|
|
|
|
Diving regulator
|
| |
|
| |
A diving regulator is a pressure regulator used in a scuba set that supplies the diver with breathing gas at ambient pressure from one or more diving cylinders. The gas may be air or one of a variety of specially blended breathing gases. A gas pressure regulator has one or more valves in series, which let the gas out of a gas cylinder in a controlled way, lowering air pressure at each stage.
The terms "regulator" and "demand valve" are often used interchangeably, but a demand valve is the part of a regulator that delivers gas to the diver's mouth in a regulator with more than one stage.
For the history of the diving regulator, see Timeline of diving technology.
parts of a regulator are described in downstream order as following the gas flow from the cylinder to its final use.
n open-circuit scuba set, the first-stage of the regulator has an A-clamp, also known as a yoke, or a DIN fitting to connect it to the pillar valve of the diving cylinder.
Discussion
Ask a question about 'Diving regulator' Start a new discussion about 'Diving regulator' Answer questions from other users |
Encyclopedia
A diving regulator is a pressure regulator used in a scuba set that supplies the diver with breathing gas at ambient pressure from one or more diving cylinders. The gas may be air or one of a variety of specially blended breathing gases. A gas pressure regulator has one or more valves in series, which let the gas out of a gas cylinder in a controlled way, lowering air pressure at each stage.
The terms "regulator" and "demand valve" are often used interchangeably, but a demand valve is the part of a regulator that delivers gas to the diver's mouth in a regulator with more than one stage.
For the history of the diving regulator, see Timeline of diving technology.
Parts of a diving regulator
The parts of a regulator are described in downstream order as following the gas flow from the cylinder to its final use.
Fastening the regulator to the cylinder or cylinder block
In an open-circuit scuba set, the first-stage of the regulator has an A-clamp, also known as a yoke, or a DIN fitting to connect it to the pillar valve of the diving cylinder. Yoke valves are the most common type by far; it clamps an open hole on the regulator against an open hole on the cylinder. The user loosely screws the clamp in place and once the cylinder valve is opened, gas pressure completes the seal along with an O-ring. The diver must take care not to screw the yoke down too tightly, or it may prove impossible to remove without tools. The DIN fitting is a type of direct screw-in connection to the cylinder. While less common worldwide, the DIN system has the advantage of withstanding greater pressure, permitting the use of high-pressure steel cylinders. DIN fittings are the standard in much of central Europe.
Most yoke-type valves are of the K-valve type, which is a simple on-off valve. In the mid-1960s, J-valves were widespread. J-valves contain a spring-operated shutoff that is triggered when tank pressure falls to 300-500 psi, causing breathing resistance and warning the diver that he or she is dangerously low on air. The reserve air is released by pulling a reserve lever on the valve. J-valves fell out of favor with the introduction of pressure gauges, which allow divers to keep track of their air underwater, especially as the valve-type are subject to accidental release of reserve air and increase the cost and servicing of the valve.
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 located on the first stage. They are compact, have no dangling hoses and few points of failure. They are generally not used on back mounted cylinders, because the diver cannot easily see them there when underwater. They are sometimes used on side slung stage 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 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 other sources.
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 reserve valve and surface using the reserve gas. Occasionally, a diver would inadvertently trigger the mechanism while donning gear or performing a movement underwater and, unaware that the reserve had already been accessed, could find himself out of breathing gas with no warning. 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. This link goes to a site with a picture of both types of cylinder valves, about half way down. http://www.geocities.com/Baja/Canyon/9588/scuba_page/tank_markings.html
First stage
The first stage of the regulator (mounted to the cylinder via one of the aforementioned valves) reduces cylinder pressure to an intermediate pressure, usually about 10 bar (150 psi) higher than the ambient pressure. A balanced regulator automatically keeps this constant as the tank pressure lowers with consumption and the ambient pressure varies with depth. The first stage generally has several low-pressure outlets for second-stage regulators, BCD inflators and other equipment; and one or more high-pressure outlets, which allow a submersible pressure gauge (SPG) or gas-integrated diving computer to read the cylinder pressure.
Types
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 changes as the cylinder pressure falls, usually becoming slightly harder breathing. A balanced regulator keeps about the same ease of breathing at all depths and pressures. Over-balanced regulators provide more gas than the diver requires.
Piston type
Piston-type first stages are easier to make and have a simpler design than the diaphragm type. This may help to improve reliability. They need more careful maintenance because some of the internal moving parts are exposed to water and contaminants in the water.
With the piston-type first stage, the piston is rigid and acts directly on the seat of the valve. When the pressure in the medium pressure drops because the diver has used gas from a second stage valve, the piston lifts off the valve seat and slides towards the medium pressure chamber. This brings high pressure gas into the medium pressure chamber until the pressure in the chamber has risen enough to push the piston back onto the seat and close the valve.
Diaphragm type
Diaphragm-type first stages are more complex and have more components than the piston type. They have an environmentally sealed design, and are thus particularly suited to cold water divers and those working in water containing a high degree of suspended particles, silt, or other contaminating materials.
The diaphragm is a flexible cover to the medium-pressure chamber. When the diver consumes gas from a medium-pressure second stage, the pressure falls in the medium-pressure chamber and the diaphragm collapses inwards pushing against the valve lifter. This opens the valve letting high-pressure gas pass the valve seat into the medium-pressure chamber. When the pressure in the medium-pressure chambers rises, the diaphragm inflates outwards reducing the force on the valve lifter, letting the spring behind the valve close it.
Risk of the regulator becoming blocked with ice
As gas leaves the cylinder it decreases in pressure in the first stage, becoming very cold due to adiabatic expansion. Where the water temperature is less than 5°C any water inside the regulator may freeze, preventing the valve closing, causing a free-flow that can empty a full cylinder within a minute or two. Generally the water that freezes is in the ambient pressure chamber around a spring that keeps the valve open and not in moisture in the dry breathing gas from the cylinder.
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 of the ambient pressure chamber and teflon coatings around springs 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 valve
The diver uses a button or lever or knob to blow gas or air into a device, such as buoyancy compensators, drysuits, and many rebreathers. This type of valve is connected to the first stage with a medium pressure hose commonly called a "direct feed". (The valves on blowtorches are this type also.)
Demand valve
A demand valve detects when the diver starts inhaling and supplies the diver with a breath of gas at ambient pressure.
The demand valve was invented in 1865 in France, and forgotten in the next few years, and was not invented again until the late 1930s.
The demand valve has a chamber, which in normal use contains breathing gas at ambient pressure. A valve which supplies medium pressure gas can vent into the chamber. Either a mouthpiece or a fullface mask is connected to the chamber, for the diver to breathe from. On one side of the chamber is a flexible diaphragm to control the operation of the valve.
When the diver tries to breathe in, the inhalation lowers the pressure inside the chamber, which moves the diaphragm inwards operating a system of levers. This operates against the closing spring and lifts the valve off its seat, opening the valve and releasing gas into the chamber. The medium pressure gas, at about 10 bar/140 psi over ambient pressure, expands, reducing its pressure to ambient pressure, blowing out any water in the chamber and supplying the diver with gas to breathe. When the chamber is full and the lowering of pressure has been reversed, the diaphragm expands outwards to its normal position to close the medium pressure valve when the diver stops breathing in.
When the diver exhales, one-way valves, made from a flexible and air-tight material, flex outwards under the pressure of the exhalation allowing gas to escape from the chamber. They close making a seal when the exhalation stops and the pressure inside the chamber reduces to ambient pressure.
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.
Most modern demand valves use a downstream rather than an upstream valve mechanism. In a downstream valve, the moving part of the valve opens in the downstream direction and is kept closed by a spring. In an upstream valve, the moving part works against the pressure and opens in an upstream direction. If the first stage jams open and the medium pressure system over-pressurises, the second stage downstream valve opens automatically resulting in a "freeflow". With an upstream valve, the result of over-pressurisation may be a ruptured hose or the failure of another second stage valve such as one that inflates a buoyancy device.
Pressure relief valve
A demand valve serves as a fail safe for over-pressurisation: if a first stage with a demand valve malfunctions and jams in the open position, the demand valve will be over-pressurised and will "free flow". Although it presents the diver with an imminent "out of air" crisis, this failure mode lets gas escape directly into the water without inflating buoyancy devices. The effect of unintentional inflation might be to carry the diver quickly to the surface causing the various injuries that can result from an over-fast ascent. There are circumstances where regulators are connected to inflatable equipment such as a rebreather's breathing bag, a buoyancy compensator or a drysuit but without the need for demand valves. Examples of this are argon suit inflation sets, and "off board" or secondary diluent cylinders for closed-circuit rebreathers. When no demand valve is connected to a regulator, it should be equipped with a pressure relief valve so that over-pressurisation does not inflate any buoyancy devices connected to the regulator.
Valve operated by a solenoid
Fully closed circuit, electronic rebreathers have electronically controlled valves to inject fresh oxygen into the loop. The valve is opened with a solenoid in response to falling oxygen partial pressure detected by the electro-galvanic fuel cells that monitor the loop. These valves are connected to the first stage with a direct feed. See Rebreather#Fully closed circuit rebreather.
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 rebreathers. 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.
In some rebreathers, 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 the need to put the second-stage on/off valve where it could be easily operated by the diver. Examples were:-
Twin-hose
The "twin", "double" or "two" hose type of scuba demand valve was the first in general use. It has two (or occasionally one or three) stages in series in a large circular valve assembly mounted on top of the cylinder. The last (or only) stage is the demand valve.
In Europe and the USA, as officially made, regulators were always fastened to the cylinder with an A-clamp.
This type of regulator has two wide corrugated breathing tubes. The second tube was for exhalation; it was not for rebreathing but to keep the air inside the breathing tube at the same 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 out of water, but when he tested the aqualung in the river Marne air escaped from the regulator before it could be breathed 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, when they were snorkeling on the surface to save air while reaching the dive site, put the loop of hoses under an arm to avoid the mouthpiece floating up causing free flow.
Divers had to carry more weight underwater to compensate for the buoyancy of the 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 became obsolete for most diving in the 1980s.
The original Cousteau twin-hose diving regulators could deliver about 140 litres of air per minute, and that was officially thought to be adequate; but divers sometimes needed a faster rate, and had to learn not to "beat the lung", i.e. to try to breathe faster than the regulator could supply. Between 1948 and 1952 Ted Eldred designed his Porpoise air scuba to supply 300 litres/minute if the diver need to breathe 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 setup with a mouthpiece or fullface mask has reappeared in modern rebreathers, 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 1950s 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 tadpoles 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 medium pressure hoses run to various equipment listed below. The first make of this sort of scuba was the Porpoise which was made in Australia which was invented by Ted Eldred. At the same time in France, The Cristal Explorer (single hose) by Bronnec & Gauthier.
Unusual designs
Twin-hose without visible regulator valve (fictional)
This type is mentioned here because it is very familiar in comics and other drawings, as a wrongly-drawn twin-hose two-cylinder aqualung regulator, with one wide hose coming out of each cylinder top with no apparent regulator valve, much more often than a correctly-drawn twin-hose regulator: see Frogman#Drawing and artwork. It would not work in the real world.
Demone regulator
This type was designed by Robert J. Dempster and made at his factory in Illinois, USA, from 1961 to 1965. It operates like a single-hose regulator. The second-stage looks like the mouthpiece of a twin-hose regulator, but with a small diaphragm on the front. The second-stage valve is inside one end of the mouthpiece tube. The exhaled air goes into a twin-hose-type exhalant tube which surrounds the intermediate-pressure hose and blows out at its end about 60% of the way back to the first-stage, to keep the bubbles away from the diver's face. Near the mouthpiece is a one-way valve to let outside water into the exhalant hose to avoid air run-away if the diaphragm (at the mouth) is below the open end of the exhalant hose. Many Demone regulators have two intermediate-pressure tubes and two exhalant hoses and two second-stages, one assembly on each side of the diver's head, causing a superficial resemblance to the fictional "Twin-hose without visible regulator valve".
Practical Mechanics design
This design was described in Practical Mechanics magazine in January 1955, as a home-made aqualung with a first-stage on the cylinder top leading through an intermediate-pressure hose to a large round second-stage (a converted Calor Gas regulator) on the diver's chest connected to the diver's mouthpiece by a twin-hose loop.
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. All unused ports must be blanked off.
With regulators that are used as breathing sources, 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.
Second stage valve
A second stage valve can be:-
Direct feed or power inflator
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 medium 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 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).
Octopus
As a nearly universal standard practice in modern diving, the typical single-hose regulator has a spare demand valve for use by the diver's buddy, typically referred to as the octopus. The medium pressure hose on the octopus is usually longer than the medium pressure hose on the DV that the diver uses, and the demand valve is colored yellow to aid in locating during an emergency.
Combined DV and BC inflator
The demand valve could be a hybrid DV and buoyancy compensator inflation valve. Both types are sometimes 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".
Full face mask
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:-
- A version of the Le Prieur breathing set. Yves Le Prieur patented it in 1946 and the patent was granted on 10 February 1947.
- Captain Trevor Hampton invented independently a similar regulator-mask in the 1950s and submitted it for patent, but the Royal Navy requisitioned the patent, but found no use for it and eventually released it, but by then the market had moved on and it was too late to make this regulator-mask in bulk for sale.
Dive/surface valve or bailout valve
A Dive/surface valve (DSV) or bailout valve (BOV) is a device in the mouthpiece on the loop of a rebreather which connects to a bailout demand valve and can be switched to provide gas from either the loop or the demand valve without the diver taking the mouthpiece from his or her mouth. An important safety device when carbon dioxide poisoning occurs.
Performance of regulators
In Europe, EN250:2000 defines the minimum requirements for breathing performance of regulators.
In the United States Military, scuba regulators must adhere to performance specifications as outlined by the Mil-R-24169B which was based on equipment performance until recently.
Various breathing machines have been developed and used for assessment of breathing apparatus performance. ANSTI has developed a testing machine that measures the inhalation and exhalation effort in using a regulator; publishing results of the performance of regulators in the ANSTI test machine has resulted in big performance improvements.
Manufacturers
- Air Liquide: and
- HTM Sports: and
- ROMI Enterprises: and
-
Value Added Reseller
External links
-
-
- by Scuba Diving magazine.
- by DIVERNET magazine.
- by DIVERNET magazine.
- by DIVE magazine.
-
|
| |
|
|
