GB2165980A - Safety device for gas supply - Google Patents

Abstract

An atmospheric vibration sensor (15) comprises a flame (13) and an adjacent temperature-sensing junction (14) of a thermocouple. When the atmosphere is vitiated the flame lifts and the junction (14) cools thus allowing a microswitch (18) to open and shut off the electricity supply to a solenoid operated valve (2). Thus a gas supply controlled by valve (2) is shut off. The vitiation sensor may be mounted remote from the valve (2). A non-electric device is also described. <IMAGE>

Description

SPECIFICATION Safety device for gas supply This invention relates to safety devices for use with a gas supply and is intended to reduce accidents due to vitiation of an air supply when one or more gas appliances are being used.

The invention provides a safety device comprising means for detecting vitiation of an atmosphere and means for cutting off a gas supply automatically when a predetermined level of vitiation is detected.

Preferably the safety device comprises a vitiation detector of the kind in which a temperature at or adjacent a flame is sensed, and said means for cutting off the supply is a valve operated directly or indirectly by the temperature sensor.

The temperature sensor may be a thermocouple, the electrical output of which indirectly controls a solenoid-operated valve.

Alternatively the temperature sensor may be a sealed system including an expansible chamber which controls the valve.

The safety device operates independently of any of the gas appliances being used, and its valve means may be located to cut off any selected part or all of the gas supply.

Specific embodiments of the invention are shown in the accompanying drawings, in which: Figure 1 shows diagrammatically an electrically-operated atmospheric device, and Figure 2 shows diagrammatically a non-electric atmospheric safety device.

Referring first to Fig. 1, the device comprises a housing (12) in which is mounted an atmospheric vitiation sensor (15). This comprises a gas-fuelled pilot flame (13) adjacent which is the temperature sensing junction (14) of a thermocouple. It is a feature of a gas flame that if it is burning in an atmosphere which becomes vitiated with carbon dioxide to a known level the flame lifts off the burner and the gas burns a distance away from the burner. This effect is due to the flame seeking sufficient oxygen to support burning. The thermocouple junction is located close to the burner so that when the flame lifts by a predetermined amount the junction is distanced from the flame and so cools. Thus the thermocouple effectively indicates vitiation of the atmosphere by indicating a drop in sensed temperature.

The vitiation sensor (15) is fed with gas on line 3 from a main gas supply line. An igniter (8) is operated by push button (6) to light the pilot flame (13). Upstream of line 3 in the main gas supply line is a solenoid-operated gas valve (2) of the kind in which a valve head (not shown) is lifted off a seat to allow gas flow when the solenoid is energized. An electricity supply to the solenoid on lines 16 is controlled by a normally open micro-switch (5) through a relay (17).

The contact button of micro-switch (5) is operated by a lever (18), which is itself operated by a spring-loaded manual push button (4). Lever (18) is secured to operate a magnetic capsule (7). This is of the kind commonly used in gas fuelled appliances where a weak electrically powered magnetic field is generated sufficient to hold a plunger depressed when it is manually urged into the depressed position but insufficient to move the plunger into the depressed position without assistance. The thermocouple (14) is connected so that its electrical output provides the electrical power for said magnetic field.

In use, the gas supply to the supply line is first turned on. The solenoid valve (2) is at this time closed. The push button (4) is then manually depressed, so urging lever (18) to close micro-switch (5) and thus opening the solenoid valve. A supply of gas now reaches the line 3. The igniter (6) is then operated and the pilot flame (13) is lighted. Button (4) is maintained depressed for about ten seconds, thus holding the plunger in the magnetic capsule (7) depressed until the thermocouple has achieved sufficient electrical output to hold the plunger depressed. The button (4) is then released. Because lever (18) is secured to move with the plunger, the weak magnetic field also holds the lever in its depressed position, holding micro-switch (5) closed. Thus the solenoid valve (2) is maintained open so long as thermocouple (14) detects a normal temperature at the pilot flame (13).

If the air surrounding the pilot flame becomes vitiated the flame lifts, the thermocouple detects a drop in temperature, the plunger is released, lever (18) is released, microswitch (5) opens and the solenoid valve closes. Thus the whole of the gas supply downstream of the solenoid valve is shut off until such time as the safety device is re-set.

It will be noted that the device cannot be reset until the air has recovered its oxygen content since the pilot flame will not burn normally. The solenoid valve (2) is connected to the device only by electrical connections so may be mounted remote from it. For instance, the solenoid valve may be mounted adjacent a gas meter or even form part of the gas meter, while the vitiation sensor (15) is mounted in a position where vitiation is of greatest likelihood, e.g. in a sitting room containing a gas fire.

The vitiation sensor 15 has a window through which the flame (13) can be viewed to check the correct operation. Alternatively or additionally, a thermocouple interrupter is fitted and connected to a small ammeter (10) which indicates the level of energization of the thermocouple.

A manual by-pass valve (19) may be incor porated to over-ride the solenoid in case of failure of the electrical supply.

In an alternative arrangement push button (4) also operates the igniter (8).

The above described arrangement depends on an electrical supply to operate. The arrangement shown in Fig. 2, however, needs no electrical supply and is independent. In this figure a main gas supply passes through a valve (11) to supply gas to appliances and also to a line 3 to a vitiation device (20). This device operates generally similarly to that described with reference to Fig. 1, but instead of a thermocouple has a sealed temperature sensitive system. This comprises a phial (21) sealed to a capillary tube (22) and an expansible operating chamber (e.g. a bellows or a capsule). The system contains a fluid which expands on increase of temperature. Thus increase of temperature at the phial causes expansion of the expansible chamber, which movement is used to lift a valve head off a seat in valve (11).

In order to start this system valve (11) is manually opened via button (23), igniter (8) is operated by button (6), and when phial (21) has heated sufficiently to maintain the valve open, button (23) is released.

The system shown in Fig. 1 may have a normally-closed micro-switch operated by the magnetic capsule (7) so that when the capsule is energized the switch is opened. This switch is connected in series with a manual ON/OFF switch and an alarm system. When both switches are closed as would occur when the manual switch is ON and the magnetic capsule is de-energized, then the alarm operates. The ON/OFF switch may over-ride the alarm to allow faults to be rectified.

It will be understood that vitiation of the air supply is a problem when gas appliances are used either with inadequate ventilation or with an inadequate or blocked flue. The oxygen content of a room may drop to a level where the occupants are asphyxiated or poisoned by carbon monoxide produced by an appliance.

The invention is concerned with a device independent of the appliances themselves, which will cut off the gas supply when it detects vitiation from whatever cause, and which can be connected to cut off the supply to several or all appliances even if only one of the appliances is at fault.

Claims (9)

1. A safety device for connection in a gas supply comprising means for detecting vitiation of an atmosphere and means for cutting off a gas supply automatically when a predetermined level of vitiation is detected.

2. A safety device as claimed in claim 1, wherein the vitiation detector is of the kind in which a temperature at or adjacent a flame is sensed, in which said means for cutting off the supply is a valve operated directly or indirectly by the temperature sensor.

3. A safety device as claimed in claim 1 or claim 2, wherein the vitiation-detecting means and gas cutting-off means are connected by means allowing them to be mounted remotely from one another.

4. A safety device as claimed in claim 2 or claim 3, wherein said temperature sensor is a thermocouple, the electrical output of which indirectly controls the valve.

5. A safety device as claimed in claim 2.or claim 3, wherein said temperature sensor is'a sealed system including an expansible chamber which controls the valve.

6. A safety device as claimed in claim 4, comprising also a microswitch which interrupts ; a power supply to the valve, manual means for operating said microswitch while the flame is being established, said thermocouple powering magnetic means for maintaining the microswitch operated when the flame is established.

7. A safety device as claimed in claim 5, which operates without any requirement for electricity, and having a manual valve opening device for holding the valve open while a flame is being established.

8. A safety device as claimed in any of claims 1 to 7, when the valve is connected in a gas supply to a plurality of gas appliances, the vitiation device being mounted on a position remote from the valve where vitiation is anticipated.

9. A safety device substantially as described hereinbefore with reference to Fig. 1 or to Fig. 2 of the accompanying drawings.