How Pressure Relief Valves Protect Your Propane Tank System

Propane is a liquid stored under pressure in ASME and DOT-regulated vessels. Most propane appliances and applications require it to be in a vapor state for use. For propane to become vapor, the liquid needs to boil, which increases the pressure in the tank. Unlike water, which boils at 212°F, propane boils at a much lower temperature of -44°F.

Propane vapor is like steam rising from a boiling pot of water. Because propane is cold and boils at such a low temperature, the pressure inside the tank can become exceedingly high. This is especially prevalent in the summertime when temperatures are hottest.

Propane liquid expands seventeen times more than water when turning into vapor. We fill propane tanks to 80-85% of their capacity to allow extra space for vapor. This extra space provides a safe buffer to prevent the tank from expanding or rupturing. This is where the pressure relief valve comes into play. 

Each relief valve contains a spring. If the pressure inside the tank is at a safe level, the spring keeps the valve closed. When the pressure in the tank becomes too high, the valve will open to release some pressure. This helps to bring the pressure back down to a safe level. You may hear a hissing sound and potentially smell propane gas. 

If the pressure in the tank gets too high, you may hear a pop, which indicates the valve is fully opening to release pressure more quickly. Once the pressure drops below the spring’s threshold, the valve closes on its own. If the valve pops open, it may need to be replaced. Never attempt to work on a propane tanks or systems on your own; this requires a trained professional.

If you smell gas, the pressure relief valve may be doing its job by keeping your tank at a safe operating level. However, if you smell gas around the tank, it could also indicate a leak. Always call a professional to check your tank if you smell gas to perform a system leak check. A specialist will also inspect the valves and other working parts to ensure your safety is maintained.