GB2130402A

GB2130402A - Electro-pneumatic system

Info

Publication number: GB2130402A
Application number: GB08329525A
Authority: GB
Inventors: Alan Joseph Hillier
Original assignee: NOISCO DEVELOPMENTS Ltd
Current assignee: NOISCO DEVELOPMENTS Ltd
Priority date: 1982-11-05
Filing date: 1983-11-04
Publication date: 1984-05-31
Also published as: GB8329525D0

Abstract

A system (e.g. for life support system) (10) supplying pressurised gas has an electrical compressor (12) as a primary source of gas and a gas bottle (14) as a secondary source. The primary and secondary air lines from these sources are connected through a shuttle valve (22) to an outlet line (16). Solenoid valves (20, 26) in the primary and secondary gas lines are connected in the electrical circuit which also powers the compressor (12) and are controlled by a pressure-sensitive switch (30) monitoring the gas pressure in the primary gas line. Normally, the primary gas line valve (20) is open while the secondary gas line valve (26) is closed when the valves are energised through the switch, during operation. If, however, the power supply fails or there is a loss of pressure in the primary line the valves are de-energised to close the primary line and open the secondary line, allowing pressurised gas from the gas bottle (14) to be supplied to the outlet line (16). Additional controls can be provided for monitoring minimum and maximum gas pressure levels in the secondary and outlet lines. <IMAGE>

Description

SPECIFICATION Electro-pneumatic system The present invention relates to an electropneumatic system There are a considerable number of industrial, commercial and medical areas where a continuous supply of pressurised gas is required to enable various products to be manufactured, processes to be carried out or services provided. In many cases any loss of supply of pressurised gas, even for relatively short periods, can be extremely serious, especially in the medical field. A typical application is the provision of pressurised air for life support systems such as ventilators where it is essential that pressurised air from an alternative, secondary source is provided immediately a failure of the primary source occurs, for whatever reason.

The present invention seeks to provide an improved system which automatically switches the supply of compressed gas from a primary source to a secondary source on failure of the primary source.

The present invention provides a system for controlling the flow of pressurised gas or fluid from a first, primary source of pressurised gas or fluid and a second, secondary source of pressurised gas or fluid to an outlet of the system, the system comprising a primaryfluid or gas line for connecting said primary source to said outlet, a secondary gas or fluid line for connecting said secondary source to said outlet and first control means for monitoring a selected operating condition of said system and controlling said primary and secondary lines and wherein said first control means is operable to switch from a first operating state in which said primary line is open and said secondary line is closed to a second operating state in which said primary line is closed and said secondary line is open in response to a preselected change in the operating condition of said system.

In a preferred embodiment of the present invention the system further comprises means for monitoring gas pressure in said primary line and operable to cause said control means to close said primary line and open said secondary line in response to the gas pressure in said primary line falling below a preset level. Preferably, where, for example, the primary source of pressurised gas in an electrically operated compressor, the control means is operable to close said primary line and open said secondary line in response to a failure in the power supply to the system.

Advantageously, the system also comprises means for monitoring gas pressure at the outlet of the system said means being operable to close an outlet line of the system when said pressure drops below a preselected level which is preferably less than the pressure level in the primary line at which the primary line is closed.

Conveniently, means are also provided for monitoring the gas pressure in the secondary line and operable to cause the system to close down in response to the secondary line gas pressure falling below a preselected level.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a preferred embodiment of an electro-pneumatic system according to the present invention; Figure 2 is a schematic diagram of a second embodiment of an electro-pneumatic system according to the present invention; Figure 3 is a schematic diagram of a third embodiment of an electro-pneumatic system according to the present invention; Figure 4 is a schematic diagram of a fourth embodiment of an electro-pneumatic system according to the present invention; and Figure 5 is a schematic diagram of a fifth embodiment of an electro-pneumatic system according to the present invention.

Referring firstly to Figure 1 this shows an electropneumatic system 10 which controls the supply of compressed gas, such as air, from a primary source in the form of a compressor 12 and a secondary source in the form of a compressed gas bottle 14 to an outlet 16 of the system which may be connected, for example, to a life support system such as a ventilator (not shown in the drawings).

The system 10 has a pneumatic circuit in which a primary line connects the compressor outlet to the outlet 16 of the pneumatic circuit. The primary line has a pressure regulator 18 which regulates the pressure of the air supplied by the compressor, a three-port, two-position normally closed solenoid valve 20 connected to the pressure regulator output and a shuttle valve 22, one input of which is connected to the solenoid valve output and the output of which is connected to the pneumatic circuit outlet 16. The pneumatic circuit also has a secondary line which connects the air bottle 14through a further pressure regulator 24 and a three-port, two-position normally open solenoid valve 26 to a second input of the shuttle valve 22.

The solenoids of the two solenoid valves 20 and 26 are connected in parallel in an electrical circuit of the system and to one terminal of a power supply input 28 through a pressure-controlled switch 30 in parallel with a momentary action change-over switch 32.

The pressure-controlled switch 30 is controlled by the air pressure in the primary line between the regulator 18 and solenoid valve 20.

Before the system is switched on, in the absence of any electrical power the solenoid valve 20 is closed, shutting off the primary air line while the solenoid valve 26 is open allowing pressurised air to be supplied to the system outlet 16 from the air bottle 14. When the power supply is switched on the compressor 12 runs up to its normal operating speed and delivers compressed air through the solenoid valve 20 which, in its closed position, vents the pressurised air to atmosphere. Once the compressor has reached normal running speed the operator presses the switch 32 to energise the solenoid valves 20 and 26 so that the valve 26 closes the secondary air line while valve 20 opens the primary air line allowing the compressor to supply pressurised air through the shuttle valve 22 to the outlet 16.To set the operating conditions, if these have not already been set, the operator first adjusts the regulator 18 to provide the minimum acceptable air pressure in the primary air line. The pressure switch 30 is then adjusted so that its electrical contacts just close at this minimum acceptable air pressure. The switch 32 is then released by the operator. The air pressure in the primary line maintains the pressure switch 30 closed and this in turn maintains the solenoid valves 20 and 26 open and closed respectively. The pressure regulator 18 is then readjusted to provide a normal working air pressure greater than the minimum acceptable air pressure in the primary line.

In the event of a failure of the power supply the solenoid valves 20 and 26 de-energise, closing the primary air line and opening the secondary airline to allow pressurised air from the air bottle 14to be supplied to the outlet 16. Since a failure of the power supply also cuts off the compressor 12 the air pressure in the primary line falls and the pressure switch 30 opens. The supply of pressurised air from the air bottle 14 is therefore maintained even when power supply is reconnected until the operator once again closes the switch 32 to re-energise the solenoid valves 20 and 26.

If the air pressure in the primary line drops below the minimum pressure at which the pressure switch 30 closes, for any reason such as failure of the compressor 12, the pressure switch 30 opens, deenergising the valves 20 and 26 which respectively close the primary air line and open the secondary air line allowing pressured air to be supplied from the air bottle 14 to the outlet 16. As is mentioned above, in its de-energised state the solenoid valve 20 vents that portion of the primary line from the compressor to the valve to atmosphere and this ensures that the air pressure applied to the pressure switch 30 remains below the closing pressure of the pressure switch 30.Figure 2 shows a modification to the system of Figure 1 in which a three-porttwo-position normally open solenoid valve 34 is connected in the outlet line between the shuttle valve 22 and the outlet 16 and a normally closed pressure switch 36 is connected to the outlet line between the valve 34 and the outlet 16 to monitor the outlet air pressure.

The solenoid of the valve 34 and the normally closed contacts of the pressure switch 36 are connected in series with a pair of normally closed contacts on the switch 32 and the normally closed contacts of the pressure switch 30.

As previously described with reference to Figure 1, in the absence of any electrical power supply the solenoid valve 20 closes the primary line and the solenoid valve 26 opens the second line. Solenoid valve 34 is also open, allowing air from the secon dary source 14to be supplied to the outlet 16. The procedure for setting up the system is similar to that described for the system of Figure 1. The pressure regulator 24 is adjusted to provide a working air pressure from the secondary source 14 while the threshold pressure of the pressure switch 36, above which pressure the switch opens, is set at a value less than the minimum acceptable air pressure in the outlet line. When the power supply is connected the compressor runs up to normal speed and the compressed air provided from the compressor is vented to atmosphere through the solenoid valve 20.

The switch 32 is then pressed, disconnecting the electrical supply to the pressure switch 36 and connecting it to the solenoid valves 20 and 26 causing them to change state to open the primary line and close the secondary line. Compressed air is thus supplied from the compressor 12 to the outlet 16 at a normal working air pressure set by the regulator 18. The pressure switch 30 is also actuated by the air pressure in the primary line to maintain valves 20 and 26 energised. The switch 32 is then released allowing the system to function normally.

Because of the finite time that pressurised air takes to reach the pressure switch 36 and open it it is preferable to ensure that early release of the switch 32 does not prematurely close the circuit of valve 34.

This is effected by including a time delay 37 in series with the pressure switch 36. The time delay maintains the circuit open for a preselected period set to be greater than the time pressurised air takes to flow to and open the pressure switch 36. The time delay may be effected in an electrical or pneumatic or any suitable manner.

The system reacts in the same manner as the system of Figure 1 to a failure of the power supply or a drop in primary line air pressure below the minimum acceptable air pressure. In the latter case the pressure switch 30 switches the electrical supply from the solenoids of the valves 20 and 26 to the solenoid of the valve 34. However, since the pressure switch 36 is held open by the air pressure in the outlet line the valve 34 remains open.

If, however, under normal operating conditions when pressurised air is supplied by the compressor 12 the air pressure in the outlet line and thus the primary line drops below the minimum acceptable pressure as a result, for example, of a fracture in or disconnection of an external air line connected to the outlet line then the pressure switch 30 opens, de-energising the valves 20 and 26 to allow air to be supplied from the secondary source Iitthrough the secondary line to the outlet 16. If this, too, fails to maintain the outlet air pressure above the minimum acceptable pressure then the pressure switch 36 closes completing the electrical circuit through the solenoid of valve 34 and the pressure switch 30 to energise and close the valve 34, thus shutting off complete the supply of pressurised air. Where the system is being used to supply potentially hazardous gasses to an external apparatus the closing of the output line prevents the discharge to atmosphere of such gasses through a fractured or disconnected gas line in the external apparatus. If the switch 32 is then pressed it opens the electrical circuit of the valve 34, allowing the valve to open, and energises the valves 20 and 26 to close off the secondary line and connect the compressor 12 to the outlet 16 until the switch 32 is released. This facility can be used to trace the location of the pressure loss in the external apparatus. Alternatively the supply can be switched off resulting in the connection of the secondary air source 14 to the outlet 16 to allow the pressure loss to be traced using the secondary source 14.

Referring now to Figure 3, it is preferable to ensure that the compressor 12 is allowed to operate only if there is an adequate air pressure supply from the secondary source 14. To this end, a third, normally open pressure switch 38 is electrically connected in series with the electrical input to the switch 32, pressure switch 30 and compressor 12, the pressure input to the switch 38 being connected to the secondary line between the pressure regulator 24 and valve 26. The pressure switch 38 is set to open if the pressure in the secondary line drops below the minimum acceptable operating pressure so that, in this event, the power input is switched off by the switch 38.

Figure 4 shows a further embodiment of an electro-pneumatic system according to the present invention in which a relay 40 is connected in the electrical supply line between the closed output of the pressure switch 30 and the solenoid of the valve 20. The relay controls an alarm circuit 42 which can provide either or both an audible and visual alarm when any failure occurs in the system.

A further modification shown in Figure 5 is the provision of a further pressure switch 44 whose pressure input is connected to the outlet line downstream of the solenoid valve 34. This pressure switch is responsive to pressure in the outlet line exceeding a preselected safe level and can be used either to activate the alarm circuit 42 orto close offthe pressurised air supply altogether.

The above described systems are preferably constructed using a solid connecting block made, for example, of metal for added safety.

Although described as a pneumatic system the system according to the present invention is equally applicable to fluid systems.

Claims

1. A system for controlling the flow of pressurised gas or fluid from a first, primary source of pressurised gas or fluid and a second, secondary source of pressurised gas or fluid to an outlet of the system, the system comprising a primary fluid or gas line for connecting said primary source to said outlet, a secondary gas or fluid line for connecting said secondary source to said outlet and first control means for monitoring a selected operating condition of said system and controlling said primary and secondary lines and wherein said first control means is operable to switch from a first operating state in which said primary line is open and said secondary line is closed to a second operating state in which said primary line is closed and said secondary line is open in response to a preselected change in the operating condition of said system.

2. A system as claimed in Claim 1 wherein said primary source is adapted to be energised by an external power source and said first control means is operable in response to loss of said external power to close said primary line and open said secondary line.

3. A system as claimed in Claim 2 wherein said first control means comprises a respective valve controlling each of said primary and secondary lines and actuable in response to loss of said external power to close said primary line and open said secondary line.

4. A system as claimed in Claim 1, 2 or 3 wherein said first control means comprises first means for monitoring the pressure level in said primary line and operable responsively to said pressure level falling below a first preselected lead to close said primary line and open said secondary line.

5. A system as claimed in Claim 4 when appen- dant to Claim 3 wherein said primary source is an electrically operated compressor means, said valves are electrically operated valves energisable to open said primary line and close said secondary line, and said first pressure monitoring means is a first pressure controlled switch coupling said external power source to said valves and operable responsively to said pressure level falling below said first preselected level to de-energise said valves to close said primary line and open said secondary line.

6. A system as claimed in any of Claims 1 to 5 further comprising second control means for monitoring the pressure level at said outlet and operable responsively to said pressure level falling below a second preselected level to close said output.

7. A system as claimed in Claim 6 wherein said second control means comprises a valve in an output line of said system and second means for monitoring the pressure level in said line and controlling said valve in dependence thereon.

8. A system as claimed in Claim 7 when appendant to Claim 5 wherein said second control means valve is an electrically operated valve energisable to close said output line and said second pressure monitoring means is a second pressure controlled switch operable responsively to said output pressure level falling below said second preselected level to close said second control means valve.

9. A system as claimed in Claim 8 wherein said first and second pressure controlled switches are connected in series in a power supply circuit for said second control means valve and that said valve is energised to close said output line only in response to operation of both said first and second pressure controlled switches.

10. A system as claimed in any of Claims 6 to 9 when appendantto Claim 4 or 5 wherein said second preselected pressure level is less than said first preselected pressure level.

11. A system as claimed in any of Claims 1 to 10 further comprising third control means for monitoring the pressure level at said outlet and operable responsively to said pressure level rising above a third preselected level to inhibit the supply of pressurised gas or fluid through said outlet.

12. A system as claimed in any of Claims 1 to 10 further comprising third control means for monitoring the pressure level at said outlet and operable reponsively to said pressure level rising above a third preselected level to actuate an alarm.

13. A system as claimed in any of Claims 1 to 12 further comprising means for monitoring the pressure level is said secondary line and operable responsively to said pressure level falling below a preselected level to inhibit operation of said system.

14. A system as claimed in Claim 13 wherein said monitoring means is operable to inhibit operation of said primary source of pressurised gas or fluid.

15. A system for controlling the flow of pressurised gas or fluid from a first, primary source of pressurised gas or fluid and a second, secondary source of pressurised gas or fluid to an outlet of the system, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

16. A system for controlling the flow of pressurised gas or fluid from a first, primary source of pressurised gas or fluid and a second, secondary source of pressurised gas or fluid to an outlet of the system, substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

17. A system for controlling the flow of pressurised gas or fluid from a first, primary source of pressurised gas or fluid and a second, secondary source of pressurised gas or fluid to an outlet of the system, substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

18. A system for controlling the flow or pressurised gas or fluid from a first, primary source of pressurised gas or fluid and a second, secondary source of pressurised gas or fluid to an outlet of the system, substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

19. A system for controlling the flow of pressurised gas or fluid from a first, primary source of pressurised gas or fluid and a second, secondary source of pressurised gas or fluid to an outlet of the system, substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.