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 only while the diver is breathing in and reduces the
gas pressure to ambient. In single hose regulators, it is part of
the second stage held in the diver's mouth by a mouthpiece. In
double hose regulators it is part of the regulator attached to the
cylinder.
For the history of the diving regulator, see
Timeline of diving
technology.
Parts of a diving regulator
A diving regulator A-clamp type first
stage
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. Adapters are
available enabling a DIN first-stage to be attached to a bottle
with a yoke fitting.
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
A button contents gauge on an
'A' clamp type first stage
These are coin-sized analogue pressure 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.
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.
Diagram of the internal components of a piston-type first
stage
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.
Diagram of the internal components of a diaphragm-type first
stage
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
compensator,
drysuits, and many
rebreathers. This type of valve is connected to
the first stage with a medium pressure hose commonly called a
"direct feed".
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 the failure of another
second stage valve such as one that inflates a buoyancy device.
When 2nd stage up stream tilt valve is used relief valve should be
included by manufacture on 1st stage regulator to protect
intermediate hose.
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', unless it has a built in over
pressure 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:-
Old-type "twin-hose" Cousteau-type
aqualung
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.
Diver orientation changes breathing characteristic of regulators.
With double hose regulator on back at shoulder level. Roll on back
and regulated air pressure was higher than lungs. Divers learned to
restrict flow with tongue in mouthpiece. Air running low and air
demand effort rising, roll to right side made breathing
easier.
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 drysuit direct feed a.k.a. a power
inflator
A connection to inflate a
buoyancy compensator or a
drysuit, is manually operated by a button or
lever or knob.
Demand valve
A pair of demand valves
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
A combined diving regulator demand
valve and BC inflation valve
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
diagram of the 1946 version of the Le
Prieur breathing set
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
Value Added Reseller
References
- Vintage European Two Hose Regulator
Collection
- Historical Diving Times, #42,
Summer 2007, pp5-7
-
http://www.vintagedoublehose.com/downloads/MakinganAqualung2.pdf
- http://www.divenet.com/divematics/mouthpiece/
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