By Skip Dunham, Diving Systems International – Santa Barbara
Does your bail-out have an overpressure relief valve? An overpressure relief valve is considered essential for all bail-out regulators, yet few divers use them. Without an overpressure relief valve, it’s possible to lose your entire bail-out supply in a matter of minutes. There’s also the possibility that you could be injured in the event your bail-out whip were to fail.
Most divers using a bail-out system dive with the cylinder turned on, and the emergency valve on the mask, helmet or bail-out manifold closed. When the system is used in this manner, if the topside air supply fails, you only need to open the emergency valve to breathe the air from the bail-out. This type of system is extremely reliable, but can cause difficulties if the regulator on the bail-out bottle experiences what is known as “first stage creep.”
When a first stage creeps, air bleeds into the low pressure hose connected to the emergency valve. In a SCUBA system, when this happens there is no problem, since each time the diver breathes, he or she reduces the pressure in the low pressure hose. The pressure never has the chance to build to the point where the hose ruptures. In a downstream style regulator, the second stage will bleed off (free-flow) if the pressure in the hose builds beyond what the inlet valve springs will hold.
In a bail-out system, with the emergency valve closed, if the first stage creeps, pressure builds throughout the dive. If the low pressure hose is old or otherwise weak, or the pressure in the hose builds to a sufficient level, the hose will rupture. When this happens, the diver loses his or her bail-out air supply and may be injured by the hose as it whips about. This problem is especially common with first stages of the diaphragm design.
To prevent your bail-out whip from rupturing, mount an overpressure relief valve on any one of the low pressure ports on your bail-out regulator. The valve is pre-set at 180 PSI but can be adjusted to a higher pressure if you prefer.
(This article originally appeared in the May 1990 issue of UNDERWATER Magazine in the Squawk Box. The information in this article is still relevant today, nearly 30 years later.)