GB2228104A

GB2228104A - Control of forced flue gas appliance

Info

Publication number: GB2228104A
Application number: GB8824564A
Authority: GB
Inventors: Edward Trevor Marshall
Original assignee: GSM SYNTEL Ltd
Current assignee: GSM SYNTEL Ltd
Priority date: 1988-10-20
Filing date: 1988-10-20
Publication date: 1990-08-15
Anticipated expiration: 2008-10-20
Also published as: GB8824564D0; GB2228104B

Abstract

When push switch PB is pressed by the user a control voltage is supplied, via a flow switch 12 located in the flue, in its "no-flow" position, to a relay AR and to a holding relay CR. Activation of AR causes mains electricity to be supplied to a fan 10 to draw gases through the flue. If a timer 14 times out and the flow switch 12 is still in its "no-flow" position the system is turned off. If, on the contrary, switch 12 moves to the "flow" position, then a relay BR maintains energisation of the fan and holds a gas supply valve open. Electricity supply to the fan is now preferably via a choke to lower the fan's speed to a value appropriate for normal running. The gas valve is controlled by a thermocouple located adjacent the main or pilot flame. <IMAGE>

Description

CONTROL OF FORCED FLUE GAS APPLIANCE The present invention relates to circuitry and a method for controlling a forced flue gas appliance, that is, a gas appliance associated with a flue through which exhaust gases are drawn or forced by, typically, a fan.

Forced flue gas appliances, such as forced flue gas fires, are employed when, for example, there is no chimney breast in which exhaust gases can rise by convection.

According to a first aspect of the invention there is provided control and supply circuitry for a forced flue gas appliance, the appliance being associated with a gas supply valve and a means for drawing exhaust gases through a flue, the circuitry comprising: start-up switching means under the control of a user; a timing means; flow-sensitive switching means which is sensitive to flow in the flue and which has a "no flow" condition and a "flow" condition; wherein the flow-sensitive switching means, in its "no flow" condition, and when the start-up switching means is "on", (1) enables a control signal to be delivered to a switching means A, whereby switching means A is in a start-up condition enabling voltage supply to the means for drawing exhaust gases, and (2) enables a control signal to be delivered to the timing means which then activates a switching means C which enables a control signal to be delivered to the flow-sensitive switching means notwithstanding that the start-up switching means may thereafter be released, the flow-sensitive switching means, in its "flow" condition, isolating the switching means A from a control signal and enabling a control signal to be delivered to a switching means B which, provided the switching means C is and remains activated, causes voltage to be supplied to the means for drawing exhaust gases and the gas valve to be "on", the timing means de-activating the switching means C if it receives a control signal from the flow-sensitive switching means for longer than a predetermined interval.

The circuitry may comprise a DC control part and an AC supply part, the parts being linked by a transformer, from which may be derived a rectified supply for the control part.

Preferably, the means for drawing exhaust gases through the flue enables exhaust gases to be drawn through the flue at two or more rates. To this end there may be provided more than one fan. Alternatively, one fan may be made to operate at different speeds by provision of more than one motor. Preferably, however, there is provided a single motor fan which may be operated at more than one speed. Two speeds are most useful, a faster speed for clearing the flue, for example on start-up or in the event of abnormal operation, and a slower speed for normal operation. The circuitry of the invention may suitably comprise more than one supply path to the fan with a least one path having a component across which some of the supply voltage is dropped. This component may comprise a reactance, for example an inductance. It may be adjustable, for example an adjustable thyristor controlled device.

Suitably, the switching means A, when in its start-up condition, enables higher voltage supply to the means for drawing exhaust gases and the switching means B, when closed, enables lower voltage supply to the means for drawing exhaust gases. Preferably, the switching means A is arranged such that, when not in its startup condition, it provides a contact in series with the supply pathway for lower voltage supply to the means for drawing exhaust gases. The switching means B may suitably be in series with a contact of the switching means C and with a thyristor whose gate receives an activating signal once the flow-sensitive switching means switches to its "flow" condition.

The circuitry preferably comprises a diode located upstream of the flow-sensitive switching means, such that the initial control signal delivered to the timing means must be via the flow-sensitive switching means, but such as to permit a control signal to be delivered to the timing means other than via the flowsensitive switching means once the switching means C has been actuated.

The circuitry preferably comprises a diode located such that when the flow-sensitive switching means is in its "flow" condition no control signal can be delivered to the switching means A.

The circuitry may comprise a thermocouple to control the gas supply valve, the integrity of the thermocouple circuit being under the control of the circuitry.

An LED may be used to indicate that power is available to circuits for starting up.

Switching means within the circuitry, for example switching means A, B and C, may comprise electromagnetic relays.

According to another aspect of the invention there is provided control and supply circuitry for a forced flue gas appliance, comprising a thermocouple for location in the gas flame of the gas appliance, a gas supply valve for the appliance being under the control of the thermocouple and the thermocouple circuit being breakable by the circuitry to effect closure of the valve.

Suitably, the thermocouple circuit is breakable by switching means which is under the control of the switching means B.

According to another aspect of the invention, there is provided a method of controlling a forced flue gas appliance, which method comprises using control and supply circuitry as herein defined and/or described.

According to another aspect of the invention there is provided a forced flue gas appliance under the control of control and supply circuitry as herein defined and/or described.

According to another aspect of the invention there is provided control and supply circuitry for a forced flue gas appliance, the appliance being associated with a gas supply valve and a means for drawing exhaust gases through a flue, the circuitry comprising: start-up switching means which is under the control of a user; a further switching means which is sensitive to flow in the flue and which has a "no flow" condition which causes the means for drawing exhaust gases to be switched on upon the operation of the start up switching means, and a "flow" condition which permits the means for drawing exhaust gases to continue running and causes the gas supply valve to be switched on; and a timing means which causes the means for drawing exhaust gases and the gas supply valve to be switched off after a pre-determined interval should the flow switch remain in or return to its "no flow" condition for this interval.

The invention will now be further described, by way of example, with reference to the accompanying drawings in which Figs 1-4 show the alternative circuits which may typically be used to control a forced flue gas fire, and Fig. 5A and 5B show a mounting unit for mounting a part of the control circuit.

Figure 1 represents one preferred embodiment of the present invention. The circuit consists of two parts, a controlling part indicated generally as 2 and a controlled part indicated generally as 4, the two parts being linked by a transformer 6.

The controlled part 4 is connected to the mains electricity and comprises a fan 10 in the flue. The fan is connected by means of relay contact AR1 either directly across the mains or via a further relay contact BR1 and a speed reduction unit SRU which reduces the voltage across the fan 10.

A thermocouple 4 (not shown; connected in series with terminals TT) in the pilot or main flame controls the gas supply valve and may itself be controlled by means of relay contact BR3.

The controlling part 2 operates from a 12-volt full-wave rectified supply from the controlled AC part and consists of a flow switch 12 which may adopt either of two conditions, indicative of "flow" and "no flow" respectively, a timer 14 which, when activated, will begin a safe switching off procedure after a predetermined interval, relays AR, BR and CR, diodes D1, D2, D3, D4, D5, D6 and D7, an LED which is energized whilst the circuit has power but has not been activated, and a self-releasing push button PB which may be used to activate the circuit.

Whether or not the gas fire is in operation when power is supplied to terminals L and N an LED is energized via relay contact CR1 (position A-B), indicating that power is available within the controlled part 4. Upon the depression of PB a DC supply is established, via the flow switch in its "no flow" condition A-B, to the relay AR and to the timer 14. An output exists at the timer output line 18 which energizes relay CR. Relay contacts CR1, CR2 and AR1 now change state, each adopting the alternative state to that shown in Fig. 1. The fan 10 now receives the full mains voltage through relay contact AR1 and the fan begins to accelerate to full speed drawing air/gases from the flue and removing any minor blockage which may be present. The LED is isolated when relay contact CR1 changes state.

When PB is released supply to the circuit is maintained via relay contact CR1 and diode D3.

At the same time or at any time after PB is pressed, the user depresses a push button to manually open the gas supply to a pilot or burner, igniting this by means of a piezoelectric spark generator. Thereafter the main burner is ignited from the pilot by manually opening the gas supply to the main burner.

Alternatively, after the PB is pressed the main burner may be lit automatically by means of a pilot, the latter being lit automatically by a safety sequence control.

Whilst the flow switch is in its "no flow" condition A-B the control input 16 to the timer 14 is HIGH and if this condition persists for a pre-determined interval the circuit will be de-activated, relay CR being de-energized after this interval.

Provided that there is no blockage in the flue, the air flow produced by the action of the fan causes the flow switch 12 adopt its "flow" condition B-C. Since CR2, in series with relay BR, has now closed, relay BR becomes energized and thus contact BR2 now closes.

Contact BR3, in the thermocouple circuit, also closes, completing that circuit and maintaining the gas supply valve open (whereby the user may release the push button which initially opened the gas supply valve) provided the thermocouple senses the flame. Moreover, relay AR is now de-energized and the control input to the timer goes LOw halting the countdown to switch off. Relay CR remains energized via the timer, provided relay contact CR1 remains in position A-C.

Relay contacts AR1 must now return to their original position and the supply to the fan is via BR1 and the speed reduction unit. The potential across the fan 10 reduces by an amount equal to that which is dropped across the speed reduction unit. Hence the fan slows and the flow in the flue reduces and remains steady. The system is now running in its steady state, and the gas supply is provided to the gas fire, the gas supply valve being maintained open by the thermocouple.

Upon depression of push button PB the reversebiasing of diode D3 ensures that, until relay CR is activated, the timer 14 and hence the relay CR is activated through the flow switch 12 only.

Forward biasing of the same diode D3 subsequently maintains the supply to the flow switch once the relay contact CR1 has switched and the push button PB has been released.

Once normal running conditions have been established and the flow switch has adopted the "flow" condition the reverse-biased diode D4 ensures that relay AR is not re-energized and the fast fan operation not reinstated, unless the flow switch switches to its "no flow" condition.

Should there be a failure of the flow switch such that it remains in position A-B, then relay BR would never be energized and the gas supply valve would close when released. The control input 16 to the timer would remain HIGH and, after a pre-determined interval the output at the timer would fall to zero de-energizing relay CR. In this particular embodiment of the present invention this time interval is about 10 seconds.

Once relay CR is de-energized, relay contact CR1 reverts to its original position A-B and the LED lights.

The rest of the controlling part of the circuit is then isolated and thus relay AR becomes de-energized turning off the fan.

Should the flow switch return to its no flow condition (position A-B) after stable conditions have been established, for example in the event of a temporary blockage of the flue, relay BR would remain energized and so the gas supply would remain on. Relay AR would become energized switching relay contact AR1 to its start-up position and causing the fan motor to experience full mains voltage. The fan would therefore operate at full speed with the purpose of removing the blockage. The control input to the timer would go HIGH and should the no-flow condition persist beyond the pre-determined interval, the "lock out" sequence would commence as detailed above, switching off the fan and the gas supply.

If however, the flow switch were to return to the flow condition (position B-C) before "lock out", the normal running condition would be re-established and the control input to the timer would go LOW again.

If the flow switch were to have stuck in the "flow" condition (B-C) from the previous use of the gas fire then the condition detailed above for turning on could not occur and even with the push-button PB depressed no relay could be energized.

In the event of the gas flame going out, for example, due to a strong draught, the thermocouple would sense the loss of the flame and turn off the gas supply safely.

In the event of failure of the mains electricity, even for a very short period, such as lOmS, the relays will be de-energized and the system will shut down.

Short-circuit protection for the fan, valve, transformer etc., is provided by an integral fuse 20.

A mains override switch (not shown) is provided.

Figure 2 represents a second embodiment of the present invention and the circuit operates in a similar way to the first embodiment with the following exceptions: - In the controlled part 4 of the circuit a solenoid gas supply valve 19 in series with relay contact BR1 is connected across the mains such that the state of BR1 determines whether or not the gas valve is on. Thus, in this embodiment the gas supply can only commence once the flow switch switches to its "flow" position B-C.

- The speed reduction unit is an inductive choke 22.

- The timer interval after which the timer switches off is provided by the time constant of a C-R network. When the flow switch is in position A-B capacitor C2 begins to charge through resistors R1 and R2. When it becomes fully charged the output on the timer goes LOW turning off the transistor T1 and hence the relay CR.

- When the flow switch is in the flow position B-C and relay contact CR2 is closed thyristor T2 is in its conducting state and so relay BR is energized.

Thyristor T2 remains conducting during normal operation because the current through it and the voltage across it are never zero at the same time due to the inductive effect of relay BR, with which it is in series.

- During normal operation mains transient suppression is provided by the surge-suppressor 23 in parallel with the gas supply valve 19, connected across terminals X and Y. This also suppresses any reverse transient generated by solenoid components during switch off.

Figure 3 represents another embodiment of the present invention and the circuit operates in a similar way to that of the second embodiment except that the gas supply valve is controlled by a thermocouple which is, itself, controlled by a relay DR in parallel with the relay BR. Relay DR has gold contacts and is of very low resistance. In parallel with relay DR is a capacitor to ensure a smoothed supply therefor. Diode D8 serves to prevent the capacitor influencing the operation of the rest of the circuit.

Figure 4 represents another embodiment of the present invention and the circuit operates in a similar way to other circuits. In common with the circuit of Figure 3, the thermocouple is controlled by a relay DR in parallel with relay BR, but the arrangement is such that thyristor T2 and the gate-controlling resistor/capacitor network is dispensed with. As in Figure 1, BR can be energized via the flow switch, in the flow position.

provided contact CR2 is closed; and once BR is energized, contact BR2 closes to provide a supply path to BR alternative to the supply path via the flow switch. In series with contacts BR2 and CR2 is a diode D9. In series with relay DR is a diode D10. D9, CR2 and BR are in parallel with D10 and DR. In parallel with DR is a smoothing capacitor. Diode D9 acts to prevent current being supplied to relay DR via the flow switch, so that current must be supplied by the alternative pathway mentioned above, containing contact BR2. Thus DR is under the control of relay BR. Diode D10 acts to prevent the capacitor influencing the operation of the rest of the circuit.

In Figures 1 - 4, the commons of the relay contacts AR1 and CR1 are indicated by a hollow circle.

Figure 5A shows in side view a mounting unit for the control part of the circuitry. Also shown is the side panel 24 of a gas fire. The mounting unit is mounted flush to the panel 24 with top and bottom flanges of the mounting unit, 26 and 28 respectively, against the outer surface of the panel. The unit carries a printed circuit board 30 on which the control part (not shown) is located. The top end of the printed circuit board is located within a slot in an end plate 32 perpendicular to the flange 26 and the lower end of the printed circuit board is screwed to a plate 34 which is parallel to the flange 28. Between the plates 34 and the flange 28 there is a projecting part 36. Between the flange 28 and the projecting part 36 there is a recess of size to snugly receive the panel of the gas fire.

Between that part 36 and the plate 34 is a wider recess.

The flange 28 extends to a lower position than the ends of the parts 34 and 36.

When it is required to inspect the control part the screw connecting the flange 26 and the panel 24 is removed. The unit is then lifted slightly so that the panel is no longer located in the space between the flange 28 and the part 36, the unit is tilted and the panel is located in the recess between the part 34 and the part 36, such that the unit tilts at a substantial angle to the vertical, to allow access to the circuitry (Fig. 5B).

The reader's attention is directed to all papers and documents which are filed concurrently with this specification, and which are open to public inspection with this specification and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in the specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. Control and supply circuitry for a forced flue gas appliance, the appliance being associated with a gas supply valve and a means for drawing exhaust gases through a flue, the circuitry comprising: start-up switching means under the control of a user; a timing means; flow-sensitive switching means which is sensitive to flow in the flue and which has a "no flow" condition and a "flow" condition; wherein the flow-sensitive switching means, in its "no flow" condition, and when the start-up switching means is "on", (1) enables a control signal to be delivered to a switching means A, whereby switching means A is in a -enabling condition enabling voltage supply to the means for drawing exhaust gases, and (2) enables a control signal to be delivered to the timing means which then activates a switching means C which enables a control signal to be delivered to the flow-sensitive switching means notwithstanding that the start-up switching means may thereafter be released, the flow-sensitive switching means, in its "flow" condition, isolating the switching means A from a control signal and enabling a control signal to be delivered to a switching means B which, provided the switching means C is and remains activated, causes voltage to be supplied to the means for drawing exhaust gases and the gas valve to be "on", the timing means de-activating the switching means C if it receives a control signal from the flowsensitive switching means for longer than the predetermined interval.

2. Circuitry as claimed in Claim 1, wherein the circuitry comprises a supply part and a DC control part, the parts being linked by a transformer, the output from the transformer to the control circuit being rectified to provide the DC supply.

3. Circuitry as claimed in Claim 1 or 2, wherein the means for drawing exhaust gases enables exhaust gases to be drawn through the flue at two or more alternative rates.

4. Circuitry as claimed in Claim 1, 2 or 3, wherein the means for drawing exhaust gases is a fan, the circuitry comprising more than one supply path to the fan, one supply path having a component across which part of the supply voltage is dropped, whereby the fan may be made to operate at more than one speed.

5. Circuitry as claimed in Claim 4, in which the component across which part of the supply voltage is dropped is a reactance.

6. Circuitry as claimed in any preceding Claim in which an LED is used to indicate when power is available for starting up.

7. Circuitry as claimed in any preceding Claim wherein the switching means are constituted by relays.

8. Circuitry as claimed in any preceding Claim, wherein the switching means A, when in its start-up condition, enables higher voltage supply to the means for drawing exhaust gases and the switching means B, when closed, enables lower voltage supply to the means for drawing exhaust gases.

9. Circuitry as claimed in any preceding Claim, wherein the switching means B is in series with a contact of the switching means C and with a thyristor whose gate receives an activating signal once the flow-sensitive switching means switches to its "flow" condition.

10. Circuitry as claimed in any preceding Claim, wherein a diode is located upstream of the flow-sensitive switching means, such that the initial control signal delivered to the timing means must be via the flowsensitive switching means, but such as to permit a control signal to be delivered to the timing means other than via the flow-sensitive switching means once the switching means C has been actuated.

11. Circuitry as claimed in any preceding Claim, wherein a diode is located such that when the flowsensitive switching means is in its "flow" condition no control signal can be delivered to the switching means A.

12. Control and supply circuitry for a forced flue gas appliance, comprising a thermocouple for location in or adjacent to the main gas flame or a pilot flame therefor, a gas supply valve for the appliance being under the control of the thermocouple and the thermocouple circuit being breakable by the circuitry to effect closure of the valve.

13. Control and supply circuitry as claimed in Claim 12, in association with control and supply circuitry as claimed in any of Claims 1 to 10.

14. Control and supply circuitry as claimed in Claim 13, wherein the thermocouple circuit is breakable by switching means which is under the control of the switching means B.

15. Circuitry substantially as described herein, with reference to the accompanying drawings.

16. A method of controlling a forced flue gas appliance by using control and supply circuitry as claimed in any of Claims 1 to 15 above.

17. A forced flue gas appliance under the control of control and supply circuitry as claimed in any of Claims 1 to 15.

18. A mounting unit for control and supply circuitry, the mounting unit being substantially as described with reference to Fig. 4.

19. Control and supply circuitry for a forced flue gas appliance, the appliance being associated with a gas supply valve and a means for drawing exhaust gases through a flue, the circuitry comprising: start-up switching means which is under the control of a user; a further switching means which is sensitive to flow in the flue and which has a "no flow" condition which causes the means for drawing exhaust gases to be switched on upon the operation of the start up switching means, and a "flow" condition which permits the means for drawing exhaust gases to continue running and causes the gas supply valve to be switched on; and a timing means which causes the means for drawing exhaust gases and the gas supply valve to be switched off after a predetermined interval should the flow switch remain in or return to its "no flow" condition for this interval.