[d4nnyb0y02]

I have a two story house. Basement>main level>2nd story.

When running the dishwasher on the main level, I get water hammering during some point of it running.

When using the shower in the master bathroom on the 2nd floor (probably the furthest unit using water from the main), I also get water hammer.

Where is the best place to install water hammer arrestors? Or, how do I take care of this knocking?

[cdad]

If its just knocking then you could have loose clamps along the pipeline. Allowing for the pipes to move when they resonate. The pressure is steady from the pipes correct ?

[speedball1]

Can you furnish more details? Age of house. The water pressure in the house.
"Water hammer" happens when you abruptly shut off the water. You have at least 40 pounds of pressure pushing the water flow. The weight of the water hitting a 90 degree bend causes the sound that you hear. We put in air chambers to cushion the hammer much like the shocks on your car.
Back in the 60's we were required to to put air chambers on all bath lavatories and kitchen sinks. Over time water and condensate built up in them and they must be recharged. First turn off the house at the main house shut off valve. Then open hot and cold faucets at the farthest bathroom to prevent air lock.(This is important.) You will find under each fixture little brass or chrome valves. These are called angle stops. With a small pail held under the angle stop to catch the run off look under the handle of the stop and you will see a nut with the stem running through it. This is called the bonnet packing nut. Put your wrench on it and back it off counterclockwise. Now open the stop and remove the stem and washer assembly, The stop will began to drain. When it has quit draining reassemble the stop and move on to the next one. Do this on each one of your angle stops. There will be six of them in a two bath home. When you are done, close off the faucets you have opened, turn on the water to the house, and give yourself a pat on the back.
You have just recharged your air chambers and saved yourself a hefty service call bill. Hope this helps you out and thank you for rating my reply. TOM

[d4nnyb0y02]

Can you furnish more details? Age of house. The water pressure in the house.
"Water hammer" happens when you abruptly shut off the water. You have at least 40 pounds of pressure pushing the water flow. The weight of the water hitting a 90 degree bend causes the sound that you hear. We put in air chambers to cushion the hammer much like the shocks on your car.
Back in the 60's we were required to to put air chambers on all bath lavatories and kitchen sinks. Over time water and condensate built up in them and they must be recharged. First turn off the house at the main house shut off valve. Then open hot and cold faucets at the farthest bathroom to prevent air lock.(This is important.) You will find under each fixture little brass or chrome valves. These are called angle stops. With a small pail held under the angle stop to catch the run off look under the handle of the stop and you will see a nut with the stem running through it. This is called the bonnet packing nut. Put your wrench on it and back it off counterclockwise. Now open the stop and remove the stem and washer assembly, The stop will began to drain. When it has quit draining reassemble the stop and move on to the next one. Do this on each one of your angle stops. There will be six of them in a two bath home. When you are done, close off the faucets you have opened, turn on the water to the house, and give yourself a pat on the back.
You have just recharged your air chambers and saved yourself a hefty service call bill. Hope this helps you out and thank you for rating my reply. TOM

House built in 1978. I here knocking once I'm done taking a shower in the master bathroom shower, or one the dishwasher has finished it's wash/rinse cycle (when it stops pulling water into it). It doesn't happen when the water is running.

If its just knocking then you could have loose clamps along the pipeline. Allowing for the pipes to move when they resonate. The pressure is steady from the pipes correct ?

Yes, pressure is steady.

[speedball1]

You should have aiur chambers installed. Recharge them according to my instructions. Good luck, Tom

[d4nnyb0y02]

You should have aiur chambers installed. Recharge them according to my instructions. Good luck, Tom

Under every single sink in my house (3 bathrooms, and 1 kitchen), I have brand new compression shut off valves, installed less than 3 months ago. Nothing leaks.

Does this change anything about what you suggested? Where would these air chambers be located? Behind the walls where I can't see them?

[d4nnyb0y02]

I've been asking similar question, but I may have been wrong about the issue before. Here is what is happening.

I hear the noise while water is running (for instance, when I'm running the dishwasher). Sometimes it's every 10 seconds... sometimes it's every second. It's a slight knock in the pipes. Last night, we went to bed and the dishwasher had been done running for a good 10 minutes or more... and when I was upstairs on the 2nd level... I could still hear a slight knock every 15-20 seconds. It was driving me nuts so I had to get out of bed and see if I could get rid of it.

I turned on the faucet in the upstairs bathroom (master bath), both hot and cold, thinking maybe if it was air, that would clear it. It kept doing it even after doing that.

It doesn't just do it right after I shut the water off or anything... it continues to do it for awhile, even after no water is running. Eventually it stops, but I haven't found any reason for it. I never get any "spitting" when opening a faucet, ever.

[speedball1]

OK! Perhaps it's not water hammer after all. Water hammer can be fixed.
Contracting end expanding pipes in the wall can be a little more difficult to locate and repair.
Knocking, popping, creaking and crackling pipes are a common complaint, especially in colder weather. I can tell you what's happening and take the mystery out of it but you're not going to like the repair. When a draw is made on a hot water line the line expands against a pipe strap next to a stud and when you drain hot water from your tub or shower it goes into a chase that is a little cooler then room temperature. The heat expands the pipe causing it to rub against the stud to which it is pipe strapped. This is the sound you hear. As it cools it contracts and the noise is heard again. To repair it you must tear open the walls and locate the pipe strap that's causing the problem and shim it tight. Most people when they learn what causes it just elect to live with it. Good luck and thank you for rating my answer. Tom