Preparation of regulators for cold water diving

by Nick Drakich, B.Sc., M.E.Sc. The most common problem occurring in the cold with most conventional regulators with downstream valve second stages is free flow at the regulator second stage. This occurs because the rubber seat for the second stage valve becomes harder in the cold and has more difficulty sealing on the air orifice. Also, ice crystals may form on the edge of the air orifice not allowing the seat to seal.

This problem can be minimized by increasing tension on the second stage valve poppet spring which will provide a greater closing force to seal the valve seat on the orifice. Depending upon what features the regulator has, this can be achieved by adjusting the orifice closer to the poppet, shimming the poppet spring, or compressing the poppet spring with an adjustment that moves the base of the spring. Also, the intermediate pressure of the regulator can be lowered which will result in a greater force to seal the second stage valve seat on the air orifice. When lowering the intermediate pressure, force from the gas to open the poppet is reduced while the force from the poppet spring to close the poppet remains the same resulting in an overall increase of closing force. However, dropping the intermediate pressure will reduce air flow, so this method is less preferrable. Metal housings on second stages are good heat sinks and conduct heat to the orifice to minimize formation of ice crystals. Most older model second stages use metal housings and a number of manufacturers are bringing back metal housings for some of their new regulators. Plastic housings on second stages are poor heat sinks. However, some second stages with plastic housings have metal heat conductors installed to bring heat to the orifice and are good for cold water diving. Some second stages have the metal working parts coated with plastic to minimize formation of ice crystals that would intefer with the working of the regulator. Conversion kits to replace metal working parts with plastic coated parts are available for some regulators and should be considered when preparing regulators for cold water diving. In the regulator first stage, the valve spring is exposed to the water. Cooling takes place when the valve is open due to the expanding gas absorbing heat. Here, the heat is drawn out of the regulator body and may cause ice to form. Since the valve spring is in the extended state when the valve is open, buildup of ice between the coils of the spring will not allow it to compress leaving the valve open and creating a free flow.

In the diaphragm actuated upstream valve first stage or piston actuated upstream valve first stage, this problem is usually solved by filling the ambient pressure chamber with silicone oil and closing it in with an external diaphragm. On some regulators, the ambient pressure chamber is kept dry and a push post is used to deliver the force from the external diaphragm to maintain intermediate pressure over ambient for changes in depth. In either situation, the valve spring is kept out of water so ice will not form between the coils allowing the spring to compress and the valve to close. In piston first stages, because of the location of the ambient pressure chamber, the use of a silicone oil filled ambient pressure chamber with an external diaphragm is not feasible. Some manufacturers have recommended heavily covering the piston spring with silicone grease to minimize chance of ice formation. Some piston regulators have solved the problem of exposure of the piston spring to the cold water by using a dry air purge. A small bleed of air is provided into the ambient pressure chamber of the first stage and exhausts from the regulator through a check valve keeping the chamber dry but allowing adjustment for depth. The main problem being dealt with in preparing regulators for cold water is to minimize risk of free flow due to build up of ice. However, some regulators on the market can freeze closed and should not be used for cold water diving. These regulators are usually issued with a warning to not use in cold water. Other regulators, designed for use in cold water, may not have been prepared for cold water use and adjustments may have to be made. Adjustments of a regulator for cold water diving will vary with the make and model of regulator. Therefore, it is recommended to check the manufacturer's specifications before preparing the regulator for use in cold water.

Nick Drakich has extensive experience diving and preparing equipment for diving in the fridgid waters of North America's Great Lakes. He may be contacted at Technical Diving Systems, Kingston Diving Centre Inc., Kingston, Ontario or via email: [e-mail].

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