Diving Equipment

Alternative Air Source – New Guidelines

In Europe divers should be aware that there have been changes to European Standard EN250. This Standard concerns the manufacture of underwater breathing apparatus. The changes concern how alternate air sources are used.

As equipment manufactured under the requirements of the previous version of the standard will be around for many years, the implentation of these changes will be slow. However, divers should be aware of these changes and know when to implement some of the changes concerning the configuration of alternate air sources.

The main changes that will affect any regulators manufactured in accordance with the new (2014) version of the standard are as follows:

  • An octopus rig is not a preferred option if the depth is greater than 30m or the water temperature is less than 10°C, instead an alternative fully independent system is advised.
  • Regulator first stages which are not designed for cold water performance shall be marked with “>10°C”.
  • Regulator first stages may be marked with a lower working temperature if specified by the manufacturer.
  • Regulators first stages will be stamped with an “A” if they are compatible to be fitted with an alternate air source (octopus rig).

These changes will come into effect gradually as more regulators are manufactured according to the revised standard. If you have any questions on how you can use a particular regulator, you should approach the manufacturer for advice.

Queue for the Dive Lift

The dive lift is a standard accessory to any good dive boat these days. I had one fitted as soon as I purchased the boat. Just because, I felt it was no longer a luxury but something that should be part of any good dive operation. The first dive lift I came across was in Skin Deep in the days of Andy Smith. Designed by Len Hurdiss it was a revolution to the diving at the time.

The problem is that it now seems too popular at times. Here you see a queue already forming to use the lift.

Divers waiting to get on the dive lift

Divers waiting to get on the dive lift

What is a Dive Lift

Technically a dive lift is a man-over-board recovery device. A dive lift is a platform which can be lowered into the water to recover people from the water. As divers seem very keen on doing this the MOB system seems very useful. For divers it is a stress free way to be picked up out of the water and be raised to deck level for them to step off for an easy return to the boat.

Diver stepping onto the dive lift

Diver stepping onto the dive lift

The platform lowers into the water to a depth of a few feet so a small bend of the knees enables the diver to stand upright onto the dive lift. Once the crew see the diver is stable the lift is raised to the deck level.

Diver on-board

Diver on-board

Once at deck level the diver can walk off the lift to the seating to get unkitted without the fear that the exertion of climbing a ladder could raise issues for of DCS. Te diver ussually has a big smirk on his face at this point, particularly if he has not used a dive lift before.

The best dive lift

This picture shows the commercial dive lifts that lower the diver right down to the wreck. This may be some time off for the recreational diver.

Commercial dive cage

Commercial dive cage


Compressed Air Purity for divers

Standard BSEN12021

Compressed air used by divers should conform to BS EN12021. This standard gives the basic parameters for the composition of the air and the limitfor for contaminants that are often found in breathing air. These limits are based on a value that is 10% of the 8-hour time weighted average in the workplace in the UK. (Carbon Monoxide is 8%).


Oxygen (O2) should make 21% (±1%)by volume in dry air.


Lubricants such as oil droplets/mist must not exceed 0.5mg/m³

Carbon Dioxide

Carbon Dioxide (CO2) must no exceed 500ml/m³ (or 500ppm)

Carbon Monoxide

Carbon Monoxide (CO) shall be as low as possible and must not exseed 3.5mg/m³ (or 3ppm)

Water content

for a cylinder pressure greater than 200bar measured at the outlet must not exceed 35mg/m³


The air must be without significant odour or taste.

Air Purity Testing

BSEN12021 specifies that the air purity should be at least tested every 3 months. For clubs operating their own compressor who need not strictly comply with this standard should have the air tested every year as an absolute minimum and again after any work or maintenance that may affect the air purity.

In addition to these parameters the compressor manufacturer may also specify that tests for specific chemicals be carried out. The compressor operator should also test for contaminents in the vicinity that may find their way into the system. A good example may be a test for chlorine if the compressor is located near a swimming pool.

Air Purity Test

Firstly you will need to fill a cylinder from the compressor. The cylinder should be clean, a freshly oxygen cleaned cylinder is ideal, this will minimise any contaminants that may have built up inside a frequently used cylinder. The compressor should be run up to it’s normal working temperature and in normal conditions. The cylinder should be empty to start with and filled to at least 100Bar. The air cylinder should then be emptied again and then filled for testing. Doing this will reduce the contaminants that may have been in the existing air in the cylinder down to a minimal level.

There are many ways to test for air purity. The following is a simple method using gas detection tubes. Most detection tubes require a fixed volume of air to pass through them. This can be done using a fixed volume syringe type pump that will be available from the manufacturer. The following example uses a constant flow valve.

Step 1 – fit flow regulator

Firstly a regulator is fitted to the cylinder that will provide a fixed flow of gas from the cylinder under test.

Flow regulating valve fitted to cylinder

Flow regulating valve fitted to cylinder

Step 2 – Fit gas detector tube

With the test tube in place the regulator is turned on to provide a fixed flow rate that is specified for the tube. The tube will also have a time that the test flow should be allowed to run through the tube. It is very important to allow free flow of gas through the tube and not to restrict the outlet.

Gas detector tube fitted to flow regulator

Gas detector tube fitted to flow regulator

 Step 3 – Take the reading

During the test the reagent in the tube will change colour in proportion tot he amount of contaminent in the sample. At the end of the test the measurement can be read of the scale where the reagent has changed colour.

Colour change in tube during test

Colour change in tube during test

Step 4 – Repeat for other contaminents

Each tube is designed to detect a specific contaminant in a specific range. So the test is repeated with all the relevant tubes necessary.

The instructions with the tube will give the color change as well as the time and flow (or volume) of gas that should be used during the test. |Other parameters such as corrections for temperature and which other contaminants may give rise to a false reading are detailed. Lastly instructions for safe disposal information and first aid for the chemicals in the tubes are included.

Example of test tube

Example of test tube

Further guidance can be found from the Health and Safety Exective Divers Breathing Air Standard

Cylinder – Hydro Test

A hydro static or hydro test is performed once every 5 years on diving cylinders. Before the Hydro test the cylinder will need to be visually inspected. You may want to read the post on the visual test

Step 1 – Fill with water

The cylinder is filled with water. Liquid is used as it does not compress greatly under pressure. So if a cylinder does fail there is not a great mass of expanding gas to cause damage.

Filling a cylinder with water

Filling a cylinder with water

Step 2 – Fit test adapter

A hydraulic hose is fitted into the cylinder with a connector to attach to the hydraulic pump

Fitting the hydraulic hose

Fitting the hydraulic hose

Step 3 – Connect to Hydraulic pump

The cylinder is dropped into the water jacket and the hose is connected to the hydraulic pump. This is done by a fitting in the side of the water jacket.

Placing the cylinder into the water jacket

Placing the cylinder into the water jacket

The test hose is connected to the hydraulic pump through a fitting inthe jacket

The test hose is connected to the hydraulic pump through a fitting inthe jacket

The lid of the water jacket is then then fitted which has a water tight seal. The jacket is then purged of air with water. The level of the water is set on a graduated tube attached to the jacket.

Step 4 – The Hydro Test

The cylinder is then pumped to the test pressure. This is usually 1.5x the working pressure so 348Bar for a standard 232Bar cylinder. The pressure is then held for 30 seconds.

Pressurising the cylinder

Pressurising the cylinder

As the pressure increases the cylinder will stretch. As it does so the water in the jacket is displaced and the amount of displacement is measured on the graduated tube. When the pressure releases the cylinder relaxes and the water level drops below the initial level. The amount of water displaced during the pressure cycle and after is used to calculate the permanent set of the cylinder.

The cylinder is then removed from the jacket and emptied of water.

Step 5 – Drying

Water inside a cylinder is not good so it must be dried. If left in the cylinder will rust, even a short exposure to the atmophere can cause flash rusting. Once empty the cylinder is inverted over a steam jet. This heats the cylinder and with the addition of chemicals the cylinder can be hot oxygen cleaned. When hot the cylinder is dryed with an air jet and again inspected internally to ensure all the water is removed. The main danger of cold oxygen cleaning of cylinders is the fact that it is almost impossible to dry the cylinder adequately or fast enough.

Drying with an air jet

Drying with an air jet

Step 6 – Stamping the cylinder

This is done with a set of punches. The year and month of the test is put on the cylinder along with the test stations unique identification stamp. A “V” is stamped at the end if the cylinder has just had a mid-term inspection and not a full hyro test.

Stamping the cylinder

Stamping the cylinder

Step 7 – Refitting the valve

The valve is re-inserted into the cylinder with a new O’ring. A tool is inserted into the valve outlet and a torque wrench is fitted so the valve is fitted to the correct setting. If this is done the cylinder does not leak. It is not acceptable to fit the cylinder valve with a spanner and a hammer.

Replacing the valve with a torque wrench

Replacing the valve with a torque wrench

Cylinder – Visual Test

A visual test or  inspection of a diving cylinder is made before a hydrostatic test is made. It is also done half way between the hydrostatic test cycle to verify the condition of the cylinder.

You may also want to read about the  Hydrostatic test next, or the taking the cylinder valve apart

Step 1 – Checking the threads

The first step is to inspect the threads for damage and to gauge them to see if they are in tolerance.  This is done with a pair of calibrated gauges called the “GO” and “NO-GO” gauge. Simply the GO should wind on or into the thread and the NO-GO should not. Threads are one of the major causes of cylinders to fail and usually it is due to maintenance by non-trained persons.

Gauging the valve thread

Gauging the valve thread

Gauging the outlet thread

Gauging the outlet thread

Gauging the cylinder thread

Gauging the cylinder thread

Step 2 – Visual Inspection

This is done externally and internally. Externally the boot is removed and the general condition of the cylinder is checked. Defective paint will not fail a cylinder. Deep rust marks and damage are the problem. Internal visual inspection is done by using a bright light and endoscope. This can even look back a the shoulder of the valve internally. Deep rust marks are the issue. Cylinders may have a light rusting over the inside. This is not a fail.

Looking inside a cylinder

Looking inside a cylinder


Cylinder Testing – Cylinder Valve

The first part of a cylinder test whether it is hydrostatic or visual is to remove and disassemble the valve.

Step 1 – Remove the handle

This is done with a special flat bladed tool that straddles the centre thread. This one is in fact made from a flat bit. This is done so that it can be attached to an impact driver, as they can become difficult to remove after a couple of years use. The nut once removed allows the spring, then the handle and finally the nylon washer to be removed.

Removing the handle

Removing the handle

 Step 2 – Remove the screw mechanism

Removing the screw mechanism

Removing the screw mechanism

Next the screw mechanism is removed. This is done by unscrewing the nut at the end of the valve. Once removed the spindle should be removed from the cylinder valve. There is a nylon washer on the shaft and o’ring seals at either end of the body.

The screw mechanism

The screw mechanism

Step 3 – Valve Seat

The final step is to remove the valve seat itself. There are various types. Some are all nylon whilst others like the one pictured are brass with a nylon face. This one has a slot in the back that the blade on the spindle fits into. Others are the reverse with the spindle having a saddle that fits over a flat on the back of the seat. All are basically the same.

Valve seat removed with a screwdriver

Valve seat removed with a screwdriver

Step 4 – Remove the cylinder valve

Lastly a tool is inserted into the valve and very delicately loosened with the aid of a large hammer. A-Clamp valves have an adapter that fits over the body to allow the DIN tool to be used. Spanners are not recommended as they will damage the chrome and brass of the valve.

Removing the valve

Removing the valve

These parts are then put to one side, cleaned and serviced with new O’rings. Information on cleaning can be found here which details cleaning of a regulator first stage

Regulator Servicing – 1st stage Assembly

Now that all the parts are cleaned we can start the process of assembly. First we get all the parts and tools together.

Step 1 – Diaphragm End

IMG-20140327-00472 IMG-20140327-00473

Take the main body and drop the mushroom into the body. The diaphragm can then be pushed into place and the metal disk that the spring sits on goes next. The top part of the body can now be fixed ensuring that the body does not clamp onto the disk. Set the body upright and make sure it is free to move in its housing. Then tighten down with the pin spanner.

IMG-20140327-00474 IMG-20140327-00475

The main spring goes in next and must sit on the metal disk centrally. Then screw down the adjuster so that it is almost flush with the body. This pushes the spring and so the mushroom down

Step 2 – Valve Seat Assembly


This is the only tricky bit. Grease and press the small O’ring into the top of the body. Also fit the medium sized O’ring around the middle.  The spring goes on and then push the valve seat into the centre of the small O’ring. That’s it. The larger O’ring and bearing washer is in fact easier to fit at the next step.

Step 3 – Turret Assembly


Grease the large turret washer and fit to the body. Place the turret on top. Then fit in the blue bearing washer and larger Valve O’ring into the top. With the valve upright the valve assembly can be dropped down into the body so that the hole in the seat itself sits on the mushroom from the other side. A small amount of pressure is needed to push down to be able to tighten everything up.

The turret O’rings are the main moving parts and may need a bit more grease. All other O’rings should have just sufficient for assembly.

It is very important to assemble the diaphragm end before the turret as the spring keeps the seat of the knife edge in the body. If that is damaged it is likely to be the end of the valve.

Step 4 – A-Clamp or DIN fitting

IMG-20140327-00478 IMG-20140326-00464
There is a slight difference between the two systems. For the A clamp the white filter is pressed into the shaft from the “cylinder” end. The DIN fitting has a cone shaped filter inserted from the “valve” end.  With the filter in place the shaft goes through the A-clamp or DIN fitting through the plastic spacer and screwsinto the main body with the O’ring in to seal. It is best to put it all together and hold everything upright to screw into the body as the O’ring can easily pop out and be damaged when tightened.

Step 5 – Attach the peripheral parts.

IMG-20140327-00479 IMG-20140327-00480

Step 5 – Testing

IMG-20140327-00482 IMG-20140327-00483

With everything back together the valve is connected to an air supply. This should be around 70 Bar and not a full cylinder.  For the first time at least it is a good idea to press the purge on the second stage when applying the pressure to bring the pressure up slowly. Purge the valve several times to allow for a bit of settling.

Attach a pressure gauge to one of the intermediate ports. Adjust the pressure using the allen key to the required pressure. This is typically between 9 and 10 Bar, but may vary due to the application. It is better to purge the air first before each adjustment.

Step 5 – Refit dry seal


Lastly the dry seal system can be attached with the new service date sticker fitted to below the clear plastic membrane.

The second stages may also need adjustment to match the new interstage pressure.

Regulator Servicing – 1st stage Cleaning


The reason to service a regulator is to maintain it in first class working order. To keep the regulator working the parts that deteriorate with age such as O’rings and the parts that wear with use need to be replaced. It is also an opportunity to inspect all the parts for damage. The picture below shows where the chrome has disappeared, this is probably due to the regulator being left with water inside.



Cleaning is also important in this process. It is the opportunity to remove foreign particles that may have entered the valve. Removing all the old grease so that new can be used. Also all the limescale that inevitably builds up can be removed. The photograph below shows limescale build up from just over a years use.


Cleaning is best done in an ultrasonic bath. Limescale is removed with acid. You can use vinegar but other acids are preferable. e.g. citric acid. Better still are the cleaners specifically designed for this purpose.  The parts should only be left in the bath long enough to remove the limescale. Leave the parts too long and the metal will become damaged. If the brass parts become pink in colour they have definitely been in too long.


Once out of the bath then the parts need to be rinsed in fresh water. Hot soapy water is also a good cleaning process but again rinse in fresh water afterwards.IMG-20140326-00455

Oxygen cleaning

Oxygen cleaning involves the removal of hydrocarbons from the parts.  Again this is done in an ultrasonic tank with a specialist cleaning solution. I use Metaclean. A good tip with an ultrasonic bath is to use a container within the main bath. It saves on expensive chemicals and the solution can be made deeper than the main bath to totally immerse the part. The ultrasonic waves pass straight through the container and into the liquid inside. Once again rinse in freshwater after cleaning.


The last stage is to dry the parts. This is best done having done the last rinse in fairly hot water and then using an air gun to remove the excess water. With all this done you have a set of shiny parts ready for reassembly.


Regulator Servicing – 1st stage Disassembly

A starting point is the need to service some regulators. The ones shown are all Apeks regulators. (Actually there is also a domiflow oxygen valve on the right). These regulators are typical of diaphragm first stages. Other manufacturers will look very different but on the whole the principle of operation is the same and the servicing procedure is very similar.

A few tools are needed. Most are standard, but a pin spanner and a bar to insert into the regulator ports are fairly essential.


Step 1 – Remove all the peripheral parts


By this I mean the contents gauge, inflation hoses and the second stages as well. Also remove the blanking plugs and any dust covers.

Note: that a numbered box is really useful to keep parts together and to identify the regulator if you are servicing more than one.

Step 2 – Remove dry seal and cylinder adapter


Use the special tool to lock the valve body. Once in place a large spanner can remove an A-clamp adapter or use an Allen key to remove the DIN adapters. The dry seal system can be removed using a pin spanner.  This stage is not required with the non-sealed first stages.

Step 3 – Remove the IP adjuster


With the dry seal system removed the intermediate pressure adjuster can be removed with the spring below. Once this is done the top body part can be removed with a pin spanner. This reveals the diaphragm with its protective metal plate. This can be removed with the metal mushroom below.


Step 4 – Remove Valve seat


Now the turret can be removed with the valve seat assembly.


And that is it, the first stage disassembly is complete. Here is the exploded view: