This is a statement propane cylinder users sometimes make following the exchange or re-filling of their bottle. The bottle feels heavier and obviously is filled with propane but opening the valve produces no escaping gas. OPD valves are designed so that propane will not flow from the service valve unless it is hooked up to a hose end connection. This is the way the OPD cylinder valve was designed. Unattached propane cylinders equipped with OPD valves will not allow gas to flow when the service valve (handwheel) is opened. The same is true of forklift cylinder valves.
The design of the OPD valve is such that turning the cylinder service valve handwheel will not produce any effect if the cylinder is not hooked up to an appliance. In other words, a connection must be made between the appliance hose end and the cylinders service valve. The inside of the OPD valve is engineered to only allow propane in or out if the internal valve is actuated by being depressed. This OPD valve feature adds additional safety in case the handwheel is turned, opening the valve. For this reason, OPD equipped cylinders will not allow gas out of the cylinder when opened. The same is true for industrial forklift cylinders. Click the photo of the OPD valve (left) to see a larger and more detailed picture of the of the internal flow valve.
See additional OPD Valve Information
The hose end connection on either a fill hose or appliance supply line is designed to work only with OPD equipped cylinders. For the OPD valve to operate with the handwheel open, the hose end connection must be securely attached. The picture to the left shows a hose end connection. Notice the elevated brass fitting is surrounded by acme threads. When attached to a cylinder valve and tightened, the brass fitting will push the internal valve open and allow gas to flow out of the cylinder to the appliance, if the handwheel is in the open position. This fitting must be in place for gas to flow out of the cylinder. Otherwise, turning the handwheel will not produce the intended result.