Demand valve
Diving regulator: First and second stages, low pressure inflator hose and submersible pressure gauge
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| Other names | Demand valve |
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| Uses | Reduces pressurized breathing gas to ambient pressure and delivers it to the diver |
| Inventor | Manuel Théodore Guillaumet (1838), Benoît Rouquayrol (1860) |
| Related items |
Lightweight demand helmet Full-face mask Diving cylinder Buoyancy compensator |
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 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 - mainly the umbilical - and not influenced by the breathing of the diver, and 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.
The performance of a regulator is measured by the cracking pressure and work of breathing, and the capacity to deliver sufficient breathing gas at peak inspiratory flow rate at high ambient pressures. For some applications the capacity to deliver high flow rates at low ambient temperatures without freezing is important.
The diving regulator is a mechanism which reduces the pressure of the supply of breathing gas and provides it to the diver at approximately ambient pressure. The gas may be supplied on demand, when the diver inhales, or as a constant flow past the diver inside the helmet or mask, from which the diver uses what is necessary, while the remainder goes to waste.
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Wikipedia