150 Bar vs 165 Bar Cylinder Filling: Which Specification Is Right for Your Station?

Two Standards, One Decision Point

When specifying a new oxygen cylinder filling station, the fill pressure — 150 bar or 165 bar — is one of the first decisions you will make. It affects the compressor specification, the cylinder valve specification, the manifold and hose rated pressure, and the cylinder testing schedule your gas authority will require.

Most buyers already know which standard applies to their cylinders before they specify the compressor. But we regularly receive enquiries from operators who are expanding capacity, converting from one standard to another, or setting up a new station in a market where they are unfamiliar with local cylinder standards. This article sets out the practical differences between the two specifications and the factors that determine which is appropriate for your operation.

The Physical Difference: Fill Density

The difference between 150 bar and 165 bar fill pressure is a 10% increase in the mass of gas stored per cylinder at the same temperature. For a standard 40-litre water capacity T-type cylinder:

For a filling station operator, the benefit of 165 bar is clear: more gas per cylinder, fewer deliveries for the same volume sold, or the ability to serve customers who require more than 150 bar working pressure in their cylinders.

Cylinder Compatibility: The Critical Constraint

You cannot fill an existing 200 bar-rated cylinder to 165 bar and consider it compliant. The fill pressure must not exceed the cylinder’s design fill pressure, which is determined by its working pressure rating and the applicable national cylinder standard.

In most markets, standard T-type industrial oxygen cylinders carry a 200 bar test pressure and a 150 bar working (fill) pressure. Filling to 165 bar would require either:

• Cylinders with a 230 bar test pressure and 165 bar working pressure, specifically marked for this service; or
• Application of the local cylinder standard’s fill ratio (e.g., if the standard allows filling to 5/6 of test pressure, a 200 bar test cylinder may be filled to approximately 167 bar in some jurisdictions)

⚠️ Before specifying a 165 bar compressor, verify with your cylinder supplier and gas authority which cylinders in your current fleet are compatible with 165 bar fill pressure. Fitting a 165 bar compressor to an existing station with 200 bar test / 150 bar working pressure cylinders creates a compliance and safety issue.

Where 150 Bar Is the Appropriate Specification

150 bar (15.0 MPa) is the dominant cylinder fill standard worldwide. It applies in:

• All medical oxygen cylinder filling operations (ISO 10083, EN 1089-3 compliant cylinders rated at 200 bar test / 150 bar working)
• Standard industrial oxygen distribution using T-type and equivalent cylinders
• Markets where the local gas cylinder standard specifies 200 bar test pressure cylinders as the norm
• Stations where the existing cylinder fleet is 200 bar test / 150 bar working

If you are establishing a new station and are uncertain about local cylinder standards, 150 bar is the safer default specification — it is compatible with the widest range of cylinders available globally.

Where 165 Bar Is the Appropriate Specification

165 bar (16.5 MPa) fill pressure is appropriate in a narrower set of circumstances:

• Markets where 230 bar test cylinders are standard: Some industrial gas markets — particularly for high-volume welding gas distribution — have standardised on 230 bar test pressure cylinders that support 165 bar fill.
• Operations where transport cost per Nm³ is a significant factor: The 10% additional gas content per cylinder delivery translates to 10% fewer cylinder movements for the same volume. For high-volume distributors with significant transport costs, this is commercially meaningful.
• Stations that need to serve customers with high-pressure specification cylinders: Some downstream applications — particularly in aerospace, defence and specialised industrial gas markets — use cylinders rated above 200 bar that accept higher fill pressures.

Compressor Differences Between /150 and /165 Variants

In our ZW series, the /150 and /165 variants share the same mechanical frame, the same cylinder bore sizes for the first three or four stages, and the same drive motor configuration. The differences are confined to:

• Final stage compression ratio: adjusted to achieve 16.5 MPa rather than 15.0 MPa from the same penultimate stage pressure
• Valve specification: higher pressure rating on final-stage discharge valve
• Pressure relief valve setting: set at 110% of design outlet pressure (18.15 MPa for /165)
• High-pressure test: hydrostatic test conducted to 1.5 × MAWP — at 24.75 MPa for /165 compared to 22.5 MPa for /150

The motor power requirement for /165 is marginally higher than for an equivalent /150 machine at the same flow rate — approximately 8 to 12% more power for the same inlet flow — due to the higher final compression ratio. This should be factored into your electrical supply planning if you are converting an existing /150 station to /165.

Operating Considerations for 165 Bar Stations

A 165 bar filling station places higher demands on the complete system:

• Manifold and hose ratings: All high-pressure pipework, manifolds, valves, and fill hoses must be rated for at least 200 bar working pressure (preferably with a design factor of 1.4 or higher over the fill pressure)
• Cylinder valve compatibility: Confirm that the cylinder valve specified for your cylinders is compatible with 165 bar fill pressure — some valve designs for standard T-type cylinders are limited to 200 bar service at 150 bar fill
• Pressure gauge range: Panel gauges must read to at least 200 bar with adequate readability at 165 bar
• Burst disc rating: Safety burst discs in the high-pressure system must be selected for 165 bar service conditions

Our Recommendation

For most new filling stations, we recommend specifying 150 bar unless there is a specific commercial or regulatory reason to use 165 bar. The reasons are practical: 150 bar cylinders are available worldwide from a wider range of suppliers, the compressor and station components are standard, and the regulatory path is simpler in most markets.

If you are building a station for a market or customer base that specifically requires 165 bar, we supply that configuration — and where a station may need to serve both standards in future, we offer dual-pressure configurations that allow the final fill pressure to be set at installation.

To discuss your station specification in detail, contact our engineering team. For technical specifications on both variants, visit our oxygen cylinder filling compressor page.