Gas Cylinder Valves
Gas cylinder valves
Gas cylinders are open-ended. To allow a gas to be contained within a cylinder a valve is usually fitted into the open end of the cylinder, normally at the top, or shoulder of the cylinder. The valve may have several functions.
- It is a means of closing an opening in a cylinder.
- It provides an inlet port to allow a cylinder to be filled.
- It provides closure to contain the contents within the cylinder.
- It provides an outlet port to allow the gas to be released.
- it can accommodate safety devices, such as non-return valves, pressure relief valves and residual pressure valves.
- It can incorporate an integrated pressure regulator.
- It can incorporate an outlet flow regulating device
- It can incorporate a contents level (pressure) gauge
- It can provide a mounting for external components, such as regulators and pipelines.
Gas cylinders and their associated valves that are, or are intended to be, used to transport dangerous goods have to comply with the Carriage of Dangerous Goods and Use of Transportable Pressure Equipment Regulations.
Valves are designed, constructed, inspected, tested and approved against authorised standards. Due to the many properties of the various gases, valves have to be manufactured from compatible materials.
Valves are required to have the same service life and performance as gas cylinders to allow their test pressure and their periodic inspection and test dates to align. Typically this can mean a minimum service life of at least 10 years for many valves, however, where cylinders have an extended life of up to 15 years, the valve life will need to be taken into consideration. Valves should not be used if their test pressure is below that of the cylinder.Some common valve standards include:
- BS 341, Transportable gas container valves.
- BS EN ISO 10297, Transportable gas cylinders. Cylinder valves. Specification and type testing.
- BS EN ISO 13340, Transportable gas cylinders. Cylinder valves for non-refillable cylinders. Specifications and prototype testing.
Valves, especially on larger cylinders, are designed to withstand mechanical impact, and do not need additional protection, but they are often protected from general damage in a variety of ways. The following methods are common:
A valve guard - a device that is securely fixed around the valve, but stands higher than the valve hand wheel. They can be of cast or welded construction or made from non-metallic moulded plastics. They can be attached to either the cylinder shoulder, the cylinder neck (with a Cir-clip), or in some cases, the base of the valve. It does not need to be removed for access to the valve.
A valve shroud - a type of valve guard but which is an integral part of a welded cylinder or pressure drum, most commonly seen on LPG or refrigerant gas service.
A valve protection cap - a cover that is securely fixed over the valve during handling, transport and storage which is removed for access to the valve. It is designed not to contact the valve or the hand wheel.
The valve outlet port may be protected by:
- A temporary covering, such as a plastic sleeve, often heat shrunk over the outlet port.
- A specialist security cap, typically manufactured from plastic, which requires a small amount of effort to break open. Once open it cannot be refitted.
- A removable (plastic) plug, that screws onto the thread in the outlet port.
- A re-useable fill port plug, (which may be gas-tight) particularly for very high value, risk or purity gases.
This type of protection is fitted once a cylinder has been filled and is used to prevent contamination of the outlet port, but it also provides an indication that the gas cylinder has not been used or tampered with.
A variety of different valve outlets exist. Whilst modern standards have attempted to standardise valve outlets such that there is an international system to prevent the interconnection of non-compatible gases, there remain many outlets in use which are based on traditional national standards. Care should therefore be taken to ensure that only appropriate connections are made.
The valve outlet is designed for a specific gas, or a specific hazard group. For example, valves for non-flammable gases are fitted with right-hand threaded valve outlets, whereas valves used for flammable gases are fitted with left-hand threaded valve outlets.
Components that fit into valve outlets with a left-hand thread are often identified by having a notch cut into the hexagonal connecting nut.
Diagram: Component with a left-hand thread.
Some common valve outlet standards include:
- BS 341, Transportable gas container valves.
- BS EN ISO 407, Small medical gas cylinders. Pin-index yoke-type valve connections.
- BS ISO 5145, Cylinder valve outlets for gases and gas mixtures. Selection and dimensioning.
It is notable that the UK has a lower number of standard outlet connections compared with the rest of Europe. Specifically UK valves for inert gases ≤ 300 bar (nitrogen, helium, argon etc.) share a BS 341-3, 5/8" right hand female outlet with oxygen. Most EU states have a separate oxygen outlet. BS ISO 5145 addresses this for pressures above 300 bar, refer to BCGA TIS 10. Medical pin index valves are the UK exception to this, where separate pin arrangements exist for oxygen valves.
Valve outlets may be configured as a top outlet or as a side outlet. More complex valves may have more than one type of valve outlet.
Do not use an adaptor to connect equipment to the valve outlet if it is not compatible.
Valves with a dip tube
Some gas cylinders that are used to contain liquefied gases incorporate valves fitted with dip tubes. These may be identified by a white line painted on the side of the cylinder, and / or an ‘indicator' ring under the valve.
Dip tubes can be of various length and design and are fitted to the inlet of the valve. They can have several functions in use, such as, allowing liquid to be withdrawn, enabling a homogenous gas mixture during filling, and maintaining an adequate ullage space within the cylinder.
Some valves may also have twin outlets, allowing a choice between gas or liquid delivery.
Remove any valve outlet protection which may be fitted. Carry out a visual inspection of the gas outlet. Ensure it is clear of any contaminants. Any visible material or moisture should be removed by cleaning with a clean, dry, lint-free cotton cloth. Do not apply any oils or greases. For advice on connecting gas cylinders refer to BCGA TIS 22.
The cylinder valves on all gas cylinders are opened by turning the spindle anti-clockwise and then closed by turning the spindle clockwise. Some valves are permanently fitted with handwheels to rotate the spindle, but others rely on the use of an external spindle key. Spindle keys are available from your gas supplier.
Before opening a valve, point the outlet away from personnel. Valves are only to be opened slowly. An opened spindle should NEVER be left against the backstop, but should be turned back at least half a turn to avoid seizure in an open position.
NOTE: Whilst this applies to the majority of valves, there are valves with a specific operating requirements. It is therefore important that the correct operating procedures are fully understood before attempting to operate a valve.
When the cylinder is in use and the valve is open, keep the spindle key inserted into the valve. In-use a cylinder should always be secured to prevent it toppling over. Be aware that a loose cylinder falling over with a spindle key inserted can act as a lever, causing damage.
Valves should be checked for leaks using an appropriate leak detection fluid. Care needs to be taken regarding the choice of leak detection fluids. Many valves are manufactured from non-ferrous material such as a brass or bronze, but as copper-based materials they are susceptible to stress corrosion cracking if exposed to amines or ammonia, yet many leak detection fluids contain these chemicals. For further information refer to EIGA Document 78, Leak detection fluids cylinder packages.
Always connect a gas cylinder to the item being charged via a regulator and any appropriate pressure system components. Note that some valves are designed complete with a regulator, such as a VIPR (Valve with Integrated Pressure Regulator), which include pressure and sometimes flow regulation, making them suitable for connection directly to devices, or even people!
Where the gas cylinder valve assembly has a residual pressure valve and/or a non-return valve fitted the user shall not interfere with or remove these devices. A residual pressure valve retains a positive gas pressure inside the cylinder. This pressure prevents the possible ingress of contaminants into the cylinder should the valve be left open. The non-return feature prevents back flow from the customer's process whenever the cylinder is at a lower pressure than the application (involving a fluid) to which it is connected. The use of these devices will have been assessed by the cylinder owner (usually the gas supplier) and will form part of the construction requirements of the cylinder and valve assembly.
Connecting a valve to a cylinder
There are a variety of threaded connections available for connecting a valve to a gas cylinder. The choice of valve will be determined by the gas supplier. Before fitting a valve, it should be inspected to ensure it is serviceable, it is suitable for the gas contained within the cylinder, and it has sufficient life remaining, for example, to allow its use until the gas cylinder is due its next inspection and test.
The type of threaded connection used is important in terms of achieving a seal without causing valve material strain. There are two common types:
Tapered thread - these seal through the use of a sealant on the threads, such as PTFE tape, and the application of a specified torque. European examples include 17E, 18T and 25E.
Parallel thread - these seal against a captured ‘O' ring seal to the shoulder of the valve body, as the valve is clamped down on to the flat face of the cylinder. For this type of seal an additional sealant should not be used. European examples include M18, M25 and M30.
Disconnecting a valve from a cylinder
Cylinders contain gases under pressure. Valves should only be removed under the authority of the cylinder owner taking all necessary precautions to do so safely. In-use, valves should never be removed or exchanged by customers.
Valves in operation
There are two main types of valve design for controlling the flow of gas.
The simplest design makes use of an ‘O' ring. This operates in a similar manner to a domestic water tap. The wetted area is sealed against the spindle by an ‘O' ring(s) located around the spindle. This type of valve is acceptable for general use.
A more comprehensive design utilises a diaphragm. The spindle is connected to a flexible diaphragm, which it moves up and down to open and close the flow. This design prevents any possible gas flow past the spindle. This type of valve is used to control high value or high risk gases, where even small leaks are undesirable, for example in laboratory situations.
Storage and transport
When a gas cylinder is not in use, for example when in storage or being transported, the valve should always be closed. This will not only stop gas escaping, but on a nominally empty cylinder it will also prevent contamination entering the cylinder and help to maintain its integrity.
Where provided, valve protection caps should always be fitted.
If you have a gas cylinder with a damaged valve, do not use the cylinder and seek the advice of your gas supplier. If safe to do so, move the gas cylinder to a secure place and quarantine it until appropriate action is taken.
If you are not sure who your gas supplier is, refer to the ‘Cylinder Recovery & Disposal' page.
Within BCGA gas cylinder valves for industrial gases are the responsibility of Technical Sub-Committee (TSC) 2, gas cylinder valves for medical gases are the responsibility of TSC7. Members can access information on TSC2 and TSC7 via the ‘Members' area.
BCGA publish many publications providing advice and guidance on how to use, store, transport and handle gas cylinders safely. All BCGA publications are accessible via the ‘Publications' page. The following are of interest:
Gas cylinder valve providers
BCGA member companies can provide gas cylinder valves and/or a range of services and associated equipment.