MK25 Regulator Usage in 6oC or Less

      No Comments on MK25 Regulator Usage in 6oC or Less
Anyone using a SCUBAPRO MK25 regulator in water temperatures colder than 6oC should carefully read the following information. Much of this information has come to us directly from SCUBAPRO’s European Techincal Director. SCUBAPRO’s MK25 regulator is an excellent choice for recreational divers. Its universal ranking as a flagship regulator is due to an extremely high air delivery and overall performance excellence. However, it is important to note that the MK25 is not being sold as an environmentally sealed regulator; the MK17 is SCUBAPRO’s only environmentally sealed regulator. Anyone considering cold/freshwater diving in Ireland on a regular basis will need to look at their overall equipment configuration. Remember that diving in water temperatures less than 6oC has its own specific considerations, and will need to be viewed as a unique diving discipline. As with all diving disciplines, you the diver must take responsibility for ensuring your equipment is suitable. However, those of you looking to dive in water temperatures less than 6oC, using standard recreational dive gear should follow the advice provided to us by SCUBAPRO:

SCUBAPRO’s European Technical Director Advises the Following:


First it is important to note that cold water diving cannot be considered as normal diving. Cold water diving is extreme diving and should be treated with appropriate care.
The European Norm EN 250 for diving regulators considers that water is cold when the temperature reaches below 6° C.
It is easy to understand that a regulator being fed with air at 300 bars, generates more cold when working, than air coming from a cylinder at 200 bars. So, obtaining the CE approval at 300 bars is more difficult to achieve, it also proves that our regulators have remarkable qualities in resistance to freezing.
All Scubapro regulators since the introduction of T.I.S versions are CE approved for cold water diving with 300 bars according to EN 250 norm (Germanischer Lloyd – December 2001).
A diving regulator is a device that automatically delivers air on demand at ambient pressure. The air reserve is usually contained in high-pressure single, twin tanks or more. Modern tanks have a working pressure varying between 200 and 300 bars. This pressure has to be reduced to ambient pressure by the regulator.
This important pressure drop will also generate an important drop of temperature of the internal parts of the regulator. For temperate water diving, the cooling down of the regulator has no influence on the good performance of the regulator, but it is completely different for cold water diving. Some parts of the 1st stage can reach –55° C as the air pressure is reduced Therefore, already cold ambient water in contact with very cold regulator parts will increase the possibility of freezing. The formation of ice crystals will modify the behaviour of the regulator that will then “freeze”.

In cold conditions we advise the following steps prior to diving:

1. Do not free flow a regulator out of water by pressing the purge button when preparing for a cold water dive as the air temperature could be much lower than the water temperature.

2. Slowly open the tank valve only when the regulator is immersed.

At the 2nd stage, the pressure drop is less than at the 1st stage. Therefore cooling down of the internal parts is less important, however, another factor that will affect the good performance of the regulator, is the very high water vapour content of the human breath in exhalation. The water vapour will condense on the cold parts of the 2nd stage and can form ice crystals that will modify the behaviour of the 2nd stage making it “freeze”.

3. If the air temperature is much lower than the water temperature, it is advisable not to breathe from the 2nd stage before immersion.

There is also a very important factor that will affect the performance of a regulator in cold water, it is the water vapour content of the compressed air inside the tank. It is most important to use very dry air when diving in cold water. The CE norm for breathing air (EN 12021) recommends maximum limits of water vapour content, CO, CO2 and hydrocarbons. To be concise, the compressed air used for cold water diving should be very dry to minimise freezing problems.

Here is a list of recommendations to improve the resistance to freezing of our MK20 and MK25 regulators
1. Fit the new piston (MK 25 is already equipped) with the polished stem and the new ivory colour softer silicone sleeve (the older version had a dark colour sleeve) The T.I.S 2 version (the latest one) has 2 ivory colour silicone sleeves for optimal cold resistance.
2. Lubrication should be light, excess grease is not recommended.
3. Fit the new Anti Freeze cap.
4. Remove the swivel protector to improve thermal dissipation.

For all 2nd stages:
1. Verify that the diaphragm and exhaust valve are watertight to prevent all water entry.
2. To momentarily improve the seal of the exhaust valve, a very small film of grease can be applied to the housing where the exhaust valve edge comes in contact. DO NOT GREASE THE EXHAUST VALVE.
3. Check the o rings that can retain impurities like sand grains or hair that can induce ice crystals formation.
4. Check the housing for cracks or internal scratches
5. The initial cracking effort should be increased 4.5 millibars. When the 2nd stage is equipped with an inhalation effort adjustment knob, it is recommended to screw the knob in by at least 1.25 turn.
6. For cold water diving only: Lower the lever by 2 mm, DO NOT GO BEYOND THAT ADJUSTMENT (by screwing the orifice by ¼ turn in more than usual).
7. The points 5 and 6 can be reached simultaneously.
8. For 2nd stages fitted with a hose sleeve, it is recommended to move the sleeve to the 1st stage end to improve thermal dissipation.

Scubadive West, as an authorised SCUBAPRO UWATEC dealer and service agent, is happy to make the above alterations to your regulator. Feel free to drop into us or call us.

Happy Diving!

Leave a Reply