US2816605A - Control means for gas or liquid fuel fired burners - Google Patents

Description

Dec. 17, 1957 J. R. SEVILLE ONTROL MEANS 'FOR GAS OR LIQUID FUEL FIRED BURNERS Filed Jan. 25, 1955 @1252 6 due United States Patent@ CONTROL MEANS FOR GAS ORLL'IQUID FUEL FIRED vBURNERS John Richard Seville, i/Vaterfoot, Rossendala'England assrlgnor to S pooner Food Machinery Engineering Company Limited, Ii-kley, England, a British company Application January 25,, 1955, #Serial No. 483,897

Claims priority, application Great Britain February 1 8, 1954 3 Claims. (Cl. 158-28) This invention relates to .the automatic control "of 'gas or liquid fuel fired furnaces for baking or drying ovens or the like, having a burner or system of burners, which having been lighted at the beginning of the firing zperiod, alternates between a high flame and .a 'low flame according to the heat requirements of the oven, which is fitted'with a thermostat for controlling means to regulate the 'fuel supply.

The invention 'has for an object to ensure that the burner can only be lighted up on low flam-e and that fuel at the high flame rate cannot he passed to the burner until the flame is established.

According tothe invention, the fuel is fed to thefburner or burners through an electrically operated cut-01f valve and through a motor driVen valve :for high/low flame regulation, and nneans :are provided whereby when the flame is extinguished by turning off the fuel or otherwise, the motorised valve immediately begins to move :to its low flame position, and the burner cannot be relighted until the valve has reached the limit of its travel in this direction.

The motorised valve, which is designed to come to rest in either the open or closed position, is provided with an adjustable stop so adjusted that when :its operating lever moves towards the closed position, the valve .is (held open sufl'iciently to maintain a low flame of the desired size.

Preferably a flame-detecting device is arranged to 'deenergise a relay when the flame is extinguished, the relay when de-energised closing contacts which sHPp y current to the valve motor to drive it for closing the valve.

One convenient arrangement .in accordance with the invention is illustrated in the accompanying circuit'diagra n The diagram shows a gas fired burner control which comprises a purging relay A, an ignition relay -B, and a flame signal operated relay C. A regulating thermostat D .is shown as a changeover switch in "which the centre contact makes on to the ,left hand contact when the high flame is called for, and changes over to the right [hand contact when the oven is up to vtemperature, and the burner requires to .be turned down to low flame.

A motor :E drives a switch-operating cam and a disc 11 having a crank-pin 12 connected by a link 13 to a lever 14 for operating a high/low flame valve20. One side of the motor E is connected rby-a wire 6 to the main supply terminal 2, and .the other side is connected to the control circuit by contact arm 43,-contact36 and wire 5 or by arm 44., contact '37 and wire 7 according to the :position of the cam It]. The wires 8 and 9 from the control circuit are connected to a limit switch which closes as shown when the valve lever 14 has reached the full extent of its travel in "the low flame direction.

Whena suit'abl'e supply is connected to terminals 1 and 2 and the current switched on by a switch Which may be associated a circulating fan for "circulating gases forming the heating medium "through 'the ovens or the like, a circuit is completed through the operating coil 17 2 contacts C1 on the relay C. The relay A is designed to pull in after a purging period of 30-40 seconds, and is thereafter maintained in its operated position by means of its upper pair A1 of normally open contacts and wire 39 regardless of theconditionof the'flame relay C.

Current now flows through the centre pair A2 of normally open contacts on relay A and wire 8 to the limit switch contact 19, which is coupled with the arm 44, and-providing the motor E has moved the valve 2% fully over to its low flame p0sition-via the limit switch contact 21 and wire 9 to the .ignition pushbutton F.

Pressing the ignition ,pushbutton F now pulls in the ignition relay B which, through its lower pair B2 of normally open contacts and wire .22, energ'ises the electrically operated gas cut-off valve G connected to terminals 3 and 4 thereby allowing gas to .pass to the burner via the cutofl valve G, fuel supply line .23 and the high/ low flame valve 20at the low flame rate.

In .the example shown electric ignition is provided, and the ignition transformer H is energised through the upper pair B1 of contacts on .the relay B and wire 24. Alternatively ignition may be by gas torch or pilot flame in which case the flame will have been lighted and inserted into the combustion chamber before pressing the ignition pushbutton.

As soon as the flame is established the flame switch I or other flame sensitive element becomes conductive and allows current to pass by way of wire 25, switch arm 26, contact 27 and wire 28 to the actuating coil of the flame relay C thereby causing the relay to pull in. The establishment of the flame is indicated by the extinction of the no flame warning light 15 which is fed through the normally closed contacts C2, wire '29, transformer T and wire 30. The ignition pushbutton F is now released, .but the electrically opened gas cut-off valve G is held open by current passing through the normally open contacts C4 and wire 31. Current also passes via the upper terminal of the changeover contacts C3 and wire 32 to the center terminal 33 of the thermostatic switch D. The other terminals 34,, 35 of the switch D are connected to the wires '5 and 7 leading to the motor IE, for causing the motor driven Lhigh/ lowflame valve 2'0 'to assume either its high flame or low flame position according to the temperature of the oven. If, when the valve is 'in the low flame position as shown, the switch D connects with the wire 5, the motor B will run until the valve lever 14 reaches the high flame position when the cam 10 after turning half a revolution will open the contacts 36 in the wire '5 so as to stop the motor. At the same time the contacts 37 con nected to the wire '7 close so that when the switch D changes its position the motor B will again run in the same direction to move the valve lever 14 back to the low flame position, when the cam 10 after turning a further half revolution will open the contacts 36 connected to wire 7 to stop the motor. The burner will now operate normally, alternating between high flame and 'low flame according to the heat requirements of the oven as interpreted by the thermostat.

When the flame is extinguished by turning off the gas (or due to gas failure or instability of the flame) the flame sensitive element I immediately interrupts .the 'flow of current to the flame-relay C thereby causing it to drop out. This'closes thegas'cut-otf va'lve G ('by opening C4) and illuminates the no flame warning light 15 (by closing C2"). C3 changes 'over to its lower contact there- I by connecting'supply'terminal 1 to contact 35 through wire of the relay A via wire 1% and a pair of nonnally closed 38 and over-riding the thermostat D and causing the motorised valve 20 to move'to the low flame position if it is not already *inthatposition. Contacts 'CS may be used to give an audible or other additional warning of flame failure.

Before an attempt to re-lig'ht the burner can be made,

the motor E must have driven the valve lever 14 to the end of its travel in the low flame direction and have closed the limit switch contacts 18, 21 between wires 8 and 9 to allow current to flow from contacts A2 to the ignition pushbutton F. Thus the burner can only be lighted on low flame, and gas at the high flame rate cannot be caused to pass to the burner until the flame relay C pulls in, i. e. until the burner is alight.

Interruption of the electricity supply to the control unit (due to stopping the circulating fan or interruption or failure of the supply current) causes the electrically opened gas cut-off valve G to close immediately. It also allows the purge relay A and the flame relay C to drop out, thereby re-setting the control circuit. When the supply is restored (or the circulating fan re-started) the motor driven high/low flame valve 20, if it is not already in the low flame position, immediately begins to move over to this position, completing its excursion in about thirty seconds, i. e. within the delay period provided for by the purging relay A. At the conclusion of the purging period (which is signalled by the green indicator light J) the limit switch to which wires 8 and 9 are connected has therefore already closed, and pressing the ignition pushbutton F causes the gas cut-off valve G to open and allows gas to pass to the burner at the low flame rate as already described.

The normally closed contacts C1 on the flame relay C serve to impose a check on the correct operation of the flame responsive element I and its associated switch or amplifier. If the flame relay C has failed to drop out, or if the flame switch or amplifier gives a false signal which causes the relay C to pull in during the 40 seconds purge period, the relay A will not operate, and the indicator I, which is connected in series with the wire 40, contacts A3, wire 42, transformer T and wire 41, will not therefore give the normal running signal. This circuit check is applied automatically each time the oven is started up.

If desired, the motor E may be replaced by a reversible motor which will run in the valve opening or closing direction according to the position of the switch D, limit switches being provided to stop the motor at the end of the travel of the valve operating means.

The circuit may be modified to include additional safety or limit switches, for example an air flow switch or a door actuated switch as described in British patent specification No. 728,302.

While in the example given gas has been referred to as the fuel in use, it is to be understood that the invention may be applied with equal facility to oil fired burners.

What I claim is:

1. Automatic control means for a gas or liquid fired burner, comprising a fuel supply line for the burner, 21 valve in the fuel supply line for high/ low flame regulation, a first circuit means including a motor for driving said valve from the low to the high position and vice versa, flame-detecting means, a second circuit means including a flame relay having a coil connected to said flame detecting means and a plurality of contacts operated thereby, which coil is energised by the flame-detecting means when the burner is alight, a third circuit means including contacts of the flame relay which close when said relay coil is de-energised owing to absence of flame to supply current via said first circuit means to said motor to cause it to drive said valve to the low flame position, if not already in that position, a fourth circuit means including electrically operated ignition means, a fifth circuit means in cluding an electrically operated cut-off valve in said fuel supply line, a sixth circuit means including an ignition relay having a coil and a plurality of contacts operated thereby, and a manually operable switch for supplying current to energise the ignition relay coil, said fourth circuit means also including contacts of the ignition relay adapted when the relay coil is energised to supply current to the ignition means and said fifth circuit means also ineluding contacts of said ignition relay adapted when the relay is energised to supply current to open the cut-off valve, said sixth circuit means also including contacts, in series with the ignition relay coil, operated by said motor, said last mentioned contacts being closed to allow the ignition relay to be energised only when said valve is in the low flame position, terminals adapted for connection to a source of electric power, and conductors leading from said terminals to all of said circuit means.

2. Automatic control means for a gas or liquid fired burner, comprising a fuel supply line for the burner, a valve in the fuel supply line for high/low flame regulation, a motor for driving said valve from the low flame position to the high flame position and vice versa, flamedetecting means, a first circuit means including a flamerelay having a coil connected to said flame detecting means and a plurality of contacts operated thereby, which coil is energized by the flame-detecting means when the burner is alight, a first motor feed circuit means including a thermostatically operated two-way switch and contacts of the flame relay for supplying current to said twoway switch when said relay is energised, said two-way switch being connected to the motor to supply current to cause it to drive the valve to the high or low flame position according to heat requirements, a second motor feed circuit means including further contacts of the flame relay which close when said relay is de-energised owing to absence of flame to supply current direct to the motor to cause it to drive the valve to the low flame position, if not already in that position, and a cam driven by the valve-driving motor, said first motor feed circuit means also including two pairs of contacts respectively connected in series with the contacts of the thermostatically operated two-way switch and actuated by the cam, one pair of contacts being opened and the other being closed in each of the high and low positions of the valve, so that when the thermostatic switch causes the motor to drive in one direction, the cam opens the corresponding contact and stops the motor when the valve reaches the required poistion, terminals adapted for connection to a source of power, and conductors leading from said terminals to all of said circuit means.

3. Automatic control means for a gas or liquid fired burner comprising a fuel supply line for the burner, a valve in the fuel supply line for high/low flame regulation, a motor for driving said valve from the low flame position to the high flame position and vice versa, a cam driven by said motor, first contacts operated by said cam so that they are opened only when the cam is in the position corresponding to the low flame position of said valve, second contacts operated by said cam so that they are opened only when the cam is in the position corresponding to the high flame position of said valve, a thermostatically operated switch having a first change over contact which is made only when the thermostat temperature is below a predetermined temperature and a second change over contact which is made only when the thermostatically operated switch temperature is above the predetermined temperature, a flame detecting means, a first circuit means including a flame relay having a coil connected to said flame detecting means and a plurality of contacts operated thereby, which coil is energised by the flame-detecting means when the burner is alight, a first motor feed circuit means including contacts of said flame relay which are closed when said relay is operated, and including said first changeover contact of said thermostatically operated switch, said second cam operated contacts and said motor to supply current to cause said motor to drive said valve to the high flame position when the flame is present and the predetermined temperature is not exceeded, a second motor feed circuit including said same contact of said flame relay, said second changeover contact of said thermostatically controlled switch, said first cam operated contacts and said motor to supply current to cause said motor to drive said valve to the References Cited in the file of this patent UNITED STATES PATENTS Burns Nov. 22, 1932 Kuempel Mar. 9, 1937 Denison Apr. 13, 1937

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