The mechanism of diving regulators is the arrangement of components and function of gas pressure regulators used in the systems which supply breathing gases for underwater diving. Both free-flow and demand regulators use mechanical feedback of the downstream pressure to control the opening of a valve which controls gas flow from the upstream, high-pressure side, to the downstream, low-pressure side of each stage. Flow capacity must be sufficient to allow the downstream pressure to be maintained at maximum demand, and sensitivity must be appropriate to deliver maximum required flow rate with a small variation in downstream pressure, and for a large variation in supply pressure, without instability of flow. Open circuit scuba regulators must also deliver against a variable ambient pressure. They must be robust and reliable, as they are life-support equipment which must function in the relatively hostile seawater environment, and the human interface must be comfortable over periods of several hours. Diving regulators use mechanically operated valves. In most cases there is ambient pressure feedback to both first and second stage, except where this is avoided to allow constant mass flow through an orifice in a rebreather, which requires a constant absolute upstream pressure. Back-pressure regulators are used in gas reclaim systems to conserve expensive helium based breathing gases in surface-supplied diving, and to control the safe exhaust of exhaled gas from built-in breathing systems in hyperbaric chambers. The parts of a regulator are described here as the major functional groups in downstream order following the gas flow from the cylinder to its final use. Details may vary considerably between manufacturers and models.
Types of diving regulators
Gas pressure regulators are used for several applications in the supply and handling of breathing gases for diving. Pressure reducing regulators are used to reduce gas pressure for supply to the diver in demand and free-flow open circuit breathing apparatus, in rebreather equipment, and in gas blending procedures. Back-pressure regulators are used in the exhaust systems of the built-in breathing systems of diving chambers, and in the recovery of used helium based breathing gas for recycling. Some of these regulators must work underwater, others in the more forgiving conditions of the surface support area. All must work consistently and reliably, but some are parts of safety-critical life-support systems, where a single point of failure must not put lives at risk.
Open-circuit scuba regulators
Connection to the high pressure supply
The first-stage of the scuba regulator may be connected to the cylinder valve by one of two standard types of fittings. The CGA 850 connector, also known as an international connector, which uses a yoke clamp, or a DIN screw fitting to connect it to the valve of the diving cylinder. There are also European standards for scuba regulator connectors for gases other than air.
CGA 850 connection CGA 850 Yoke connectors (sometimes called A-clamps from their shape) are the most popular regulator connection in North America and several other countries. They clamp the high pressure inlet opening of the regulator against the outlet opening of the cylinder valve, and are sealed by an O-ring in a groove in the contact face of the cylinder valve. The user screws the clamp in place finger-tight to hold the metal surfaces of cylinder valve and regulator first stage in contact, compressing the o-ring between the radial faces of valve and regulator. When the valve is opened, gas pressure presses the O-ring against the outer cylindrical surface of the groove, completing the seal. The diver must take care not to screw the yoke down too tightly, or it may prove impossible to remove without tools. Conversely, failing to tighten sufficiently can lead to O-ring extrusion under pressure and a major loss of breathing gas. This can be a serious problem if it happens when the diver is at depth. Yoke fittings are rated up to a maximum of 240 bars (3,500 psi) working pressure. The outlet of the CGA 850 valve is on a flat surface on the valve body, inside a concentric face-sealing O-ring groove, with a conical indentation on the opposite surface of the valve body, co-axial with the O-ring groove. The yoke clamp fits around the valve body and the sealing face of the regulator inlet seats over the O-ring groove. A conically tipped screw locates in the indentation and when tightened, presses against the valve body and pulls the sealing face of the regulator inlet against the O-ring. This screw must be tightened sufficiently to maintain metal-to-metal contact between the regulator inlet and the valve body when the valve is opened at full cylinder pressure, and under normal working loads including minor impacts and using the regulator as a handle to lift the set, to prevent failure of the seal by O-ring extrusion and consequent loss of breathing gas. The screw must also not be over-tightened, as after use it must be removed by hand. The rigidity of the yoke varies depending on design, tightening is by hand and is left to the discretion of the user. Fortunately the mechanism is fairly tolerant of variation in contact force. When the valve is opened, gas pressure on the O-ring presses it against the outer cylindrical surface of the groove and the face of the regulator inlet, squeezing the O-ring towards the contact surfaces of these parts. The pressure exerts a force to push the regulator away from the valve body, and if pre-load of the screw is insufficient the elasticity of the clamp will allow a gap to form between valve and regulator through which the O-ring may be extruded. When this happens, gas loss is rapid, and the valve must be closed and the clamp loosened, the O-ring inspected and possibly replaced. Recovery from an extruded O-ring underwater is often not possible and bailout to an independent gas supply or an emergency ascent may be necessary.
DIN connection
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