What is an OPD?
Required by national fire and safety standards, an OPD is a safety feature that helps prevent small propane cylinders from being overfilled.
Why Have an OPD?
There are limits on how much propane can be put into a cylinder. A properly filled cylinder will have a vapor space left in the top of the cylinder to allow room for expansion of the liquid with a change in atmospheric temperature. An overfilling prevention device is a secondary means of assuring that cylinders are not overfilled.
What Can Happen if a Cylinder is Overfilled?
An overfilled cylinder doesn’t have enough space left if the liquid expands when exposed to warmer temperatures. This can cause an increase in cylinder pressure and create potentially hazardous conditions, such as the pressure relief valve may open, discharging propane from the cylinder or propane liquid could enter the piping system, resulting in higher than normal pressures to appliances.
How Does an OPD Work?
During the refilling process, a valve inside the cylinder closes when the proper level of propane is reached. Since the OPD currently in use measures the volume of propane in the cylinder, the weight of the propane will vary depending on its temperature. Check the posted information where you purchase propane to determine the net weight of propane in your cylinder.
When Will OPD-Equipped Cylinders Be Available?
All DOT cylinders with capacities of 4 pounds up to 40 pounds must have OPD valves.
What Happens if I Don’t Have an OPD Installed on My Cylinder?
As of April 1, 2002, cylinders without OPDs cannot be refilled.