What is a vacuum relief valve, and why is it required in a solar pool heating system?
A valve must be installed in every solar pool heating system to allow air into the system when pool water drains out of the panels. This relieves the vacuum that would be created by falling water inside the solar panels and plumbing on the roof. There are various styles of vacuum relief valves, but all automatically allow air into the system when there is a vacuum created by a void of water pressure. We in the industry refer to a vacuum relief valve as a VRV.
Properly installed systems are designed to drain back to the pool every night when the pool pump shuts off. The main purposes of this is to eliminate the risk of freeze damage in the panels and plumbing. Freezing water expands and can bursts panels and pipes, and solar panels have a high ability to emit heat to the night sky, making them susceptible to freezing, even here in Southwest Florida at times. Another reasons panels should drain is to reduce the risk of stagnation in the summer, causing overheating and warped and discolored plumbing. Finally, draining panels for service purposes is helpful.
Some panels cannot drain automatically because of the way they are plumbed (either purposely or because the installer doesn’t know what they are doing). Systems that do not drain naturally with gravity should have a manually operable drain valve installed. In this case, a vacuum relief valve is still required.
A vacuum relief valve is required in every solar pool heating system!
Not installing a proper vacuum relief valve, or installing it in the wrong position could result in collapsed plumbing or panel failures. A VRV should be installed at the highest point in the system whenever possible.
Some people erroneously believe the relief valve in a solar pool heater is there to relieve excess pressure and heat. That is not the case. Because a solar pool heater is an open loop system, expanding water and air due to heat easily escapes back to the pool, and no pressure relief is necessary. It is a vacuum (negative air pressure) that we are trying to avoid.
A good vacuum relief valve will allow air into the plumbing efficiently and allow the panels to drain quickly. VRVs can cause a bit of noise during draining, so quick draining is ideal. We use a high quality VRV that uses a simple ball and spring principle. It can be inspected and checked for proper operation easily by removing the threaded cap. This valve type is highly reliable and efficient. Other valve types are plastic with rubber bladders or brass with steel springs. Failed VRVs are a common service issue for these other valves, and we believe our design is superior in construction and operation. A failed VRV will result in water oozing out, or in severe cases pouring out in large quantities. While swapping out a VRV is easy, they can be expensive, so installing a good valve from the start is a good idea.