sludge and iron. I thought it was strange that a neighbor's shutting of a faucet or washer would have an effect in our house which is 300-350 ft. away. I don't know the pressure or the details at the well house. The "community water system" supports 40-45 customers. The recirc punp is for domestic hot water only. Our floor hydronic system is separate from the potable water system. I need to crawl under the house to see if there are any check valves in the recirc line. I believe there are two faucet bibs off the long stretches of pipe so as to drain the system for winterization. The house is one year old. We will get our plumbing contractor involved as soon as I learn a little more.