GB2058580A - Emergency air supply - Google Patents

Abstract

A safety device for ensuring an operator retains an air supply even if a ring mains supply (1) or his individual hose (4) thereto should fail there is an emergency supply (6) from a compressed air bottle which is fed to the operator's face mask (2) via a valve (3). The valve (3) switches from mains/mask to emergency supply/mask when the mains pressure falls below the emergency supply pressure. <IMAGE>

Description

SPECIFICATION Safety devices for air supplies This invention relates to safety devices for air supplies.

It is often necessary for factory operators in an hostile environment to wear face masks and breathe air supplied from a ring main via an individual hose.

An emergency air supply is required for use in the event of failure in either the ring main or part of the individual hose between the ring main and junction with the emergency supply. The emergency supply must last long enough for such an operator to escape from the hostile environment, and it is therefore desirable that besides being available immediately the ring main supply is lost, none of the emergency supply should be dissipated through the failed supply line.

An object of the present invention is to tend to provide a safety device for an air supply which is able to operate in the above-described environment.

According to the present invention, a safety device for air supplied from an external hose or from a mobile emergency supply, comprises a valve means sensitive to pressure of air supply from the external hose, the valve means being operable to cut off the air supply from the external hose and switch to the emergency supply if the sensed pressure falls below a pre-selected pressure level.

Preferably, the pre-selected pressure level is determined by supply pressure of the emergency supply. When in use, the emergency supply may operate an audible alarm. Advantageously, the valve operates switch means connected thereto. The switch means may operate visual or audible electronic alarms.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a diagram showing an air supply system for an hostile environment, Figure 2 shows parts of Figure 1 including an emergency supply in elevation, Figure 3 is a plan of Figure 2, Figure 4 is a planned view of a valve shown in Figure 2, Figure 5 is a section looking along V-V of Figure 4, Figure 6 is an incomplete section looking along VI-VI of Figure 4, Figure 7 is a block electrical circuit diagram of circuitry used in Figures 2 and 3, and Figure 8 is a more detailed view of Figure 7.

Reference is directed firstly to Figure 1, wherein part of a ring mains air supply for an hostile environment is indicated by 1. The ring main supply is coupled to a face mask 2 and by a valve 3 and hoses 4 and 5. If the mains air supply should fail or the hose 4 become defective, then an emergency supply 6 is connected to the face mask 2 through the valve 3.

The emergency supply is of sufficient duration for an operator wearing the face mask to remove himself from the hostile environment. Consequently, safety for the operator is provided.

Reference is now directed to Figure 2, wherein a pressurised air supply bottle is indicated by 8. The supply bottle is an emergency supply bottle and is strapped into a moveable container 10 by straps 11.

A yoke and pressure reducer assembly for the air supply bottle are indicated by 12 and a pre-set pressure reducer by 13. A bottle stop valve 14 is connected via the valve 3 to a mask outlet which is indicated by 15 in Figure 3 which should now be referred to. In Figure 3, wherein like reference numerals are used for like parts as in Figure 2, a reset button for the valve 3 is indicated by 16. A connection for the air mains is indicated by 17, a low air pressure whistle by 18 and a bottle contents gauge by 20.

The valve 3 is now described in more detail with reference to Figures 4, 5 and 6. The valve comprises a housing 21 and contains a spool 22 in a chamber 23, which chamber is divided into areas of differing pressure in operation. (The spool 22 is not shown in Figure 6.) An inlet port 24 is provided from the mains air supply and an inlet port 25 from the emergency air supply. An outlet port 26 is provided to the mask 2 (not shown) and a pneumatic audible warning device 27 terminates one by-pass tube (44 as will be explained below). The spool 22 carries an upper annulus 28 and a lower annulus 29 which are provided with seals 30. The lower annulus is stepped and carries three seals. The spool has an upper branch 31 which carries an abutment head 32 for operating a microswitch 33. The spool valve is sealed within the housing 21 by a screw end cap 34 and seal 35.

The mains inlet port 24 is connected to the chamber 23 by linked passageways 36 which are terminated at the housing surface by bolts 37. The emergency inlet port 25 is connected to the chamber 23 by passageways 38, which are terminated at the housing surface by bolts 39. The chamber 23 is connected to the mask outlet by passageways 41, one of which is terminated at the housing surface by a bolt 42. The chamber 23 is connected to the audible warning device 27 by passageways 44 having a housing surface terminus constituted by a bolt 45. A spool positioning screw 48 terminates the lower chamber 23 at its lower end and is used to position the spool from outside the valve.

Electrical circuitry associated with air supply is now described with reference to Figure 7. In Figure 7, the valve 3 and microswitch 33 are shown to the left of the Figure. The microswitch makes or breaks a line connected to an audio-visual warning unit 50.

The audio-visual warning unit is provided with amber warning lamps 51 and 52 and a loudspeaker 53. The unit can be charged from the mains through a plug 55. Connections to the audio-visual warning unit are indicated by A, B, C, D, E and F.

The audio-visual warning unit 50 is now described in more detail, with reference to Figure 8. To the left is shown an input 56 for the plug 55. The charging input 56 is connected to a transformer T1 via a fuse F1.

The transformer's secondary output is rectified by a rectifier arrangement 57. A smoothing capacitor C1 smooths the direct current output from the rectifier which charges a cell 58. The cell 58 is connected to integrated circuit drivers 59 and 60 for the loudspeaker 53 and lamps 51, 52 respectively. An inte grated circuit switch/timer 61 is connected to control the signal to the drivers 59, 60 via switching transis tors TR1, TR2. A Zener diode ZD1 controls the base voltage of transistor TR1. Resistors, capacitors and protective diodes are also shown in the Figure but are not annotated. It will be appreciated that Points A and B in the Figure are connected/disconnected under the action of the microswitch 33.

Operation of the apparatus is now described with reference to Figures 1,4,5 and 6. In normal operation, mains air is fed to the mask 2, from the supply 1 via the valve 3 and hoses 4 and 5. The valve 3 is held in the position shown in Figure 5 because the force due to the main supply pressure acting downwardly upon the annuli 28 and 29 and fed to the chamber 23 (see Figure 6) via passageway 36 is greater than the upward force due to the emergency supply pressure fed to chamber 23 via the lower of passageways 38 and acting upwardly on the step of the annulus 29.

Thus, the mains air is fed to the mask via the passageway 36, chamber 23, passageway 41 and outlet port 26. At the same time the emergency supply port 25 is cut off from the chamber 23 by the upper annulus 28 and the seals 30 which it carries. Also, the lower seal 30 on the annulus 29 seals the passageway 44 so that the audible warning is not sounded.

Now suppose that the mains air supply fails, owing to a general failure of Supply 1 orto a fracture in the hose 4. In this situation, the supply pressure will fall so that the pressure in port 24 falls below that in port 25. Consequently, the upward force exerted on the step of the lower annulus 29 by the emergency pressure will exceed the downwardly acting force from passageway 36. Therefore, the spool 22 moves upwardly and in doing so allows access of air from passageway 38 into the chamber 23. Therefore, the emergency supply air is connected to the mask 2. Upward movement of the spool also causes the upper annulus 28 to block the upper passageway 36 and the lower annul us 29 to block the lower passageway 36. Thus the emergency supply air cannot be vented through the supply port 24.In addition, upward movement of the spool causes the lowest of the seals 30 to move about the passageway 38 so that a through-path from the passageway 38to passageway44is provided and in this way the audible warning is sounded. Furthermore, upward movement of the spool 22 and the upper branch 31 causes the abutment head 32 to close the microswitch 33.

Reference is now made to Figures 7 and 8, wherefrom it can be seen that closure of the microswitch 33 causes Points AB in the circuit to be linked so that power is supplied to the drivers 59 and 60, whereby an electronic audible and an electronic visible warning is given by the loudspeaker 53 and lamps 51,52, respectively.

The emergency supply from the gas bottle 8 (see Figure 2) lasts sufficiently long for an operator to leave the hostile environment after the warnings have sounded, the pneumatic audible warning only taking a small part of the available air supply. When the mains air supply 1 or the defective hose, as the case may be has been repaired, then the spool 22 can be reset by pressing the reset button 16 (see Figure 2) which causes the abutment head 32 to be pressed down.

From the foregoing description, it can be seen that a safety device for an air supply is provided which offers warning to operators of a defective mains supply and a time period within which they can leave the hostile environment after being warned.

Claims (6)

1. A safety device for air supplied for an external hose or from a mobile emergency supply, comprising a valve means sensitive to pressure of air supply from the external hose, the valve means being operable to cut offthe air supply from the external hose and switch to the emergency supply if the sensed pressure falls below a pre-selected pressure level.

2. A safety device as claimed in Claim 1, in which the preselected pressure level is determined by supply pressure of the emergency supply.

3. A safety device as claimed in Claim 1 or Claim 2, in which the emergency supply operates an audible alarm when in use.

4. A safety device as claimed in any preceding claim, in which the valve operates switch means connected thereto.

5. A safety device as claimed in Claim 4, in which the switch means operates visual or audible electronic alarms.

6. A safety device substantially as hereinbefore described and as shown in the accompanying drawings.