GB2179134A - Valve arrangement - Google Patents

Abstract

A valve arrangement for controlling a supply of gas to one or more burners provided with a cover displaceable, by a user, between open and closed positions includes a first valve (20) which assumes the closed condition if the cover is in the closed position, a second, user operable valve (10) on the downstream side of the first valve and a third valve (30) intermediate the first and second valves which assumes the closed condition if the pressure on the downstream side of the first valve is less than a threshold value. Gas cannot escape unlit from the burners if a user raises the cover when the user-operable valve is open.

Description

SPECIFICATION Valve arrangement This invention relates to a valve arrangement for controlling a supply of gas to one or more burners provided with a cover displaceable, by a user, between open and closed positions and it relates particularly, though not exclusively, to such an arrangement for controlling a supply of gas to a hob unit provided with a pivotal cover.

Hob units mounted in an existing worktop or forming part of a stand-alone cooking appliance are commonly provided with pivotal covers, sometimes referred to as "shutdown" covers. Such covers, which are usually made of toughened glass, have an aesthetically pleasing appearance and, in the closed position, provide an additional work surface.

A hob unit provided with a cover of this kind is often fitted with a safety cut-off valve effective to interrupt a supply of gas to the burners whenever the cover is lowered to the closed position. This valve ensures that the burners are extinguished even if the user forgets to shut off the supply and so prevents the cover from being damaged.

A potentially hazardous situation could still arise however if the user fails to turn off the gas supply before raising the cover thereby allowing gas to escape unlit. It is an object of the present invention to provide a valve arrangement which substantially alleviates this problem.

Accordingly there is provided a valve arrangement for controlling a supply of gas to one or more burners provided with a cover displaceable, by a user, between open and closed positions, the arrangement including a first valve adapted to assume a closed condition, to block a flow of gas to the burners, whenever the cover is in said closed position; a second valve, positioned downstream with respect to the first valve and being operable by a user to control said flow of gas; and a third valve, intermediate the first valve and the second valve, adapted to block a said flow in response to a decrease in gas pressure caused by closure of the cover while the second valve is open and to enable said flow to be restored, by opening the cover, provided the second valve is caused to be closed temporarily.With this arrangement the gas supply may be restored provided the second valve is closed temporarily by a user, thereby preventing an undesirable loss of gas.

In order that the invention may be carried readily into effect an embodiment thereof is now described, by way of example only, by reference to the accompanying drawings of which Fig. 1 shows a valve arrangement in block schematic form and Fig. 2 shows a cross-sectional view through a valve used in the arrangement of Fig. 1.

Referring to Fig. 1, the valve arrangement shown comprises three valves 10, 20, 30 which are coupled together in series and control a supply of gas to a hob unit fitted with a pivotal cover. The hob unit has four burners each coupled to a respective, user-operable control valve 10, though for clarity of illustration one only of the valves 10 is shown in the drawing.

Valve 20 is connected, as shown, to a gas supply inlet I and is coupled operatively to the cover. To this end valve 20 incorporates a mechanical linkage effective to close the valve, and so block a flow of gas to the burners, whenever the cover is lowered to the closed position. This arrangement ensures that the burners are always extinguished when the cover is in the closed position, even if the user forgets to turn off the supply at valve 10.

As shown in Fig. 2, valve 30 which interconnects valves 10 and 20 includes a diaphragm 31 which is urged resiliently by a spring 32 towards a valve seating 33 at one end of a main gas passageway 34 which interconnects inlet and outlet ports 35, 36.

If the pressure of gas on the downstream side D of valve 30 exceeds a threshold value the diaphragm is held away from seating 33 allowing an uninterrupted flow of gas. If, however, the gas pressure falls below the threshold value diaphragm 31 is urged against the seating to form a gas tight seal thereby closing the valve and blocking a flow of gas to the burners. Such a fall in gas pressure arises if the cover is lowered, to effect closure of valve 20, while the user operable valve 10 remains open. It will be appreciated that valve 30, while in the closed position, prevents gas escaping unlit, as might otherwise occur if the cover is raised again before the supply has been shut off at valve 10.

Valve 30 is also provided with a duct 37 of relatively small bore size which by-passes the main gas passageway 34 and allows a controlled leakage of gas from the upstream to the downstream side of the valve.

In order to return valve 30 to the open condition a user must first close valve 10 so as to allow a pressure, in excess of the threshold value, to develop on the downstream side D of the valve. When this pressure is attained diaphragm 31 is urged away from the seating 33 allowing gas to flow through the valve via the main gas passageway 34. It will be appreciated therefore that a supply of gas can only be restored to the burners provided valve 10 is first shut off by the user, albeit temporarily-this arrangement eliminates a potentially hazardous situation which could arise if valve 10 is left open, inadvertently before the cover is raised.

The inventor has found that a preferred leakage rate through duct 37 is 0.4+0.05 cu ft hr 1 of natural gas at a pressure drop of 2mbar. With this leakage rate the valve is effective in different operating conditions ranging from a situation when one only of control valves 10 is left open at a relatively low (simmer) setting to a situation when all four valves are left fully open.

It will be appreciated that although valve 20, described hereinbefore, incorporates a mechanical linkage, equivalent forms of valve could alternatively be used-for example, a valve incorporating a microswitch engageable with a cam surface on the cover.

Moreover a valve arrangement in accordance with the present invention may be used in conjunction with other forms of gas installation-for example a grill burner mounted in a compartment provided with a drop-down door, coupled to a safety cut off valve.

Claims (4)

1. A valve arrangement for controlling a supply of gas to one or more burners provided with a cover displaceable, by a user, between open and closed positions, the arrangement including a first valve adapted to assume a closed condition, to block a flow of gas to the burners, whenever the cover is in said closed position; a second valve, positioned downstream with respect to the first valve and being operable by a user to control said flow of gas; and a third valve, intermediate the first valve and the second valve, adapted to block a said flow in response to a decrease in gas pressure caused by closure of the cover while the second valve is open and to enable said flow to be restored, should the cover be opened, provided the second valve is caused to be closed temporarily.

2. A valve arrangement according to Claim 1 wherein said third valve includes a valve actuator effective to close the valve provided the pressure on the downstream side of the actuator is less than a threshold value.

3. A valve arrangement according to Claim 2 wherein said third valve has resilient means effective to bias the actuator to a closed position, to block a flow of gas, provided the pressure of gas on the dowstream side of the actuator is less than said threshold value, and a by-pass allows a controlled leakage of gas past the actuator even when the actuator assumes the closed position, the actuator being displaced to an open position in opposition to the action of said resilient means, in response to a pressure of gas on the downstream side which equals or exceeds said threshold value.

4. A valve arrangement substantially as hereinbefore described by reference to the accompanying drawings.