Editing Scuba set (section)

=====Twin-hose demand regulator=====
{{main|Diving regulator#Twin-hose open-circuit demand scuba regulators}}
[[Image:Aqualung old type.jpg|thumb|Classic twin-hose Cousteau-type aqualung]]
This is the first type of diving demand valve to come into general use, and the one that can be seen in classic 1960s television scuba adventures, such as [[Sea Hunt]]. They were often use with manifolded twin cylinders.

All the stages of this type of regulator are in a large valve assembly mounted directly to the cylinder valve or manifold, behind the diver's neck. Two large bore corrugated rubber [[Breathing tube (in breathing apparatus)|breathing hoses]] connect the regulator with the mouthpiece, one for supply and one for exhaust. The exhaust hose is used to return the exhaled air to the regulator, to avoid pressure differences due to depth variation between the exhaust valve and final stage [[diaphragm (mechanical device)|diaphragm]], which would cause a free-flow of gas, or extra resistance to breathing, depending on the diver's orientation in the water. In modern single-hose sets this problem is avoided by moving the second-stage regulator to the diver's [[Mouthpiece (scuba)|mouthpiece]]. The twin-hose regulators came with a mouthpiece as standard, but a [[full-face diving mask]] was an option.{{citation needed|date=December 2016}}