The six standard fittings
- Service valve — main on/off for gas supply to the regulator and home. The shutoff you use in an emergency.
- Fill valve — where the delivery truck connects to fill the tank. Standard ACME thread.
- Vapor outlet — connection to the first-stage regulator that drops tank pressure to ~10 psi for the line to your home.
- Pressure relief valve — vents propane to atmosphere if internal pressure exceeds rated maximum (e.g. during fire or extreme heat).
- Liquid level gauge — small fixed-tube valve drivers use to verify 80% fill (vapor escapes from the tube when liquid reaches it).
- Dial gauge — the percentage gauge you read as the homeowner. Reads 0–80%, not 0–100% (because 80% is max fill).
The first-stage regulator
Located on the tank dome, the first-stage regulator drops tank pressure (~120 psi at 70°F) to about 10 psi for the underground line to your home. A second-stage regulator at the house drops it further to about 11 in WC (water column) — the operating pressure for residential appliances. Some installations use a single two-stage regulator integrating both functions.
Regulator service life
Regulators have a manufacturer-recommended service life of 15–25 years. Most propane dealers replace regulators preventively at 15 years for leased tanks. Symptoms of an aging regulator: hissing sounds, frost on the body in moderate weather, inconsistent appliance flame heights.
FAQ
Why does my tank gauge max out at 80%?
NFPA 58 requires tanks to be filled to a maximum of 80% of water capacity to leave 20% headroom for thermal expansion. The dial gauge is calibrated 0–80% so it reaches 'full' at the legal fill maximum.
What should I do if the relief valve activates?
Leave the area immediately and call the dealer or fire department. Relief valve activation usually indicates extreme overheating (often during a fire) or overfill — both serious. Do not approach the tank.