Banging Pipes

My name is John Scott. I have 20 year old townhome. The two upstairs bathroom tubs drain into one drain, which is under the floor. In the last monhts we've noticed that the pipes of the drain bang when the water is let out of the tubs. We've tried to get any air out of the pipes by bleeding them, etc. Doesn't seem to work. The banging continues, etc.

Don't want to have to take down a wall to get to the banging pipes, etc Doesn't seem as if its the pipers hitting something but that air or someting is inside the pipers.

Ideas? John Scott

Drains always have some air in them...

PVC drain pipe expands and contracts with changes in temperature...draining the hot water from a tub will cause it to expand, then it will contract back to "normal" size when it cools off. If the pipe rubs agains anything, or is clamped too tightely, it is likely to make some popping sounds or clicking sounds as it rubs/jerks through holes that may be binding. Even if it isn't rubbing on anything, it can make noises on its own as it expands and contracts. It is also more prone to passing the sound of the water draining than say cast iron drain lines.

So, what you have may be entirely normal...maybe not desireable, but normal. If it isn't rubbing on things, then adding some insulation to the walls may help a little.

The only time a drain line has water in it when it is actually draining water. The rest of the time it is full of air except for the traps which always have water in them.