Originally Posted By: John Clayton This post was automatically imported from our archived forum.
I believe what you are asking about is a ball valve with a built in pressure relief valve. You should be able to find info about them on the manufacturers website. The two brands I stock are Watts and Conbraco.
They do have a flow direction, be sure they are installed in the correct orientation so that the relief valve is on the proper side of the ball valve. They can be used in most any situation where you require both a shut off valve and a pressure relief valve. They are available in different relief valve settings I think from 80psi - 150psi. In the situation you described I would assume it is being used for thermal expansion protection as an alternative to an expansion tank for the water heater. This type of installation is good to bring a closed loop water distribution system up to code as long as it does not reach pressures that activate the pressure relief valve on a recurring basis. That would waste a tremendous amount of water over its lifetime. However on installations in closed loop systems that never reach that high of pressure it is a great substitution for an expansion tank. Which will save on material cost, installation cost, usable space and I believe less likely to fail as many expansion tanks do.