Scuba & Snorkeling

A diving regulator is a pressure regulator that reduces pressurized breathing gas to ambient pressure and delivers it to the diver. The gas may be air or one of a variety of specially blended breathing gases. The gas may be supplied from a scuba cylinder carried by the diver or via a hose from a compressor or high-pressure storage cylinders at the surface in surface-supplied diving. A gas pressure regulator has one or more valves in series which reduce pressure from the source, and use the downstream pressure as feedback to control the rate of flow and thereby the delivered pressure, lowering the pressure at each stage.The terms regulator and demand valve are often used interchangeably, but a demand valve is a regulator that delivers gas only while the diver is inhaling and reduces the gas pressure to ambient. In single-hose regulators, the demand valve is the second stage, which is either held in the diver's mouth by a mouthpiece or attached to the full-face mask or helmet. In twin-hose regulators the demand valve is included in the body of the regulator which is usually attached directly to the cylinder valve or manifold outlet. A pressure-reduction regulator is used to control the delivery pressure of the gas supplied to a free-flow helmet, in which the flow is continuous, to maintain the downstream pressure which is provided by the ambient pressure of the exhaust and the flow resistance of the delivery system and not influenced by the breathing of the diver. Gas-reclaim systems use a third kind of regulator to control the flow of exhaled gas to the return hose. Rebreather systems may also use regulators to control the flow of fresh gas, and demand valves, known as automatic diluent valves, to maintain the volume in the breathing loop during descent. The performance of a regulator is measured by the cracking pressure and work of breathing, and the capacity to deliver breathing gas at peak inspiratory flow rate at high ambient pressures without excessive pressure drop. For some applications the capacity to deliver high flow rates at low ambient temperatures without jamming due to freezing is important.
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