What is this and why would you have it?

[Frank Magdefrau]

I don't think I have seen this yet but it was on the water line to the hall bathroom toilet only.

[Bruce A. King]

Looks like a small water hammer arrestor, have not seen one that small before.

[rcooke]

Originally Posted by fmagdefrau

I don't think I have seen this yet but it was on the water line to the hall bathroom toilet only.

Looks like a air chamber to me to stop water hammer when you shut the tap of some homes with high presure need this to help.
Cookie

http://www.factsfacts.com/MyHomeRepair/PipeNoises.htm

[Thomas H. Dietrich]

That size is used for ice makers, right?

tom

[Henry Valenzano, CMI]

Originally Posted by fmagdefrau

I don't think I have seen this yet but it was on the water line to the hall bathroom toilet only.

It looks like a home owner that doesn't know what he is doing or a plumber that is trying to make money by shafting his customers.

[bdoles2]

Originally Posted by bking

...have not seen one that small before.

Words we dread to hear!

[Russel Ray]

It is an air chamber to stop water hammer. I find them quite often in the laundry. Almost all new construction here has them in the laundry.

[relliott]

never saw that on a plastic supply line to a toilet.
overkill.

[Scott Gilligan, CMI]

Toilets, washing machines, and dishwashers are the biggest culprits when it comes to water hammer. Valves and seats get worn and do not seal as good as they normally do when new parts are working as designed. One way to to solve the problem is to replace the $7.00 fill valve for the toilet or take the effort to dismantle the washing machine to get to the fill valve selinoid. You can install a hammer arrestor like pictured, but sooner or later the valve is going to completely fail and you are going to have to replace it anyway. People have to learn, when they hear that hammering noise, it is more than likely a bad toilet fill valve. It is the most commonly used plumbing device in a house. Makes you think how many times everyone really washes their hands afterwards!