EP0430089B1 - Actuator - Google Patents

Description

TECHNICAL AREA

The invention is based on an actuator according to the preamble of claim 1.

STATE OF THE ART

From the document US-A-3 495 501 a plate valve is known which works as a safety valve to ensure a quick closing of a downstream valve. This valve is not intended for control functions.

An actuator for the actuation of a control valve with which, for example, the steam supply to a turbine of a power plant is regulated, has a main piston which is acted upon on the one hand by spring force and on the other hand by oil under pressure. When the oil pressure drops, the spring force securely closes the control valve, thereby interrupting the steam supply. This ensures that the turbine does not get out of control if the pressure of the oil should fail. The oil pressure in a drive volume, which acts on the main piston and actuates the control valve via it, is generated by an electro-hydraulic converter. When the control valve moves in the opening direction, oil is fed into the drive volume under pressure, however, because this movement comparatively slow, comparatively small cross-sections are sufficient for the supply of the oil. However, the control valve must close at a speed about ten times higher. This requires a comparatively quick emptying of the drive volume, which however cannot be achieved due to the small cross-sections of the oil supply. An actuator for operating a control valve is known for example from DE-A-3 432 890. In this actuator, the drive volume is emptied by means of a plate valve during a rapid closing process, the advantage of the large cross-section released by the plate valve being fully effective. With the help of the plate valve, a comparatively high dynamics of the actuator when closing can be achieved. In regular operation, when only small strokes of the actuator are required, the valve plate opens only for a very short time to allow the comparatively small amounts of oil to pass through. The comparatively large mass of the valve plate to be moved can influence the result in fine control processes.

In addition, it is shown that, as a result of the increase in the turbine outputs, the control valves and thus also the actuators actuating them must be designed larger or stronger. A corresponding proportional enlargement of the actuators leads to arrangements with comparatively large amounts of oil under pressure for their actuation. With commercially available valves, such quantities of oil can only be controlled with difficulty and the dynamics of the actuator also suffer as the size increases.

PRESENTATION OF THE INVENTION

The invention, as characterized in the claims, solves the problem of creating an actuator for a control valve which has a plate valve, the valve plate of which does not need to be moved in normal control operation.

The advantages achieved by the invention are essentially to be seen in the fact that the actuator can be constructed in a comparatively simple and reliable manner. Furthermore, normal control operation is simplified in that any moving masses that have a delaying effect are completely eliminated or are reduced to a minimum.

The further developments of the invention are the subject of the dependent claims.

The invention, its further development and the advantages which can be achieved therewith are explained in more detail below with reference to the drawing, which represents only one possible embodiment.

BRIEF DESCRIPTION OF THE DRAWING

Fig.1

eine Prinzipskizze eines erfindungsgemässen Stellantriebes,

Fig.2

eine erste Ausgestaltung eines Details eines Plattenventils,

Fig.3

eine zweite Ausgestaltung eines Details eines Plattenventils,

Fig.4

eine dritte Ausgestaltung eines Details eines Plattenventils, und

Fig. 5

eine vierte Ausgestaltung eines Details eines Plattenventils.

Bei allen Figuren sind gleich wirkende Elemente mit gleichen Bezugszeichen versehen.Show it:

Fig. 1

a schematic diagram of an actuator according to the invention,

Fig. 2

a first embodiment of a detail of a plate valve,

Fig. 3

a second embodiment of a detail of a plate valve,

Fig. 4

a third embodiment of a detail of a plate valve, and

Fig. 5

a fourth embodiment of a detail of a plate valve.

Elements with the same effect are provided with the same reference symbols in all the figures.

WAYS OF CARRYING OUT THE INVENTION

FIG. 1 shows an actuator 1, which actuates a control valve 2, which regulates the amount of hot steam flowing through a hot steam line 3 to a turbine (not shown). The control valve 2 is connected by a valve spindle 4 to a main piston 6 sliding in a master cylinder 5. A drive volume 7 pressurized with oil is arranged below the main piston 6. Instead of the oil, another hydraulic fluid or a gaseous medium can also be provided. An oil-filled buffer volume 8 is provided above the main piston 6, in which an additional one Spring 9 is arranged, which counteracts the oil pressure in the drive volume 7. A rod 10 is provided on the spring side on the main piston 6 and connects it to a displacement measuring device 11. The rod 10 and the valve stem 4 penetrate the master cylinder 5 on opposite sides. The design of these pressure-tight penetrations is known and need not be described further here.

A tubular connecting piece 15 is attached to the master cylinder 5 in the area of the drive volume 7, the end 16 of which is remote from the master cylinder 5 is designed as a sealing seat. This end 16 is closed by a plate valve 17 shown in simplified form. A plate 18 is pressed against the end 16 by a compression spring 19. The compression spring 19 is arranged in a spring chamber 20 which is pressurized with oil. In addition to the end 16 of the tubular connecting piece 15, the plate 18 simultaneously closes pressure-tightly a volume 21 which concentrically surrounds the connecting piece 15 and which merges into a comparatively short, direct connecting line 22 which leads along the master cylinder 5 into the buffer volume 8. This connecting line 22 has a comparatively large cross section. The size of the spring chamber 20 is approximately 1,000 times smaller than the drive volume 7 with which it is in operative connection. The spring chamber 20 is also operatively connected to a proportional directional valve 25.

As a proportional directional control valve 25, for example, the directly operated proportional directional control valve with position control of the type KFDG 4V - 3/5, series 20, from Vickers Systems GmbH, D 6380 Bad Homburg vdH can be used. The proportional directional valve 25 has two actuating magnets 26, 27, which cooperate with return springs, not shown, and in this case three hydraulic connections 28, 29, 30. In Fig. 1, the proportional directional control valve 25 is shown in the so-called "fail-safe" position. The proportional directional valve 25 has a stroke measurement 31 connected to a slide of the valve, which measures the respective position of the slide and, as indicated by an action line 32, passes this information on to a position controller 33 with an integrated power amplifier. As indicated by lines of action 34, 35, the actuating magnets 26, 27 receive their commands from this position controller 33 with an integrated power amplifier. A power amplifier EEA-PAM-533-A, series 20, from Vickers Systems GmbH, D 6380 Bad Homburg vdH, which is specially matched to the proportional control valve 25, can be used as the position controller 33, for example. This position controller 33 works together with a higher-order controller 36, as indicated by an action line 37. The controller 36 has further inputs 38, through which information and commands are fed in by a higher-level plant control system which controls the entire power plant. Furthermore, it has an input 39 for feeding in an electrical signal, as indicated by an action line 40, from the displacement measuring device 11.

Oil is fed in under pressure through a line 45, and the necessary oil pressure is generated by a pump (not shown). The flow rate of the oil is limited to a maximum amount by an orifice 46 arranged in the line 45. This aperture 46 can have a constant or an adjustable cross section. The line 45 leads to the connection 28 of the proportional directional control valve 25, which in the illustration in FIG. 1 is not connected to the connection 29. The connection 29 is connected on the one hand to a line 47 which leads into the spring chamber 20 of the plate valve 17, and on the other hand with a line 48 which leads to a normally closed safety valve 49 designed as a plate valve. After the safety valve 49, a line 50 leads into the buffer volume 8 of the master cylinder 5. A line 51 branches off from the line 50 and establishes the connection with the connection 30 of the proportional directional valve 25. A line 52 leads from the buffer volume 8 to a drain device, not shown. From this drain device, the oil continues through the aforementioned pump back into line 45.

The safety valve 49 is designed as a plate valve with a cylinder 53, a volume 55 which is pressurized with oil under pressure from a safety oil circuit through a line 54 and which is delimited by a valve plate 56 and with a valve spring 57 which controls the oil pressure acting on the valve plate 56 counteracts. It cannot be seen from the schematic illustration of the safety valve 49 that the valve plate 56 is designed in such a way that it is impossible to jam it. The line 54 normally leads through a directional valve 58. The directional control valve 58 is actuated by an electromagnet 59. An action line 60 indicates the path of the trigger command for the electromagnet 59. For safety reasons, this trigger command is usually locked with the higher-level system control system, so that no unwanted false triggers can occur. A line 61, which branches off from line 45, leads to directional control valve 58. Via this line, if e.g. the safety oil circuit is depressurized, the oil pressure from line 45 after switching directional control valve 58, apply volume 55 and keep safety valve 49 closed.

It is particularly advantageous with regard to increased dynamics of the actuator if the proportional directional control valve 25 is connected to the plate valve 17 and the master cylinder 5 to form a monolithic unit. In this case, the lines 47 and 48, like the lines 50 and 51, can be made comparatively short, so that the oil-filled line volumes are correspondingly small, which increases the dynamics. However, it is also possible to provide one or more other valves instead of the plate valve 17, if this appears desirable due to the operational requirements placed on the actuator 1. It is also possible to replace the proportional directional control valve 25 with at least one electrohydraulic valve or with a combination of different electrohydraulic valves in order to adapt the actuator or its dynamic behavior to the specified operating conditions. The actuator is therefore very versatile.

The interaction of the position controller 33 with the integrated power amplifier and the controller 36 as a common electronic control arrangement of a control circuit is particularly advantageous because the position controller 33 is specially adapted to the proportional directional control valve 25, so that no additional adjustments and adjustments are necessary. However, it is entirely possible to assemble this electronic control system from other elements or to transfer its function to a higher-level system control system if, for example, the protection concept of the power plant would require this. In the electronic control arrangement, signals originating from the displacement measuring device 11 and from the stroke measurement 31 are processed continuously together with at least one setpoint value specified by the higher-level system control system according to a specified logic. In the event of deviations from this target value, this control arrangement generates correction signals which act on the actuating magnets 26, 27 of the proportional directional control valve 25 and cause the same to be reversed accordingly.

2, part of the plate 18 of the plate valve 17 is shown schematically in section. The spring chamber side surface 65 of the plate 18 is arranged on the right; this also applies to the following figures. A breakthrough through the plate 18 has a cylindrical opening 66, which is followed by a conical extension. A ball 67 is pressed into this conical extension by a spring 68, which is supported against a holder 69 connected to the plate 18, and closes the opening 66. Oil 66 can flow under pressure into the drive volume 7 as soon as one Pressure difference occurs that is large enough to overcome the force of the spring 68 and the oil pressure acting on the ball 67.

FIG. 3 is similar to FIG. 2, except that in this case an opening with the opening 66 through the plate 18 is designed in such a way that oil can flow from the drive volume 7 into the spring chamber 20. In addition, there is also a rigid orifice 70 which allows oil to flow in both directions. The cross section of the diaphragm 70 is designed to be significantly smaller than that of the opening 66.

It is of course also possible, as shown in FIG. 4, to insert only a rigid diaphragm 70 into the plate 18 as a breakthrough and thereby limit the oil passage.

FIG. 5 shows a plate 18 with two valve arrangements similar to that shown in FIG. 2, but which allow oil to pass through in opposite directions with a corresponding differential pressure. The opening 66, which leads from the drive volume 7 into the spring chamber 20, has a substantially larger cross section than the second opening 66.

To explain the mode of operation, FIG. 1 is considered in more detail. The control valve 2 must be able to be closed comparatively quickly during operation. The closing speed is normally around 1 m / sec, while the opening speed, on the other hand, only requires speeds around 0.02 m / sec. These speed specifications are guide values; depending on the design of the power plant, there may also be significant deviations from these specifications. The actuator 1 can be adapted to the respective operating conditions with comparatively little effort.

If the control valve 2 is to be moved in the opening direction, the proportional directional control valve 25 is actuated by the position controller 33, namely that it is actuated in such a way that the scheme to the left of the position shown applies. The connections 28 and 29 are then connected through and oil under pressure flows from the line 45 through the proportional directional control valve 25. No oil can flow through line 48 in normal operation, since the safety valve 49 closes this line 48. The oil flows through the line 47 into the spring chamber 20 of the plate valve 17 and from there through the opening of the plate 18 and the connector 15 into the drive volume 7. The oil pressure in the drive volume 7 moves the main piston 6 upwards and thus via the valve spindle 4 the control valve 2 in the opening direction. The displacement measuring device 11 monitors the stroke of the main piston 6 and reports its position continuously to the controller 36. As soon as the predetermined setpoint of the stroke has been reached, the controller 36 controls the proportional directional control valve 25 via the position controller 33 such that the oil flow is interrupted. The stroke measurement 31, the signals of which are processed in the position controller 33, monitors the operating behavior of the proportional directional valve 25. The movement of the main piston 6 is ended at the same time as this control.

If, on the other hand, the control valve 2 is to be quickly transferred from an open position into a closed state, the proportional directional control valve 25 is reversed such that the scheme to the right of the position shown applies. The connections 29 and 30 are connected to one another and oil from the spring chamber 20 flows out through the line 47, through the proportional directional valve 25, through the lines 51 and 50 further through the buffer volume 8 and the line 52 into the drain device. However, this flow process takes only a very short time because, as soon as the pressure in the spring chamber 20 is less than the pressure in the drive volume 7, the plate 18 moves to the right against the pressure of the spring 19 and the oil from the drive volume 7 through the volume 21 and the connecting line 22 can flow into the buffer volume 8 filled with oil under low pressure and from there further into the drain device. The spring 9 presses the main piston 6 down and thus the oil from the drive volume 7 into the buffer volume 8 until the end position of the control valve 2 is reached. The oil flows out very quickly, since the cross section released by the plate valve 17 and also the cross section of the direct connecting line 22 are comparatively large and do not adversely affect the flow process. The movement of the main piston 6 creates a suction in the buffer volume 8, which additionally supports this oil flow and increases the dynamics of the actuator 1.

Such a rapid pressure relief of the drive volume 7 and such a rapid outflow of the oil from the same would not be possible due to the comparatively small cross sections of the lines 47, 51 and 50. If these cross sections and the proportional directional control valve 25 were to be increased accordingly, it would not be possible to achieve the dynamics of the actuator 1 that nearly as good as with the embodiment according to the invention because of the large amounts of oil to be moved on comparatively long paths.

Only a comparatively small amount of oil under pressure is required to act on the spring chamber 20, which is very small compared to the drive volume 7. This spring chamber 20 is therefore very quickly relieved of pressure by the lines 47, 51 and 50 when a corresponding control command reaches the proportional directional control valve 25. As a result, the plate valve 17 opens immediately after the control command and initiates the rapid closing movement of the main piston 6 and thus of the control valve 2. The volume of the lines 47, 51, 50 therefore does not influence the dynamics of the actuator, or only has an extremely slight effect.

In normal operation, small deviations from the target value are recognized by the controller 36 and corresponding correction signals are transmitted to the proportional directional control valve 25 via the position controller 33. If the control valve 2 is to open a little, only a small amount of oil is fed under pressure into the drive volume 7 until the setpoint is reached again. For opening movements of the control valve, the at least one opening through the plate 18 is sufficient, as is shown schematically in FIG. 2 through the opening 66, in FIG. 3 and FIG. 4 through the diaphragm 70 and in FIG. 5 through the upper opening 66 . If the plate 18 is designed according to FIG. 2, the closing movement of the control valve is initiated, as already described, by lowering the oil pressure in the spring chamber 20, whereupon, if only a small stroke is to be made in the closing direction, the plate valve 17 only for a short time opens and oil can escape through the connecting line 22 into the buffer volume 8. As soon as the desired value is reached, the plate valve 17 closes again immediately.

3, smaller closing movements can take place without opening the plate valve 17, since oil can flow out of the drive volume 7 into the spring chamber 20 through the opening 66 and through the diaphragm 70 until pressure equalization is established as soon as the Setpoint is reached. If larger setpoint deviations are to be compensated for in this case, if the cross sections of the opening 66 and the diaphragm 70 are insufficient, the plate valve 17 also opens briefly. The execution of the closing process in the embodiment according to FIG. 4 is similar to that in FIG. 3rd

The design of the plate 18 according to FIG. 5 also allows a small closing movement, for larger strokes of the main piston 6 it is also necessary to open the plate valve 17 in this case.

The proportional directional control valve 25 is shown in the central position in FIG. 1. This position is assumed if, for example, the actuating magnets 26, 27 should not receive any voltage due to a power failure. Reaching this position is ensured by spring force of springs provided in the interior of the proportional directional valve 25 under all circumstances. In this position, the spring chamber 20 is relieved of pressure by the lines 47, 51 and 50, so that the plate valve 17 opens, which, as already described, leads to a quick closing of the control valve 2. In this way it is ensured that the control valve 2 is always definitely closed even in the event of a fault, so that under no circumstances can damage to the turbine being operated as a result of a defect in the actuator 1.

The safety valve 49 normally prevents a pressure drop in the line 48 in the direction of the drain device. However, if the pressure in the safety oil circuit drops, the pressure in the volume 55 also drops and the safety valve 49 releases the line 48, regardless of the position of the proportional directional control valve 25, so that the pressure can escape from the spring chamber 20 of the plate valve 17 the lines 47, 48 and 50, whereby, as already described, a quick closing process of the control valve 2 is initiated. This measure can also be used to reliably shut off the steam supply to the turbine.

During start-up attempts, it can happen that the safety oil circuit is not yet pressurized or cannot be pressurized yet. In this case, the directional control valve 58 is installed, which, as soon as it is switched electromagnetically to the diagram shown to the right of the position shown, enables oil to act on the volume 55 under pressure from line 45 through line 61 and through directional control valve 58 can, whereby the safety valve 49 is closed. The command route for the directional control valve 58, as indicated by the line of action 60, must be blocked as soon as it is switched to normal operation, since otherwise the safety oil circuit may no longer be able to act on the safety valve 49, so that the protective function of this circuit can no longer be guaranteed would.

Claims (10)

1. Actuating drive (1) for a control valve (2), comprising an automatic control circuit which adjusts the actuating drive (1) in accordance with a desired value preset by a superordinate installation control system; comprising a main piston (6) sliding in a main cylinder (5), and comprising a driving space (7), which can be loaded with oil under pressure in a controlled manner, on one side of the main piston (6) and an oil-filled buffer space (8) on the other side of the main piston (6), the drive space (7) and the buffer space (8) being connectable by a connecting pipe (22) closable by at least one first valve (17), and the at least one first valve being able to be directly operated hydraulically by means of at least one controlled second valve (25), the at least one first valve being in the form of a plate valve (17) having a plate (18) loaded in the closing direction by a compression spring (19) arranged in a spring chamber (20), characterized

   - in that the plate (18) has at least one through passage which permits cooperation of the oil under pressure in the spring chamber (20) and the oil in the driving space (7).
2. Actuating drive according to Claim 1, characterized

   - in that the spring chamber (20) has a volume of the order of about one-thousandth of that of the driving space (7).
3. Actuating drive according to Claim 1, characterized

   - in that the at least one passage through the plate (18) is in the form of a fixed orifice (70) or of a valve arrangement which in the two directions has the same or different passage cross-sections.
4. Actuating drive according to Claim 1, characterized

   - in that the at least one passage through the plate (18) is in the form of a third valve which permits a flow of oil into the driving space (7).
5. Actuating drive according to Claim 1, characterized

   - in that the at least one passage through the plate (18) comprises a fixed orifice (70) and in addition a fourth valve which permits a flow of oil out of the driving space (7).
6. Actuating drive according to one of the preceding claims, characterized

   - in that the at least one second valve is in the form of an electrohydraulic proportional directional valve (25) having at least one operating magnet (26, 27) and a stroke measuring system (31).
7. Actuating drive according to Claim 6, characterized

   - in that the proportional directional valve (25) is connected to the plate valve (17) and the main cylinder (5) to form a monolithic unit.
8. Actuating drive according to Claim 6, characterized

   - in that in the automatic control circuit an electronic automatic control arrangement is provided,

   - in that in the electronic automatic control arrangement signals originating from a distance measuring device (11) and from the stroke measuring system (31) are continuously processed, together with the respective preset desired value, in accordance with a preset logic, and

   - in that in the event of deviations from the desired value this automatic control arrangement generates correction signals which energize the operating magnets (26, 27).
9. Actuating drive according to Claim 8, characterized

   - in that the electronic automatic control arrangement has a positioning system (33) provided with an integrated power amplifier, and an automatic controller (36) cooperating therewith, and

   - in that the signal originating from the stroke measuring system (31) is fed into the automatic controller (36) and the signal originating from the distance measuring device (11) is fed into the positioning system (33).
10. Actuating drive according to one of the preceding claims, characterized

    - in that in the event of disturbances the closing of the control valve (2) is ensured by the action of a safety valve (49).

Images