SINGLE ACTING HYDRAULIC ACTUATOR WITH VARIABLE RETURN FORCE

Abstract: It is the object of the present in­ vention to provide a spring operated valve actuator with variable return force, utilizing a compact and space efficient spring system which can establish closing forces on a valve mechanism which are closely adapted to the closing characteristics needed for the valve. This is provided according to the invention by the use of a compact spring mechanism with a brief, but very powerful closing characteris­ tic, and where the energy provided by the spring mechanism is distri­ buted during the whole movement of the valve with varying forces loca­ lized according to needs. The essential novel and charac­ teristic mechanical feature by this actuator means, which according to the invention is provided with a spring mechanism and a movable piston, is that the spring mechanism and the piston is mechanically, drivingly interconnected by the means of a variable gear mecha­ nism (3, 4, 10).

Description: This invention relates to a single acting hydraulic actuator with variable return force, which is suited for automatic control of safety valves and for rapid closure of such valves in emergency situations. Such single acting hydraulic actuators are normally used to work on gate valves and are mounted directly to a valve stem which is movable for opening as well as for closing of the valve. An example of practical utilization in the oil industry is on the so-called Xmas Trees, as emergency blow out preventor valves for the main production stream of hydrocarbons, where the valves will be closed safely and efficiently when an ab­ normal situation arises. Such valve actuators are known for use both in sub sea and in top side equipment, for example on the deck of an offshore oil production platform. Such actuators will normally be mounted directly on the bonnet of the valve and the piston rod of the actuator will be connected to the valve spindle for control and regulation of the valve. As long as the control circuit is pressurized the valve rod or spindle is moved to and kept in open position and a spring in the actuator is tensioned or loaded. When pressure is removed the pressure or force of the spring will be released and act via the piston rod directly on the valve spindle and move this against the frictional resistance of the valve to a position where the valve is completely closed. The prior known valve actuators of this type, as example is re­ ferred to US patent No. 4,527,631 and the brochure "Model "OOH" Linear Hydraulic Gate Valve Actuator" - AVA-International - of February 7, 1984, have direct connection between the valve spindle and the spring mechanism. This implicates that when the spring is extended 10 mm, the valve spindle will have moved a corresponding distance. This is unpractical and inconvenient due to the fact that the demand for available closing powers usually is highest when the spring is depressurized and near the end of its extension. Furthermore, it is a requirement that the valve in addition to securing efficient closure also should have the capacity to cut through a possible hindrance, such as tubes, wires and the like, which are blocking the free closure of the gate valve within the bore or in the tube string. This has resulted in that the actuator equipment is voluminous and requires a great deal of space. Correspondingly, the dimensions of the spring are very great, the spring mechanism itself having an extended length of 1.5 m or more. It is an object of the present invention to provide a spring controlled valve actuator with variable return force not having these drawbacks where, by utilization of a compact and space-­ saving spring mechanism, there can be established closing powers which are precisely adapted to the closing characteris­ tics of the valve mechanism and furthermore, where near the end of the spring movement high closing powers are available to cut through possible obstructing objects preventing the closing of the valve. According to the invention, this is obtained by the utilization of a sturdy spring mechanism having brief but very powerful closing characteristics, where the energy from the spring mechanism is distributed or shifted over the complete closing movement of the valve, and where the energy or the power output can be varied and adapted to the need in different areas using the strongest forces, for example where it may be necessary to cut through obstructing objects and for the closing of the valve in its outermost position. The new and characteristic constructional features of the actua­ tor means according to the present invention are defined in the accompanying patent claims 1-4. Below, the invention will be described more closely in connec­ tion with a preferred embodyment which also is illustrated on the drawing, Fig. 1-3. The same reference numbers are used through out to identify identical parts on the drawings. Fig. 1 illustrates partly in longitudinal, sectional view the actuator mechanism with the spring mechanism in re­ leased and deactivated state. Fig. 2 illustrates a corresponding longitudinal, sectional view through the complete actutator unit, but where the upper half illustrates the spring unit in deactivated state and where the lower half illustrates the spring unit in tensioned or "loaded" state. Additionally is de­ monstrated how the short movement of the spring unit is transformed via a specific gear mechanism according to the invention to the valve spindle, which is performing an extended movement under variable power output. Fig. 3 is a diagram illustrating the power outlet through the tensioning or loading and detensioning or releasing of the spring mechanism. As apparent from Fig. 1 upper sectional half, the actuator unit is made from a cylinder 2 wherein is slidably mounted a piston member 10. Via a lifting rod 3 and a spring guidemember 4 the piston 10 is connected to and in engagement with a spring mechanism consisting of a number of plate springs 27. On the drawing the spring mechanism is shown in detensioned position, and this results in the piston is positioned in the outermost right position. The spring mechanism and the spring guide­ member 4 are mounted in a housing 5 which is attached to the cylinder 2 by means of bolts 23. An O-ring 24 is sealing the connection between housing and cylinder. A lid 6 is attached by means of screw bolts 15 to the end section of the cylinder 2. Pressurized fluid to the cylinder 2 and the piston 10 is introduced via an inlet opening in the middle part of the lid. An O-ring 16 is providing a sealed airtight connection be­ tween the lid and the cylinder 2. A pressure sleeve 19 and ball 20 are terminating the inlet flange of the lid. The packing system 18 of the piston is kept in position by means of a piston ring 14, which is connected to the piston with screw members 17. To obtain permanent and safe support of the piston in its circumferential direction, there is provided three levers 3 whereof one of these is shown on Fig. 1. The levers are rotatable mounted in studs or ears on the house 5 by means of a shaft 9 which is kept in position by means of segerrings 25. The opposite end of the lever is provided with a spring guide roller 8 which is rotating in glider bearings 26 and is engaged against the under side of the spring guiding means 4. Additionally, at the lower edge of the lever there is provided a piston rod roller 7 which is fastened and supported correspondingly to the roller 8, which is supported against inclined planes or slopes machined in the surface of the piston rod. The actuator housing 5 is terminated by a flange 11 which is connected to the housing by means of bolts 23, and a packing cord 28 provides sealing engagement between the housing and the flange. Furthermore, the flange is provided with bolts 15 or the like, for connecting it to the bonnet of a valve (not shown). The piston 10 is directly connected to a valve spindle and moves this forwards and backwards. The spindle is not shown on Fig. 1, but is outlined in Fig. 2 in its two end positions. The valve spindle 29 is firmly connected to the piston and the piston rod by means of a bolt 21. Two O-rings 22 provide sealing between the spindle and the piston. Further, there is provided an adjustment ring 12 and a ringformed stopper 13 at the end part of the piston. These are used for axial adjustment of the valve spindle and the piston. The function of the mechanism: The bottom side of the spring guiding means 4 is supported against the spring guide roller 8 of the lever. Additionally, the piston rod roller 7 is engaged against inclined planes in the surface of the piston rod. The piston rod and the spring guiding means are shown in shaded form on Fig. 1. When the hydraulic pressure is activated, the piston is forced from the outer to the inner position and the working force is utilized to move the valve spindle to an open position simultaneously as the spring mechanism is compressed and the plate springs 27 are loaded or activated. As seen from Fig. 3, the piston rod with valve spindle connected will move over a distance of approx. 180 mm. This movement is obtained by means of a spring mechanism having a total extension of 20 mm, which means that the gear ratio is about 10:1. The spring mechanism has a total length of 0.2-0.3 m, this being a substantially shorter length than the lengths obtained in prior known embodiments. The angle of inclination of the surface of the piston rod and the contour or outline of the bottom face of the guide member 4, determine the gear ratio. The spring mecha­ nism can therefore be made very short, but still have a high driving power during this short length of movement. The stored energy can hereby be utilized efficiently while the physical dimensions at the same time will be small. The bottom face of the guide member 4 is running at an angle of up to 20° in re­ lation to the vertical plane, and the outer contour or outline of the piston rod is so adjusted in relation to this inclination that a gear or exchange ratio of 5:1 to 10:1 is obtained. The power output during tensioning and release of the spring mecha­ nism is illustrated by the diagram shown in Fig. 3. When the hydraulic pressure is applied, the piston will start its move­ ment from its 0-position with the spring mechanism in released state, as seen in the upper sectional half according to Fig. 2. After a movement of approx. 20 mm length, during which a spring pressure of approx. 1000 kp has to be overcome, the slope or angle of inclination is increased to 20° and the spring pres­ sure which has to be overcome is increased to approx. 6000 kp over a distance of approx. 35 mm. Thereafter the angle of inclination will decrease and the pressure in the spring will decrease to approx. 1000 kp. After a movement of approx. 125 mm the angle of inclination will increase again corresponding to a spring force of approx. 1500 kp. Finally, near the end of the movement the inclination angle will increase again, corres­ ponding to a spring pressure of approx. 2000 kp. The pressure at this open state is to be kept continuously and this corresponds to stable operation conditions with the gate valve (not shown) kept in open position. If the pressure of one reason or another is failing, the safety procedure is activated. The spring mechanism is released and moves the spindle controlling the closure of the gate valve in opposite sequence of what is described above.. At the beginning a relatively high spring power is released to overcome any frictional forces and to start the movement of the mechanism. Thereafter the valve spindle is moved slowly, but determined without release of the very high spring forces. Near the end of this movement the closing power is strongly increased to secure the cutting through of possible unwanted obstructions and the remaining spring energy is then employed for the com­ plete closing of the valve. However, this is only an example of the utilization of the special spring power gear according to the invention. It is, however, possible to alter the power output by changing the angle of the inclining faces. Hereby it is possible to adjust the power output in correspondence to different valves and valve-closing characteristics without changing the outer physical dimensions of the mechanism. The mechanism is compact and provides a very flexible utiliza­ tion of the energy in the spring, which gives a near to ideal utilization of sturdy plate springs moving very short lengths during release of energy. The thickness of the adjustment ring 12 can be varied and this will provide a flexible and simple adjustment means to be used for centration of the mov­ able part of the valve by an axial movement of the outward piston rod 29, shown on Fig. 2. The piston 10 is connected to the outward piston rod 29 via the bolt 21.

Claims: 1. Single acting hydraulic actuator with variable return force and having an actuator unit consisting of a cylinder (2) and a co-operating piston (10) which is connected to an outward valve spindle (29) and having means for supply of pressurized fluid to cylinder and piston, the actuator also having a driving member consisting of a housing (5) wherein is mounted a spring mechanism (4, 27), where the driving member is mecha­ nically connected to the movable piston and the actuator unit having means for connection to a valve bonnet with a passage means for the valve spindle, and where the movement of the valve spindle is controlled by the move­ ment of the piston and the piston rod,characterized in that the spring mechanism and the piston are mechanically, drivingly connected by means of a variable gear mechanism (3, 4, 10). 2. Single acting hydraulic actuator with variable return force according to claim 1,characterized in that the gear mechanism consists of a number of levers (3), each formed as a single arm lever, where one end of the levers is rotatably mounted within the housing (5) of the actuator, and where the opposite end at the same time is mounted against the bottom side of a spring guiding member (4) and against the outer surface of the movable piston (10). 3. Single acting hydraulic actuator with variable return force according to claim 2,characterized in that the piston (10) has an extended piston rod member whose outer surface forms an inclining face with varying inclination angle and is engaged in power transmission relation with three piston rod rollers (7) which are rotatingly connected to the end of three levers (3) evenly distributed along the outer circumference of the piston member, and that each of these arms is provided with rotatably mounted spring guiding rollers (8) which are supported against the outer end surface of the spring guiding member (4). 4. Single acting hydraulic actuator with variable return force according to claim 3,characterized in that the outer end surface has an angle of inclination of up to 18° in relation to the vertical plane, and that the outer contour of the piston is having such a relation to this inclination angle that a gear ratio of from 1:5 to 1:10 is obtained.

Inventors: HEIM, EDGAR, SANDE, KURT, STAALAND, TORBJORN
Applicants: SKARPENORD CONTROL SYSTEMS A.S.
Application year: 1987
Main classification: F16K31
IPC codes: E21B34, F16K31