Understanding Extinguisher Jargon - Overhaul

We've covered Condemned, Corrective Action, Basic & Extended Services in previous articles - today we look at the Overhaul.

First to note is that this type of service only applies to high pressure extinguishers - those with a working pressure over 30 Bar (420 psi) - which in the UK at least means CO2 (Carbon Dioxide) extinguishers which typically operate around 55 Bar (770 psi).

Under previous versions of the UK Servicing standard BS5306-3 & in general industry practice the Overhaul has been known as the Pressure Test, Hydraulic Test, Hydrostatic Test, Stretch Test & more, being descriptive of the main component of the service.

High pressure gas cylinders present a severe safety hazard, especially to filling stations, if the cylinders are in any way damaged or deteriorated and for many decades the relevant British Standards for steel & aluminium high pressure cylinders as well as industry standards have contained a requirement for routine internal & external inspection coupled with a hydraulic pressure test. The Pressure Systems Safety Regulations 2000 put testing on a clear statutory footing as only low pressure extinguishers (under 25 Bar) are exempted from the Regulations.

How often is an Overhaul required?

Originally the testing interval regime was quite complex:

• First retest at 10 years from original manufacturing test date; but
• First retest can be delayed to 20 years if the extinguisher is annually serviced to BS5306-3; however
• If discharged between 10 & 20 years whilst under the 20 year first retest relaxation the extinguisher must be tested before recharging; then
• Second retest at 10 years;
• Third and subsequent retests every 5 years

It's now far simpler! Overhaul every 10 years!

How can I tell when a test has been carried out?

High pressure cylinders are required to have certain information indelibly stamped into the cylinder shoulder (never the side!) including the pressure test date for the original & subsequent retests. The stamp should be in the form of month and year and include the special identification stamp of the test station.

If the extinguisher is over 10 years from the last stamped test then it should be withdrawn from service and sent for Overhaul

What does an Overhaul entail?

The overhaul involves:

• discharging the extinguisher,
• removing and discarding the head assembly as it cannot be tested (Before 2000 this wasn't mandatory and you would still find extinguishers in the late 90's with a full test record, but still using the original 1960's valve)
• carefully examining the cylinder interior & exterior for corrosion, cracks and flaws
• and then subjecting the body to a hydraulic pressure test in excess of 200 bar. If the body passes the test, it is stamped on the shoulder with the date of the pressure test and a new head assembly fitted, giving it another ten years of life. It may also be repainted and relabelled.

The pressure test checks to see not only if the cylinder withstands the pressure without rupturing but retains elasticity, returning to normal shape when pressure is relieved.

The Overhaul is usually coupled with a full refurbishment of the extinguisher where it is shot blasted, resprayed and a new label applied. To the casual observer the extinguisher looks identical to a brand new one.

Is there ever 'fake' overhauling?

Before 2000 the original valve could be retained and it wasn't unheard of for unscrupulous workshops to stamp the neck without testing, however it's easy to check that the test is likely to be genuine as in addition to the test stamp (MM/ID/YY or YYYY format) the valve, which generally now also has a stamped manufacture date, should be of the same year as the stamp (or certainly no older than a year before)

Next in the series

Recharge, Commissioning and alternative systems of maintenance. If anyone has suggestions for other future extinguisher related knowledge articles please comment below!