US3583842A

US3583842A - Burner control unit

Info

Publication number: US3583842A
Application number: US805631A
Authority: US
Inventors: Roger A Hancock; David J Moppett
Original assignee: Gas Council
Current assignee: Gas Council; British Gas PLC
Priority date: 1968-03-12
Filing date: 1969-03-10
Publication date: 1971-06-08
Anticipated expiration: 1988-06-08
Also published as: GB1250161A; DE1912622A1; NL161579C; NL6903839A; CH514813A; DE1912622B2; BE729693A; NL161579B; AT292263B; FR2003726A1

Abstract

Control apparatus for a burner installation including two shutoff valves in a line for supplying fuel to the burner, which comprises means for testing the effective closure of each of the valves by applying a source of suction pressure to the volume in the fuel line between the valves and checking by pressure sensing means that the reduction of the pressure in the volume is consistent with the two valves being closed.

Description

United States Patent Inventors Roger A. Hancock;

David J. Moppett, both of Solihull, England Appl. N0v 805,631 Filed Patented Assignee Mar. 10, 1969 June 8, 1971 The Gas Council London, England Priority Mar. 12, 1968 Great Britain BURNER CONTROL UNIT 26 Claims, 5 Drawing Figs.

US. Cl

References Cited UNITED STATES PATENTS 2,707,390 5/1955 Beretish 73/46 3,358,732 12/1967 Stuart 431/22 FOREIGN PATENTS 603,423 8/1960 Canada 431/16 Primary Examiner-Carroll B. Dority, Jr. Attorney-Kemon, Palmer and Estabrook ABSTRACT: Control apparatus for a burner installation in cluding two shutoff valves in a line for supplying fuel to the burner, which comprises means for testing the effective closure of each of the valves by applying a source of suction pressure to the volume in the fuel line between the valves and checking by pressure sensing means that the reduction of the pressure in the volume is consistent with the two valves being closed.

1 0 15 13 I X I X 1 PATENTEU JUN 8:911 3,583,842

sum 1 OF 4 PATENTEU-JUN 81971 3.583842 SHEET $.UF 4

K2 I 27 H} Tami" 57 T1204 RELAY] L9 (:4 K J 7 STOP i 22%;

c3 W H M Z5 87 L/VE E 1 1 2 NEUTRAL 7724 74 g Qw -29 P83 K A ,+F-q 3 PRESSURE EN I we s [4 T82 84 swag ecu B W187 0 M W Z5 LIVE NEUTRAL Q I v fz wm/b inf "I v 04 3,, 9 A am m BURNER CONTROL UNIT This invention relates to apparatus, generally known as a burner control unit, for automatically controlling a burner installation.

The present invention consists in apparatus for automatically controlling a burner installation having fuel shutoff means in a line for supplying fuel to the burner comprising means for testing the effectivenessof the closure of the fuel shutoff means, means for initiating each of the steps necessary for starting up and/or shutting down the burner in time ordered sequence and including the actuation of the testing means prior to the opening of the fuel shutoff means and/or after its closure.

The present invention provides combined apparatus for controlling the burner control and testing the fuel valves.

The fuel shutoff means may comprise two ,fuel shutoff valves in series in the line for supplying fuel to the burner and the means for testing the effectiveness of the closure of the fuel shutoff means comprises means for testing the effective closure of each of the fuel valves.

The fuel valves may each be in the form ofa slide, gate or, sluice valve, or they may be a disc-on-seat type of valve, a rotary cock type or any other type of valve. The fuel valves may be combined in a single unit in which two sets ofsealing means are provided between the movable member of the valve and the seat, the arrangement being such that when closed the two sets of sealing means define between them a volume which is utilized by the apparatus according to the invention as will be described hereinafter.

This invention relates to apparatus, generally known .as a burner control unit, for automatically controlling a burner installation.

The present invention consists in apparatus for automatically controlling a burner installation having fuel shutoff means in a line for supplying fuel to the burner comprising means for testing the effectiveness of the closure of the fuel shutoff means, means for initiating each of the steps necessary for starting up and/or shutting down the burner in time ordered sequence and including the actuation of the testing means prior to the opening of the fuel shutoff means and/or after its closure.

The present invention provides combined apparatus for controlling the burner control and testing the fuel'valves.

The fuel shutoff means may comprise No fuel shutoff valves in series in the line for supplying fuel to the burner and the means for testing the effectiveness of the closure of the fuel shutoff means comprises means for testing the effective closure of each of the fuel valves.

The fuel valves may each be in the form ofa slide, gate or, sluice valve, or they may be a disc-on-seat type of valve, a rotary cock type or any other type of valve. The fuel valves may be combined in a single unit in which two sets of sealing means are provided between the movable member of the valve and the seat, the arrangement being such that when closed the two sets of sealing means define between them a volume which is utilized by the apparatus according to the invention as will be described hereinafter.

Embodiments of the inventionwill now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a diagram of part of a burner installation comprising testing apparatus included in the apparatus accordingto the invention for automatically controlling the burner installation;

FIG. 2 is a schematic circuit diagram of one form of apparatus for automatically controlling a burner installation according to the invention;

FIG. 2a is a continuation of the diagram ofFlG. 2;

FIG. 3 is a schematic circuit diagram ofa modified form of the apparatus having a circuit diagram according to FIGS. 2 and 2a; and

FIG. 3a is a continuation of the diagram of FIG. 3.

In FIG. 1, a fuel supply line 10 to a burner 11 is controlled by two

fuel valves

12 and 13 in series. Air is supplied to the burner 11 under pressure through line 14. For safety it is necessary to prove periodically that when the

fuel valves

12 and 13 are in the shutoff position, they are both effectively closed. This is done by subjecting the volume 15 between the

fuel valves

12 and 13 to suction pressure and confirming that the resulting pressure conditions in the volume are consistent with the fuel valves being closed.

Testing apparatus for this purpose added to the basic burner installation so far described is included in FIG. 1. The suction side of an ejector 17 is connected through a stop valve 18 and a restricting orifice 19 to the volume 15. The main flow of air for operating the ejector 17 is in this example, provided from the air supply line 14 through a branch pipe 20 including a stop valve 21. The stop valve 21 is not essential to the valve testing procedure but its presence enables the ejector 17 to be shut off when not required and so removes a source of noise which could be objectionable.

A pressure sensitive switch 6 whose contacts are closed except when it is subjected to a predetermined subatmospheric pressure is alsoconnected to the volume 15. The design of some burners to which this testing apparatus might be applied is such that quite large subatmospheric pressures would be created in the fuel supply line 10. Such pressures will occur not only when the burner is operative but also under test conditions while the

fuel valves

12 and 13 are closed but air is flowing to the burner through air supply line 14 to operate the ejector 17. To prevent the testing apparatus from indicating a safe condition when a suction leak through valve 13 exists, the predetermined subatmospheric pressure at which the pressure sensitive switch 6 is actuated must be greater than any subatmospheric pressure occurring in the fuel supply line 10 downstream of valve 13. This requirement should be met even though suction pressure for the testing apparatus is not derived from the air supply line 14 since'the test procedure will usually be carried out while the burner is being purged with air. This testing apparatus has the necessary provisions for carrying out two methods of confirming that the

valves

12 and 13 are effectively closed.

ln the first'method ofconfirmation the volume 15 starts substantially at atmospheric pressure. The

stop valves

18 and 21 are opened and the ejector applies suction to the volume 15. The size of the orifice 19 is such that a significant time interval elapses between the opening of the stop valve 21 and the opening of the pressure sensitive switch 6 at the predetermined subatmospheric pressure. A check is made after a predetermined time interval that the pressure sensitive switch 0 has opened.

If the second method of confirmation is also to start from the condition in which the volume 15 is substantially at atmospheric pressure, the

stop valves

18 and 21 are opened and the pressure in the volume 15 reduced just below that at which the pressure sensitive switch 6 opens. The stop valve 18 is then automatically or manually closed and a check made after a predetermined time interval that the pressure sensitive switch 6 has not closed again and therefore that the pressure in the volume 15 has not risen above the predetermined pressure.

If only the second method of confirmation is to be employed the orifice 19 need not be provided. The provision of both stop valve 18 and orifice 19, however, enables the two methods of confirmation to be combined. lmmediately after the opening of the pressure sensitive switch 6 at the end of the first method of confirmation the stop valve 18 is closed so that the pressure in the volume 15 is only slightly less than that necessary to open .the pressure sensitive switch 6. A check is then made after a predetermined time interval, in accordance with the second method of confirmation, that the pressure sensitive switch 6 has not closed again and therefore that the pressure in the volume 15 has not risen above the predetermined pressure.

The time intervals in the first. second and combined methods of confirmation may be checked by personal observation but this is preferably done automatically by means which includes a timing device and which is used in the absence of correct conditions, to operate an alarm and prevent the initiation of. or stop, a burner control run.

From the start at time T of a burner ignition sequence the first period T is usually one in which air alone is allowed to flow to the burner. This is known as the prepurge period. In the installation of FIG. 1 this air flows through line 14 and as this flow enables the ejector 17 to be energized while the

fuel valves

12 and 13 are closed, the prepurge period T provides a convenient occasion for carrying out the testing procedure.

The circuit diagram of FIG. 2 is for apparatus for automatically controlling a burner installation including pilot and main burners, two safety shutoff fuel valves in series being provided in the fuel supply line to each burner.

The apparatus according to the invention comprises combined burner control and fuel valve testing apparatus. For simplicity FIGS. 2 and 2a show the circuit of the valve testing apparatus for the main valve only. The equivalent circuit for the pilot valve is a repetition of the diagram of FIG. 2a and the addition of two further pairs of contacts in the remainder of the circuit shown in FIG. 2 as will be described later.

Reference numerals

22 and 23 indicate the live and neutral lines through which electric power is supplied to the various components of the combined apparatus.

A relay L/ll is connected to the

lines

22, 23 by a start switch S and an interlock circuit 85 through which there must be electrical continuity before the start switch S can operate the relay L/ll. Details of the interlock circuit will be described later. The relay L/11 has a total of eleven pairs of contacts of which seven L2, L3, L6, L8, L9, L and L11 are normally open and four L1, L4, L5, and L7, are normally closed.

Timing of the burner control and valve testing sequence is by a cam timer having a synchronous motor SM which drives a set of cams actuating pairs of contacts C1 to C4, C6 to C10 and C12 to C16 defining periods in the sequence. The conventional designations for the time intervals in the burner control period, which are used in this specification and are indicated on the drawing, together with typical durations for the present apparatus are as follows:

At the end of T the cam timer is back at the T position. T the air set down period is a period for adjusting the air flow from the maximum flow used during the prepurge period to a reduced flow for ignition. In the present example the period T is not used but it may readily be provided if required. It has been introduced so that the designations of the time intervals are consistent with those which would be used in apparatus requiring a setdown period.

Testing the fuel safety shutoff valves is effected during the prepurge period T and the post purge period T For testing purposes these periods are subdivided as follows:

Period Description Approximate Duration TH Period for reducing pressure in the 2 seconds volume defined between the two shut-off valves in series Tm Period for testing that the prel/2 second determined pressure has been reached Tm Waiting period at reduced pressure 20 seconds TH Period for testing that the prel/2 second determined pressure in the volume has been maintained during T T 5 The remainder of the pre-purge period Tm Post-purge period for reducing pressure 2 seconds in the volume TH: Postpurge period for testing that the H2 second pre-determined pressure has been reached T Post-purge waiting period at reduced 20 seconds pressure TM Postpurge period for testing that the 1/2 second pre-determined pressure in the volume has been maintained during TRIP T The remainder of the post-purge period The individual pairs of contacts of the cam timer are closed as follows:

These periods of closure are indicated in the drawing against the individual contacts.

The circuit connecting the motor SM to the supply includes a line 25 in series with two

branches

28, 29 in parallel. Branch 28 comprises relay contacts L1 and cam timer contacts C1 in series, and in branch 29 relay contacts L2 and cam timer contacts C2 are connected in series.

The

stop valves

18 and 21 of FIG. 1, for the purposes of the present apparatus, are solenoid valves which are normally closed but are opened by energizing the solenoid means W. The solenoid means W is connected to the supply by a line in series with two

branches

81 and 82 in parallel. Branch 81 includes stop valve contacts C of the cam timer and normally open, relay contacts L3, in series. Branch 82 includes stop valve contacts C7 of the cam timer and normally closed relay contacts L5 in series.

A valve test alarm relay K/3 is connected to the supply through a pressure sensitive switch 6, of which only the contacts 6 are shown in the FIGS. 2a and 3a, the contacts 6 being connected in series with

parallel branches

83, 84. Branch 83 includes normally open relay contacts L9 and alarm contacts C4 of the cam timer in series. Branch 84 includes further alarm contacts C6 of the cam timer and normally closed relay contacts L4 connected in series.

The relay K/3 has three pairs of contacts K1, K2 which are normally open and isolating contacts R 3 which are normally closed. Contacts Kl when closed connect valve test alarm N to the electric supply. Contacts K2 are hold-on contacts and are connected in series with contacts Z1 of a pushbutton reset switch having two pairs of normally closed

contacts

21 and 22. When the relay K/3 has been actuated through contacts C4 or C6 and the pressure sensitive switch 6, it is maintained through the hold-on contacts K2 and reset switch contacts 21 until the reset switch is actuated manually to open the contacts Z1. Normally closed relay contacts K3 and normally closed reset switch contacts Z2 are connected in series in the interlock circuit 85. The reset contacts 22 are provided to prevent the dangerous practice of forcibly retaining the reset button in the reset position, by wedging for example.

A flame detector F/2 of suitable known type has a normally open pair of contacts F1 and a pair of normally closed contacts F2. A flame alarm relay J/3 is connected to the supply through normally open relay contacts L in series with

parallel branches

86, 87. Branch 86 includes normally open contacts F1 and flame detector contacts C of the cam timer, connected in series. Branch 87 includes normally closed contacts T 2 and flame detector contacts C16 of the cam timer. As the contacts F1 and'FZ are respectively normally open and normally closed, the flame alarm relay will be actuated if the contacts F1 are closed when contacts C15 of the cam timer are closed or the contacts F2 have not opened when the contacts C16 are closed. The contacts C15 and C16 are therefore timed to close at periods when there should be no flame or flame respectively. The relay .l/3 has two normally open pairs of contacts J1 and J2 and one normally closed pair of contacts J3. Contacts J1 when closed connect a flame alarm 88 to the electric supply. Contacts J2 are hold-on contacts and are connected in series with contacts R1 of a pushbutton reset switch having two pairs of normally closed contacts R1 and R2. When the flame alarm relay J/3 has been actuated through contacts C15 and F1 or C16 and F2 it is maintained through the hold-on contacts J2 and reset switch contacts R1 until the reset switch is actuated manually to open the contacts RI. Normally closed contacts J3 and reset contacts R2 are connected in series in the interlock circuit 85. The contacts R2 are provided for the same reason as the contacts Z2 to prevent abuse of the reset button.

An electric motor V driving the fan for the forced air supply to the burner is connected to the electric supply by a line 89 in series with two

parallel branches

90 and 91. The branch 90 includes normally open relay contacts L6 and fan contacts C8 of the cam timer, connected in series. The branch 91 includes fan contacts C9 of the cam timer and normally closed relay contacts L7 connected in series. The air supply line is provided with an air flow or air pressure switch A which is closed when the air flow or pressure is above a predetermined value. The air pressure switch A is connected in series in the interlock circuit 85. Contacts C10 of the cam timer are connected in parallel with the series connected air pressure switch A and hold-on contacts L8.

The interlock circuit 85 in series between the start switch S and the relay L/11 comprises, all connected in series, the air pressure switch A, reset contacts R2 and Z2'relay contacts J3 and K3 and hold-on contacts L8. As the air pressure switch A and the hold-on contacts L8 are open at the start condition T they are short circuited at that time by the contacts C10 ofthc cam timer. For a successful start therefore on closing start switch S all the contacts R2, J3, Z2, and K3 must be closed before the relay L/11 can be energized. After period T all these contacts and additionally air pressure switch A and hold-on contacts L8 must remain closed.

Contacts equivalent to contacts K3 and 22 in the pilot burner test apparatus would in practice also be provided. These would be connected in series in the interlock circuit 85 at point X and would also have to be in the closed position at the start and to remain closed thereafter in a successful start, run and shut-down sequence.

Relay contacts L11 when closed makes the power supply available to circuits for electrical ignition apparatus 1, the solenoid means P for the pilot fuel shutoff valves and solenoid means M for the main fuel shutoff valves. Cam timer contacts C12 in series with the ignition apparatus 1, C13 in series with solenoid means P and C14 in series with solenoid means M control the application of the power supply to these components at the relevant times.

The full sequence of a successful burner control run is as follows:

The start switch S is closed manually and as cam timer contacts C10 are closed during T provided that contacts R2, J3, Z2 and K3 are all closed relay L/11 is energized. Relay contacts L6 close and as contacts C8 are closed during T the fan V starts for the prepurge. Relay contacts L10 also close and as contacts C15 are closed during T and T the flame detector contacts Fl must not close, that is there must be no flame simulation, or the flame alarm relay J/3 will be energized. Relay contacts L2 close starting the cam timer motor SM as contacts C2 are closed during T At the end of period T, contacts C10 open but relay L/ll is maintained through pressure switch A and contacts L8. Since contacts L3 were closed on actuation of the relay L/11, when contacts C3 close at the beginning of period T the solenoid means W is energized to open the stop valves and apply suction pressure to the volume between the two fuel shut-off valves. Contacts C3 remain closed for period T defining a first predetermined time interval for the application of suction pressure to the volume. At the end of T contacts C3 reopen causing the stop valves to close, isolating the volume which by the end of period T should be at a subatmospheric pressure sufficient to actuate the pressure sensitive switch 6 and open its contacts.

Relay contacts L9 are closed and for a short period T contacts C4 close and provided that the pressure sensitive switch 6 has opened indicating that the predetermined suction pressure in the volume has been reached, the relay K/3 will not operate. No change of contacts occurs during T which constitutes a second predetermined time interval for proving that the fuel valves are maintaining the suction pressure in the volume between them. For a short period T the contacts C4 again close and provided that the pressure sensitive switch 6 is still held open the relay K/3 will again not operate. Alternatively the cam timer could be modified to close contacts C4 for the whole of the periods T T and T At the beginning of period T cam timer contacts C12 close to energize the electrical spark ignition apparatus I. Cam timer contacts C13 also close to energize solenoid means P and open the fuel shutoff valves for the pilot burner. The pilot burner lights and at the beginning of T the cam timer contacts C16 close. Provided that there is a flame at the pilot burner the flame detector contacts F2 will be open and the flame alarm relay 1/3 will not be actuated.

At the beginning of period T cam timer contacts C close and the solenoid means M is energized to open the fuel shutoff valves for the main burner. The pilot burner lights the main burner. At the end of period T the contacts C open, the fuel valves for the pilot burner close and the pilot flame goes out. The main flame is proved during period T At the end of period T contacts C open and the cam timer motor SM stops.

The main run period T, of indefinite length follows. During that period contact C16 remain closed so that the flame detector contacts 1 2 are in circuit with the relay 1/3 but provided they remain open the flame alarm relay J/3 will not be actuated.

When the burner is to be shut down, the switch S is opened manually. This deenergizes the relay L/1l which opens contacts L11 thus deenergizing solenoid means M and closing the main fuel shutoff valves: it also allows relay contacts L1, L4, L5 and L7 to close. Cam timer contacts C remained closed while the cam timer was at rest during period T, and closure of contacts L1 restarts the cam timer motor SM. This marks the beginning of the postpurge period T The fan V energized through branch while the relay L/11 was energized is kept running through branch 91 by the reclosing of the contacts L7. Cam timer contacts C and C are both closed during period T, and contacts C remain closed during period T Closure of relay contacts [4 and I5 bring cam timer contacts C and C, into circuit with the pressure test alarm relay K/3 and stop valve solenoid means W respectively. A test sequence similar to that performed during periods T to T is carried out during periods T to T, under the control of the cam timer contacts C6 and C7. At the end of period T cam timer contacts Cl open and the cam timer stops in the T position. Similarly cam timer contacts C open and the fan driving motor V stops.

The above described successful sequence may fail upon any one of several contingencies.

On closing the start switch S if either of the reset contacts R2 and 22 are open or there is already a flame indication or valve test alarm condition so that contacts 13 or R3 are open, the relay L/ll will not close and the sequence will not begin.

After relay Llll has operated, if the contacts F1 are closed at T or during T showing flame when there should be none, relay J/3 is operated, contacts J1 close to give the alarm, contacts J2 maintain the relay 1/3 in the operated condition and contacts 33 open breaking the circuit of relay L/ll which reopens.

Again, after relay L/ll has operated, if, from period T onwards, the fan fails, the pressure switch A opens and relay L/ll reopens.

If relay L/ll reopens, contacts [I close and the cum timer motor SM continues to run through the full sequence back to the T position where it stops due to the opening of contacts C]. A fuel valve test will be made during periods T to T because contacts t4 and K5 are closed. Similarly the fan motor V will be energized through contacts t7 until the cam timer reaches the T position.

If at T or T the contacts of pressure switch 6 are closed relay K/3 is operated. lts contacts K1 operate the valve test alarm N, contacts K2 maintain the relay K/3 and contacts K3 open so that relay L/ll reopens. The cam timer runs on as described in the previous paragraph but the second series of tests will not be indicated as the relay K/3 has already operated.

If during periods T to T there is no flame or the flame goes out the flame detector contacts F2 will close the relay 1/3 will be operated with the results previously described for a flame indication at T or during T,.

If during periods T or T the pressure switch 6 is closed, valve test alarm relay K/3 is operated as for the prepurge test at T or T and any attempt to restart the burner will be abortive until relay K/3 has been reset manually by use ofthe reset button to open contacts 21.

The method of retaining the alarm condition on relays K/3 and J/3 relies on electrically maintained relays. This can be undesirable since removal of the power either accidentally or deliberately from the control unit could cancel the alarm before corrective action has been taken. This defect can be over come by the use ofa mechanically-latching relay for this duty. This would require some form of mechanical or electrical reset to unlatch the relay. However, the reset contacts R2 and reset contacts 22 should still be manually operable.

The symbols used to refer to the main components of the apparatus are consistent with Boolean terminology in which the bar operator represents NOT, for example A represents NOT A.

The conditions under which the individual functions controlled by the apparatus will be performed can be expressed in the form of algebraic equations in which the elements are connected by symbols namely the addition symbol representing OR and the multiplication symbol x simplified to a dot representing AND. The symbols used for the inputs and outputs of the apparatus are:

INPUTS A Air supply interlock indicating air 0 Pressure switch indicating negative pressure S Start device in on' or start position R Flame alarm reset device in reset position Z Valve test reset device in reset position F Flame detector indicating flame OUTPUTS J Flame alarm energized K Test alarm energized M Main fuel valve energized P= Pilot fuel valve energized l= Ignition energized V Fan energized SM Cam timer operating ln Boolean terminology the apparatus illustrated in the diagram satisfies the following equations.

The above equations do not include the term T since it is not shown on the FIGURE accompanying this specification. However, if it is desirable to include a period T the term T, must be appropriately inserted into equations i, v and vi.

FIGS. 3 and 3a show a schematic circuit diagram of a modified form of the apparatus having the circuit diagram of FIGS. 2 and 2a. The modifications which are apparent in interlock circuit and in valve test alarm relay K/3 circuit, ensure that pressure sensitive switches A and O are in their appropriate states before the start-up cycle can commence.

A relay B/l is connected in series with the pressure sensitive switch 6 across the supply and in parallel with

branch circuits

83, 84 and the relay K/3. Relay B/l has one set of contacts B1.

lnterlock circuit 85 is modified in that it is provided with two, two branch parallel circuits in one branch of one ofwhich are cam timer contacts C10 while in the other branch are normally open contacts A of the air pressure switch. In one branch of the other parallel circuit are hold-on contacts L8 while in the other branch contacts B1 of relay B/l are connected in series with a further set of contacts A of the air pressure switch which are normally closed. These two parallel circuits are connected in series with start switch S and relay L/ll together with the remaining interlock circuit components, reset contacts R2, 22, relay contacts 33 and K3, across the supply.

In operation at time T the contacts of the air pressure switch should be in their appropriate normal states, that is, contacts A should be open and contacts A closed. As pressure sensitive switch contacts 6 should be closed at T relay B/l should be energized closing normally open contacts B1. Since cam timer contacts C10 are closed at T manual closing of start switch S should energize relay L/ll provided no alarm relays have been energized.

At the end of period T contacts C10 open, but as the air pressure should be at the predetermined value, relay L/ll is maintained through the closure of normally open contacts A and hold-on contacts L8.

If contacts O are open at time T relay 8/1 is not energized and contacts B1 are open so that operation of start switch S does not energize relay L/ll. Similarly if normally closed air pressure switch contacts A are open, relay L/ll cannot be energized.

To provide additional protection against false energization of one or more of the ignition apparatus I and the solenoid means P and M of the fuel shutoff valves, a modification of the circuits shown in FIGS. 2 and 3 could be made.

The modification comprises the provision of an extra pair of normally closed contacts on each of the valve test alarm relay K/3 and flame alarm relay 1/3. These contacts jand K are connected in series with contacts L11 of relay L/ll as shown in dotted outline on H05. 2 and 3. If either alarm relay is energized the associated contacts I, K, are opened and no energization of I, P or M can take place.

We claim:

1. An automatically controlled burner installation comprising a burner, a fuel supply line to said burner, two fuel shutoff valves connected in series in said line and defining between them an enclosure, means for testing the effectiveness of closure of said shutoff valves, and means for automatically controlling the operation of said burner, said means including a timing device, said timing device enabling said control means to control the operation of said burner in timed order, said control means causing the actuation of said testing means in a period in which the valves are closed, said testing means including a pressure sensor which can be put in fluid communication with said enclosure, and a source of suction applicable to said enclosure, and means for applying, during a test, said source of suction to said enclosure to reduce the pressure in said enclosure, a check being made after a predetermined time by said pressure sensor that the pressure conditions in said enclosure prove that said shutoff valves are closed.

2. A burner installation according to claim 1 wherein the pressure sensor comprises a pressure sensitive switch actuated when subjected to a predetermined reduced pressure.

3. A burner installation according to claim 2 and which includes an electrically operated valve test alarm, said timing device of said control means having alarm contacts operative in an alarm actuating circuit, the pressure sensitive switch also being included in the alarm actuating circuit the arrangement of which is such that the alarm will be operated upon the actuation of the alarm contacts of the timing device unless the pressure sensitive switch is in the actuated condition.

4. A burner installation according to claim 3 wherein said means for applying said source of suction to said enclosure comprises a restricting orifice and a stop valve between said enclosure and said source of suction and wherein means for operating the stop valve is electrically operated and the stop valve operating means includes in its circuit stop valve contacts of the timing device, which are so actuated that the stop valve is open for a first predetermined time interval timed by the timing device to open the source of suction to the enclosure and shut for a second predetermined time interval timed by the timing device, the alarm contacts of the timing device being actuated at the ends of both the first and second predetermined time intervals.

5. A burner installation according to claim 3 comprising isolating contacts operated on actuation of the alarm and included in an interlock circuit of the installation in a manner such as to prohibit, under alarm conditions, the initiation or continuation ofa burner control run.

6. A burner installation according to claim 3 wherein the alarm actuating circuit includes a relay and wherein means are provided for maintaining the alarm until cancelled by operation of reset means.

7. A burner installation according to claim 6 and comprising isolating contacts included in an interlock circuit of the apparatus in which the relay operates said isolating contacts in the interlock circuit.

8. A burner installation according to claim 6 in which the relay operates a pair of contacts connected in series in a circuit with the alarm.

9. A burner installation according to claim 6 and having an interlock circuit wherein the reset means operates isolating contacts included in the interlock circuit in series and operating in a manner such as to prohibit the initiation or continuation ofa burner control run unless the reset means is in the inoperative condition.

10. A burner installation according to claim 3 wherein means are provided for ensuring the return of the timing device to its starting position whenever the electrically operated alarm is actuated.

11. A burner installation according to claim 3 in which actuation of the testing means takes place prior to the opening of the fuel shutoff valves and also after the closure of said valves wherein there are provided circuits alternative to those operative for the testing sequence prior to opening the fuel valves, the timing device having a pair of contacts in each of the circuits and actuable to determine a period during which each of the alternative circuits is operative.

12. A burner installation according to claim 11 wherein there is provided in each of the alternative circuits a pair of isolating contacts operable so as to isolate one of the alternative circuits when the other is to be operative.

13. A burner installation according to claim 11 and including a stop valve operated by electrical means including a circuit having stop valve contacts of the timing device wherein there is connected across the contacts of the timing device in the stop valve operating circuit a further set of contacts of the timing device operating for the testing of fuel shutoff valves after the closure of said shutoff valves, said further set of contacts being so actuated that the stop valve is open for a first predetermined time interval timed by the timing device to open the source of suction pressure to the volume and shut for a second predetermined time interval by the timing device, said alarm contacts of said timing device being actuated at the ends of both the first and second predetermined time intervals.

14. A burner installation according to claim 13 wherein there is provided a set of isolating contacts in series with each of the pairs of contacts of the timing device, one set of isolating contacts being closed when the other set are open.

15. A burner installation according to claim 12 and having an interlock circuit including a relay, and alternative valve test alarm actuating circuits comprising isolating contacts wherein the isolating contacts are operated by said interlock circuit relay.

16. A burner installation according to claim 14 having an interlock circuit including a relay and a stop valve operated by one of two sets of stop valve contacts in parallel, each set being connected in series with a set of isolating contacts, wherein said isolating contacts are operated by the interlock circuit relay.

17. A burner installation according to claim 2 including an interlock circuit including a relay wherein the contacts of the pressure sensitive switch are connected across the supply in series with a relay which operates normally open contacts connected in series in the interlock circuit in parallel with hold on contacts operated by the interlock circuit relay.

18. A burner installation according to claim 6 having a valve test alarm actuating circuit which includes a relay wherein said relay operates normally closed contacts connected in series in any one of circuits controlling electrical ignition apparatus, pilot fuel shutoff valves and main fuel shutoff valves.

19 A burner installation according to claim 1 and including a flow restricting orifice between said enclosure and said source of suction, and a valve test alarm means, said control means rendering said alarm means operative after the elapse of a predetermined time interval timed by said timing device and commencing at the instant of said application of said source of suction to said enclosure unless said pressure sensor indicates that said shutoff valves are closed.

20. A burner installation according to claim 1 and including a valve test alarm means, said control means rendering said alarm means operative after the lapse of a predetermined time interval timed by said timing device and commencing after the termination of said application of said source of suction to said enclosure unless said pressure sensor indicates that said shutoff valves are closed.

21. A burner installation according to claim 14 wherein said control means renders said alarm means operative after the elapse of a further predetermined time interval timed by said timing device and commencing after the termination of said application of said source of suction to said enclosure unless said pressure sensor indicates that said shutoff valves are closed.

22. A burner installation according to claim 1 wherein said source of suction comprises an ejector, a supply of compressed air being connected to an inlet of said ejector, and a stop valve being connected in a line between said ejector and said enclosure.

23. A burner installation according to claim 22 wherein said supply of compressed air is that which supplies said burner with combustion air.

24. A burner installation comprising a fuel line, two shutoff valves connected in series in said fuel line and defining between them an enclosure, an air line for supplying air for combustion to the burner of said installation, suction means for reducing the pressure in said enclosure, said means comprising an ejector, an inlet for main flow fluid of said ejector being connected to said air line, means for isolating said enclosure from said ejector, and means for checking that the pressure conditions in the enclosure, after said suction means has reduced the pressure in the enclosure, prove that said shutoff valves are closed, said checking means comprising a pressure sensor connectable to said enclosure.

25. A burner installation according to claim 3 wherein said means for applying said source of suction to said enclosure includes a restricting orifice between said enclosure and said source of suction, said alarm contacts of said timing device being actuated after a predetermined time interval timed by the timing device and commencing upon the application of said source of suction to said enclosure.

26. A burner installation according to claim 2 wherein said means for applying said source of suction to said enclosure comprises a stop valve, electrical means for operating said stop valve including in its circuit stop valve contacts of the timing device actuable to open the stop valve for a period, sufficient to allow the source of suction to reduce the pressure in the enclosure to the predetermined reduced pressure, and then to close the stop valve at the start of the predetermined time interval, the alarm contacts being actuated after a predetermined time interval timed by the timing device and commencing upon the closure of the stop valve.

Claims

5. A burner installation according to claim 3 comprising isolating contacts operated on actuation of the alarm and included in an interlock circuit of the installation in a manner such as to prohibit, under alarm conditions, the initiation or continuation of a burner control run.

9. A burner installation according to claim 6 and having an interlock circuit wherein the reset means operates isolating contacts included in the interlock circuit in series and operating in a manner such as to prohibit the initiation or continuation of a burner control run unless the reset means is in the inoperative condition.

18. A burner installation according to claim 6 having a valve test alarm actuating circuit which includes a relay wherein said relay operates normally closed contacts connected in series in any one of circuits controlling electrical ignition apparatus, pilot fuel shutoff valves and main fuel shutoff valves. 19 A burner installation according to claim 1 and including a flow restricting orifice between said enclosure and said source of suction, and a valve test alarm means, said control means rendering said alarm means operative after the elapse of a predetermined time interval timed by said timing device and commencing at the instant of said application of said source of suction to said enclosure unless said pressure sensor indicates that said shutoff valves are closed.

20. A burner installation according to claim 1 and including a valve test alarm means, said control means rendering said alarm means operative after the lapse of a predetermined time interval timed by said timing device and commencing after the termination of said application of said source of suction to said enclosure unless said pressure sensor indicates that said shut-off valves are closed.