SAQCC Gas LPG Commercial/Industrial key terms

A mixture of hydrocarbon gases, mainly propane and butane, kept as a liquid under moderate pressure or by refrigeration. It vaporises when pressure is released and is used as a fuel for heating, cooking and engines.

A three-carbon hydrocarbon gas that liquefies at about 8 bar at ambient temperature. It boils at roughly minus 42 degrees Celsius at atmospheric pressure, making it suitable for outdoor storage in colder climates.

A four-carbon hydrocarbon gas that liquefies at about 2 bar at ambient temperature. It boils at roughly minus 0.5 degrees Celsius, so it performs poorly in cold weather and is often blended with propane.

The pressure exerted by a gas in equilibrium with its liquid at a given temperature. For LPG it rises steeply with temperature and determines the strength required in cylinders, tanks and pipework.

A fixed pressure vessel, usually installed above or below ground, that stores LPG in liquid form for supply to a building. It is fitted with filling, withdrawal, relief and level-indication connections.

The maximum mass of liquid gas permitted per unit of water capacity in a cylinder. It leaves a vapour space so the cylinder is not liquid-full at the highest expected temperature.

A withdrawal arrangement that draws gas from the vapour space above the liquid in a cylinder or tank. It is used for small loads and produces gas at the storage pressure.

A withdrawal arrangement that draws liquid LPG from near the bottom of a vessel for feeding through a vaporiser or to an appliance. It allows higher flow rates than vapour withdrawal.

A heat exchanger that boils liquid LPG into gas before it reaches an appliance or burner. It may be electrically heated, steam heated or direct fired and must have controls to prevent liquid carry-over.

A device that reduces and holds gas pressure at a steady outlet value regardless of changes in inlet pressure or flow. LPG systems commonly use a first-stage and a second-stage regulator in series.

The outlet pressure a regulator settles at when no gas is flowing. It is normally slightly higher than the flowing delivery pressure and is used to check regulator condition and setting.

The lowest concentration of a flammable gas in air that will support combustion, about 1.8 percent by volume for propane. Gas detectors often show readings as a percentage of this limit.

The highest concentration of a flammable gas in air that will support combustion. Above this level the mixture is too rich to burn until it is diluted with more air.

The practice of electrically connecting metal parts of a gas installation and connecting them to earth. It prevents static sparks and stray currents from igniting leaked gas.

A pressure test in which a vessel or cylinder is filled with water and pressurised to check strength and leak-tightness. It is repeated at intervals set by the applicable standard.

Electrical apparatus enclosed so that an internal explosion cannot ignite the surrounding flammable atmosphere and the enclosure will withstand the resulting pressure. It is required in hazardous zones around gas installations.

The process of dividing a site into zones according to how often a flammable gas atmosphere is likely to be present. It governs the selection of electrical equipment and ignition sources.

A naturally occurring fuel gas composed mainly of methane, supplied by pipeline or as liquefied natural gas. It is lighter than air and ignites readily in air.

The simplest hydrocarbon, with one carbon atom, and the principal component of natural gas. It is lighter than air, colourless and odourless, and burns with a clean blue flame.

The addition of a small amount of a smelly compound, such as a mercaptan, to otherwise odourless fuel gas. It allows people to detect leaks by smell before a dangerous concentration builds up.

The controlled removal of air or inert gas from a pipe or appliance and its replacement with fuel gas, or the reverse. It is done to avoid a flammable mixture forming inside the system.

An instrument that measures the volume of gas passing through it so consumption can be billed and checked. It also provides a point for isolating supply to the installation.

The amount of heat released when a unit quantity of gas is completely burned. It is used to compare fuels and to size burners and appliances correctly.

The air supplied to a burner to provide the oxygen needed for complete burning of fuel gas. Too little causes carbon monoxide and soot; too much wastes heat.

The amount of air supplied to a burner beyond the theoretical quantity needed for complete combustion. A controlled excess ensures full burning but lowers efficiency if too high.

A colourless, odourless and highly toxic gas produced when carbon-based fuel burns with insufficient oxygen. It binds to haemoglobin and can kill in enclosed spaces.

The measurement of oxygen, carbon dioxide, carbon monoxide and temperature in the exhaust of a combustion appliance. Results are used to set the air-fuel ratio and confirm safe, efficient operation.

A fluid that absorbs heat by evaporating at low pressure and releases it by condensing at high pressure in a refrigeration circuit. Common types include hydrofluorocarbons, ammonia and carbon dioxide.

A number expressing how strongly a substance destroys stratospheric ozone compared with a reference chlorofluorocarbon. Refrigerants with a high value are restricted or banned.

A number expressing how much heat a gas traps in the atmosphere over a set period compared with carbon dioxide. Refrigerant choice and leak control are driven by this value.

The number of degrees by which a vapour is above its saturation temperature at a given pressure. Measuring it at the evaporator outlet shows whether the expansion device is feeding correctly.

The number of degrees by which a liquid is below its saturation temperature at a given pressure. Measuring it at the condenser outlet confirms the condenser is fully condensing the refrigerant.

A metering device that controls refrigerant flow into the evaporator by sensing suction line temperature and pressure. It maintains a set superheat across the evaporator.

The removal of refrigerant from a system into a suitable container for reuse, recycling or destruction. It is required before opening a circuit and prevents release to atmosphere.

A portable pressure vessel used to store gas at high pressure, fitted with a valve and marked with its contents, test date and working pressure. It must be handled and stored according to its gas type.

The hand-operated fitting at the top of a gas cylinder that starts, stops and regulates flow. It must be opened slowly and kept closed when not in use.

A safety fitting on a cylinder or vessel that releases contents if internal pressure rises above a safe limit. It may be a bursting disc, a relief valve or a fusible plug.

High-purity oxygen supplied in cylinders or by pipeline for patient therapy. It is stored and handled with strict cleanliness rules because oil and grease can ignite in its presence.