“A new compressor can still need a Written Scheme of Examination before you switch it on.”
Buying a new air compressor does not automatically make the complete installation ready for use under the Pressure Systems Safety Regulations 2000 (PSSR).
The compressor may arrive with a manual, a data plate and manufacturer documentation. The business using it still needs to establish whether the pressure system requires a Written Scheme of Examination (WSE), what parts it covers and what examination is required before operation.
This guide gives you a practical way to check a new compressor or air receiver before it enters service.
Quick Answer: Does a new air compressor need a Written Scheme of Examination?
Yes, if the compressed air system is subject to the written-scheme requirements of PSSR. A new unit is not exempt simply because it has not been used. For a typical compressed air system, check the pressure and internal volume of each receiver: the small-system exception applies only where every vessel is less than 250 bar litres. If a WSE is required, it must be drawn up or certified as suitable by a competent person before the system is operated, with any examination required before first use completed.
Explore Velocity Safety’s PSSR examinations and Written Scheme of Examination support.
Key Takeaways – New Compressors and PSSR
- A brand-new compressor or receiver can require a WSE before operation.
- The 250 bar litre check is made against each pressure vessel, using the appropriate pressure and its internal volume.
- Exactly 250 bar litres is not covered by the “less than 250” exception.
- A supplier’s manual or conformity marking does not replace a site-specific WSE.
- The competent person determines the scope of the scheme, the examination intervals and whether an examination is required before first use.
- A compressor service and an examination under PSSR serve different purposes.
Jump to:
What Must Happen Before a New Compressor Is Used?
Start by identifying the complete pressure system. A compressor package may include an air receiver, protective devices and associated pipework. It may also connect to an existing receiver or fixed air distribution system.
For a qualifying system, HSE states that a suitable WSE must be in place before operation. The scheme must be drawn up or certified as suitable by a competent person. It specifies what needs examination and, where appropriate, provides for an examination before the system is used for the first time.
Before putting the system into service:
- Identify the receivers and system connections. Include existing vessels and pipework connected to the new equipment.
- Check the vessel details. Obtain the internal volume and relevant pressure information from the data plate and manufacturer documentation.
- Check whether the small-system exception applies. Consider each pressure vessel and any other relevant PSSR provisions or exceptions.
- Arrange a suitable WSE if required. A competent person must draw it up or certify it.
- Complete any examination required before first use. The scheme and competent person establish what is needed for the particular system.
- Keep the documentation. Retain the WSE, examination report and information about the system’s safe operating limits.
For the wider rules applying to pressure systems, see our PSSR Written Scheme of Examination guide.
How Does the 250 Bar Litre Check Work?
For a compressed air receiver, multiply its relevant pressure in bar by its internal volume in litres:
Pressure (bar) × internal vessel volume (litres) = bar litres
The PSSR exception from the written-scheme and examination provisions applies to a non-steam pressure system only when the pressure-volume product of each pressure vessel is less than 250 bar litres. A result of exactly 250 is not less than 250.
These examples use an assumed pressure solely to illustrate the calculation:
| Receiver Volume | Example Pressure | Result | 250 Bar Litre Check |
|---|---|---|---|
| 24 litres | 8 bar | 192 bar litres | Below the threshold for this vessel. |
| 25 litres | 10 bar | 250 bar litres | Not covered by the “less than 250” exception. |
| 50 litres | 8 bar | 400 bar litres | Above the threshold. |
| 100 litres | 8 bar | 800 bar litres | Above the threshold. |
Use the appropriate pressure for the actual receiver and system, rather than assuming that the compressor’s current gauge reading is the correct figure. If the data plate, safe operating pressure or system arrangement is unclear, ask a competent person to assess it.
Check every receiver in the system
A small new receiver connected to a larger existing vessel should not be assessed in isolation. The competent person needs to understand the system and establish the correct scope of its Written Scheme of Examination.
What Does a Written Scheme of Examination Cover?
A WSE identifies the parts of a pressure system that require periodic examination and sets out the nature and frequency of those examinations.
For a compressed air installation, its scope may include:
- Air receivers and other pressure vessels where a defect could create danger.
- Protective devices, including relevant pressure relief equipment.
- Parts of associated pipework where a defect could create danger.
- Any particular preparation needed to examine the system safely.
- An examination before first use, where appropriate.
The content must reflect the actual installation. A generic form that has not been assessed and certified as suitable by a competent person is not a substitute.
An appropriately competent person may be external or, where the necessary expertise and independence exist, within the organisation. The user or owner remains responsible for ensuring the scheme has the right scope.
Does Manufacturer Paperwork Replace the WSE?
No. A manual, conformity marking or supplier inspection record provides useful information about the equipment, but it does not automatically establish a suitable WSE for the pressure system as installed and used.
Keep the manufacturer’s documentation. The competent person may need it to identify vessel details, safe operating limits, protective devices and previous examinations. Also check whether a supplier has already provided a suitable WSE and current examination report, especially for hired or leased equipment.
For a fixed installation, the business using the system normally has PSSR duties. For a mobile system that can readily move between sites, the owner has the corresponding duties. Hired equipment should come with clear confirmation of who is responsible and whether the required documents and examinations are current.
What If You Replace a Compressor or Add a Receiver?
A new compressor can change an existing pressure system. Replacing a receiver, adding a second vessel, changing protective devices or altering pipework may change the scope or suitability of the current WSE.
Before using the changed installation, provide the competent person with the new equipment details and ask them to review the scheme and examination requirements. Do not assume that an existing WSE automatically covers the replacement.
The same principle applies to second-hand equipment: its age does not determine whether PSSR requires a scheme. Check the system and its documentation before it is put into use at the new location.
Is Compressor Servicing the Same as a PSSR Examination?
No. Both matter, but they answer different questions.
| Activity | Purpose | Typical Output |
|---|---|---|
| Routine servicing | Maintain the equipment and its operation, for example through filters, oil, belts or other planned maintenance. | Service record. |
| Written Scheme of Examination | Specify which safety-critical parts need examination, how and when. | Scheme drawn up or certified as suitable by a competent person. |
| Examination under the WSE | Assess the condition of the parts identified in the scheme. | Competent person’s examination report. |
A maintenance contract should not be treated as proof that the written-scheme and examination duties have been met.
New Compressor Checklist: What Should You Send for Review?
If you are buying or have just received a compressor, gather:
- Photos of the compressor and each receiver, including legible data plates.
- The internal volume of each receiver in litres.
- Pressure ratings and the manufacturer’s operating information.
- Details of safety valves and other protective devices.
- A description or photos showing how the compressor connects to existing vessels and pipework.
- Any WSE, examination report or service history already supplied.
- Whether the system is fixed, mobile, purchased or hired.
This gives a competent person the information needed to establish the system boundaries and advise on the written scheme and first-use examination.
Final Takeaway
A new compressor is not automatically exempt from PSSR. Check the complete compressed air system before it is operated, including the pressure-volume product of each receiver and any equipment already connected to it.
Where a WSE is required, arrange for a competent person to draw it up or certify it, and complete the examination called for before first use. Keep the scheme and report alongside the equipment records.
Just bought a compressor or air receiver?
Velocity Safety can review the installation and provide Written Schemes of Examination and PSSR examinations for qualifying pressure systems.
Send us the equipment data plates and a description of the proposed setup so we can advise on the next steps.
📞 Call: 01254 933 486
📩 Email: info@velocitysafety.co.uk
🌐 Or contact Velocity Safety online.
Frequently Asked Questions
Do new air compressors need a Written Scheme of Examination?
They can. If the compressed air system is subject to PSSR’s written-scheme requirements, the WSE must be in place before the system is operated. New equipment is not automatically exempt.
Does a 50-litre compressor need a WSE?
It depends on the relevant pressure and the complete system. At an illustrative pressure of 8 bar, a 50-litre receiver gives 400 bar litres, above the 250 bar litre threshold.
What happens at exactly 250 bar litres?
The small-system exception applies where the pressure-volume product of each vessel is less than 250 bar litres. A vessel at exactly 250 does not satisfy that condition.
Do you add the volumes of several receivers together?
The small-system exception refers to the pressure-volume product of each pressure vessel. The competent person should still assess the complete system, its connections and the appropriate scope of the WSE.
Is an examination always needed before first use?
The WSE must be in place before a qualifying system is operated. It must provide for an examination before first use where appropriate. The competent person establishes what examination is required for the particular system.
Can the supplier’s WSE be used?
Possibly, if it is suitable for the actual system and has been drawn up or certified as suitable by a competent person. Check that it covers the equipment and installation being used and that the relevant examination documentation is current.
Can someone within the business prepare the WSE?
Yes, where the organisation has a person with the necessary competence and independence to draw up or certify a suitable scheme. An external competent person can also provide this service.
Does annual compressor servicing cover PSSR?
No. Servicing maintains the equipment. A WSE specifies the statutory examination requirements, and a competent person examines the relevant parts in accordance with it.
Does a replacement receiver need a new WSE?
A replacement should prompt a review of the existing scheme. Changes to the receiver, pressure rating, protective devices or system layout may require the WSE and examination arrangements to be updated before use.
