The safety relief valve is one of the most important and vital valves on any LP Gas container. All propane tanks and cylinders are required by law to be fitted with pressure relief devices designed to relieve excess pressure. The function of a safety relief valve is to keep a propane tank from rupturing in the unlikely event of excessive pressure buildup. Propane tank relief valves are also known as pop off valves, pressure venting valves or relief valves.
Relief valves are held in the closed position by the force of a powerful spring. As long as the pressure inside the tank is less than that of the spring, the valve will remain closed. If tank pressure rises to that of the spring, the valve will open resulting in a hissing sound outside the tank. If the pressure in the tank rises significantly higher than that of the spring, the valve will fully open. When the valve fully opens, it initially makes a loud pop followed by a blast of released propane gas. Once the pressure is released and the tank pressure falls below that of the spring, the valve closes.
Most propane tanks in residential and commercial service have internal safety relief valves. The reason for an internal valve as opposed to an external pressure relief valve is it presents less of an obstruction when moving the tank. Internal relief valves are generally placed near the end of the propane tank on above ground containers.
Found primarily on older tanks, external relief valves operate in the same manner as an internal relief valve with the spring mechanism being outside the propane tank itself. Relief valves on multvalves are always fitted with external safety relief valves. Older tanks with an external relief valve installed on the container are generally replaced with internal pressure relief valves, provided they are connected to a dedicated tank opening specifically designed for the placement of the relief valve.
Because the safety relief valve performs such a vital role in the protection of the propane tank, it should be maintained and repaired by licensed propane professionals only. Do not ever look into a relief valve or stand over it.
Pictured left is a relief valve that was apparently leaking. Instead of calling the propane company to replace the valve, the customer decided to fix the problem himself. Using a soldering iron, he soldered the leak until it stopped leaking. In the process of "repairing" the leak, the customer completely sealed the relief valve in a closed position placing himself and his family in a very dangerous situation.
In this type of situation, a relief valve that is sealed shut will not allow the tank to vent excess pressure if it is overfilled or the pressure inside the tank exceeds the working pressure of the container. In a case where the tank is unable to vent to the outside, the tank is subject to rupturing causing more harm and damage than money saved by trying to fix it yourself. Let the propane company or LPG professional handle any problems with thesafety relief valve.