It’s summertime, folks, and that means it’s the grilling season. Sure, we all love grilling year round but there’s nothing quite like a summer barbecue. Before you fire up that grill I allow me to engage you in a quick discussion about our ‘propane bottles.’

Grilling cylinders are technically known as 20 lb. DOT cylinders because they are built to DOT specifications. DOT specifications include rules that deal with metal thickness, pressure capabilities, and longevity of the tank. These cylinders can only legally contain 20 lbs. of propane. Propane weighs 4.24 lbs. per gallon. That means there is approximately 4.7 gallons of propane in your grilling cylinder when it’s full.

20 lb. DOT cylinder

Grilling cylinders can be refilled or exchanged at a cylinder exchange cage. Refilling stations must refill the cylinder by weight. That’s why when you get your grilling cylinder refilled, the attendant will place it on a set of scales before they start the pump. Sometimes the attendant even uses a screwdriver and opens a small hole in the valve. You’ll hear a hissing noise as the bottle fills. When the grilling cylinder reaches 80% capacity, a white mist will shoot out of the small hole indicating that the cylinder is full. ‘Full’ in the propane industry, when regarding tanks and cylinders, is actually 80% of the water capacity of the tank or cylinder being filled. Propane is very susceptible to temperature changes and will expand or contract greatly with changes in the outside temperatures. To compensate for this possible dangerous expansion, we never completely fill up a tank or cylinder. We always stop at the 80% level.

Grilling cylinders are equipped with all kinds of safety features. One such feature is the OPD valve. The OPD valve ensures that your grilling cylinder isn’t over filled. All cylinders that hold less than 100 lbs. of propane are required by law to have this type of valve installed. OPD stands for Overfill Protection Device and that is exactly what it is designed to do. As the cylinder is being filled and the liquid level rises, it also raises a small float attached to the bottom of the valve. As this float rises to approximately 809% of the volume of the tank, the valve will shut and stop propane from being allowed into the cylinder. Despite the OPD being required by law to be on your grilling cylinder, the law also says it must still be filled by weight. The OPD is a safety backup.

OPD valve diagram

Your grilling cylinder is rated to be used for a period of 12 years from the date of manufacture. On the cylinder collar you will ding the date of manufacture in a month-year format, stamped into the metal. Each time that your cylinder is filled it must be visually inspected and looking at the date of manufacture is usually one of the first items that the refilling agent will look for. A cylinder may be re-qualified by doing a visual inspection by a properly trained agent and will require a new date followed by the letter E stamped into the collar. This will allow the cylinder to be filled for another 5 years. Some companies do this re-qualification for their customers but most do not.

Many customers find that the cylinder exchange cages are the way that they prefer to get a full cylinder of propane for their grill. The customer brings an empty cylinder to the cage location, leaves the empty, and gets a full cylinder. The price for exchange is generally higher than having your cylinder refilled yourself but the exchange cage locations are generally open when a cylinder filing station may be closed. When using the exchange cages, the customer is assured that the cylinder has benen inspected and filled by a professional. Another drawback of the exchange process is that some companies will, by policy, not put a full 20 lbs. of propane in the exchange cylinder. Be sure to check the cage before purchasing to ensure that you are getting a full 20 lb. cylinder.

Another safety measure installed in grilling cylinders is an excess flow valve. The excess flow will engage and stop the full flow of propane through the valve if it sense that the gas line may have been broken or installed incorrectly. Over the years, I have seen customers open the valve swiftly, allowing gas to fill unpressurized gas hose so quickly that the excess flow ‘thinks’ that there is a problem and will shut the gas. It will release a small amount of gas to pressurize the hose on the downstream side of the valve in order to reset itself. For an unknowing customer, this small amount of gas being released is just enough to light a very small flame in their grill. This usually lends to the assumption that there’s something wrong with the grill.  If this happens to you, simply turn off the burners on the grill and turn the cylinders valve to the off position and the excess flow will reset itself. You may even hear a small click when the reset occurs. After being reset, open the valve slowly (very slowly). Once the hose is pressurized, full gas flow will occur.

One last thing to be aware of when handling your grilling cylinder is a hissing sound coming from the back side of the valve. This is the pressure relief valve. It is designed to relive excess pressure that may build up inside of the cylinder. If you discover the valve is hissing or leaking, move the cylinder away from people and buildings in a cool place and away from any source of ignition. Call the person that filled the cylinder and follow their directions.

Now, get out there, grill, and remember to be safe.