| Diving Regulator |
Article Index for Diving |
Website Links For Diving |
Information AboutDiving Regulator |
| CATEGORIES ABOUT DIVING REGULATOR | |
| diving equipment | |
|
A diving regulator is such a regulator which is used in a Scuba Set and supplies its user with Breathing Gas at ambient pressure from one or more Diving Cylinder s. The gas may be air. People often use the words "regulator" and "demand valve" interchangeably, but here a demand valve is part of a regulator. The first stage is usually designed to release the gas at a constant rate despite the pressure in the cylinder becoming less as the gas in the cylinder is used. FASTENING THE REGULATOR TO THE CYLINDER OR CYLINDER BLOCK In an open-circuit scuba set, the regulator, or its first-stage, has an A-clamp or a DIN Fitting to connect it to the Pillar Valve of the Diving Cylinder . A-clamp This is the traditional type. It clamps an open hole on the regulator against an open hole on the cylinder. The connection is made gas pressure tight with an O-ring . See A-clamp . DIN fitting This is a modern type of direct screw-in connection. It was designed when cylinder pressures got too high to be handled by an A-clamp . PRESSURE GAUGE To monitor breathing gas pressure in the diving cylinder, a diving regulator usually has a ''high pressure'' hose leading to a ''contents gauge'' (also called ''pressure gauge''). The port for this hose leaves the first-stage upstream of all pressure-reducing valves. The ''contents gauge'' is a Pressure Gauge measuring the gas pressure in the Diving Cylinder so the diver knows how much gas remains in the cylinder. It is also known as ''submersible pressure gauge'' or ''SPG''. There are several types of contents gauge:- Standard type This 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''. It displays with a pointer moving over a dial. Sometimes they are fixed in a ''console'', which is a Plastic or Rubber case that holds the air pressure gauge and also a Depth Gauge and/or a Dive Computer and/or a Compass . Button gauges These are coin-sized analogue gauges 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 Computer s are designed to measure and display and monitor pressure in the Diving Cylinder . This can be very beneficial to the diver, but if the Dive Computer fails, the diver can no longer monitor his or her gas reserves. Most divers using a gas-integrated computer will also have a standard air pressure gauge. 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; The signals are encoded to eliminate the risk of one diver's computer picking up a signal from another diver's transducer, or radio interference from some other source. Mechanical reserve valves In the past, some types of diving cylinder had a mechanical reserve valve that restricted air flow when the pressure was below 500 psi. Alerted to having a low gas supply the diver would pull a lever to open the valve and surface using the reserve gas. These valves are known as "J valves" due to the letter J being next to that valve in the US Divers product catalog. Valves without the reserve lever are called "K valves" for the same reason; being the next item in the catalog they were denoted by the letter K. Modern divers using "J valves" dive with the reserve valve in the open position and depend on a contents gauge or computer to monitor gas supply. TYPES OF FIRST STAGE The mechanism inside the first stage can be of the diaphragm type or the piston type. Both types can be balanced or unbalanced. A diaphragm first stage may be over-balanced as well. The performance of unbalanced regulators decreases as the cylinder pressure falls. A balanced regulator will keep the same ease of breathing at all depths and pressures. The over-balanced regulator will become easier to breath at depth. Piston type Here the piston is rigid and acts directly on the seat of the valve. Diaphragm type These are simpler than the piston type, but need more careful maintenance, so are less suitable for diving at places with limited services. The diaphragm is flexible and lifts a rod and opens and closes a gap at the seat. Risk of the regulator becoming blocked with ice As gas leaves the cylinder it decreases in pressure in a regulator, becoming very cold. Where the water temperature is less than 5°C any moisture inside the regulator may freeze, preventing the valve closing, causing a free-flow that can empty a full cylinder within a minute or two. The modern trend of using more plastics, instead of metals, within the regulators encourages freezing because it insulates the inside of a cold regulator from the warmer surrounding water. Environmental sealing and Teflon coatings are used to reduce the risk of freezing inside the regulator. TYPES OF LAST STAGE Not present If there is only one stage, and that stage is constant flow, the gas must be turned on and off at the cylinder. Manually operated by a button or lever or knob These are used to blow gas or air into an equipment item manually, such as Buoyancy Compensator s, Drysuit s, and many Rebreather s. (The valves on Blowtorch es are in this class also.) Operated by a solenoid The Solenoid is controlled by Electronics . This is used in automated fully closed-circuit Rebreather s to maintain the Oxygen Partial Pressure of the loop, as described in Rebreather#Fully Closed Circuit Rebreather . Demand valve The demand valve was Invented In 1865 in France, and forgotten in the next few years, and was not invented again until the late 1930's. A demand valve detects when the diver starts inhaling and supplies the diver with a breath of gas at ambient pressure. It has a chamber. A valve feeding from the previous valve stage feeds into the chamber. Either a Mouthpiece or a Fullface Mask is connected to the chamber, for the diver to breathe from. One side of the chamber is a flexible Diaphragm . When the diver tries to breathe in, the inhalation lowers the pressure inside the chamber, which moves the diaphragm operating a system of levers, which opens the valve, releasing gas into the chamber. This blows out any water in the chamber and provides the diver with ambient pressure gas to breathe. When the chamber is full and the lowering of pressure has been reversed, the diaphragm returns to its normal position so that the valve closes when the diver stops breathing in. The diaphragm is protected by being covered by a second chamber, which the outside water can enter freely through large holes or slits. Some passive semi-closed circuit rebreathers use a form of demand valve, which senses the volume of the loop and injects more gas when the volume falls below a certain level. ARRANGEMENTS OF THE ASSEMBLY OF VALVES Often one first stage supplies in parallel two or more second stages of various types. Each of these second stages should be looked for below according to its type. Often a branch tube goes off without going through any pressure-reducing valve stages, to a Pressure Gauge . TYPES OF REGULATOR Constant flow In constant-flow regulators the first stage is constant flow, and the second stage is a plain on/off valve. (In a Blowtorch the first stage is fastened to the cylinder and the second stage is on the torch head.) They are the earliest type of breathing set regulator. They are used now in many Rebreather s. The only control the diver has is to open or close the second stage. Constant flow valves in an open-circuit breathing set consume gas less economically than demand valve regulators because gas flows even when it is not needed. twin-hose regulator made in the 1980's. It has one low-pressure port, which feeds the left (inhalent) hose. Its Mouthpiece can be strapped in.]] In some Rebreather s, e.g. the Siebe Gorman Salvus , the oxygen cylinder has two first stages in parallel. One is constant flow; the other is a plain on-off valve called a Bypass ; both feed into the same exit pipe which feeds the Breathing Bag . In the Salvus there is no second stage and the gas is turned on and off at the cylinder. Some simple oxygen rebreathers had no constant-flow valve, but only the bypass, and the diver had to operate the valve at intervals to refill the breathing bag as he used the oxygen. With active semi-closed circuit rebreathers, the diver installs one of a number of different sized orifices in the valve before the dive. For safety reasons these should be chosen to provide more gas than the diver needs, to avoid Hypoxia . Before 1939, diving and industrial open-circuit breathing sets with constant-flow regulators were designed and made, but did not get into general use due to excessively short dive duration for its weight. Design complications resulted from need to put the second-stage on/off valve where it could be easily operated by the diver. Examples were:-
Twin-hose This is the first type of scuba demand valve that got into general use. This type of regulator has two (or occasionally one or three) stages in series in a large circular valve assembly mounted on top of the cylinder pack. The last (or only) stage is the demand valve. In European and USA as officially made it always had an A-clamp to fasten it to the cylinder. This type of regulator has two wide corrugated breathing tubes. The second tube was for breathing out through; it was not for Rebreathing but to keep the air inside the breathing tube at the same depth pressure as the water outside the regulator diaphragm. This second breathing tube returns the exhaled air to the regulator on the wet side of the diaphragm, where it is released through a Duck 's-beak-shaped rubber one-way valve, and comes out of the holes in the wet-side cover. Nearly always in the mouthpiece assembly there are one-way valves to stop air or water going from the mouthpiece into the inhaling tube or from the exhaling tube into the mouthpiece. In Cousteau 's first Aqualung as first made, there was no second tube and the exhaled breath exited to the outside through a one-way valve at the mouthpiece. It worked OK on land, but when he tested the aqualung in the river Marne the air ran away when the mouthpiece was above the regulator. After that, he had the second breathing tube fitted. Even with both tubes fitted, raising the mouthpiece above the regulator increases the flow of gas and lowering the mouthpiece increases breathing resistance. As a result, many aqualung divers put the loop of hoses under one arm to avoid the mouthpiece floating up causing free flow, when they were Snorkelling on the surface to save air while reaching the dive site. Divers had to carry more weight underwater to compensate for the bulk of air in the hoses. An advantage with this type of regulator is that the bubbles leave the regulator behind the diver's head, increasing visibility, and not interfering with Underwater Photography . They have been superseded by the single hose regulator and become obsolete for most diving in the 1980s . The original Cousteau twin-hose diving regulators could deliver about 140 Litre s of air per minute, and that was officially thought to be adequate; but divers sometimes needed a fster rate, and had to learn not to "beat the lung", i.e. to try to breathe faster than the regulator could supply. In 1948 to 1952 Ted Eldred designed his Porpoise air scuba to supply 300 litres/minute if breathed from that fast, and that soon became British and Australian Naval standard. Some modern twin-hose regulators have one or more low-pressure ports that branch off between the two valve stages, as ''direct feeds'', as described under #Two Stage, Single Hose below. Someone made a twin-hose type regulator where the energy released as the air expands from cylinder pressure to the surrounding pressure as the diver breathes in, is not thrown away but used to power a Propeller . ''The twin hose Mouthpiece or Fullface Mask has reappeared in modern Rebreather s, but as part of the breathing loop, not as part of a regulator.'' Twin-hose, home-made In 1956 and for some years afterwards in Britain, factory-made aqualungs were very expensive, and many aqualungs of this type were Made By Sport Divers in diving clubs' workshops, using miscellaneous industrial and war-surplus parts. One necessary raw material was a Calor Gas bottled Butane gas regulator, whose 1950's version was like an aqualung regulator's second stage but operated constant-flow because its diaphragm was spring-loaded; conversion included changing the spring and making several big holes in the wet-side casing. The cylinder was often an ex- RAF pilot's oxygen cylinder; some of these cylinders were called Tadpole s from their shape. In least one version of Russian twin-hose aqualung, the regulator did not have an A-clamp but screwed into a large socket on the cylinder Manifold ; that manifold was thin, and meandered somewhat. It had two cylinders and a pressure gauge. There is suspicion that those Russian aqualungs started as a factory-made improved descendant of an aqualung home-made by British sport divers and obtained unofficially by a Russian and taken to Russia. Two stage, single hose Most modern scuba regulators are of this type. Its main components are: a ''first stage'', from which one or more ''low pressure'' hoses run to various equipment listed below. The first make of this sort of scuba was the Porpoise (make Of Scuba Gear) which was made in Australia . First stage valve The first stage has a high-pressure "port" for the high-pressure hose to the Pressure Gauge . It has a number of "ports" for low-pressure hoses to carry gas to other components which serve as second-stage valves of various sorts. The first stage takes gas from the Diving Cylinder at pressures of 200 - 300 bar (3000 - 4500 psi) and reduces its pressure down to 10 bar (150 psi) higher than ambient pressure in the low pressure hoses. Sometimes the low-pressure hoses are called "medium-pressure hoses". All unused ports must be blanked off. At least one low-pressure hose connects to a ''demand valve''. Some low-pressure hoses connect to the Diving Suit inflation valve and the Buoyancy Compensator inflation valves: these low-pressure hoses are called ''direct feeds''. Pressure relief valve Sometimes regulators are connected to inflatable equipment such as a Rebreather 's Breathing Bag (plus the diver's Lung s) or a Buoyancy Compensator or a Drysuit but not to any demand valves. Examples of this are Argon suit inflation sets, and "off board" or secondary diluent cylinders for closed-circuit Rebreather s. For safety, the regulator should be equipped with a ''pressure relief valve''. This lets gas escape from the system if the first-stage jams open in free-flow, as otherwise the buoyancy device would fully inflate and carry the diver quickly to the surface causing the various Injuries That Can Result From An Over-fast Ascent . Normally, if present, a demand valve safely vents off the excess gas from a first stage malfunction. This is called a ''free flow'' and is a Fail Safe design feature so that the diver can continue to breathe for a few seconds or minutes until all the gas is rapidly exhausted. Second stage valve A second stage valve can be:- Direct feed A connection to inflate a Buoyancy Compensator or a Drysuit , is manually operated by a button or lever or knob. Demand valve This type of second stage is called ''demand valve'' or ''DV''. It is fed by a ''low pressure hose'' from the first-stage. It works as described in the ''Types of last stage'' section above. When the diver breathes out, the air goes to the dry side of the diaphragm, and is released to the outside through (usually two) one-way valves. It also has a ''purge button'', which the diver can press to depress the diaphragm to make gas flow to blow water out of the mouthpiece (or for other purposes such as filling a Lifting Bag ). Sometimes (nowadays nearly always) a single-hose regulator has more than one demand valve (= DV). If the extra DV is simply a spare DV for use by the diver's Buddy it is usually called an octopus. The low pressure hose on the octopus is usually longer than the low pressure hose on the DV that the diver uses. The demand valve 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 called an "alternate air source". There have been at least two cases of a single-hose-type demand regulator last stage built into a circular Fullface Mask so that the mask's big circular front window plus the flexible rubber seal joining it to its frame, was a very big and thus very sensitive regulator diaphragm:-
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
|
|
|