How Often Do I Need My Pressurisation System Tested & Why?

Paul Thomas Pumps UK

In this article I shall outline why you need to test your pressurisation system and have procedures in place. There are many reasons why, but I shall mostly focus on the aspect we cover and outline what a WSE is. 


There are regulations in place, in particular the Pressure Systems Safety Regulations 2000, which mean that both the owner and user are required by law to show that understand and know the safe operating limits of any system(s). The main focus is to ensure they know the safe operating limits of the pressure and temperature of the system. They must also certify they are safe under said conditions.


The above can be achieved by having an appropriate Written Scheme of Examination (WSE) in place before the system itself is even activated. You must also ensure that the pressure system is actually examined in accordance to the WSE.


So, what actually is a Written Scheme of Examination? A WSE is essentially a file which covers all the important information about different components which form a pressurisation system, work under pressure and contain a ‘relevant fluid’.

The term relevant fluid is defined in the Regulations and covers compressed or liquefied gas, including air, at a pressure greater than 0.5 bar (approximately 7 psi) above atmospheric pressure; pressurised hot water above 110 °C; and steam at any pressure.” []


There are many different types of systems which require a WSE, ranging from a steam boiler all the way to a fixed liquefied petroleum gas storage system. But the main one we focus on and carry out at Pumps UK Ltd is for expansion vessels (accumulators). These are usually fitted to a booster set or a pressurisation unit and can be pressurised up to 18bar.


The reason you would need a WSE for an expansion vessel is due to any interaction between water and the vessel itself. Most vessels contain a bladder where the water is stored and if this splits it could damage the integrity of the vessel itself due to rust. The bladder can split due to many reasons, a main one being time. The integrity can also be corrupted due to the vessel being re-pressured incorrectly. If re-pressured with air, this can cause rust and this is simply because air contains water and if it is over pressurised the vessel itself can rupture. We carry out a non-intrusive test which focuses mainly on the vessel integrity; not the operation side.


What does this file contain? The WSE contains various documents which must be read by all users. It includes a document which outlines the different components within the system; the main parts which need to be and are testable; the nature of the test required; the prep work required for the component to be tested safely; the maximum time allowed between tests; and the critical elements of the system that, if modified in any way, should be re-tested before use again. It will also contain the name of the person/company and date that the WSE is carried out.


How often do I need to have a WSE carried out? The WSE must remain relevant during the course of the pressurisation systems lifetime; therefore it should be revised where necessary. The WSE file should also outline the maximum time period between tests, so this should give you a rough idea. Plus, as the time goes on, the different components of the system will age and may have its performance may hinder. Consequently, this could affect how often it should be tested.


Pumps UK Ltd have a service side, Pumps UK Service, who have fully qualified and trained members of staff who can carry out and can offer expansion vessel WSE examinations and contracts. Please call us on 01322 292 415 or send us an email on for more information.