The tank service valve is the point at which propane vapor enters the gas plumbing system for use by downstream LP Gas appliances. All ASME propane tanks have a service valve that functions as a primary shut-off device when used in vapor service systems. Proper operation of the service valve is important for safety reasons and gas utilization. If you smell propane in your house, the service valve should be turned off immediately!
The propane service valve is the controlling mechanism allowing propane gas to flow into the house or building by way of the gas piping system. Although other gas valves may be present throughout the gas plumbing, the service valve, on the propane tank, is the valve that controls 100% of the gas flow into the gas system. Basically, propane service valves function as the "on / off switch" in propane gas systems and is for vapor service only.
Operation of a propane tank service valve is similar to that of a water faucet . The operational part of the valve consists of a handwheel that closes and opens gas flow by turning the wheel clockwise and counter-clockwise. Inside the valve is a stem and seat that when opened, allows gas to exit the tank and when closed, stops the flow of gas. Although it may seem that the functionality of a service valve is identical to that of a water faucet, it is has one very distinct difference - The proper use of propane requires an LP Gas regulator which reduces the amount of pressure introduced into the gas service line to a level that is safe and acceptable for the application requirements. In other words, the service valve is only used for turning the gas on or turning the gas off, not for regulating the flow of gas.
Like all moving parts, gas service valves are subject to wear and tear. When these essential valves leak, malfunction or fail, they need to be either repaired or replaced. Repairing a service valve is much easier and cheaper than replacing one but this has to be performed by a gas service technician. Depending on the age, type and make of the service valve, repair kits are often available through licensed propane companies and can be used to replace the faulty parts. These repair kits commonly consist of several independent parts that may or may not all be used to fix the valve's problem. If the entire LP Gas service valve needs to be replaced, the propane tank needs to be completely empty. When repair kits are used to correct a malfunctioning valve part, the severity of the problem will dictate whether or not a tank needs to be empty when repairing or replacing the faulty part(s) of a propane tank service valve.