Diving regulator

A diving regulator is a device used by a SCUBA diver in an Aqualung to supply the diver with breathing gas at ambient pressure from a high pressure diving cylinder.

Table of contents

1 Parts of a regulator 2 First Stage 3 High pressure hose 4 Low pressure hose 5 Contents gauge 6 Demand valve 7 Pressure relief valve 8 Old style twin hose regulators 9 Performance of regulators 10 Links to Manufacturers

Parts of a regulator

A diving regulator with one demand valve, a contents gauge and two direct feeds

The main components of a diving regulator are:

• the first stage
• the high pressure hose
• the contents gauge
• one or more 'low pressure'' hoses
• one or more demand valves or second stages
• a pressure relief valve

A diving regulator A clamp type first stage

The first stage is a pressure reducing valve that take gas from the diving cylinder at pressures of 200 bar to 300 bar (3000 psi to 4700 psi) and reduce its pressure down to 10 bar (140 psi) higher than ambient pressure.

The first stage has either an A clamp or a DIN fitting to connect it to the pillar valve of the diving cylinder. It has a number of "ports", which allow low and high pressure hoses to transport gas to other parts of the regulator.

High pressure hose

The high pressure hose takes gas, at cylinder pressure, direct from the inlet of the first stage to the contents gauge.

Low pressure hose

All breathing regulators have a hose that connects the first stage to the demand valves.

Some low pressure hoses are known as direct feeds. They supply gas to the diving suit and the buoyancy compensator inflation valves.

The first stage delivers gas at about 10 bar above ambient pressure to low pressure hoses.

Contents gauge

A diving regulator standard contents gauge

The contents gauge measures the gas pressure in the diving cylinder so the diver knows how much gas remains in the cylinder.

There are several types of contents gauge:

• The standard type is an analogue gauge that can be held in the palm of a hand and is connected to the first stage by a high pressure hose. Sometimes they are fixed in a console, a plastic or rubber box, that holds the air pressure gauge and one or more of a depth gauge, a dive computer and a compass.
• Button gauges are coin-sized, analogue gauges that are connected directly to the first stage. They are often used on decompression cylinders. Due to their small size, it can be difficult to read the gauge to a resolution of less than 20 bar / 300 psi.
• Air integrated computers. Some dive computers are designed to measure, display and monitor the diving cylinder pressure. Although this can be very beneficial to the diver, it does mean that if the dive computer fails, the diver can no longer monitor his or her gas reserves. The computer is either connected to the first stage by a high pressure hose or has two parts, the pressure transducer on the first stage and the display at the wrist or console, which communicate by radio link.
• In the past, some types of diving cylinder had a mechanical reserve release lever that provided a warning to the diver that the gas supply was nearly exhausted

A diving regulator demand valve

The demand valve, second stage or DV is the device connected to a low pressure hose from which the diver inhales. It detects when the diver starts inhaling and supplies the diver with a breath of gas at ambient pressure. It reduces the gas pressure in the hose from 10 bar (140 psi) above ambient pressure to ambient pressure.

It consists of a chamber, a valve at the end of the low pressure hose and a mouthpiece, which the diver grips between his or her teeth. A diaphragm at the front of the chamber controls the valve on the low pressure hose. The diaphragm operates when the "purge button" on the front of the DV is pressed or when the diver lowers the pressure inside the chamber by trying to inhale. In either case low pressure gas is released into the chamber removing any water in there, allowing the diver to inhale and pushing the diaphragm back so that the valve closes. When the diver exhales the diaphragm flex allow the gas to escape to the water outside the DV.

A diving regulator demand valve and BCD inflation valve

Sometimes a regulator has more than one DV. If its is simply a spare DV for use by the diver's buddy it is generally called an octopus. Another possibility is: it could be a hybrid DV and buoyancy compensator inflation valve. Both types are called alternate air sources and more confusingly a DV on a regulator connected to a separate, independent diving cylinder would also be given that name.

Pressure relief valve

A pressure relief valve is a safety device that must be used if no demand valves are present on the regulator. It allows gas to escape from the first stage in the event of a malfunction, without over-pressurising any other regulator components, such as diving suit or buoyancy compensator inflation valves.

Normally, if present, a demand valve will vent off safely the excess gas from the first stage malfunction. This is called a "free flow" and is designed as a "fail safe" so that the diver can continue to breathe for a few seconds or minutes until all the gas is rapidly exhausted. If there is neither a demand valve nor a pressure relief valve there is a danger the excess gas will "free flow" to the buoyancy compensator or diving suit resulting in a rapid increase in buoyancy causing a potentially lethal ascent to the surface.

Old style twin hose regulators

Earlier models of regulators had the two stages combined into one. Air was supplied to the diver via a large corrugated hose to the divers mouth piece. Exhaled gas returned via a second hose back to the regulator where it was released into the water. The twin hose has reappeared in modern rebreathers.

Performance of regulators

ANSTI has developed a testing machine that measures the inhale and exhale effort in using a regulator. Publication of results of the performance of regulators in the ANSTI test machine has resulted in big performance improvements.

Links to Manufacturers

AP Valves AquaLung Apecs Poseiden ScubaPro Spiro