GB2196150A

GB2196150A - Gas burner control

Info

Publication number: GB2196150A
Application number: GB08622771A
Authority: GB
Inventors: Sum Pang
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-09-22
Filing date: 1986-09-22
Publication date: 1988-04-20
Also published as: GB8622771D0

Abstract

In a gas burner assembly (31) having a solenoid valve (14) in a gas supply pipe (12) and a thermo- couple (18), responsive to a flame, to hold the valve (14) open, a timer (32) is connected in series with the thermo-couple (18) for interrupting the supply of electric current to the solenoid (19) at the end of a preset time interval. An audible alarm (37) may be energized by a capacitor (35), normally charged by a battery (34), at the end of said time interval. <IMAGE>

Description

SPECIFICATION A gas burner assembly The present invention relates to a gas burner assembly and, in particular to a gas burner assembly with a timer control.

-It is known to use flame failure devices to interrupt a gas supply to a gas burner if and when a flame at the burner goes out unintentionally. A thermo-couple is commonly used as a heat sensing device to sense the presence of the flame.

Some known flame failure devices also comprise a solenoid operated on/off valve in the gas supply path to the burner. The valve is operable by the thermo-couple by electrically connecting the solenoid to the two terminals of the thermo-couple.

When a flame is present at the burner, the temperature of the thermo-couple is misted and electric current is supplied to the solenoid of the on/off valve via the curcuit connection therebetween. The valve is thus held open and gas is supplied to the burner.

If the flame goes out unintentionally, the thermo-couple cools and ceases to provide electric current. Hence the on/off valve closes and the gas supply to the burner is interrupted to prevent gas leakage.

It is also known to provide a timer control associated with the gas burner. In these known arrangements the timer operates an independent valve upstream of the aforesaid on/off valve and this results in a complicated and expensive valve arrangement.

According to the present invention, there is provided a gas burner assembly comprising a burner, a solenoid operated on/off valve in a gas supply pipe to the burner, a thermo-electric generator for generating an electric current in response to heat generated by a flame at the burner for energising the solenoid and holding the on/off valve open, and a timer connected electrically in series with the thermo-electric generator for interrupting the supply of electric current to the solenoid at the end of a preset time interval.

Preferably, the thermo-electric generator is a thermo-couple.

Advantageously, audible warning means is provided to indicate the end of said preset time interval.

In a preferred embodiment a control knob serves three purposes, namely to open the solenoid operated on/off valve to admit gas to the burner, to control the flow rate of the gas to the burner, and to ignite the gas supplied to the burner.

A time delay occurs after igniting the gas before the thermo-couple reaches a temperature at which it generates sufficient current to hold the solenoid valve open. The delay may be several seconds.

One possible way to shorten this delay is to increase the number of turns of the winding of the on/off valve solenoid. This will reduce the magnitude of electric current required to operate the valve but increase the time constant of the solenoid because of its increased inductance. This will increase the response time of the circuit to closing of the on/off valve, should the flame goes out unintentionally.

Hence, advantageously, electrical circuit means are provided for supplying electric current to the solenoid of the solenoid operated on/off valve in response to the operation of said manually operable means to hold the on/off valve open until sufficient current is generated by the thermo-electric generator.

Preferably, the electrical means comprises a battery and, conveniently, also a capacitor charged by the battery, the battery (or the capacitor when provided) being connected in series with the solenoid by for example a microswitch when the manually operable means is operated.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a known construction of a gas burner assembly.

Figure 2 shows one embodiment of a gas burner assembly according to the present invention.

Figure 3 is a front view showing the internal construction of a timer of the gas burner assembly of Figure 1 in a first position.

Figure 4 is a front view showing the internal construction of the timer of Figure 3 in a second position.

Figure 5 is a front view showing the internal construction of the timer of Figure 3 in a third position.

Referring firstly to Figure 1, the gas burner assembly 9 shown therein comprises a gas burner 10, a gas control unit 11, and a gas supply pipe 12 connecting the control unit 11 to the burner 10. The gas control unit 11 comprises a gas inlet port 13, a solenoid operated on/off valve 14, and manually operable means 15 for opening the on/off valve 14 and for operating both a gas igniter 16 and a gas flow control valve 17.

A thermo-couple 18 is mounted adjacent to the burner 10 for generating an electric current in response to the presence of a flame.

The on/off valve 14 is contained within a housing 25 of the control until and includes a solenoid 19, a slidable valve member 20, and a compression spring 21 urging the slidable valve member 20 towards a valve seat 24.

An end 22 of the slidable valve member 20 is of magnetic material, such as soft iron. Hence when the solenoid 19 is energised, the slidable valve member 20 is moved away from the valve seat 24 against the action of the spring 21.

The thermo-couple 18 is connected electri cally in series with the solenoid 19. When a flame is present at the burner 10, the temperature of the thermo-couple 18 is raised and the electric current generated by the thermocouple 18 holds the on/off valve 14 open and gas continues to be supplied to the burner 10 to maintain the flame.

If and when the flame is goes out, no electric current is supplied by the thermo-couple 18 to the solenoid 19 and the spring 21 urges the valve member 20 against the valve seat 24 to interrupt the flow of gas to the burner 10.

The manually operable means 15 comprises a control knob 27 having a spindle 28 aligned with the axis of the valve member 20. When the control knob 27 is pushed inwards, the distal end of the spindle 28 pushes the valve member 20 against the action of spring 21 to open the on/off valve 14.

The gas igniter 16 comprises a piezo-electric crystal 29 and a spring-loaded hammer 30 and is operated by the control knob 27 when the latter is angularly displaced from its "off" position.

The gas flow control valve 17 also comprises a throttle valve (not shown) in the housing of the gas control unit 11. The control valve 17 is operated by angular movement of the control knob 27 to regulate flow of gas to the burner 10.

In use, inwards movement of the control knob 27 opens the on/off valve 14 whilst angular movement of the control knob 27 operates the gas igniter 16 and opens the throttle valve. The control knob 27 is held in until the thermo-couple 18 generates sufficient electric current for the solenoid 19 to hold the on/off valve 14 open.

The gas burner assembly 31 shown in Figure 2 differs from that shown in Figure 1 in that if further comprises a mechanical timer 32 having associated contacts connected electrically in series with the thermo-couple 18 and the solenoid 19, and electric circuit means 33. which in turn comprises a battery 34, a capacitor 35, a microswitch 36, and an electrically operated alarm 37.

As shown in Figures 3 to 5, the timer 32 comprises a shaft 38, two single-pole singlethrow switches 39 and 40, and a time scale 41.

The two switches 39 and 40 have respective fixed contacts 39a and 40a, and respective movable contact arms 39b and 40b supported at 39c and 40c respectively. The two contact arms 39b and 40b are mechanically but not electrically connected together at an intermediate position where a projection 42 is provided. The free ends of the two contact arms 39b and 40b are positioned between the fixed contacts 39a and 40a.

An operating arm 44 projects radially from the shaft 38. The timer 32 is at its "off" position when the arm 44 of the shaft 38 is to the left side of the switch projection 42, as shown in Figure 3. In this position the free ends of the two contact arms 39b and 40b are urged towards the fixed contact 39a and an abutment 43 positioned adjacent thereto by virtue of their inherent resilience. The switch 39 is closed and the timer 32 can be considered to be short-circuited.

When setting the timer the shaft 38 is turned in a clockwise direction by an appropriate angle according to a desired operating time. When the shaft 38 is released, it starts to turn in an anti-clockwise under the action of a conventional spring driven mechanism (not shown).

When the shaft 38 reaches an angular position in which the arm 44 presses against the projection 42 the contact arms 39b and 40b are deformed with the abutment 43 restricting the outward deflection thereof. Hence the free end of the contact arm 40b is moved into contact with the fixed contact 40a, as shown in Figure 5, and the switch 40 is closed.

The timer 32 returns to its "off" position when the arm 44 of the shaft 38 passes beyond the projection 42 of the switch 40 in an anti-clockwise direction.

The electric circuit means 33 supplies electric current to the solenoid 19 of the on/off valve 14 in response to the operation of the manually operable means 15 to hold the on/off valve 14 open until sufficient current is generated by the thermo-couple 18.

The microswitch 36 is a single-pole doublethrow switch comprising a pole contact 46, a normally-open (N.O.) contact 47 and a normally-closed (N.C.) contact 48, and is operated whenever a push button 49 thereof is depressed.

The positive terminals of the battery 34 and the capacitor 35 are both earthed, and the negative terminals thereof are electrically connected to the N.C. contact 48 and the pole contact 46 respectively. The capacitor 35 is normally charged by the battery 34.

The N.O. contact 47 of the microswitch 36 is connected to the movable contact arm 39b of the switch 39. Hence when the microswitch 36 is operated with the switch 39 closed, the charged capacitor 35 is electrically connected to the solenoid 19 of the on/off valve 14 and the capacitor 35 discharges through the solenoid 19 The alarm 37 is electrically connected between the fixed contact 40a of the switch 40 and earth. The negative terminal of the battery 34 is electrically connected to the movable contact 40b of the switch 40. Thus with the switch 40 closed the alarm 37 is energised.

In operation the timer 32, if used, is set to a desired time interval. The control knob 27 is pushed inwards to open the on/off valve 14 and to operate the microswitch 36. When the microswitch 36 is operated, the control knob 27 is then turned in a clockwise direction to open the throttle valve and to ignite the gas supplied to the burner 10 through the on/off valve 14 and the throttle valve.

Operation of the microswitch 36 connects the capacitor 35 in series with the solenoid 19. The capacitor 35 therefore discharges through the solenoid 19 and this helps hold the valve member 20 open until such time as sufficient current is generated by the thermocouple 18.

When the timer 32 reaches the position shown in Figure 5, the thermo-couple 18 is disconnected from the solenoid 19 and the valve member 20 is urged against the valve seat 24 to interrupt gas to the burner 10.

Hence the flame at the burner 10 is extinguished. At the same time the alarm 37 is energised by the charge stored in the capacitor 35.

Finally the timer 32 returns to its first position shown in Figure 3.

The above embodiment is given by way of example only. Various modifications will be apparent to persons skilled in the art and it is desired to include all those modificatioons as fall within the scope of the invention defined by the appended claims.

Claims

1. A gas burner assembly comprising a burner, a solenoid operated on/off valve in a gas supply pipe to the burner, a thermo-electric generator for generating an electric current in response to heat generated by a flame at the burner for energising the solenoid and holding the on/off valve open, and a timer connected electrically in series with the thermo-electric generator for interrupting the supply of electric current to the solenoid at the end of a preset time interval.

2. A gas burner assembly according to claim 1, wherein manually operable means are provided to open the on/off valve initially.

3. A gas burner assembly according to claim 2, wherein a gas igniter is provided for igniting gas at the burner in response to operation of the manually operable means.

4. A gas burner assembly according to claim 3, wherein the gas igniter is a piesoelectric igniter.

5. A gas burner assembly according to anyone of claims 2 to 4, wherein electric circuit means are provided for supplying electric current to the solenoid of the solenoid operated on/off valve in response to operation of said manually operable means to hold the on/off valve open until sufficient current is generated by the thermo-electric generator.

6. A gas burner assembly according to claim 5, wherein the electric circuit means comprises a battery.

7. A gas burner assembly according to claim 6, wherein the electric circuit means further comprises a capacitor charged by the battery.

8. A gas burner assembly according to anyone of the preceding claim, further comprising a gas flow control valve.

9. A gas burner assembly according to claim 8 when dependent on claim 2, wherein the gas flow control valve is associated with the manually operable means.

10. A gas burner assembly according to anyone of the preceding claims, wherein the thermo-electric generator is a thermo-couple.

11. A gas burner assembly according to anyone of the preceding claims, wherein the timer is a mechanical timer.

12. A gas burner assembly according to anyone of the preceding claims, further comprising an audible alarm operable by the timer at the end of said preset time interval.

13. A gas burner assembly according to anyone of the preceding claims, wherein the timer can be short circuited.

14. A gas burner assembly substantially as hereinbefore described with reference to the accompanying drawings.