EP0078644B1

EP0078644B1 - Breathable gas delivery regulator

Info

Publication number: EP0078644B1
Application number: EP19820305642
Authority: EP
Inventors: Humphrey Albert Samuel Hamlin; Roger Malcolm Marsh; James Conway Foote
Original assignee: Normalair Garrett Holdings Ltd
Current assignee: Honeywell Normalair Garrett Holdings Ltd
Priority date: 1981-10-30
Filing date: 1982-10-22
Publication date: 1987-06-24
Also published as: ES8400246A1; DE3276617D1; EP0078644A3; ES516949A0; EP0078644A2

Description

This invention relates to breathable gas delivery regulators and more particularly to such regulators of the demand type as are used in aircraft applications.
Regulators of this type, one such example being disclosed in GB-A-1,228,481, have been used to deliver oxygen, or air-diluted oxygen, to aircrew members from oxygen sources that are arranged to supply gas at pressures generally in the range 485 to 1035 kPa (70 to 150 psi), which range provides ample pressure of gas to operate air entrainment means for obtaining dilution and permits ready usage of a flow demand valve of a form such that the pressure of the supply gas can be employed to provide its closing force.
However, a new generation of oxygen supply systems now beginning to emerge for use in aircraft, derives oxygen from the ambient air by passing air bled from an engine of the aircraft, through a simple on-board molecular sieve oxygen generator system (MSOGS) which delivers gas at pressures generally between 70 and 345 kPa (10 and 50 psi).
Early designs of on-board oxygen generator systems (OBOGS) were influenced by the existing aircraft oxygen installations and only considered as a replacement for the liquid oxygen converters or high pressure cylinder reservoirs, leaving the remainder of the installation in the aircraft unaltered, and were thought of solely in terms of reducing the operational logistics of providing liquid oxygen replenishment at airfields.
It is, therefore, understandable that a prime objective was then to obtain maximum oxygen concentration in the product gas supplied by an onboard oxygen generator (OBOG) for conditions of flight; excessive oxygen concentrations in the product gas, for a particular flight condition, being reduced by dilution downstream by the delivery regulator as in earlier manner. This required that the pressure of the product gas from an OBOG be increased prior to its supply to the regulator.
However, the modern concept of a complete on-board molecular sieve oxygen generating and delivery system for an aircraft, involves the use of a molecular sieve oxygen generator (MSOG) that is controlled to deliver product gas having an oxygen concentration that is appropriate to the pertaining cabin altitude. Such a system is, for example, disclosed in EP-A-0 046 369 (European Patent Application No. 81303677.9 filed 12th August, 1981). With an MSOG so controlled, there is no requirement for dilution of the product gas, so eliminating the need for the inclusion of means for entraining air into the delivery flow of the regulator associated with the MSOG and, thus, the need to increase the product gas pressure to the value needed to operate air-entrainment means. However, a problem arises with respect to demand valve operation in a regulator that will accommodate the lower supply gas pressures, particularly those at the lower end of the product gas pressure range, towards 70 pKa (10 psi), available from an MSOG.
Demand valves in contemporary aviation demand-type oxygen regulators, which operate with supply pressures of 485 kPa (70 psi) and above, require the valve to lift by only a small amount in order to deliver the desired rate of gas flow.
Although this is satisfactory for the highest gas pressure supplied by an MSOG, it is not so for the lower pressures in the range because to obtain the same desired rate of flow at these lower pressures for the same amount of valve lift, the valve must have a considerably larger than usual valve orifice: as the usual arrangement is for the demand valve to be held closed by supply gas pressure, a large orifice would give rise to excessively large valve clamping pressures at the higher pressures in the range.
Thus there is a requirement for a gas delivery regulator having a demand valve that opens easily to substantially consistent efforts of a user throughout the range of pressure of the gas supply from an MSOG. Moreover, it would be advantageous for such a regulator also to be capable of operating satisfactorily at the higher supply pressures of traditional aircraft oxygen sources so as, for instance, to enable satisfactory emergency operation from a high pressure gas bottle.
It has been proposed (see for instance US-A-4,029,120 and US-A-4,147,176) to provide a breathing gas demand type regulator for self-contained underwater breathing apparatus (SCUBA) with a pressure-balanced poppet valve controlled by a diaphragm responsive to downstream, demand, pressure. In such applications, the regulator receives gas at a controlled pressure of about 970 kPa (140 psi) above ambient and the control requirement is to obtain a suitable relationship between diaphragm movement and valve opening so as to obtain both a gradual opening of the valve and stability of operation at high flow rates. In the arrangements disclosed, the poppet valve is sealed by an 0-ring sealing sytem that inherently impedes movement of the valve, so necessitating the assistance to valve opening afforded by use of an aspirator and the solution of the consequent problem of potential instability at high flow rates.
Thus, while the concept of pressure-balancing a demand valve, which makes this insensitive to supply pressure changes, would appear to solve the problem of operation over a wide range of supply pressures, the application of this concept to breathing gas regulators, especially for aviation purposes, is not straightforward and can lead to undesirable complexity of the control arrangements associated with it.
Indeed there have been proposals - see US-A-4,127,129 (and EP-A-0 050 052 which was not published at the priority date hereof) - to use a pressure-balanced demand valve in an aviator's breathing gas regulator designed for use with oxygen sources having pressures appropriate for dilution with air by an entrainment means, that illustrate the complexities of such an application of this principle.
In the main, the complexities of the prior arrangements result from the fact that the forces, acting on a poppet valve when partly open, comprise both static components deriving from the gas pressures upstream and downstream of the valve, and dynamic components deriving from the flow through the valve; as a consequence, the net force acting on the valve varies both with the magnitude of the pressures and with the gas flow rate and an absolute pressure balance cannot in practice be attained. This leads to instability in operation.
We have, however, ascertained that the potential instability of a pressure-balanced poppet-type demand valve can be mitigated to the extent necessary to enable a breathable gas delivery regulator incorporating such a demand valve to operate satisfactorily over an acceptable range of demand flows and a very extended range of supply gas pressures, without the complexities of the prior arrangements.
Thus, according to the invention, a breathable gas delivery regulator includes a pressure-balanced poppet-type demand valve having a poppet valve head disposed downstream of a valve seat defining a demand flow path and a pressure-balance member responsive to pressure upstream of the valve seat and freely slidable in a guide bore, a labyrinth seal to restrict leakage through said guide bore, and a pressure-responsive diaphragm controlling the demand valve and being common to a demand-pressure chamber and to a breathing pressure control chamber having barostatic pressure control.
Because the poppet head is disposed downstream of the valve seat with which it co-operates to control flow in the demand flow path, upstream, pressure tends to open the valve against the balancing force provided by the pressure-balance member. The arrangement may therefore, conveniently, be termed "pressure-opening", in contrast to the converse, or "pressure-closing" arrangement exemplified by EP-A-0 050 052. The pressure-opening arrangement has been found to be significantly less sensitive to changing, and especially to high, demand flows than the pressure-closing arrangement, and operational stability can be assured by minimising frictional or like restraint to movement of the valve throughout its movement range. By use of a labyrinth seal to restrict leakage between the freely slidable pressure-balance member and its guide bore, unwanted restraint to movement of the demand valve, by the pressure-balance member, is avoided. The demand valve, being controlled by a diaphragm responsive both to demand pressure and to the pressure in the breathing pressure control chamber, causes the pressure of the gas delivered to the user to vary in response to the pressure in the breathing-pressure control chamber and thus, because of the barostatic control of the pressure in the latter, to the ambient pressure, or cabin altitude, as is required for delivery of breathable gas to an aviator.
The leakage past the labyrinth seal may be accepted by a suitably disposed vent chamber, or it may be accommodated in other ways.
The demand valve may be operably connected to the pressure-responsive diaphragm by a mechanical member.
In order that safety pressure, i.e. a small positive gas pressure in the cavity of an aviator's breathing mask to prevent ingress of toxicants around the face seal, may be maintained continuously, resilient means may act to preload the demand valve towards the open position.
In one breathable gas delivery regulator in accordance with the invention, the demand-pressure sensing chamber and the breathing-pressure control chamber are interconnected by an orifice-controlled bleed path, conveniently provided by an orifice in the pressure-responsive diaphragm, and the breathing-pressure control chamber has a barostatically controlled outlet.
A pressure-compensated relief valve may be included downstream of the demand valve for relieving excess delivery gas pressure at a predetermined value relative to pressure in the breathing-pressure control chamber.
The invention will now be further described by way of example and with reference to the single Figure of accompanying drawing, which shows in schematic section a breathable gas delivery regulator embodying the invention, the section being taken on the-longitudinal axis of a demand valve forming part of the regulator.
Referring to the drawing, a demand-type breathable gas delivery regulator 10 for use by an aviator comprises a body 11 containing three interconnected pressure chambers, namely a demand-pressure sensing chamber 12, a breathing-pressure control chamber 13 and a cabin-pressure sensing chamber 14. The body 11 also provides a housing for a demand valve arrangement 15; this housing includes a breathable gas supply inlet 16 and a delivery outlet 17 that is directed into an outlet tube 18.
The demand valve arrangement 15 includes a poppet-type demand valve member 19 comprising a valve head 20 which is carried by a spindle 21 from a spool 22. The spindle 21 is arranged to span the chamber formed by the supply inlet 16 whilst the effective areas of the spool 22 and the valve head 20, exposed to inlet pressure, are the same, the spool 22 thereby constituting a pressure-balance member. The flow path between the inlet 16 and delivery outlet 17 is partly defined by a valve seat onto the downstream face of which the valve head 20 is urged to close by a compression spring 24. Optionally, a helical plug type spring adjuster (not shown) is provided for adjustment of the spring 24. The spool 22 is arranged to project into the demand-pressure sensing chamber 12 and is freely slidable in a guide bore in the body 11 but is provided on its circumferential surface with grooves in a manner forming a labyrinth seal 25. The plain portion of the spool 22 on the low pressure side of the labyrinth seal 25 spans a vent chamber 26 in the regulator body 11, whereby leakage of supply gas past the labyrinth seal 25 is dissipated without affecting the balance of the valve.
The demand-pressure sensing chamber 12 is fluidly connected to the outlet tube 18 and is separated from the breathing-pressure control chamber 13 by a pressure-responsive flexible diaphragm 27 which is provided with a bleed orifice 28 in order to permit a small flow to pass from one chamber to the other. The centre of the diaphragm 27 is attached to one end of a valve- operating lever 29 which is arranged to rock about its appropriately formed opposite end within a location 30 in a wall of the demand-pressure sensing chamber 12. Intermediate of its ends the lever 29 is provided with a pad 31 which contacts the projecting end of the spool 22. A compression spring 32 is arranged axially of the spool 22 and is held between a location on the lever 29, behind the pad 31, and a spring adjuster 33 that is adjustable from outside the regulator body 11. The chosen adjustment is such that when the pressure-responsive diaphragm 27 is in the null position, the valve-head 20 is held off the valve seat 23, against the closing pressure exerted by the other compression spring 24, sufficiently to maintain a positive pressure (safety pressure) of 250 Pa (1 in/WG) in the outlet tube 18 and thus in an aviator's breathing mask (not shown) connected to the tube 18.
An 'on/off' lever arrangement 34 includes a shaft that projects through a wall of the regulator body 11 and carries a sprag-arm 35 within the demand-pressure sensing chamber 12 and a manually operable lever 36 externally of the regulator 10. The arc of movement of the sprag-arm 35 takes it into and out of engagement with the valve operating lever 29 so that when in engagement the effect of compression spring 32 is negated whereby the valve-closing spring 24 causes the valve to seat and prevents wastage of breathable gas during non-use of the regulator.
The breathing-pressure control chamber 13 is provided with a large outlet port 37 in one wall which, on its outer side within the cabin-pressure sensing chamber 14, provides a seat 38 for a valve-head 39 that is mounted on an aneroid capsule 40. The capsule 40 is carried on an adjusting screw 41 which projects through an outer wall of the sensing chamber 14. Discharge from the sensing chamber 14 is enabled by an outlet 42 which is normally open, but can be closed by a spring loaded push button 43 to provide a test facility.
A pressure-compensated relief valve 44 is mounted on the outlet tube 18 of the regulator and comprises a valve head 45 carried on a flexible diaphragm 46. The valve is connected so as to be responsive to gas pressure in the breathing-pressure control chamber 13 by way of a duct 47 and is arranged, by inclusion of a light spring 48, to relieve when pressure in the outlet tube 18 is, say, 125 Pa (0.5 ins WG) above that in the control chamber 13.
The duct 47 is branched and connects also with a pressure-relief valve 49 that is arranged to open when a predetermined maximum pressure, say, 4.5 kPa (18 ins WG) occurs in the breathing-pressure control chamber 13. This pressure is determined by the maximum altitude at which the aircraft is expected to operate; in this example 15250 m. (50000 feet).
In operation of the demand type breathable gas regulator 10, when supply gas is available at the inlet 16, the demand valve member 19 responds to the inhalatory and exhalatory phases of a user aviator's breathing cycle by way of movement of the pressure responsive diaphragm 27. Breathing cycle pressure exists in the outlet tube 18 and in the fluidly connected demand-pressure sensing chamber 12, being sensed by the diaphragm 27. The diaphragm 27 is drawn in a downward direction, as viewed in the drawing, during inhalation so as to deflect the valve operating iever 29 to rock within its terminal location 30 and move the valve member 19 to the right as viewed in the drawing from the preset slightly open valve-head 20 position, that gives the safety pressure condition, to a full flow state giving a rapid maximum flow response feeding breathable gas into the outlet tube 18. Because the valve member 19 is pressure balanced by the supply gas pressure the spring force providing safety pressure and valve closure can be small, thereby allowing a substantially consistent response characteristic of the valve over the entire operating pressure range of an associated MSOG (not shown). Exhalation causes a cessation of flow through and subsequent pressure build-up in the outlettube 18 and in the chamber 12 to an extent where the diaphragm 27 is raised above its null position and the valve operating lever 29 is moved to a position enabling the valve-head 20 to move to its nearly closed position giving safety pressure as described, until the cycle is repeated.
Breathable gas bleeds from chamber 12 to ambient by way of the orifice 28 in the sensing diaphragm 27, the breathing-pressure control chamber 13, the large outlet port 37 thereof, and the cabin pressure sensing chamber 14 and its outlet 42.
With increasing cabin altitude (decreasing ambient pressure) from, say, 12000 m. (40000 feet) the aneroid capsule 40, which contains a compression spring (not shown), becomes expanded to carry its valve-head 39 towards engaging the valve-seat 38 and restricting the flow through the large outlet port 37, thereby developing increasing pressure in the breathing-pressure control chamber 13 and, consequently, an increasing closure pressure on the diaphragm 46 of the relief valve 44, and an increasing pressure in the outlet tube 18 and in the aviator's breathing mask (not shown). As the cabin altitude returns to 12000 m. the capsule 40 contracts and this restriction of the large outlet port 37 is progressively removed.
The pressure-compensated relief valve 44 ensures that pressure in the outlet tube 18 and in the breathing mask (not shown) will relieve should the pressure therein reach a value of 125 Pa (0.5 ins. WG) greater than the pertaining control-pressure in chamber 13; whereas the pressure-relief valve 49 will relieve when the breathing-pressure control chamber pressure reaches the predetermined pressure of 4.5 kPa (18 ins WG) which is slightly above that of the maximum desired control pressure which is appropriate to the minimum cabin pressure the regulator must satisfy.
The push-button 43 provides a manual test facility for checking, before flight, that the aviator's breathing mask (not shown) is fitting correctly and that there are no appreciable leaks in the gas delivery system fed from the regulator 10. By closing the push-button 43, with gas being supplied to the regulator, the venting to ambient of safety 'pressure bleed is prevented until the breathing-pressure control chamber pressure reaches the pressure at which the pressure-relief valve 44 opens.
In most prior art regulators, safety pressure gas flow into the breathing-pressure chamber is taken from the gas supply to the demand valve and is controlled by a very small orifice. In the regulator of the present invention, because the demand valve member 19 itself is arranged to deliver the safety pressure flow, the gas flow into the breathing-pressure control chamber 13 is taken from the demand-pressure sensing chamber 12 by way of the relatively large orifice 28 which is less likely to become obstructed than the fine orifices of the prior art regulators.
Where required, a follower diaphragm (not shown) may be accommodated to maintain the volume of the breathing-pressure control chamber 13 constant during movement of the pressure responsive diaphragm 27, the follower diaphragm being exposed to cabin pressure on its outer surface and to the pressure in the breathing-pressure control chamber on its inner surface.

Claims

1. A breathable gas delivery regulator including a pressure-balanced poppet-type demand valve (15) having a poppet valve head (20) disposed downstream of a valve seat (23) defining a demand flow path and a pressure-balance member (22) responsive to pressure upstream of the valve seat and freely slidable in a guide bore, a labyrinth seal (25) to restrict leakage through said guide bore, and a pressure-responsive diaphragm _.(27) controlling the demand valve and being common to a demand-pressure sensing chamber (12) and to a breathing-pressure control chamber (13) having barostatic pressure control.

2. A breathable gas delivery regulator as claimed in claim 1, further comprising a vent chamber (26) spanned by a plain length of said pressure-balance member, for receiving and venting leakage past said labyrinth seal.

3. A breathable gas delivery regulator as claimed in claim 1 or 2, wherein said demand valve is operably connected to said pressure-responsive diaphragm by a mechanical member (29).

4. A breathable gas delivery regulator as claimed in any preceding claim, comprising resilient means (32) preloading said demand valve towards an open position.

5. A breathable gas delivery regulator as claimed in any preceding claim, wherein the demand-pressure sensing chamber (12) and the breathing-pressure control chamber (13) are interconnected by an orifice-controlled bleed path, and the control chamber (13) has a barostatically controlled outlet.

6. A breathable gas delivery regulator as claimed in claim 5, wherein said orifice-controlled bleed path comprises an orifice (28) in the pressure-responsive diaphragm.

7. A breathable gas delivery regulator as claimed in any preceding claim, further comprising a pressure-compensated relief valve (44) downstream of the demand valve and adapted to relieve excessive delivery gas pressure at a predetermined value relative to pressure in the breathing-pressure control chamber (13).