Do New Air Compressors Need a Written Scheme of Examination Before First Use?

Buying a new air compressor does not automatically mean it is ready to use under PSSR.

A new air compressor can arrive with manuals, CE/UKCA marking and manufacturer paperwork, but that does not automatically mean it is ready to use under PSSR.

One of the most common mistakes businesses make is buying a compressor online, plugging it in, and only later discovering that the air receiver should have had a Written Scheme of Examination in place before first use.

Under the Pressure Systems Safety Regulations 2000, certain compressed air systems must have a Written Scheme of Examination in place before they are used for the first time.

A new compressor, replacement receiver or newly modified compressed air setup can still fall under PSSR if the system creates a relevant pressure risk.

If your air receiver or compressor system reaches the relevant threshold, you may need a competent person to certify a Written Scheme of Examination and carry out the required examination before the system is put into operation.

Here’s what this guide covers:

What Is a Written Scheme of Examination?

A Written Scheme of Examination, often shortened to WSE, is a formal document required for certain pressure systems under PSSR.

It sets out what needs to be examined, how it should be examined, how often it should be examined, and which parts of the system are included.

For an air compressor or compressed air system, a Written Scheme of Examination may cover:

• Air receivers
• Pressure vessels
• Safety valves
• Pressure gauges
• Protective devices
• Associated pipework where relevant
• Examination intervals
• Any preparation needed before examination

The Written Scheme of Examination should be drawn up or certified by a competent person. It is not just a generic template. It needs to reflect the actual pressure system on site.

Does My Air Compressor Need a Written Scheme of Examination?

Your compressor may need a Written Scheme of Examination if it forms part of a pressure system covered by PSSR.

For compressed air systems, one of the most common triggers is the 250 bar litre threshold.

Many businesses assume this only applies to large industrial systems. In reality, a lot of workshop, manufacturing, engineering, vehicle repair and fabrication compressors can exceed the threshold quite easily.

For example, a 100 litre receiver operating at 8 bar equals 800 bar litres.

That is well over the 250 bar litre threshold.

How Does the 250 Bar Litre Rule Work?

The calculation is simple:

Working pressure in bar × vessel volume in litres = bar litres

Here are a few examples:

Receiver Size	Working Pressure	Bar Litres	WSE Likely Required?
24 litres	8 bar	192 bar litres	Usually no
50 litres	8 bar	400 bar litres	Yes
100 litres	8 bar	800 bar litres	Yes
200 litres	10 bar	2,000 bar litres	Yes

This is why even a relatively standard compressor can fall under PSSR.

If you are unsure, check the receiver volume, working pressure and system layout, then speak to a competent person before putting the system into use.

Why New Does Not Automatically Mean Compliant

A brand-new compressor can still require a Written Scheme of Examination.

PSSR is not only concerned with whether the compressor is new, old, clean or recently serviced. It is concerned with the risk created by stored pressure.

A new air receiver can still exceed 250 bar litres. It can still need safety valves, gauges and protective devices identified. It can still need an examination interval set by a competent person.

This is why “brand new” should not be treated as a shortcut around PSSR compliance.

What Needs to Happen Before a New Compressor Is Used?

If your compressor system requires a Written Scheme of Examination, it should be in place before the system is used for the first time.

Before first use, the process may include:

• Reviewing the compressor and air receiver details
• Checking the pressure, vessel size and bar litre calculation
• Identifying safety-critical parts of the system
• Drawing up or certifying the Written Scheme of Examination
• Carrying out the required initial examination
• Setting future examination intervals
• Providing documentation for your records

This matters because new equipment can still be installed incorrectly, missing key documentation, connected to existing pipework, or used in a way that changes the overall pressure system risk.

A new compressor is not automatically compliant just because it has arrived from a supplier.

Is Compressor Servicing the Same as a Written Scheme of Examination?

No. This is one of the most common misunderstandings.

A compressor service is usually focused on keeping the equipment working. It may include oil changes, belt checks, filter replacement, leak checks and general maintenance.

A Written Scheme of Examination and PSSR examination are different. They are focused on statutory safety requirements for pressure systems.

In simple terms:

• Servicing helps keep the compressor maintained and operational.
• A Written Scheme of Examination defines what needs statutory examination under PSSR.
• A PSSR examination checks the relevant parts of the pressure system in accordance with the written scheme.

You may need both. Having a compressor serviced does not automatically mean you have met your PSSR duties.

Common Compressor WSE Mistakes We See

Most issues we see are not caused by businesses deliberately ignoring PSSR. They happen because compressors are often bought, installed and treated like ordinary workshop equipment rather than pressure systems with statutory inspection duties.

Common issues include:

• Buying a new compressor online and using it straight away
• Assuming new equipment is exempt
• Forgetting to calculate bar litres
• Assuming annual servicing covers statutory examination
• Adding another receiver without updating the written scheme
• Changing pipework or system layout without review
• Waiting for an insurer to highlight the issue after the system is already in use

The safest approach is to check the requirement before the compressor is put into service.

Who Can Write or Certify a Written Scheme of Examination?

A Written Scheme of Examination must be drawn up or certified by a competent person.

This means someone with the knowledge, experience and independence needed to assess the pressure system properly.

The competent person should understand the type of pressure system, the risks involved, the examination requirements, and the relevant legal duties under PSSR.

For many businesses, using an external competent provider is the simplest route because it gives clear documentation and helps avoid conflicts of interest.

What Should You Do If You Have Just Bought a New Compressor?

If you have recently bought or installed a new air compressor, do not assume it is ready to use.

Start by checking:

• The air receiver volume in litres
• The maximum working pressure in bar
• Whether the system exceeds 250 bar litres
• Whether it connects to existing pipework or receivers
• Whether a Written Scheme of Examination has already been provided
• Whether an initial PSSR examination is required before use

If you are not sure, Velocity Safety can review your compressor setup and advise what is needed.

Velocity Safety provides PSSR examinations and Written Schemes of Examination for compressors, air receivers and pressure systems across the UK.
Useful information to gather before asking for advice:

• A clear photo of the compressor data plate
• A photo of the air receiver data plate
• The receiver size in litres
• The maximum working pressure in bar
• Details of any additional receivers or fixed pipework
• Any installation, service or inspection paperwork already supplied

FAQs

Here are answers to common questions about new air compressors, Written Schemes of Examination, 250 bar litres and PSSR compliance.

Do new air compressors need a Written Scheme of Examination?

Yes, they can. If the compressor system falls under PSSR and exceeds the relevant threshold, a Written Scheme of Examination should be in place before the system is used for the first time.

What is the 250 bar litre rule?

The 250 bar litre rule is commonly used for compressed air receivers. It is calculated by multiplying the working pressure in bar by the vessel volume in litres. If the result equals or exceeds 250 bar litres, a Written Scheme of Examination is likely to be required.

Does a 50 litre compressor need a Written Scheme of Examination?

It depends on the working pressure. For example, a 50 litre receiver operating at 8 bar equals 400 bar litres, which is above the 250 bar litre threshold.

Is compressor servicing the same as a PSSR examination?

No. Servicing is maintenance. A PSSR examination is a statutory examination carried out in accordance with a Written Scheme of Examination. You may need both.

Who can write a Written Scheme of Examination?

A Written Scheme of Examination must be drawn up or certified by a competent person with suitable knowledge, experience and independence.

Can I use a Written Scheme of Examination template?

A generic template is unlikely to be enough on its own. A Written Scheme of Examination must be specific to the pressure system and should be drawn up or certified by a competent person. Using a template without proper system review can leave important safety devices, limits or examination requirements missing.

How often does an air compressor need examining?

The examination frequency should be set by the competent person within the Written Scheme of Examination. Many systems are examined annually, but the correct interval depends on the equipment, risk and scheme requirements.

Do I need to update my WSE if I replace my compressor?

Yes, the written scheme should be reviewed if the compressor, receiver, pressure rating, pipework or system layout changes. Replacing equipment can alter what needs to be examined and how the pressure system should be managed.

Do second-hand compressors need a Written Scheme of Examination?

Yes, they can. Second-hand equipment is not automatically exempt. If the system falls under PSSR, a Written Scheme of Examination and suitable examination may be required before use.

Can Velocity Safety provide Written Schemes of Examination nationwide?

Yes. Velocity Safety provides Written Schemes of Examination, PSSR examinations and pressure system compliance support for businesses across the UK.

Resources

• HSE: Written schemes of examination guidance
• HSE: Pressure Systems Safety Regulations guidance
• Legislation.gov.uk: Pressure Systems Safety Regulations 2000
• Velocity Safety: PSSR examinations and Written Schemes of Examination