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.
How does a 2 stage relief valve work?
The relief valve opens when the supply pressure exceeds the set pressure. As the flow increases the actual fluid pressure will also increase slightly. ... High flow valves tend to have two stages with a small pilot relief valve that opens a larger, second, main stage valve.
Where should a vacuum relief valve be installed?
Bottom fed water heaters and bottom fed tanks connected to water heaters shall have a vacuum relief valve installed. The vacuum relief valve shall comply with ANSI Z21.