GB2150320A - Air valve control means on a two-stage oil or gas blower burner - Google Patents

Abstract

Using an automatic firing device (1) without a motorised program switch by making use of a single-wire control relay (24), and switches (21, 26, 27, 28, 29) actuated by the drive motor (22) for an air valve, and a no-voltage relay (19) being present in any case in an air valve drive means, a control circuit (4) provides a preliminary ventilation operation before each burner start-up and after a voltage failure during 7 operation with the air valve at least partially open. The air valve position is always the same both when starting the first burner stage and also after cutting out the second burner stage, since the valve is always brought to a halt in the partially open position by a movement in the closing direction. <IMAGE>

Description

SPECIFICATION Air valve control means on a two-stage oil or gas blower burner The invention relates to an air valve control means on a two-stage oil or gas blower burner.

The fact that two-stage burners are now being designed for use at the lower output end of the range means that there is a call for smaller and less expensive automatic firing equipment which also does not require motorised programmers, and which nonetheless can produce the signals required for the timed procedure for setting two burner stages in operation.

For the operation of single-stage or two-stage atomisation burners, there are automatic firing devices which generally include a thermal delay device and which can also be used (with certain limitations) in conjunction with air valve drive means, for those two-stage oil or gas blower burners for which positive preliminary ventilation is prescribed, prior to each cycle of setting the burner in operation. For that purpose, associated with the air valve drive means are two relays which are known as the single-wire control relay and a novoltage relay. For the preliminary ventilation operation, in wuch a situation of use, the air valve must first move into a low-load position which is defined by a first cam-controlled auxiliary switch in the air valve drive means.Once the starting low-load position has been reached, the procedure for starting up the first burner stage is carried out, with the commencement of a preliminary ventilation operation and, if the call for heat requires this, the second burner stage is also directly set in operation, as soon as the air valve has reached its fully open position.

When the second burner stage is cut out, the first burner stage remains in operation, initially with an excess of air, until the air valve has moved into its operational low-load position. The latter is now reached from the opposite direction of movement to that involved in the starting operation, and is defined bu a further cam-controlled auxiliary switch. For reasons of circuit design the two auxiliary switches which determine the starting and operational low-load positions should not overlap in regard to their switching points, but should be spaced from each other by a switching spacing which needs to be a significant value, in order to ensure defect-free operation. Therefore, to cope with both directions of movement, two low-load positions are required which are different with regard to the valve position, in the first burner stage.

That is undesirable for various reasons from the point of view of the combustion process, but it is difficult to adjust the auxiliary switches which perform their switching operations in close juxtaposition.

The present invention provides an air valve control means for a blower burner operable with first and second burner stages for oil or gas firing installations, with a program switch-less automatic firing device and an air valve drive means including a drive motor which, before the blower burner is set in operation, opens an air valve at least partially for a preliminary ventilation operation, switches which define the air valve position for a first burner stage and which signal to the automatic firing device the minimum required condition of opening of the air valve in the starting-up phase by connecting together an input and output terminal, and a delay device which is provided in the automatic firing device and which acts by way of a controller for the second burner stage on a single-wire control relay which controls the drive motor to operate in one direction of rotation, when voltage is applied thereto, and controls the drive motor in the other direction of rotation, in the voltage-less condition, and a no-voltage relay which, after a voltage failure, controls the drive motor into the air valve closed position when the voltage is restored, wherein in addition to the switch which connects together the input and output terminals, means are provided which cause the drive motor to continue to run when the first-mentioned switch is closed, and thereby the air valve position of the first burner stage is defined solely by an auxiliary switch of the drive motor, which auxiliary switch operates in the air valve closing direction.

Such control means is capable, although controlled by just a simple automatic firing device without motorised programmer, of always ensuring the same low-load position for the air valve.

The air valve in such burners is generally in the form of an air flap.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1 and 2 show a circuit diagram and a graph of a known control means; and Figures 3 and 4, Figures 5 and 6 and Figures 7 and 8 each show a circuit diagram according to a respective embodiment of the invention, with an associated graph.

In all the drawings, the same reference numerals are used to denote the same components.

In Figures 1, 3, 5 and 7, reference numeral 1 denotes a known automatic firing device (for example of the applicants' type LOA) which is used for all the embodiments described herein of air flap control means with air flap drives 2, 3, 4 and 5, and the mode of operation of which will first be briefly described, in conjunction with the known air flap drive means 2.

A phase conductor L feeds both the air flap drive means 2 at a terminal 6 and also the automatic firing device 1 by way of a controller 7. When a safety contact 8 of the thermal switch 9 is closed, the voltage of the phase conductor L is also applied to an input terminal 10 and to a terminal 11 of the air flap drive means 2, 3, 4, and 5. Whenever the arrangement is set in operation, the thermal switch 9 actuates a time switch 12 which then connects an output terminal 13 on the one hand to a terminal 15 by way of a further controller 14 and on the other hand to a terminal 16. Connected to the output terminal 13 is a blower 17 and the terminal 16 leads to a first fuel valve 18. A flame monitoring device which forms part of the automatic firing device 1 and which monitors the presence of a flame is not shown.If there is no flame when there should be one, then the thermal switch 9 opens the safety contact 8 in known fashion. The air flap control means is then voltage-less except for the terminal 6. A no-voltage relay 19 has a change-over switch 20; the rest contact thereof, when the no-voltage relay is unenergised, closes a circuit which, by way of a limit switch 21, causes a drive motor 22 of an air flap (not shown) to run in the direction 'close', until the limit switch 21 interrupts the circuit in the 'closed' position of the air flap. The drive motor 22 is directly connected to a neutral conductor. The no-voltage relay 19 is connected to the input terminal 10 and has a further operating contact 23.A single-wire control relay 24 is connected between the neutral conductor N and the terminal 15 and actuates a change-over switch 25 which in its rest position preselects the circuit 'close' and in the operative position preselects the circuit 'open' for the drive motor 22. Besides its limit switches 21 (close) and 26 (open), the drive motor also actuates three auxiliary switches 27, 28 and 29 which are actuated by way of adjustable control cams.

Figures 2, 4, 6 and 8 show operating graphs for the air flap position, wherein the ordinates denote position and the abscissae denote the time t. The flap is closed at Z and at maximum opening at A.

When the installation shown in Figures 1 and 2 is set in operation, the controller 7 closes and energises the no-voltage relay 19. The operating contact 23 thereof causes the drive motor 22 to operate in the direction 'open' until its auxiliary switch 28, at point 30 (see Figure 2), switches off the drive motor 22 in the start low load position M of the air flap, activates the time switch 12 by way of the output terminal 13, and switches on the blower 17 and an ignition device (not shown). After the preliminary ventilation time which is defined by the time switch 12 has expired, the contacts thereof switch on the fuel valve 18 and, after a given time (interval time), also apply voltage to the controller 14. The flame monitor detects the flame which is now produced, stops the thermal switch 9 and holds the time switch 12 thereof closed.That condition corresponds to the first burner stage, with the air flap in the start low-load position.

If the controller 14 is closed because it is also calling for heat, the single-wire control relay 24 is energised and the drive motor 22 receives an 'open' signal by way of 10, 11, 25, and 26, at point 31 in Figure 2. At following point 32, the auxiliary switch 29 switches on, initially without effect, while at point 33 the auxiliary switch 27 applies voltage by way of a terminal 34 to a second fuel valve 35.

That condition is the second burner stage. The drive motor is switched off by the limit switch 26 at point 36.

When the controller 14 is switched off at point 37 in Figure 2, the single-wire relay 24 is released and the change-over switch 25 thereof causes the drive motor 22 to run in the 'close' direction, by way of 29, 20 and 21. The auxiliary switch 27 thereof takes voltage away from the second fuel valve 35, at point 38. At point 39, the auxiliary switch 29 switches off and stops the drive motor 22 with the air flat in an operational low-load position which is greater by an amount As than the start low-load position, as has already been discussed hereinbefore.

The graph in Figure 2 also shows the final switching off of both stages.

For the purposes of the following description of the circuits according to the invention, as shown in Figures 3, 5 and 7, the details which are common to all three embodiments will first be discussed, making use of the reference numerals employed to describe the known circuit (see Figure 1).

A rest contact 40 of the single-wire voltage relay 24 is connected into the feed line of the phase conductor L between the terminal 6 and the rest contact of the change-over switch 20 which forms part of the no-voltage relay 19. From there there is a connection to the 'closed' limit switch 21 of the drive motor 22.

In addition, the voltage at the phase conductor L passes by way of the first regulator 7 and the safety contact 8 to the terminals 10 and 11. From the terminal 11 there is a connection to the change-over switch 25 of the single-wire control relay 24 and, in the rest condition thereof, to the limit switch 29 from which there is a line to the rest contact of the change-over switch 20. The operating contact of the change-over switch 25 is connected by a line 45 to the 'open' limit switch 26 of the drive motor 22. The latter has a direct connection to a neutral conductor N, and likewise the relays 24 and 19.

A further change-over switch 41 of the no-voltage relay 19, in the rest position thereof, connects the single-wire control relay 24 to the input terminal 10 while its operating contact is connected to the terminal 15 and thus to the controller 14 and there receives voltage from the time switch 12 in the automatic firing device 1 and by way of the second controller 14, only after the interval time has expired.

The switch which defines the maximum operating of the air flap during the preliminary ventilation period, as indicated at 26 (in Figures 3, 4, 5 and 6) and at 28 (in Figures 7 and 8) serves at the same for energising the no-voltage relay 19 which was previously in a voltage-less condition at its feed line 42. The line 42 is also connected by a selfholding contact 43 to one of the terminals 10 or 13, as will be described in greater detail hereinafter.

As in the case of the known circuit shown in Figure 1, in Figures 3, 5 and 7 also there is a connection from the terminal 16 connected to the first fuel valve 18, by way of an auxiliary switch 27 to the terminal 34 and to the second fuel valve 35.

In the air flap control means shown in Figures 3 and 7, the auxiliary switch 28 is connected between the input and output terminals 10 and 13 respectively. In the embodiment shown in Figure 3, the limit switch 26 which responds when the air flap is fully open is in the form of a change-over switch. The change-over switching contact 26a of the limit switch 26, which is switched in the 'open' limit position, is connected to the line 42 of the novoltage relay 19. The self-holding contact 43 thereof connects the line 42 to the output terminal 13 when the no-voltage relay 19 is energised.

In the embodiment shown in Figure 5, the seif- holding contact 43 short-circuits the input and output terminals 10 and 13 respectively when the novoltage relay 19 is energised, and the limit switch 26 which responds when the air flap is fully open is also in the form of a change-over switch. The change-over switching contact 26a thereof is connected to the line 42 and the output terminal 13.

In the embodiment shown in Figure 7, as already mentioned, the auxiliary switch 28 connects the input and output terminals 10 and 13 respectively.

The switching cam thereof is so set that the auxiliary switch 28 responds in an air flap position at indicated at point 47 in Figure 8, being the position between the position in the first and the second burner stages. In addition, the feed line 42 of the no-voltage relay 19 is connected to the output terminal 13.

The mode of operation of the air flap control means shown in Figures 3, 5 and 7 is described in greater detail hereinafter with reference to Figures 4, 6 and 8. In all three embodiments, voltage is applied to the air flap control means at the t1, for example by closure of the contacts of the controller 7. The single-wire control relay 24 is energised by way of L, 7, 8, 10, 41, 24 and N and the changeover switch 25 thereof closes an 'open' circuit to the drive motor 22 as follows: L, 7, 8, 10, 11, 25, 45, 26, 22 and N. The air flap begins to open. In the case of the air flap control means shown in Figure 3, at time t2 (see Figure 4) at point 46, the auxiliary switch 28 short-circuits the terminals 10 and 13 before the air flap is completely open, and thus the time switch 12 and the blower 17 receive voltage.

The preliminary ventilation operation begins, the duration thereof being determined by the time switch 12. As shown in the graph illustrated in Figure 4, the point 46 is beneath the air flap position M of the first burner stage. It could also be above it. The air flap opens further until at point 47 the maximum open position A thereof is reached. In the opening movement, the auxiliary switch 29 closed in a preparatory mode and at point 47 the limit switch 26 switches off the drive motor 22 and energises the no-voltage relay 19 by way of its change-over switch 26a and the line 42. By closure of its self-holding contact 43, the no-voltage relay 19 is now held in the energised condition from the input terminal 10, by way of the auxiliary contact 28.At the same time, the no-voltage relay 19 also actuates its change-over switches 41 and 20, which causes the single-wire control relay 24 to be released, for there is still no voltage at the terminal 15. A circuit is formed from the input terminal 10 to the 'close' side of the drive motor 22, as follows: 10, 11, 25, 29, 20, 21, 22 and N. The drive motor 22 therefore continues to run but now in the 'close' direction until the air flap position of the first burner stage is reached, by the auxiliary switch 29 which is operative only in the closing direction, and that switch switches off the drive motor 22 at point 48. The air flap remains in its position M. When the preliminary ventilation time as determined by the time switch 12 has expired, the first fuel valve 18 receives voltage.A flame is produced, which the flame monitor (not shown) detects and stops further heating of the thermal switch 9 by acting on the time switch 12, and also applying voltage to the controller 14 after the switch 9 has cooled down. The operation of starting up the first burner stage is thus terminated.

Assuming that the switch of the second controller 14 is closed, the single-wire control relay 24 is energised by way of the terminal 15 and the change-over switch 41. The change-over switch 25 of the relay forms, from the input terminal 10, a circuit 10, 11, 25, 45, 26, 22 and N which again causes the drive motor 22 to run in the 'open' direction (point 49 in Figure 4) until the auxiliary switch 27 responds, closes a circuit from the time switch 12 by way of 16, 27, 34 to the second fuel valve 35 and thus starts the second burner stage (point 50 in Figure 4). The drive motor 22 continues to run until the limit switch 26 switches off in the maximum position A of the drive motor 22 (point 51 in Figure 4). The full burner output is thus available.

When the controller 14 opens, the single-wire control relay 24 is then released. The circuit 10, 11, 25, 29, 20, 21, 22 and N is again formed, from the input terminal 10, causing the drive motor 22 to run in the 'close' direction, as was the case from point 47. When that occurs, the auxiliary switch 27 opens and closes the second fuel valve 35. The air flap position of the first burner stage is in turn reached, in the closing direction, and is defined by opening of the auxiliary switch 29 (point 48), in the same way as in the start-up procedure. That process can be repeated a plurality of times until the first burner stage is also cut out by response by the controller 7 (point 52).The no-voltage relay 19 is then released, and likewise the single-wire control relay 24, and the air flap is closed, by way of the circuit L, 6, 40, 20, 21, 22 and N, until the limit switch 21 opens in the 'closed' position.

For the air flap control means shown in Figure 5, the mode of operation thereof is described in greater detail hereinafter only with regard to the differences from the arrangement shown in Figure 3: in contrast to that arrangement, when the installation is set in operation, the air flap is firstly completely opened until the limit switch 26 responds at time t2, stops the drive motor 22 and at the same time energises the no-voltage relay 19 (point 47 in Figure 6). The self-holding contact 43 short-circuits the input and output terminals 10 and 13 respectively and in so doing starts the preliminary ventilation operation, at time t2. At the same time, the change-over switch 20 changes its position and the circuit 10, 11,25,29,20,21,22 and N which starts from the input terminal 10 causes the air flap to move in the 'close' direction until the auxiliary switch 29, actuated in the closing direction, switches off the drive motor 22 at point 48. With regard to the remainder of the procedure, refer ence should be made to the foregoing description relating to Figures 3 and 4.

In the last-described circuit shown in Figure 5, the auxiliary switch 28 (see Figure 3) with its control cam can be omitted. The air flap is completely open whether the arrangement is set in operation.

That construction is therefore rather more suited for short operating times in respect of the drive motor 22, as are used in oil burners.

In comparison, the air flap control means shown in Figures 7 and 8 is more suitable for longer operating times, as are employed when using gas, in that the air flap does not have to move into its fully open position when starting up the installation. The auxiliary switch 28 responds previously and also causes short-circuiting of the input and output terminals 10 and 13 respectively at the time t2 at point 47 (see Figure 8), which triggers off the preliminary ventilation operation and at the same time energises the no-voltage relay 19. The latter, with its change-over switch 28, causes the drive motor 22 to re-start in the 'close' direction, until once again, in the same manner as described hereinbefore, the auxiliary switch 29 switches off the drive motor at point 48 (see Figure 8). The remainder of the procedure is also the same as described hereinbefore with respect to Figures 3 and 5.

In all embodiments the arrangement ensures that any extinguishing of the flame or any failure of voltage, during operation of the arrangement, results in a complete re-start. In that connection, the air flap position when starting up the first burner stage is precisely the same as after an on/ off operation of the second burner stage, in which respect it should also be mentioned that the second burner stage could also be continuously controllable. The air flap always reaches the same position, although the arrangement uses a simple automatic firing device without motorised program switching mechanism, and without any need for mutual matching of the switching points of two switches which are actuated by the drive motor 22, which is a difficult operation.

Claims (7)

1. An air valve control means for a blower burner operable with first and second burner stages for oil or gas firing installations, with a program switch-less automatic firing device and an air valve drive means including a drive motor which, before the blower burner is set in operation, opens an air valve at least partially for a preliminary ventilation operation, switches which define the air valve position for a first burner stage and which signal to 4he automatic firing device the minimum required condition of opening of the air valve in the starting-up phase by connecting together an input and output terminal, and a delay device which is provided in the automatic firing device and which acts by way of a controller for the second burner stage on a single-wire control relay which controls the drive motor to operate in one direction of rotation, when voltage is applied thereto, and controls the drive motor in the other direction of rotation, in the voltage-less condition, and a novoltage relay which, after a voltage failure, controls the drive motor into the air valve closed position when the voltage is restored, wherein in addition to the switch which connects together the input and output terminals, means are provided which cause the drive motor to continue to run when the first-mentioned switch is closed, and thereby the air valve position of the first burner stage is defined solely by an auxiliary switch of the drive motor, which auxiliary switch operates in the air valve closing direction.

2. An air valve control means according to claim 1, wherein a rest contact of the single-wire control relay is connected into a feed line of a live conductor in the air valve drive means and a change-over switch of the no-voltage relay, in its rest position, connects the single-wire control relay to the input terminal which is supplied by the live conductor by way of a first controller and a safety contact in the automatic firing device, while an operating contact of the change-over switch is connected to the controller for the second burner stage.

3. An air valve control means according to claim 2, wherein a switch which defines the maximum position of opening of the air valve during the preliminary ventilation time simultaneously serves for energising the no-voltage relay which is in a voltage-less condition at its feed line until the end of the preliminary ventilation time, and the novoltage relay can be held in the energised condition, by way of the same feed line and a self-holding contact, only from the input terminal.

4. An air valve control means according to claim 3, wherein the switch for connecting together the input and output terminals is an auxiliary switch of the drive motor, which auxiliary switch responds before complete opening of the air valve, and the limit switch which responds when the air valve is fully open is in the form of a change-over switch whose change-over switching contact is connected to the feed line to the no-voltage relay while the self-holding contact of the no-voltage relay connects the feed line to the output terminal when the no-voltage relay is energised.

5. An air valve control means according to claim 3, wherein the switch for connecting together the input and output terminals is the self-holding contact of the energised no-voltage relay, and the limit switch which responds when the air valve is fully open is formed as a change-over switch whose change-over switching contact is connected to the feed line to the no-voltage relay and to the output terminal.

6. An air valve control means according to claim 3, wherein the switch for connecting together the input and the output terminals is an auxiliary switch of the drive motor which responds in an air valve position which is between the first and second burner stages, the self-holding contact of the no-voltage relay is connected in parallel with the auxiliary switch, and there is a connection from the feed line of the no-voltage relay to the output terminal.

7. An air valve control means for a blower burner operable with first and second burner stages for oil or gas firing installations, the control means being substantially as herein described with reference to and as illustrated in Figure 3, Figure 5 or Figure 7 of the accompanying drawings.