There are three types of connectors found on liquid-propane gas cylinders. The differences between types is a result of changing safety regulations. In general, it is not illegal to use or transport tanks with older connectors. However, it is against the law for older tanks to be filled. When considering a used propane appliance, such as a grill, or a used LP cylinder, identifying the connector type will be an essential part of your purchasing decision.
This is the oldest style tank you are likely to encounter. POL is short for the company that first produced this type of valve. POL valves use a female left-handed thread. This means the threads are on the inside of the connector and the connection is tightened by turning the fitting counterclockwise. POL valve connections usually require the use of a wrench to ensure a secure fit. POL valves allow the release of propane without having anything connected. A plug must be screwed into the valve before transporting the cylinder or storing it disconnected from an appliance. This valve type also includes a bleeder valve used to check for proper filling and a pressure relief device that prevents over-pressurization of the tank. Tanks with this type of valve can be used by older appliances, but cannot be refilled legally.
This valve is also known as a quick-closing coupling or QCC valve. The ACME valve looks bigger than the POL valve due to the addition of large male (outside) threads. The valve also has the older internal female threads. This combination of styles allows the valve to be used by older appliances. When checking the connection on an appliance, look for a large, hand-turned fitting that fits over the external threads. This fitting can be secured to the tank by hand. The fitting is tightened by turning it clockwise. In addition to easier use, a device must be attached before a built-in safety device opens to allow gas flow. This safety feature removes the requirement that a plug be installed before transportation or storage.
The current standard valve is the overfill prevention device, or OPD valve. The valve appears to be very similar to an ACME valve. The primary visible difference is in the handwheel. Older cylinders use five or six spoke wheels. OPD valves have handwheels with three solid lobes. For the consumer, there is little difference between an ACME valve and an OPD valve. The OPD valve incorporates a safety feature that prevents overfilling the cylinder. Tanks with the older ACME valves are legal to use and transport, but only those with OPD valves can be legally filled. Any new cylinder should come with an OPD valve installed.
What to do with an Older Valve
If you have a grill or other appliance that uses an older connection type, you do not have to replace or refit it. ACME and OPD valves both incorporate the older female, left-threaded connection. You will need to use a wrench to ensure a secure connection. If you have an empty cylinder with an older valve, you can often exchange it for a cylinder with an OPD valve. Most self-serve exchange kiosks will list rules requiring current style valves be installed on empty tanks. Some retailers will allow the exchange of cylinders with old valves for cylinders with new valves. Check with local retailers, especially those dealing exclusively with LP gas, to find out the details of their exchange programs. If they will not exchange your tank, they will be able to help you dispose of it safely. Unwanted propane cylinders should never be put out with the trash.