Cylinders

Cylinder Testing

Under Spanish law (Real Decreto 366/2005), cylinders are due for visual inspection every year, and a hydrostatic test every three years. This applies to both steel and aluminium cylinders. All cylinders must display a valid test sticker and the paperwork for the cylinder should be retained in case of inspection. Tests may only be undertaken by premises licensed with Industria. Read more about the law in Spain for tank testing here (article 13 refers to the inspection dates).

The fine for out of date cylinders can be high and cylinders may also be confiscated if the cylinder tests are not in date. This includes new cylinders - make sure you have the paperwork, a stamp on the neck is not enough and the test date will be the date on the neck of the cylinder, not the date you bought it.

AirEquipo and Paul Sturgess are fully licensed with Industria, Registration Number 23064. Our stamp pictured on the right) is registered with the Spanish Government - you can find a list of registered inspection centres here. Remember, if you choose to use a company which is not legally registered with Industria, then your inspections will not be valid. Paul is also trained by ASSET (Association of Scuba Service Engineers & Technicians) in the UK and AirEquipo is a member of the highly regarded organisation.

Visual Inspection

The procedure to visually inspect a tank is as follows:

Removal of the tank boot, nets and valve.
The exterior of the tank is then inspected for impact damage and corrosion.
The interior of the cylinder is examined using a special endoscope.
Dental mirrors may enable the inspector to examine the area around the inside of the tank neck.
The valve is checked for smooth operation and its threads lubricated to help prevent galvanic action between the dissimilar metals of the tank and valve.
Valves may also require periodic overhauls, just like scuba regulators.
If no corrosion or damage is detected, the cylinder is reassembled.
A sticker is then placed on the tank which identifies the month and year in which the inspection was done and the expiry date.
If damage or corrosion is detected, the technician will decide upon an appropriate course of action.
Extensive oxidation or deep pitting is treated by degrees of shot blasting.

Essentially this test is a detailed visual inspection, both internal and external with the following failure criteria:

Bulge - all fail
Dent - fail if any greater than 2 mm
Wear - reduction of wall thickness greater than 25%
General Corrosion - reduction of wall thickness greater than 20% OR where original surface is not visible
Area Corrosion - (ie. where corrosion is limited to less than 20% of surface) a reduction of wall thickness greater than 25%
Isolated pitting - Reduction of wall thickness greater than 40%
Thread damage - all physical damage or imperfections (recutting of threads can be achieved up to a maximum tolerance)
Weight Check - Weight of cylinder (minus valve) less than 95% of the tare weight stamped on the cylinder

Any cylinder that has been subject to impact damage should be pressure tested before use. If in the opinion of the inspector, any of the above criteria are borderline, then hydrostatic testing may also be required.

Hydrostatic Testing

In this test the cylinder is filled with water and then placed inside a water-filled, high-pressure chamber. The water pressure inside the cylinder is then increased to five thirds of it's maximum working pressure. This is sufficient to cause the cylinder to expand slightly. This expansion causes the water outside the tank to be displaced and this is channeled into marked collection tubes that allow it to be measured.

If the tank's expansion is within acceptable limits (<5%), it passes the test. If not, the tank may not be refilled.

After pressure testing, tanks that pass are cleaned and dried, then stamped with the current month and year and the test centre's registered stamp.

Valve Servicing

Most tank valves are Balanced type which means that high pressure air is acting on both sides of the valve assembly to prevent any stiffness while turning the valve. Some have a pressure relief valve fitted called a burst disc.

The cylinder valve is fitted into the neck of the cylinder and is provided with an 'o' ring seal so that the diving regulator can be connected to it. The valve is screwed into the cylinder neck with either a taper thread seal or a parallel thread seal and o ring. It is not recommended that divers attempt to service their own cylinder valves, unless they possess specialist skills. Provided that the cylinder valve is washed in fresh water after use and is kept clean, there should be no need for it to be serviced between the intervals of cylinder test.

Shot Blast Cleaning

Our shot-blasting machine cleans all the internal surfaces of the diving cylinder. It removes rust, general contamination and corrosion build-up. It does not however, remove base material, and for particularly rusty tanks, two or three cycles may be required. The tanks are cleaned by introducing steel grit under pressure. It is boosted by a higher additional air pressure via a mixing valve and a venturi action ensures optimum results.

Advantages over rumbling or tumbling: infinitely quicker. Rumbling rolls the pit edge over, obscuring the defect. Shot blasting cleans deep into the pit, precisely showing the defect.

O2 Cleaning

As well as testing, we are able to offer an O2 cleaning service.

Current recommendations for the O2 cleaning of scuba cylinders is that they are cleaned every year. Once a cylinder has been O2 cleaned, it receives a individual sticker to indicate that it has been cleaned to current standards and the date of expiry is punched into this sticker.

O2 cylinder valves are serviced at the same time as the cylinder test. Ours costs include this unless any non standard parts are required. If any non standard service parts are required these will be charged separately.