LPG supply: cylinders, tanks and service pipes

Domestic LPG comes in refillable cylinders or from a bulk storage tank, not through the natural-gas mains; a few areas have a local piped network fed from a bulk tank. Cylinder LPG is normally bought by the cylinder rather than billed from household meter readings.

Upright and secured

A vapour off-take cylinder draws gas from the space above the liquid. Stand it upright on a firm, level base and secure it.

• Tipped over, liquid LPG can reach the valve and pass into the regulator and pipework. It expands enormously as it vaporises, so appliances are over-supplied, flames flare and fittings not designed for liquid can fail.
• Where a relief device is fitted, the intended cylinder orientation also keeps it connected to the correct space.
• An unsecured cylinder can fall and damage its valve or connections.

Heat, fill level and damage

Heat raises vapour pressure and can weaken a cylinder. A relief valve, where fitted, may discharge flammable gas and does not guarantee protection from rupture. Keep storage clear of excessive heat. The authorised filling limit leaves vapour space, or ullage, for liquid expansion under the intended conditions; it does not make fire exposure safe.

Do not keep a significantly damaged or corroded cylinder in use. Ask the supplier to arrange assessment and safe recovery. A leaking, hot or fire-exposed cylinder must not simply be moved or transported: follow the emergency procedure, keep people clear and isolate only where safe. For fire, withdraw and call 999.

Enough vapour for the load

Cylinder vaporisation depends on temperature, available liquid, cylinder size and demand. In cold weather the supply can become inadequate while liquid remains; pure propane freezes near −188 °C, far below ordinary UK winter temperatures. That does not mean every component is sound, so investigate the actual supply. Where more capacity is needed, use a supplier-designed cylinder bank or storage arrangement. A reserve bottle alone does not increase delivery from the duty cylinder, and cylinders must not be heated to force greater output.

Worked example: suppose 47 kg of propane is available and the appliance’s gross heat input is 12 kW. For this calculation, use 50 MJ of gross heat per kilogram of gas.

1. 12 × 3.6 = 43.2 MJ/h
2. 43.2 ÷ 50 = 0.864 kg/h
3. 47 ÷ 0.864 = about 54.4 hours at full rate

This is the energy available divided by a constant input rate. It assumes the stated mass can be used and no other appliance draws from it. Cycling changes consumption, and a cylinder may fail to supply the required hourly rate before all that energy is used.

Changeover, pigtails and regulator

• An automatic changeover uses the reserve when the duty side cannot maintain the required supply conditions. The indicator reports reserve use rather than measuring liquid contents. Cold or sustained demand can trigger it before the duty cylinder is empty; some models may draw from both. Continued supply during replacement is possible only with an arrangement designed for it, following its instructions and closing the valve of the cylinder being disconnected.
• Pigtails carry cylinder-pressure gas. Use a suitable rated connector and inspect its condition, routing and connections at each cylinder change. Rubber and stainless-steel types have different inspection and replacement requirements; follow the actual manufacturer’s instructions. A rubber hose can harden and crack with age before it looks worn, so a pigtail past its stated service life is replaced even when it looks sound.
• Protect the regulator: damage, water or blockage can cause over- or under-pressure.
• Four or more cylinders on an automatic changeover also need over-pressure protection downstream of the regulator in case it fails (GSIUR 14(4)); HSE recommends it for every fixed-pipework cylinder installation.
• An emergency control is required for a bulk tank supply, or where two or more cylinders are connected by an automatic changeover. With a single cylinder, its own valve is the shut-off (GSIUR 9(5)).

Changing a cylinder

1. Select a well-ventilated outdoor change point clear of ignition sources. Extinguish a nearby flame before loosening the connection, or use another suitable place well away from it. Moving people aside leaves the flame in place.
2. Follow the equipment instructions, including closing the cylinder valve before disconnecting that cylinder. Inspect and remake the connection correctly. Check it for leakage by the specified method before use; a downstream pressure test may not include it. Use approved compatible fluid or a suitable detector, never a flame. A coupling that clicks, or no smell, does not prove the joint is tight.
3. If gas smells at the connection, close the valve if safe, keep people clear, prevent ignition and contact the LPG supplier's emergency service. Do not reopen it until the fault is resolved.

Storing spares

Spare and nominally empty cylinders can still hold vapour. Domestic propane spares belong outdoors in a suitable ventilated position, upright with valves closed and the required separations and access clear. Supplier guidance permits up to 30 kg of butane (two 15 kg cylinders) indoors in a home under its location and use conditions. This does not permit cellar or other below-ground cylinder storage. Purpose-designed underground tanks are a separate specialist arrangement.

Denser-than-air LPG can collect in drains, gullies, cellars and other low spaces. Airflow and mixing affect where it actually goes, so you cannot count on it going one way, or dispersing safely. Required separation reduces the chance of an escape entering those spaces.

Pipework and isolation

• Use only LPG-rated materials and hoses, because LPG attacks some rubbers and plastics. Copper is suitable.
• Use suitable polyethylene for new buried LPG service pipe. Existing buried metal needs assessment and the applicable replacement arrangements. Protect the route from impact, corrosion and other damage; inspection can identify deterioration before leakage.
• Check who is responsible for the service pipe: it may be the premises owner.
• For a suspected escape, identify the connected cylinders and labelled emergency controls. Close the ECV and cylinder valves, or the bulk-tank service valve as appropriate, only if safely accessible. Shutting one cylinder alone can leave a reserve supply connected.

Tanks and escape duties

• An LPG tank must not be sited indoors, inside a bunded area or on a roof, and needs safe access for the delivery tanker.
• Once told of an escape, the LPG supplier must stop the gas escaping within 12 hours (GSIUR regulation 37(1)), attending as soon as reasonably practicable.