Closed Circuit Breathing Apparatus

Abstract

Closed-circuit breathing apparatus comprising a source of supply of a respirable gas, a user's mouthpiece or face mask, and a gas flow-regulating device between said source and mouthpiece or face mask. The gas flow-regulating device includes a tube having a length between 1 foot and 20 feet and an internal diameter between 0.002 and 0.015 inch, which tube prevents icing. The tube is mounted in a coil about a spool having a pair of flanged ends. One end of the tube passes through one flange and the other end passes through the other flange. Each tube end communicates with a recess in its respective flange end which recess is closed by a filter. The tube may be encapsulated between the flanged ends by a synthetic plastic material.

Description

This invention relates to fluid flow control devices and has particular reference to devices used for controlling the flow of gas in closed-circuit breathing apparatus.

Known closed-circuit breathing apparatus includes between the supply and the mouthpiece a pressure reducing valve giving a constant down-stream pressure followed by a metering orifice which controls the rate of flow of oxygen at a desired value.

An object of the present invention is to provide a gas flow regulating device which occupies an advantageously small space, has no moving parts and requires no, or a minimum of maintenance. Further advantages of devices embodying the invention will be referred to hereinafter. According to the present invention, closed-circuit breathing apparatus includes a source of supply of a gas such as oxygen, a user's mouthpiece or face mask and a gas flow regulating device disposed between said source and said user's mouthpiece or face mask, which said device includes a tube through which all the gas flowing to said mouthpiece passes in normal use, said tube having a length of at least 1 foot and an internal diameter between 0.002 and 0.015 inch. The internal diameter of the tube of said device is such that it is of a desired small value while being large enough to ensure that freezing of the gas flowing through it does not occur. Preferably the tube is composed of stainless steel.

Closed-circuit breathing apparatus embodying the invention gives, in the absence of a pressure regulating valve, in contrast to the known apparatus described above, a non-uniform rate of flow, the rate of flow decreasing as the amount of gas in the supply decreases. The relatively high initial rate of flow has the advantage that the breathing circuit is more rapidly prepared for use by being flushed of unwanted gas. Also, this high initial rate of flow gives a large supply of gas at the time when, because of "panic" breathing and the stresses normally associated with the need to start using breathing apparatus, the demand of the user is high.

The apparatus requires a greater quantity of oxygen to be carried than is necessary with the known apparatus described above if the period which elapses before the supply pressure falls to a particular value is to be the same. However, the extra weight of gas to be carried is compensated for by the fact that the flow regulating device of the invention can be made lighter and manufactured more simply and cheaply than the parts it replaces. Also, it can be made removable and replaceable for easier maintenance.

The expansion of the oxygen in the flow-regulating device produces a fall in temperature, but this is spread along the length of the tube and it is found that the tube can draw heat from the surroundings at a rate which reduces the risk of ice forming if the gas is moist compared with the known apparatus, in which the expansion occurs at the valve seating and the orifice. The bore of the tube is selected so that it is of conveniently small dimensions but large enough to ensure that freezing of gas flowing through it does not occur when the device is in use.

The length of the tube may be at least three feet and it is preferably less than 20 feet. The internal diameter of the tube may be at least 0.005 inch. It is preferably less than 0.015 inch.

The tube may be coiled and preferably gas flowing through the tube passes at either end of the tube through filtering means. The flow-regulating device may be a replaceable unit comprising a mandrel around which the tube is coiled, the tube opening at either end into a chamber closed by filtering means arranged axially with respect to the coiled tube. In this form the flow-regulating device is particularly compact and convenient.

The circuit may include one or more additional flow regulating devices as specified flow through which is controlled by valves, preferably pressure sensitive, the arrangement being such that by virtue of the opening of the valve the total resistance to flow of the circuit between the supply and the mouthpiece is reduced as the supply pressure falls. This results in rate of flow remaining more nearly uniform as the supply pressure falls. The additional flow-regulating device or devices may be arranged in parallel with the first-mentioned flow-regulating device, flow through them being commenced as the supply pressure falls, or they may be in series, flow through them being by-passed as the supply pressure falls.

A gas flow-regulating device embodying the invention and a closed-circuit breathing apparatus incorporating the device will now be described in greater detail by way of example with reference to the accompanying drawings in which:

FIG. 1 is an elevation in section of the device 21,

FIG. 2 is an elevation partly in section of a cylinder valve assembly including the device, and

FIG. 3 is a sectional elevation on the line X--X of FIG. 2.

Referring to FIG. 1 of the drawings, the flow-regulating device comprises a central mandrel or spindle 1 about which is wound, in a manner hereinafter described, a tube 2. The mandrel 1 has flanges or cheeks 3 at either end so that the coil formed by the tube 2 occupies a generally annular region between the cheeks. This region is filled with synthetic plastic material 4 which encapsulates the tube. The two ends 5 of the tube pass through the cheeks and open into recesses 6 formed in the cheeks at each end of the mandrel. Each recess 6 is closed by a plug 7 of filter material fitted into larger recesses in the cheeks, these plugs serving to prevent dirt being introduced into the flow-regulating device.

The device is made by taking a length of tubing, passing the ends through opposite drillings which extend from the inner faces of the cheeks to the exterior faces thereof and leaving short ends of the tube protruding from the cheeks. At the points where the tube enters the drillings it is soft soldered to secure the tube to the mandrel and the main length of the tube is then suspended from the mandrel in the form of a loop which is wound on to the mandrel under reasonable tension to ensure compactness in winding. Before the end of the loop is finally wound into position on the mandrel, the gas flow rate through it is measured and adjustment effected if necessary, by shortening the tube and/or flattening the end with special rollers to change the cross-sectional area.

The wound mandrel is then placed in a mould to which a synthetic plastic is supplied for the purpose of encapsulating the tube. The free ends of the tube are then severed to leave only the short lengths 5 previously mentioned.

The filters 7 are retained in their recesses by turning over flanges 8, which prior to insertion of the filters, extend axially with respect to the cheeks 3. Referring now to FIGS. 2 and 3 of the drawings, an oxygen cylinder 9 is fitted to a control valve assembly indicated generally at 10, the assembly being provided with a main control hand wheel 11 operating on a spindle 12 and a valve plug 13, an adaptor 14 for connection of a pressure gauge, a blanking plug 15, a wing member 16 for operating a shut off valve 17 and a lever 18 for operating an emergency by-pass valve 19.

The shut off valve enables the pressure gauge, when fitted, to be isolated if necessary due for example, to being damaged. The boss 20 provides a connection for a low pressure warning whistle, the connection being blanked off by the plug 15 during cylinder recharging at the pressure gauge connection.

The gas flow control device 21 is accommodated in a hollow boss 22 and is held in position by a nut 23 which is itself formed with an external screw threaded boss 24 to facilitate connection of a user's breathing bag 25, indicated diagrammatically and which is fitted with a tube 26 leading to a mouthpiece 27 or the user's face mask. The drillings 28 and 29 respectively afford communication with the inlet and the outlet ends of the flow control device. It will be observed that the device can be easily inserted and removed for replacement if necessary.

The length and bore of the tube are so chosen in relation to one another that the flow-regulating device gives a rate of flow suitable for satisfactory breathing over much of the range of pressure of the supply as the pressure falls. This leads to a high initial rate of flow, which pre-flushes the equipment and accommodates any "panic" breathing of the wearer. The breathing circuit includes an automatic relief valve which releases gas from the circuit if the pressure at the mouthpiece is above a desired value, and this allows any surplus gas to escape.

In the particular construction of flow control devices described the tube is 42 inches long and has an internal diameter of 0.008 inch. This gives, for a cylinder supply pressure of 2.500 lbs/sq. inch, a rate of flow of approximately seven liters per minute when the down-stream pressure is about one atmosphere absolute, as is usually the case with closed circuit breathing apparatus. The apparatus is then still giving a rate of flow of 2 liters per minute when the pressure of the supply has fallen to 500 to 600 lb/sq. inch. Such reduction in pressure is reached after about one hour's use of the apparatus described.

As examples of suitable materials, the tube may be formed of stainless steel, which may have, for an internal diameter of 0.008 inch, an external diameter of 0.016 inch, and the encapsulating medium may be a synthetic plastic, e.g., nylon. The filter plug may be of sintered metal e.g., bronze or ceramic.

In an alternative method of making a flow control device embodying the invention the coiled tube is enclosed within a soldered metal can.

Although reference has been made to the use of the flow control device in closed-circuit breathing apparatus, the device may find other applications for example in the control of flow of liquids, that is to say in fluidics. The device in such applications would act as a restrictor or control valve. Again, the flow control device may also be used in apparatus for underwater breathing.

Claims

I claim:

1. Closed-circuit breathing apparatus including a source of supply of a respirable gas, inhalation means for enabling a user to respire said gas, and a gas flow-regulating device disposed between said source and said inhalation means, which device includes a tube through which all the gas flowing to said inhalation means passes in normal use, said tube having a length of at least 1 foot and an internal diameter of at least 0.002 inch but less than 0.015 inch, said device further including a spool provided with a central portion and a pair of flanged ends, said tube passing through one of said flanges, around said central portion in a coil and through the other of said flanges.

2. Apparatus according to claim 1 in which said flanged ends are each provided with a recess having an open end, the two ends of said tube terminating in communication with said recesses and said open end in each said recess being closed by an associated filter.

3. Apparatus according to claim 2 in which said central portion of said spool and said coiled part of said tube are encapsulated between said flanged ends by a synthetic plastics material.

4. Apparatus according to claim 3 in which said tube has a length of between 3 and 20 feet and an internal diameter of between 0.005 and 0.015 inch.

5. Apparatus according to claim 4 including a pressure relief valve situated between said gas flow-regulating device and said inhalation means.