Written and maintained by CASRAI Editorial Board
Last updated
This page describes products and general use; it is not medical advice.
Who uses it: clinic and laboratory staff, buyers and students who need to name the parts of an oxygen cylinder and know which of them the U.S. rules actually address. After reading, you should be able to tell the valve, protection cap, pressure relief device and regulator apart and state what the OSHA and DOT rules cited here say about each.
Scope note: the OSHA provisions quoted below come from 29 CFR 1910.253, which is OSHA’s standard for oxygen-fuel gas welding and cutting. They apply by their terms to welding and cutting workplaces. They are shown here as worked examples of how federal rules treat each cylinder part, not as a general rule for every setting. This page does not state which standard governs clinical or laboratory oxygen use; check the rules that apply to your facility, for example NFPA 99 or your own safety officer’s requirements.
What the main parts of an oxygen cylinder are
An oxygen cylinder (often called an oxygen tank) is a compressed gas cylinder fitted with a valve, normally covered by a protection cap, and with a pressure relief device. The gas is drawn off through a regulator that attaches to the valve outlet. Four parts carry specific obligations in the federal rules cited here: the valve, the valve protection cap, the pressure relief device and the regulator.
What each part does and what the rule says
The 29 CFR 1910.253 rows below are the OSHA welding and cutting standard; the 49 CFR 173.301 rows are DOT rules for cylinders offered for transport.
| Part | Role | What the rule says | Source |
|---|---|---|---|
| Cylinder valve | Opens and closes the flow of gas from the cylinder | Empty cylinders must have their valves closed. | 29 CFR 1910.253, (b)(2)(iii) |
| Valve protection cap | Covers the valve while the cylinder is stored or moved | Where the cylinder is designed to accept a cap, the cap must always be in place, hand-tight, except when the cylinder is in use or connected for use. It must not be used for lifting cylinders from one vertical position to another. | 29 CFR 1910.253, (b)(2)(iv) and (b)(5)(ii)(C) |
| Pressure relief device | Protects the cylinder against rupture | A filled cylinder offered for transport must have one or more pressure relief devices, selected and tested per CGA S-1.1, capable of preventing rupture of the normally filled cylinder (subject to listed exceptions). OSHA requires such devices to be installed and maintained per CGA S-1.1 and S-1.2. | 49 CFR 173.301(f)(1); 29 CFR 1910.101(c) |
| Regulator | Attaches to the valve outlet to deliver oxygen for use | Unless connected to a manifold, oxygen from a cylinder must not be used without first attaching an oxygen regulator. | 29 CFR 1910.253, (b)(5)(ii)(P) |
Oxygen cylinder valve and valve types
The valve is the cylinder’s shut-off point, and OSHA requires it to be closed on an empty cylinder. The regulator connects at the valve outlet. Outlet and inlet connections for compressed gas cylinders follow the CGA V-1 standard; the specific connection numbers and the differences between valve styles are covered in the CASRAI entries on CGA fittings and CGA Pamphlet P-1.
Oxygen cylinder cap
The cap is the valve protection cap, and it stays on, hand-tight, whenever the cylinder is not in use or connected for use. Two further OSHA points matter in daily handling: the cap must not be used to lift the cylinder, and unless the cylinder is secured on a special truck, the regulator must be removed and the cap put in place before the cylinder is moved. For moving and securing, see oxygen tank cart.
Caps matter for transport as well. For DOT-specification cylinders made on or after 1 October 2007, 49 CFR 173.301(h) requires the valve assembly to be strong enough, or protected, so that no leakage occurs when the cylinder is dropped 1.8 m (6 ft) or more. A securely attached metal cap is one of the protection methods the rule lists.
Pressure relief device and what cylinder pressure means
The pressure relief device exists to keep a normally filled cylinder from rupturing. Federal rules (DOT for transport, and OSHA through 29 CFR 1910.101) require it, and they tie its selection and testing to CGA S-1.1. This page gives no pressure figures, because the rules cited here do not state a single cylinder pressure; for capacity and size designations see compressed gas cylinder sizes. Cylinder periodic testing is covered in cylinder hydrostatic testing requirements.
Regulator interface
The regulator is a separate component rather than part of the cylinder, but the rule treats it as inseparable from use: oxygen from a cylinder is not to be used without one unless the cylinder feeds a manifold. Regulator types and their markings are covered in oxygen regulator.
Safe use and handling basics
These points restate the welding and cutting rules in 29 CFR 1910.253 and are good practice as an example, not a statement of what governs every workplace.
- Keep the valve closed on an empty cylinder.
- Keep the protection cap on, hand-tight, unless the cylinder is in use or connected for use.
- Never use the cap for lifting a cylinder from one vertical position to another.
- Remove the regulator and replace the cap before moving a cylinder that is not on a special truck.
For wider handling, storage and inspection rules, see compressed gas cylinder safety and the cylinder inspection checklist.
Common mistakes
- Lifting the cylinder by its protection cap, which OSHA prohibits.
- Moving a cylinder with the regulator still attached when it is not secured on a special truck.
- Leaving the cap off a stored cylinder that is designed to accept one.
FAQ
What are the parts of an oxygen tank?
The parts the federal rules address are the valve, the valve protection cap, the pressure relief device and the regulator that attaches at the valve outlet.
Does an oxygen cylinder need a cap?
Where the cylinder is designed to accept a valve protection cap, OSHA’s welding and cutting standard requires it to be in place, hand-tight, except when the cylinder is in use or connected for use (29 CFR 1910.253(b)(2)(iv)).
What are oxygen cylinder valve types?
Valve outlet and inlet connections follow CGA V-1. This page does not tabulate valve styles; see CGA fittings for connection standards.
What is the pressure in an oxygen cylinder?
The rules cited here give no single figure. The relief device required by DOT and OSHA rules is there to prevent a normally filled cylinder from rupturing.
Sources
- OSHA, 29 CFR 1910.253, date checked 2026-10-30.
- OSHA, 29 CFR 1910.101, date checked 2026-10-30.
- 49 CFR 173.301 via Cornell LII, date checked 2026-10-30.
