GB2301400A - Hydraulic actuator for isolators - Google Patents

Abstract

An isolator, in particular a toggle-driven diverter valve, provided at a three-way junction through which passes a high temperature gas, the isolator having a closure member pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, and hydraulic actuator means (20) for pivoting the closure member between the said first and second positions, wherein a drive shaft (11) of the closure member is operated by double acting hydraulic cylinders (22) the rods of which translate racks (23) to rotate a pinion (24) attached to the said drive shaft (11), and wherein the said actuator means provides different torques for opening and closing functions.

Description

HYDRAULIC ACTUATOR FOR ISOLATORS This invention relates to a hydraulic isolator for isolators, in particular for toggle drive diverter valves or flap isolators (herein both referred to as isolators) used for isolating gases under severe operating conditions of high temperature and/or high pressure.

For many diverter valve or flap isolator applications it is necessary or desirable to use hydraulic actuation systems.

The increasing size of gas turbines creates the need for larger diverter valves in combined cycle or cogeneration plants for directing the flow of products of combustion either to a heat recovery steam generator or to a by-pass system.

Diverter valves for the largest gas turbines are usually operated by a toggle drive system using a hydraulic actuator. The principle of the toggle drive linkage is shown in Figure 1 and Figure 2 of the accompanying drawings; the actuators for these diverters require a rotary output of typically 170 degrees.

As shown in Figures 1 and 2, a diverter valve 1 is provided at a three-way junction through which passes a high temperature gas, wherein a high temperature exhaust gas flow from a gas turbine is shown by an arrow 2, the gas flow to a heat recovery steam generator (HRSG) is shown by an arrow 3, and the alternative gas flow to a by-pass is shown by an arrow 4.

The diverter valve 1 has a valve closure member or blade 5 which comprises a flap arm 6 which is pivotably mounted at 7 to be movable between the position shown in Figures 1 and 2a (closed to HRSG position) and the position shown in broken lines in Figure 1 and in Figure 2b in which the valve closure blade 5 closes the by-pass outlet (closed to by-pass position). The flap arm 6 carries on its opposite faces a pair of sealing plates 8 each provided with peripheral seals (not shown), preferably of the type described in British patent No.

GB-A-1308801 or GB-A-2060824 or in PCT application No.

PCT/GB89/01382 (WO 90/06460) or PCT/GB89/00975 (WO 90/02279). The diverter valve further comprises a suitable frame arranged around the peripheries of the two outlet ducts of the junction in which the diverter valve is mounted. The frame is provided with two sets of sealing surfaces i.e. one set of sealing surfaces being associated with each outlet duct, the sealing surfaces of the frame being adapted to cooperate with the peripheral seals provided on the plates 8.

A toggle drive system 10 comprises a toggle drive shaft 11 and a pair of operating arms 12 connected to the valve closure blade 5 through a pair of links 13 extending from the ends of the arms 12 to the blade 5.

Only one arm 12 and one link 13 are shown in Figures 1 and 2, the other elements of each pair being disposed behind the corresponding arm 12 and link 13 shown in the drawings.

A known type of actuator consists of either two or four single acting hydraulic cylinders, the rods of which have integral racks. Application of hydraulic pressure translates the racks which rotates a pinion which is keyed to the drive shaft of the diverter. These actuators provide equal torques in each direction for a given hydraulic pressure. These actuators are typically arranged for flange mounting.

The operating torque requirement characteristics of diverter valves in a conventional configuration are such that the torque requirement for opening is very much higher than that required for closing. In addition the diverter valve requires a much reduced torque to maintain the diverter blade in its terminal position, particularly when closed to by-pass. In this context, opening means moving from the closed to HRSG position (vertical) to the closed to by-pass position (horizontal), for diverters arranged in the normal configuration.

The present invention provides an isolator, in particular a toggle-driven diverter valve, provided at a three-way junction through which passes a high temperature gas, the isolator having a closure member pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, and hydraulic actuator means for pivoting the closure member between the said first and second positions, wherein a drive shaft of the closure member is operated by double acting hydraulic cylinders the rods of which translate racks to rotate a pinion attached to the said drive shaft, and wherein the said actuator means provides different torques for opening and closing directions.

In the actuator of the invention, two double acting cylinders are suitably used to provide the thrust.

Differential areas given by the full bore side of the piston and the annul us side allow different torques to be provided in the opening and closing directions.

Actuators of this kind are preferably shaft mounted to prevent the potential for side loadings to be imparted to the actuator bearings. Shaft mounting of the actuator according to the present invention may be facilitated by the provision of a torque reaction arm integral with the actuator casing.

The actuator is designed to incorporate, as an option, a mechanical device to absorb part of the thrust near the end of the stroke to reduce the torque at the terminal position corresponding to the cylinder outstroke. This reduces loadings on the driven equipment.

An integral locking facility may be provided to lock the actuator, and hence the driven equipment, usually a diverter, in the desired position.

The actuator is conceived in such a manner so that its function may be extended to provide a complete, self contained power unit.

The actuator suitably consists of the following main components - Housing, - Two double acting hydraulic cylinders, - Two racks, - One Drive pinion, - Pinion bearings, - Covers, - Rack guide (linear) bearings.

The following items are optional - Soft hold sub-assembly; - Locking device; - Extension of concept to self contained power unit.

The cylinders in the basic design are suitably standard proprietary front end mounting type. Flexibility is introduced by the ability to select different cylinder bore sizes, each with a number of available piston rod diameters, thus allowing a range of differential area ratios, and hence torque ratios to be selected.

The piston rod ends of each cylinder are connected to a rack. These racks are arranged to rotate a pinion which provides the output torque. The pinion is suitably provided with a hollow bore. Alternatively the drive shaft can be provided integral with the pinion.

The racks are preferably connected to the piston rod ends using spherical rod ends to eliminate loading due to any misalignment between the piston rod and the rack.

The housing is preferably of fabricated steel or alternatively cast iron or steel construction. Facility may be provided for front mounting the cylinders to the housing. The drive pinion bearing housings may be integral with the actuator housing. The design of the housing is preferably such that it contains two enclosed volumes one each side of a central gearcase section.

This box construction provides the strength of the housing, but also provides the potential for use as a fluid reservoir for a complete self contained hydraulic power system.

The housing is suitably provided with sheet metal covers to enclose the rack and piston rod, and the end of the cylinder may be enclosed by an elastomeric gaiter or boot to provide a completely weatherproof housing.

Pinion bearings are preferably low friction non-lubrication bearings of the ptfe coated type. Rack guide bearings are preferably linear bearings of the Ftfe coated type.

Pinion seals are typically O-rings or wiper rings.

Racks are suitably located in non-lubricated linear bearings. The rack bearing housings may be adjustable using shims to enable the backlash to be adjusted as desired. In principle, adjustment to achieve zero backlash is possible.

Torque reduction at the end of the stroke may be provided by the use of an optional "soft hold" sub-assembly which absorbs a predetermined amount of the cylinder thrust over a short length of the stroke. This consequently reduces the output torque available from the actuator.

The assemblies each consist essentially of a belleville washer spring pack enclosed in a housing and operated by compressing the spring via a plunger connected to a buffer. As the hydraulic cylinder approaches the end of the stroke the end of the rack contacts the soft hold assembly buffer and depresses the plunger, hence depressing the spring pack, thus absorbing some of the cylinder thrust.

In many applications it is necessary to provide a form of locking arrangement. This may take the form of a mechanical device causing clamping of the two racks onto the pinion in the form of a brake.

Suitably the actuator may be fitted with a pair of hydraulic brakes. These have the function of providing positive locking of the actuator drive pinion when the isolator blade is stationary, totally eliminating any mechanical backlash between the rack and pinion, and also eliminating any possibility of instability due to the compressibility of the hydraulic fluid, and further eliminating the need for counterbalance valves on the cylinders for pipe rupture protection.

In addition, a locking device can be manually operated to provide positive locking of the isolator blade for maintenance purposes.

For normal stationary position locking, a screw adjuster is fully retracted and the brake is held applied by hydraulic pressure applied to the top of an emergency close piston, which forces a brake pad against back of the rack, so locking the rack and pinion gears. For manual locking, the screw adjuster is screwed down to provide the locking force.

To operate the valve closure blade fluid pressure is applied to the underside of a brake piston which is lifted against a belleville washer, thus releasing the brake. There is a retaining ring that limits the downward travel of the emergency close piston.

For emergency closing the brake is released by the loss of hydraulic pressure on the top of the emergency close piston.

The brake pads may be fitted with a pair of embedded wires to allow an electrical signal to provide indication that pads should be replaced.

Whilst the cylinders shown can be of a conventional double acting type, alternatively they may be oil driven on one side and having a gas-precharge on the other side, in the manner of a spring return actuator, whereby in this case the spring is in the form of nitrogen gas.

This improves the match between the torque characteristics of the actuator and the driven equipment (diverter).

This arrangement actually combines the functions of a conventional hydraulic cylinder and of a piston accumulator.

This, together with the provision of reservoir space within the housing, provides the capability for extension of the actuator concept to that of a self contained hydraulic power system, providing all those features which would normally be found in a separate power unit.

The features which can be accommodated are - Improved matching of required torque and actuator torque characteristic; - Main and standby pumps; - Emergency closure facility, by means of piston accumulators; - Mounting for all necessary valves; - No field installed hydraulic piping is required.

In the case of the design for the fully integrated actuator, the cylinder may consist of a main piston assembly, a hollow rod assembly and a secondary piston which is in effect an accumulator piston. The hollow piston rod forms the cylinder for the piston accumulator. The main piston head has a small port which allows transfer of hydraulic fluid from the annul us side of the main piston to the secondary piston which charges the accumulator gas (nitrogen). The operating pressures are much higher than for the normal cylinders used in the basic design, being typically 160 bar for the standard design and typically 350 bar for the integrated design.

In the integrated design the hydraulic fluid is applied to both full bore and the narrow annul us side of the main cylinder for the outstroke. Compression of the accumulator gas occurs simultaneously and automatically during the cylinder outstroke (opening).

Normal closing occurs under hydraulic pressure and accumulator gas pressure, but the arrangement also allows closing under power failure (i. e. no hydraulic pressure) or closing under hydraulic pressure alone, in the event that for some reason the accumulator gas pressure has decayed.

Thus the actuator which is the subject of the present invention can provide some or all of the following main features: - Different torques for opening and closing directions; - Built in torque reaction arm for shaft mounting; - Torque reduction facility at the terminal position; - Locking facility; - Potential to enable the actuator functions to be extended to become a self contained hydraulic power unit.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of a known type of toggle-driven diverter valve; Figures 2a and 2b are side views showing the closure member and toggle mechanism of the diverter valve of Figure 1, respectively in the closed to HRSG and the closed to by-pass positions thereof; Figures 3a and 3b are plan and side views respectively of an actuator of a diverter valve of the present invention; Figures 4a and 4b are plan and side views respectively of an actuator of a diverter valve according to the present invention; Figure 5 is a side view showing in more detail an actuator of a diverter valve according to the invention; Figure 6 is a cross-section taken along the line X-X in Figure 5; ; Figure 7 is a sectional side view illustrating a soft hold sub-assembly of the actuator, for absorbing cylinder thrust; Figures 8a and 8b are side and plan views respectively of another embodiment of an actuator of a diverter valve according to the invention, having a modified torque arm anchor, integrally mounted motor driven pumps, and brake/lock assemblies; Figure 9 is a partly sectional side view of an actuator, showing a preferred type of double acting cylinder and also brake/lock assemblies thereof.

Figure 10 is a partly sectional side view showing in more detail the operation of the cylinder of the actuator of Figure 9, at a part stroke position thereof; Figure 11 is a partly sectional side view showing in more detail the brake/lock assembly of the actuator of Figure 9; and Figure 12 is a still more detailed view of the brake/lock assembly shown in Figure 11.

In the drawings, like reference numerals indicate like parts.

As shown in Figure 3a, a toggle drive shaft 11 is provided to operate a closure blade (not shown in Figure 3a) via a pair of operating arms 12. The drive shaft 11 is operated by means of an actuator 20 as shown in Figures 3 to 6.

The actuator 20 essentially comprises a housing 21 and two double acting hydraulic cylinders 22 the rods of which translate racks 23 to rotate a pinion 24 attached to the drive shaft 11.

As shown in more detail in Figure 5, the cylinders 22 are standard proprietary front end mounting type.

Flexibility is introduced by the ability to select different cylinder bore sizes, each with a number of available piston rod diameters, thus allowing a range of differential area ratios, and hence torque ratios to be selected.

The piston rod ends 25 of each cylinder 22 are connected to a rack 23. These racks are arranged to rotate the pinion 24 which provides the output torque. The pinion is shown provided with a hollow bore. Alternatively the drive shaft can be provided integral with the pinion.

The racks 23 are connected to the piston rod ends 25 using spherical rod ends to eliminate loading due to any misalignment between the piston rod and the rack.

The housing 21 is of fabricated steel or alternatively cast iron or steel construction. Facility is provided for front mounting the cylinders to the housing. The drive pinion bearing housings are integral with the actuator housing 21. The design of the housing is such that it contains two enclosed volumes one each side of the central gearcase section. This box construction provides the strength of the housing, but also provides the potential for use as a fluid reservoir for a complete self contained hydraulic power system.

The housing 21 is provided with sheet metal covers 30 to enclose the rack and piston rod, and the end of the cylinder is enclosed by an elastomeric gaiter 31 or boot to provide a completely weatherproof housing.

Pinion bearings 32 (see Figure 6) are preferably low friction nc.-lubrication bearings of the ptfe coated type. Rack guide bearings are linear bearings of the ptfe coated type.

Pinion seals 34 are typically O-rings or wiper rings.

The racks 23 are located in non-lubricated linear bearings 35. The rack bearing housings 36 are adjustable using shims 37 to enable the backlash to be adjusted as desired. In principle adjustment to achieve zero backlash is possible.

As shown in particular in Figure 7, torque reduction at the end of the stroke is provided by the use of an optional "soft hold" sub-assembly 40 which absorbs a predetermined amount of the cylinder thrust over a short length of the stroke. This consequently reduces the output torque available from the actuator. The actuator shown in Figure 5 is not provided with such a soft hold sub-assembly, but the location of the soft hold sub-assembly 40 is designated in Figures 4a and 4b.

The assemblies 40 each consist essentially of a belleville washer spring pack 41 enclosed in a housing 42 and operated by compressing the spring 41 via a plunger 43 connected to a buffer 44. As the hydraulic cylinder approaches the end of the stroke the end of the rack contacts the soft hold assembly buffer 44 and depresses the plunger 43, hence depressing the spring pack, thus absorbing some of the cylinder thrust.

In the actuator described above, two double acting cylinders 22 are used to provide the thrust. The differential areas given by the full bore side of the piston and the annulus side allow different torques to be provided in the opening and closing directions.

Actuators of this kind are shaft mounted to prevent the potential for side loadings to be imparted to the actuator bearings. Shaft mounting of the actuator according to the present invention is facilitated by the provision of a torque reaction arm integral with the actuator casing. A torque reaction arm is indicated by reference 26 in Figures 4b and 5.

The actuator is designed to incorporate, as an option, a mechanical device 40 to absorb part of the thrust near the end of the stroke to reduce the torque at the terminal position corresponding to the cylinder outstroke. This reduces loadings on the driven equipment.

An integral locking facility may be provided to lock the actuator, and hence the driven equipment, usually a diverter, in the desired position.

The actuator is conceived in such a manner so that its functions may be extended to provide a complete, self contained power unit.

The embodiment of the actuator shown in Figures 8a and 8b has, as shown, modified torque arm anchors 26a, integrally mounted motor driven pumps 27, and brake/lock assemblies 28.

Figures 9 and 10 show a particular embodiment of a double acting cylinder 50, and also brake/lock assemblies 28, the latter being shown in more detail in Figures 11 and 12.

More particularly, Figures 9 and 10 show a design for a fully integrated actuator wherein the cylinder 50 consists of a main piston assembly 51, a hollow rod assembly 52 and a secondary piston 53 which is in effect an accumulator piston.

The hollow piston rod 52 forms the cylinder for the accumulator piston 53. The main piston head has a small port 54 which allows transfer of hydraulic fluid from the annul us side of the main piston to the secondary piston which charges the accumulator gas (nitrogen).

The operating pressures are much higher than for the normal cylinders used in the basic design, being typically 160 bar for the standard design and typically 350 bar for the integrated design.

In the integrated design the hydraulic fluid is applied to both full bore and the narrow annul us side of the main cylinder for the outstroke. Compression of the accumulator gas occurs simultaneously and automatically during the cylinder outstroke (opening).

Normal closing occurs under hydraulic pressure and accumulator gas pressure, but the arrangement also allows closing under power failure (i. e. no hydraulic pressure) or closing under hydraulic pressure alone, in the event that for some reason the accumulator gas pressure has decayed.

As shown in Figures 8 and 9, the actuator may be fitted with a pair of hydraulic brakes 28, shown in more detail in Figures 11 and 12. These have the function of providing positive locking of the actuator drive pinion 24 when the isolator blade is stationary, totally eliminating any mechanical backlash between the rack 23 and pinion 24, and also eliminating any possibility of instability due to the compressibility of the hydraulic fluid, and further eliminating the need for counterbalance valves on the cylinders for pipe rupture protection.

In addition, a locking device can be manually operated to provide positive locking of the isolator blade for maintenance purposes.

For normal stationary position locking, a screw adjuster 61 is fully retracted and the brake is held applied by hydraulic pressure applied to the top of an emergency close piston 62, which forces a brake pad 63 against back of the rack 23, so locking the rack and pinion gears. For manual locking, the screw adjuster 61 is screwed down to provide the locking force. The drawings show the adjuster in the manually locked position.

To operate the valve closure blade the fluid pressure is applied to the underside of a brake piston 64 which is lifted against a belleville washer 65, thus releasing the brake. A retaining ring (nv shown in the drawings) limits the downward travel of the emergency close piston.

For emergency closing the brake is released by the loss of hydraulic pressure on the top of the emergency close piston 62.

The brake pads 63 may be fitted with a pair of embedded wires to allow an electrical signal to provide indication that pads should be replaced.

The drawings also show a locating piston 66.

Figure 12 shows the brake/lock assembly 28 of Figure 11 in more detail, and in particular shows supply ports 67 for applying pressure fluid to the top of the emergency close piston 62, a supply port 68 for applying pressure fluid to the underside of the brake piston 64, and also bleed ports 69. O-ring seals are shown, which are provided as appropriate.

Claims (11)

CLAIMS:

1. An isolator, provided at a three-way junction through which passes a high temperature gas, the isolator having a closure member pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, and hydraulic actuator means for pivoting the closure member between the said first and second positions, characterized in that a drive shaft of the closure member is operated by double acting hydraulic cylinders the rods of which translate racks to rotate a pinion attached to the said drive shaft, and in that the said actuator means provides different torques for opening and closing directions.

2. An isolator as claimed in claim 1, characterized in that the actuator is shaft mounted by means of a torque reaction arm integral with an actuator housing.

3. An isolator as claimed in claim 1 or 2, characterized in that the racks are connected to ends of the piston rods by means of spherical rod ends.

4. An isolator as claimed in any of claims 1 to 3, characterized in that a housing for the actuator is provided with sheet metal covers to enclose the racks and piston rods.

5. An isolator as claimed in any of claims 1 to 4, characterized by sub-assemblies respectively located to absorb part of the cylinder thrust near the end of the respective cylinder stroke to reduce the torque at the terminal position corresponding to the cylinder outstroke.

6. An isolator as claimed in claim 5, characterized in that each said sub-assembly comprises a washer spring pack enclosed in a housing and operated by compressing the spring pack via a plunger connected to a buffer, whereby as the hydraulic cylinder approaches the end of the stroke the end of the rack contacts the buffer and depresses the plunger to thus depress the spring pack and absorb some of the cylinder thrust.

7. An isolator as claimed in any of claims 1 to 6, characterized by further comprising a mechanical locking device for clamping the two racks onto the pinion in the form of a brake.

8. An isolator as claimed in any of claims 1 to 6, characterized in that the actuator is provided with a pair of hydraulic brakes providing positive locking of the actuator drive pinion when the isolator closure member is stationary.

9. An isolator as claimed in any of claims 1 to 8, characterized in that each cylinder comprises a main piston, a hollow rod and a secondary piston which functions as an accumulator piston, in that the hollow piston rod forms a cylinder for the secondary piston, and in that the main piston head has a port which allows transfer of hydraulic fluid from the annulus side of the main piston to the secondary piston.

10. An isolator as claimed in any of claims 1 to 9, characterized by comprising a toggle-driven diverter valve.

11. An isolator substantially as herein described with reference to, and as shown in, any of Figures 3 to 12 of the accompanying drawings.