Thanks for the advise. I will try it.

water hammer arrestor is designed to absorb that knocking , its available with different sizes for different water flows , it's available in big plumbing warehouses. You can consult good plumber to chose the suitable one .

On the other hand, it is entirely possible to have a slightly loose faucet washer that doesn't leak but will cause knocking with pressure variations. A "gremlin" washer may be laughing nearby.

If anyone figures it out, let me know. I have tried endlesly to correct this prob. No such -uck!

Hi,

If the knocking sound is heard when one opens a tap, the cause is a spinning washer and spindle. Remove the washer and spindle, hit the spindle with a hammer until it fits snugly in its hole.....if the washer needs replacing..do it too. The noise that a spinning washer makes is unbelievable!

Jurie

We still don't know when the knocking occurs. Some water hammer is caused by turning water off, and some is caused by water flowing at a speed through a valve that causes resonant knocking. Before attacking the plumbing to add an air chamber, I would suggest turning the main water control valve a bit in either direction and see if that has any effect.

Good answer!

Thats what I would do. It happened to me once. A valve was partially closed and when I opened it, the hammer stopped.

Peace

Try it again, this time however after draining the system leave the faucets open. Then open the mainline and starting at the lowest point turn off the faucets until reaching the highest point in the system to bleed the air out. Then you may isolate the offending location and fix as others have described.

I agree with Planinurus - it could be one of your faucet washers - check it out. I had a similar problem to yours and the plumber sorted out the washer. Good luck!

Dhiru Soni

I had the same problem after installing a tank-less water heater, solved by installing an air chamber that I purchased at a local home improvement store.

Loose pipes will often knock.

I concur with the possiblity of loose pipes.

Pipe hangers can be snug to the point that the sliding/binding pipe (with temperature change) will cause a noise similar to a knock (a ping if copper). There are various hanger products available to mitigate this (hangers with material that allows movement)

http://www.associatedcontent.com/article/151927/quiet_your_noisy_plumbing_pipes.html

Correct, even long runs (more than 1 yard or meter) can give problems. As can sharp turns that are unsupported......

If the system is seperated with valves into say 4 seperate bits, you can test each part in turn to find out when/where the problem is......

1) You shoud've left your faucets and supply valves "OPEN" when you turned the Main back on

2) Chances are that it is not Airtrapped in the pipes but simply the inertia of the flowing water causing the pipes to move where there is a loose vertical section in balance with an elbow at the end of a run... You need to locate this. (press your ear to an inverted tumbler held against the wall) then you need to open the drywall and anchor the section (near the 90 degree elbow).

I install large water mains(up to 96") and we put "Thrust Blocks" at the down stream side of each turn to prevent this lateral movement... It can be very damaging to the integrity of the piping...

Your problem is probably a water hammer and is solved as noted by the other replies, but one other thing you should check is water pressure. If the pressure is too high, not only will you get water hammer, but it will also cause premature failure of faucets and solenoid valves (as found in dishwashers, washing machines and ice makers). Water pressure should be around 35 PSI and can be checked by putting a gauge on an outside faucet that has a water hose connection. The water department can also check it for you.

35 PSI may be too low for many users. Water Departments in our area are required to provide between 40-80 PSI range for proper fire flow and best operation of many appliances.

Dear Ernie:

What you have is known as water hammer. It's caused by air trapped in one of your pipes, and yes it can drive you crazy. You have to find which pipe has a high point where you could accumulate an air bubble. You change the inclination of the pipe so that water pressure can eliminate the bubble by itself.

That's all, good luck.

Gerald Rosenbaum.