[jjmmnn22]

Ok...so I am usually pretty good at finding my answers in other threads, but this one seems like a unique situation. I have a really old basement tub/shower. It has 4 twist on handles (hot/cold for tub and hot/cold for the shower). When the hot for the shower is turned on about half way it starts to bang (a machine-gun like sound). When you turn it to full open it is fine. I took off the shower head to see if that helps, but it still does it. Any ideas?

thanks!

[Celtic]

Air hammer

[ChrWright]

Air hammer, and your pipes are not strapped down very well in the wall/ceiling...

[PIPES]

Sounds more like a loose washer. Shut the water off and remove the stems to check them out.

Air hammers are tools in a mechanic's tool box.

[jjmmnn22]

I thought air hammer happens when the water shuts off?

[Celtic]

Originally Posted by jjmmnn22

I thought air hammer happens when the water shuts off?

Originally Posted by jjmmnn22

When the hot for the shower is turned on about half way it starts to bang (a machine-gun like sound). When you turn it to full open it is fine.

Is "half-way" open or closed

[MechanicalDVR]

The screw holding the washer to the stem is most likely corroded in two. Happens all the time in those old valves.
If that's it drill out the screw and retap it.

[PIPES]

Originally Posted by jjmmnn22

I thought air hammer happens when the water shuts off?

air hammer –noun a pneumatic hammer, usually portable.

Dictionary.com Unabridged (v 1.1)
American Heritage Dictionary - Cite This Source
water hammer
n.

1. A banging noise heard in a water pipe following an abrupt alteration of the flow with resultant pressure surges.
2. A banging noise in steam pipes, caused by steam bubbles entering a cold pipe partially filled with water.

[Herk]

The condition you are describing is water hammer, and it has to do with vibration in the valves. This also happens with toilet fill valves. Solutions vary from replacing the stems because they are worn, to replacing the valves, to adding air chambers, which is probably the least effective solution. The threads on the stems are worn enough to allow the vibration. Most new valves do not have this problem.

[Celtic]

Originally Posted by PIPES

Air hammers are tools in a mechanic's tool box.

I ain't a plumber

Water hammer then

[MechanicalDVR]

Water hammer is caused by high velocity in piping, either from running too high a pressure or too small id piping. With either condition the momemtum of the water traveling through the piping when stopped by a fast closing valve will want to keep traveling, causing the pipe to jump or bang. Mechanical arrestors will take up the impact of the hydraulic action as will air chambers properly installed.

Saying that the sound is "like a machine gun" is a sure sign of a loose washer inside a valve spinning and banging back and forth as the water flows by, this happens often when the washer retaining screw breaks off or when a stop and waste valve is installed backward to the proper flow.