what's this and what does it do?

[wward]

inline shutoff valve with a small somthing on the outflow side with a small plastic tube running into the overflow pan for water heater.
This small tube has a steady stream pooring out.
What is is and what does it do?

<a href="http://s183.photobucket.com/albums/x...t=P1020326.jpg" target="_blank"><img src="http://i183.photobucket.com/albums/x...8/P1020326.jpg" border="0" alt="Photobucket"></a>

[Michael Larson]

http://www.zurn.com/operations/wilki...ion/ISBVEC.pdf

[Wayne B. Wilson]

Would it not be better to install a expansion tank?

[Jack L. Gilleland]

Only if you don't want to waste water.

[James H. Bushart]

Sounds, by the description of it being on the "outward flow" side, that it is improperly installed.

[Larry D. Kage]

Originally Posted by wward

This small tube has a steady stream pooring out.

Sounds like it needs replacing...and Jim's right, it should be installed on the cold water inlet side, downsteam of the shut off.