what is a vacuum relief valve for?

[northman]

on a water heater/expansion tank installation?

Looking at the Watts site to size an expansion tank, they show a vacuum relief valve installed at the water heater. What is the purpose? Is it necessary or are they just trying to sell parts?


Greg

[Peanut9199]

"Vacuum Relief Valves are used in water heater/tank applications to automatically allow air to enter into the piping system to prevent vacuum conditions that could siphon the water from the system and damage water heater/tank equipment." and no you don't need it.

[jadnashua]

My city requires them on new installs along with a tempering valve. My guess is to prevent what may be heated water that has sat for awhile in the water heater from being sucked back into the rest of the potable water. Since all of the water is supposed to be potable, not sure why, but as I said, it is code in my city.

[hj]

If the heater is in an upper floor level or attic, then the negative pressure created by a broken pipe draining the heater could collapse the walls of the heater. In this case, the installation requires a vacuum vent to relieve the negative pressure. It is not required if the heater is in a basement or first floor because those installations cannot create high negative pressures.

[Dunbar Plumbing]

Required on most commercial applications regarding restaurants, nail shops, beauty salons, where chemicals/cross connections are possible above mild.

[hj]

Those applications do not require a vacuum relief valve, they require backflow prevention devices, and the higher the possible contamination level, the more sophisiticated the device has to be.