When reviewing a gas cylinder drawing or specification sheet, buyers often see several different pressure values: working pressure, test pressure and burst pressure.
Although all three are expressed in bar, MPa or psi, they describe very different conditions. Confusing them may lead to incorrect cylinder selection, unsafe filling assumptions or mismatched technical requirements.
Understanding these pressure terms is therefore an important first step when purchasing or developing a gas cylinder.
Working pressure, also called service pressure in some standards and markets, is the pressure rating intended for the cylinder's normal service.
For compressed gases, it normally refers to the settled gas pressure at the reference temperature specified by the applicable standard or regulation. The reference temperature may differ depending on the market and cylinder specification.
For example, if a cylinder is marked with a working pressure of 200 bar, this does not mean it may be filled to any pressure below the test pressure. The actual filling pressure must remain consistent with:
• The cylinder's approved working pressure
• The gas being filled
• The applicable filling regulations
• The reference temperature
• The cylinder valve and other system components
Working pressure is one of the most important values when matching a cylinder with a filling system, regulator and valve.
Test pressure is the pressure applied during a required pressure test to verify the structural integrity of the cylinder.
It is higher than the working pressure and is normally applied hydraulically, using water or another suitable liquid. Depending on the applicable standard, the inspection may evaluate leakage, permanent expansion, volumetric expansion or other acceptance criteria.
A common example is a cylinder with:
• Working pressure: 200 bar
• Test pressure: 300 bar
This means the cylinder is intended for service at its approved 200-bar rating and is tested at 300 bar as part of the required verification process.
It does not mean that the cylinder may be filled to 300 bar during normal use. Test pressure is a verification value, not an alternative filling pressure.
For refillable cylinders, hydrostatic testing may also be required during periodic inspection. The inspection method and interval depend on the cylinder standard, gas service and regulations in the country of use.
Burst pressure is the pressure at which a cylinder ruptures during a controlled destructive test.
Unlike a hydrostatic test performed to confirm that a cylinder remains fit for use, a burst test intentionally continues until the test cylinder fails. It is generally used during design qualification, certification or production verification to assess whether the cylinder design, material and manufacturing process provide the required safety margin.
The applicable standard may specify requirements relating to:
• Minimum burst pressure
• Burst location
• Failure mode
• Expansion characteristics
• Whether fragmentation is permitted
• The relationship between burst pressure and working or test pressure
Burst pressure should never be regarded as an allowable operating limit. A cylinder must not be deliberately filled above its approved working pressure simply because its theoretical or tested burst pressure is higher.
No. There is no single pressure ratio that can be applied to every gas cylinder.
The relationship between working pressure, test pressure and minimum burst pressure depends on several factors:
• Design and manufacturing standard
• Cylinder material
• Refillable or non-refillable construction
• Seamless, welded or composite design
• Water capacity and dimensions
• Intended gas service
• Target market and local regulations
For example, refillable seamless aluminum cylinders may be designed according to ISO 7866 or DOT-3AL, while seamless steel cylinders may follow the ISO 9809 series. Non-refillable cylinders may be designed according to ISO 11118 or DOT-39.
Each standard has its own design calculations, testing procedures, acceptance criteria and marking requirements. Buyers should therefore avoid specifying only a pressure ratio without first identifying the applicable cylinder standard.
The required cylinder pressure cannot be determined by cylinder size alone. The physical behavior of the gas must also be considered.
For compressed gases such as oxygen, nitrogen, argon and compressed air, internal pressure changes with temperature. A cylinder filled to its rated pressure at a specified reference temperature may show a higher pressure when its temperature rises.
The cylinder must therefore be selected and filled according to the applicable gas-filling rules and temperature conditions.
Liquefied gases such as CO₂ and N₂O are generally controlled by filling ratio or net filling weight rather than pressure alone.
Leaving sufficient internal space for liquid expansion is essential. A cylinder with an adequate pressure rating may still become unsafe if it is overfilled by weight.
For liquefied-gas projects, buyers should confirm both the cylinder pressure rating and the permitted filling quantity.
Not necessarily.
A higher pressure rating may require thicker walls, additional material and greater cylinder weight. It may also affect external dimensions, gas capacity, manufacturing cost and certification requirements.
The correct cylinder is not automatically the one with the highest pressure rating. It is the cylinder that properly matches:
• The intended gas
• Required filling quantity
• Operating conditions
• Applicable certification
• Valve and regulator
• Size and weight limitations
• Filling and transportation requirements
Selecting an unnecessarily high pressure may increase weight and cost without providing a practical benefit.
Before requesting a quotation or customized cylinder drawing, buyers should provide the following information whenever possible:
• Intended gas or gas mixture
• Target market or country of use
• Required certification or design standard
• Water capacity or required gas quantity
• Working pressure and reference temperature
• Refillable or non-refillable application
• Cylinder neck thread and valve outlet
• Required valve or pressure-relief device
• Cleaning and surface-treatment requirements
• Expected order quantity and annual demand
These details allow the cylinder manufacturer to evaluate whether an existing certified model is suitable or whether a new design and certification process will be required.
ZX manufactures aluminum and steel gas cylinders and matching cylinder valves for industrial gases, medical oxygen, beverage CO₂, calibration gases, scuba diving and other applications.
For customized projects, our technical team reviews the gas service, working pressure, capacity, dimensions, thread connection, valve configuration and target-market certification before preparing the cylinder drawing.
Whether you require an existing certified cylinder or a newly developed specification, contact ZX with your application details. We will help identify a suitable and compliant gas cylinder solution.
