RegulatorA typical liquid propane (LP) tank, called a 5- gallon tank, weighs about 20 lbs empty and holds an additional 20 lbs of fuel only if it is filled to the top, which would be unusual and perhaps unsafe should the tank get hot and vent its excess fuel. Suppliers like Blue Rhino fill the tank with just over 4 gallons, weighing 17 lbs, so that a full tank weighs about 37 lbs. One pound of LP delivers 21,600 BTUs of heat. (Thus, pounds of fuel times 21,600 divided by the BTU/hr rate of use equals hours of operation.) One gallon delivers 91,500 BTUs. Liquid natural gas (LNG) has somewhat less heat per pound than LP.
Pressure in a propane tank, ranging from 100 to 200 psi, must be reduced and regulated at the tank output. A high pressure regulator supplies 1 to 60 psi for a large appliance, like a particularly large grill or space heater, that has a high BTU/hr rating. Some can be adjusted up to 20, 40, or 60 psi by turning a the attached devices can use. The low pressure regulator usually found on a boat supplies 6 ounces per sq in, enough pressure to lift a column of water 10.5 in. Following the regulator, at the other end of the hose, might be a ball or needle valve to further restrict the flow.
icing
upIf propane output drops before the tank Tank is empty, most likely water in the fuel is icing up the regulator where the fuel changes from liquid to gas, taking in heat as it expands. Swapping in a new tank might not help unless you also change the regulator. Thaw it, instead, with a towel soaked in hot water, or a good flow of warm air, and use less fuel until it thaws.
Propane tank
connectionsThe output of a standard LP tank is threaded for an Acme connector on the outside and a POL connector (named for the company that first made them) on the inside. Acme connectors— either high- or low-pressure and always matched to the regulator—twist on hand tight in the usual way and include a protective shut-off mechanism. POL connectors, also high- or low- pressure and matched to the regulator, have a left-hand thread and twist on finger tight if there is a rubber o-ring at the tip, otherwise wrench tight. Open the valve on the tank fully, only when fuel is being used, then close it afterward, but never just crack it part way open. After opening the valve, brush soapy water on the connector and watch for bubbles to check for leaks. Keep the tank always upright, even while transporting it in a car, and well strapped in. Be mindful that propane is odorless and heavier than air. Any and ignite from the slightest spark.