When I turn the shower on sometimes I get water hammer. Does anyone know how I go about finding where this originates and fix the problem?

Water hammer, which is the loud banging of pipe against a structural member, when the flow of water is abruptly stopped. This usually occurs when a fast acting valve, such as a toilet or single lever faucet closes.

If there is a vibrating of pipes when you turn on a shower valve it is most likely a loose washer vibrating, either in the shower valve or some other valve in that line. Could also be caused by debris trapped in the valve causing a fluctuating in the water flow.

I think the main cause of water hammer is air-cushion lost within the pipe. You need to drain and re-establish an air cushion. Lots of info available on how to do that. Here's one; http://home.howstuffworks.com/home-improvement/plumbing/how-to-fix-pipes5.htm

Jaz

If this is isolated only to the shower then I am inclined to agree with Hkstroud that the cartridge assembly could be the issue. Here, you would remove the cartridge and inspect it for a loose washer...may just want to replace the cartridge since you have it out.

Of course, you could have the more "old-fashioned" water hammer bumpers Jazman presented, and if that is the case, you would need to shut off the water main, open all fixtures and wait a half hour for air to displace the water in the bumpers. Reenergize the water, bleed air from all pipes and see if that improved things.

If none of these resolve the hammering issue, you may have to make an access panel on the backside of this shower valve so you can secure the valve to the studs better...that should reduce the hammer sound! This securing of the valve may also be able to be accomplished through the front by removing the trim plate and sticking some towels or similar padding in between the valve and the back of the shower wall...;)

Good luck!

Mark

"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