GB2132489A - Underwater breathing apparatus - Google Patents

Abstract

A demand regulator for controlling the flow of oxygen-containing gas to a diver and which provides a route for exhaled gas has, in common with conventional regulators, a rubber diaphragm acting on a tilt valve to allow gas to enter the regulator and flow through a breathing aperture to a diver's mouth. The regulator has the following features:- the breathing aperture exceeds 275 mm<2> in internal cross section; only one inlet aperture to the regulator is provided, so disposed as to direct gas generally towards the breathing aperture; a plate-like venturi is provided to guide gas from the inlet to the breathing aperture, the venturi plate terminating before reaching the breathing aperture so that exhaled gas is not obstructed; a reduced tilt valve guide. The conventional swirl plate, fixed to and extending about 270 DEG around the periphery of the regulator is eliminated. Where the regulator is used with an oral-nasal mask the mask may have an outlet valve separate from the regulator so that two escape routes are provided for exhaled gas.

Description

SPECIFICATION Underwater breathing apparatus This invention relates to breathing apparatus used by divers, and inter alia to breathing demand regulators and apparatus adjacent thereto. A demand regulator is a device which controls the flow of oxygen-containing gas to a diver, and which provides a route for exhaled gas. Gas is admitted to such a regulator when the diver inhales, drawing in a rubber diaphragm to operate a tilt valve. The gas passes from the regulator to the diver's mouth via a breathing tube projecting from the demand regulator in alignment with the fresh gas outlet aperture i.e. breathing aperture of the regulator. A scuba diver usually holds the breathing tube in his mouth. Other divers generally use an oral nasal mask inside a helmet, the oral nasal mask receiving the end of the breathing tube.

Conventional regulators have two inlet apertures adjacent the periphery of the regulator, diametrically disposed about a hollow inlet nipple such that a first inlet aperture directs gas towards the breathing aperture and a second inlet aperture directs gas away from it. The inlet nipple is displaced from the breathing aperture by 900 with respect to the centre of the regulator. A gas guide commonly known as a venturi is brazed to the inside wall of the regulator. This extends around the quadrant of the regulator between the inlet nipple and the breathing aperture, and extends substantially over the first inlet aperture and the breathing aperture. Gas passing out of this aperture is guided by the venturi towards the breathing aperture. Gas passing out of the second inlet aperture does not pass under the venturi and reaches the breathing aperture by a different route.

In conventional demand regulators the breathing aperture and the tube are approximately 18.7 mm in internal diameter (i.e. 275 mm2 in internal cross-sectional area). The total crosssection of the two inlet apertures is much smaller.

It has been determined, most surprisingiy in view of the outlet/inlet area ratio, that the breathing characteristics of the regulator are significantly improved by increasing the cross-sectional area of the breathing aperture and tube over the conventional valve.

It has also been determined that regulator operation is improved if the venturi does not extend over the breathing aperture, as it has in the past, but rather extends around the regulator periphery only as far as the edge of the aperture.

Preferably the venturi has a curved profile adjacent the aperture to direct gas down towards the aperture.

Another surprising improvement to the regulator operation is achieved by eliminating or narrowing the second inlet aperture.

The conventional oral-nasal mask is provided with one aperture, the breathing aperture previously mentioned. The invention provides an oral-nasal mask with a second aperture enabling exhaled gas to be expelled from the mask via a gas outlet valve conventionally known as a body mushroom or flapper valve, separate from the demand regulator.

Conventional demand regulators are provided with an adjustable spring piston and spring assembly to bias a tilt valve actuated by the rubber diaphragm. The tile valve bears upon a valve piston to close the fresh gas inlet apertures. The spring piston, upon which the spring acts, bears against the tilt valve and is constrained to move within a hollow cylindrical guide brazed to the inside surface of the regulator. Such a guide is conventionally 16 mm in diameter. We have discovered that the guide presents a significant obstruction to gas flowing through the regulator, particularly exhaust gas, and that by decreasing the size of the guide, the operation of the regulator may be usefully improved.

The operation of a demand regulator may be further improved in the following way: removing the conventional swirl plate, which is fixed to the inside wall of the regulator and extends by about 2700, round the periphery of the regulator, between the inlet nipple and the breathing aperture. This swirl plate was intended to help to guide gas passing out of the second inlet aperture to the breathing aperture, but has been found to have a deterious effect on other aspects of the regulator operation; using a rubber diaphragm with a stiffening backing plate larger than the 25.4 mm diameter backing plate which we have used in the past; and using a smooth mushroom at the exhaust gas aperture of the regulator. Regulators presently use a mushroom which is ribbed for stiffening, designed to guard against the mushroom becoming inverted by external pressure, enabling water to enter the regulator.However, unribbed mushrooms are adequately stiff and improve the regulator operation.

The invention will now be further described, by way of example, with reference to its use by a helmetted diver.

The breathing apparatus comprises a supply of pressurised oxygen containing gas, such as air or a helium oxygen mixture, feeder apparatus, a demand regulator, located outside the diver's helmet or mask, in front of his mouth, and an oral-nasal mask inside the helmet. Two gas supplies are provided, one for normal and one for emergency use. The normal supply is commonly received from a submarine chamber via an umbilical gas line. The feeder apparatus includes two valve assemblies located in a "side block" connected to both supplies, positioned at the side of the diver's head, and a feed line connecting the side block to the demand regulator. The two valves may be opened or closed by the diver to connect one or other of the gas supplies.

The demand regulator is used to control the intake of breathing gas by the diver. The gas required is drawn through the regulator and into the oral-nasal mask. The regulator also provides an outlet route for exhaled gas.

The demand regulator comprises a substanticlly circularly cylindrical body or housing, the height of the cylinder being approximately one-half of its diameter. One end wall of the cylinder comprises an end plate with a circular breathing aperture through which fresh gas to be breathed passes in normal operation of the apparatus, and through which subsequently exhaled gas can pass. The breathing tube is approxiriately 22 mm in diameter, and is adjacent the periphery of the end plate. When the regulator is correctly positioned outside the helmet, this end plate is adjacent the helmet. When the regulator is so positioned, the aperture in the uppermost part of this inner end wall.

At the other, outer end wall, the regulator body is fitted with a rubber diaphragm. The diaphragm is held in place around its periphery and is backed by a circular central stiffening plate of diameter approximately 35 mm.

A hollow circularly cylindrical breathing tube is fixed to the inner end wall with its axis parallel to the axis of the cylindrical regulator body. The breathing tube extends away from the regulator and is aligned with, and the same size as, the breathing aperture of the inner wall. Apertures are provided in the helmet and in the oral-nasal mask to snugly receive this tube.

The gas feed line from the side block is connected to a hollow cylindrical stub externally disposed at one side of the regulator body and displaced by 900 around the periphery of regulator body from the fresh gas outlet and tube described above. A cylindrical inlet nipple of this stub passes into the demand regulator. This inlet nipple has one aperture, disposed adjacent the periphery of the regulator. This aperture is disposed on the inlet nipple such that gas entering the demand regulator is directed towards the breathing aperture. To aid the direct passage of the gas from the inlet to the breathing aperture, a gas guide commonly known as a venturi, is brazed to the inside wall of the regulator body. The venturi extends around the periphery of the regulator through one quadrant, between the inlet and breathing apertures.The venturi is positioned above the inlet aperture and extends to the edge of the breathing aperture, so that is does not cover the breathing aperture. It has a downturned curved profile adjacent the breathing aperture to help direct gas into the breathing aperture.

A tilt valve operates to move a valve piston which controls the gas flow through the aperture of the inlet nipple, and so through the regulator and into the oral-nasal mask. When gas is not required the inlet aperture is closed by the valve piston spring biassed to that position. The lever is pivotally mounted adjacent its centre, and its end remote from the inlet aperture is upturned. This upturned end is level with the inner surface of the relaxed diaphragm. When the diver inhales, the diaphragm is drawn in, depressing the contiguous upturned end of the lever and so pivoting the lever to raise the other end, against the spring bias. Gas then flows through the inlet nipple, out through the inlet aperture, underneath the venturi and thus to the breathing aperture and then, via the breathing tube provided, to the oral-nasal mask.

When the diver has completed his inhalation the spring bias returns the lever to its original position, and the inflow of breathing gas is checked.

The spring bias mentioned is provided by a small spring piston retained between a helical spring and the lever. The movement of the lever when the diaphragm is drawn in, causes the spring piston to be moved and the spring, which has residual compression when the gas inlet is closed, to be further compressed. the residual compression of the spring may be adjusted by means of a knurled knob, screw-mounted and positioned at the end of an adjuster stub opposite the stub to which the gas feed line is attached. The piston is of circular cross-section and is retained by a hollow piston guide brazed to the inside of the regulator body in line with the adjuster stub.

This piston guide is machined flat at its side which face the diaphragm, the thickness of the guide between the flat face and the opposed edge of the guide being approximately 11.5 mm.

The fresh gas outlet from the regulator, i.e. the breathing aperture, is also a route by which exhaled gas can pass from the mask to the regulator. Exhaled gas passes through the regulator and out through a regulator mushroom valve. The valve comprises a mushroom or plug, the mushroom covering an exhaled gas outlet in the wall of the regulator body, and being retained by means of the location of a stem of the mushroom in a small seating disposed in the centre of the outlet aperture. The outer and inner surfaces of the cap of the mushroom are smooth to provide a relatively unobstructed outlet route for the outgoing gas.

The apparatus further includes a second route of escape for exhaust gas. A second aperture is provided in the oral-nasal mask and gas expelled from this aperture can escape via a second outlet valve separate from the demand regulator. The second outlet valve is known as the flapper valve or body mushroom. This has conventionally been used when the diver has operated a valve to admit gas directly into the helmet, bypassing the demand regulator. When the pressure inside the mask has exceeded the external pressure the flapper valve has opened and allowed water which has penetrated the helmet and excess gas to be expelled. This valve has thus not conventionally been coupled to the oral-nasal mask.

The outlets described above may be used in conjunction with gas recovery apparatus, for example a diverter valve and a Helinault helium recovery valve. When so used, the diver, receiving a helium-oxygen mixture from a chamber via an umbilical line, exhales through these outlets. The exhaled gas is diverted by a diverter valve to a Helinault valve, a one-way valve upstream of gas recovery and purification apparatus.

A second embodiment according to the invention varies from the first embodiment in the region of the regulator inlet. A second inlet aperture is provided, diametrically opposed in the wall of the inward cylindrical extension to the first aperture previously described. The venturi extends by 900 around the periphery of the regulator body from the breathing aperture to a point between the first and second apertures. The second aperture is thus not covered by the venturi and gives rise to a second route, centrally through the regulator, by which gas can reach the upper aperture. The second aperture is smaller than the first, this provision helping to prevent the gas entering the regulator from the second aperture interfering with correct diaphragm operation.

Prior art demand regulators, as indicated previously, have first and second inlet apertures of the same size, which give rise to the problems of interference with correct diaphragm working indicated above.

The above-mentioned swirl plate of regulators used at present is not provided, such a plate being an undesirable obstacle to exhaled gas passing through the regulator.

The demand regulator according to the invention improves regulator breathing characteristics in several ways. The enlargement of the breathing aperture and tube eases both inhalation and exhalation. The use of only one inlet hole or else of two inlet ho!es with the second hole smaller than the first, improves the diaphragm operation and so the inhalation characteristics.

The diaphragm itself has a larger backing plate and a larger effective area than the diaphragms we use at present.

Exhalation characteristics are improved by removing or smoothing obstacles to provide easier gas escape from the regulator. An alternative gas escape route is provided through the body mushroom; the piston guide is smaller than in known regulators; no swirl plate is provided; and the regulator mushroom is no longer ribbed for strengthening, as it is in the regulators presently used. As mentioned above, the increase in size in the tube between the oral-nasal mask and the demand regulator also improves the exhalation characteristics.

The improved demand regulator may be used by scuba divers, who will generally receive the breathing tube directly in the mouth.

Industrial diving standards indicate that 1.7 Joules per litre is a 'desirable' WB (work of breathing) that 2.2 Jl- is 'acceptable', and that inhalation and exhalation pressures should not exceed 1.5 kPa. At a breathing rate, known as the Respiratory Minute Volume (RMV), of 62.5 litres per minute, an average rate for normal working, apparatus according to the invention has the following characteristics: WB of 1.1 Jl-1 Inhalation pressure of 0.25 kPa, Exhalation pressure of 1.25 kPa.

The characteristics were determined on a breathing machine, at a depth of 42 m using air.

This depth is equivalent to 350 m with a heliumoxygen mixture.

Claims (4)

1. An underwater breathing demand regulator having an inlet connectable to a supply of oxygencontaining gas; an outlet connectable to a breathing tube through which a diver can inhale; the outlet exceeding 275 mm2 in internal crosssection; valve means adjustably biassed to close the inlet, and a flexible diaphragm movable on inhalation to move the valve means against the bias to open the inlet.

2. A demand regulator according to claim 1, wherein the outlet is circular, and approximately 22 mm in diameter.

3. A demand regulator according to Claim 1 or 2 wherein the inlet includes an inlet nipple internal to the body of the demand regulator, the sole or principal aperture of the nipple being so disposed as to direct gas generally towards the outlet.

4. An underwater breathing demand regulator substantially as hereinbefore described.