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What is a Written Scheme of Examination for a compressed air system?

Did you know that if you have an air compressor, you need, by law to have a written scheme of examination (WSE)?

A written scheme of examination is a bit like an MOT for your compressed air system. It is carried out by a registered engineer, generally once a year, who will come to site and check that all pressure vessels in your compressed air system are in a fit condition and that all safety equipment is working correctly. Pressure vessels are generally receivers and safety equipment is usually regarded as pressure gauges, safety valves and in some cases valves.


What is a Written Scheme of examination?

The WSE is split into two parts.


Part 1  – Part 1 of the WSE is a review of your compressed air system, listing out all the ‘pressure vessels’ and ‘safety’ equipment in your compressed air system and where they are located. They are also permanently tagged and serial numbers are recorded. Note: If you make significant changes to your compressed air system through its life and add more pressure vessels / safety equipment the first part of the WSE needs to be updated with the items.

Part 2  – Part 2 of the WSE is the physical check of the condition and function of all the pressure vessels and safety equipment in your compressed air system using the first part as a guide.

If anything isn’t working correctly you are advised that it needs to be changed and it is your responsibility to make sure the item does get changed.


In order to complete a WSE the engineer needs to drain down the system, inspect any pressure vessels (this may require opening the pressure vessel and looking inside it for corrosion etc), test any gauges are reading correctly and test safety valves operate correctly at the correct pressure.

For further information take a look at our Written Scheme of Examination video take a look at our WSE page