GB2047344A - Actuator assembly for rotary valve - Google Patents

Abstract

An actuator assembly has a drive bar 21 for rotating the shaft 12 of a valve. The actuator assembly includes a Scotch yoke mechanism Y interposed between the valve shaft 11 and the drive bar 21. A longitudinally extensible bellows assembly 30 in a casing 27 has means for introducing fluid under pressure into the bellows assembly 30 to move the drive bar 21, the effective area D at the drive end of the bellows assembly being such as to provide a first force during the initial extending movement of the bellows, such area being of progressively lesser value D' as the bellows approaches the terminal end of the drive stroke, whereby lesser closing force is exerted through the Scotch yoke assembly Y to the valve shaft. <IMAGE>

Description

SPECIFICATION Actuator assembly for rotary valve The present invention is in the field of actuator assemblies generally and pertains more particularly to an actuator assembly employing a Scotch yoke connector to rotate the shaft of a rotary valve mechanism.

It is known to employ as a means for operating a rotary valve shaft, an axially extensible actuator member carrying one element (the drive pin) of a Scotch yoke assembly. The fork of the assembly is fixed to the valve shaft with the drive pin lying in the slot or guideway of the fork. The drive pin moves in a direction perpendicular to the axis of rotation of the shaft and, by virtue of its connection to the fork, translates the axial force of the pin into a rotary or torsional force on the valve shaft.

In operation of the rotary valve, it is desirable that the initial force imparted be great to unseat the valve components which may be reacting against fluids under high pressure. The force desirably exerted in the final closing movement of the valve is preferably substantially less than that required to initiate such closing movement. In the event that the valve is closed under high force components, it is possible to damage the valve or to jam the valve in its closed position in such manner that the forces required again to open the valve are unduly great and beyond the capacity of the valve actuator mechanism.

The present invention may be summarized as directed to an improved actuator assembly for rotating the shaft of a valve and employing a Scotch yoke mechanism, known per se, the apparatus for moving the Scotch yoke mechanism being characterized in that force exerted in the closing movement of the valve is lower than that applied to the Scotch yoke mechanism throughout the major movements thereof.

More particularly, apparatus in accordance with the invention is comprised of a drive bar carrying a drive pin engaged with the fork of a Scotch yoke mechanism, which fork is secured to the valve shaft. An axially extensible actuator member, preferably in the form of a collapsible and expansible bellows lying within a container or guideway is secured to the bar carrying the pin of the Scotch yoke mechanism.

The bellows is adapted to be connected to a source of fluid under pressure, e.g., oil or gas pressure, etc.

The characterizing feature of the present invention lies in the construction whereby the drive end of the bellows against which the fluid reacts is of a first and larger area during the initial stage of the expanding movement of the bellows, and of a second and smaller area in the course of the final expanding movement of the bellows, whereby the force developed by the expanding bellows is reduced at the end of the bellows stroke.

More particularly, the bellows device incorporates a rigid end plate adjacent its free or lead end, to which one end of the bellows is secured, the plate being of a smaller diameter than the portion of the bellows secured thereto. The bellows includes a radially outwardly extending portion adjacent the plate which in the collapsed condition of the bellows has a diameter D which provides the initial area against which fluid under pressure forced into the bellows will react.

The bellows is so constructed and arranged that when it is fully extended at the end of the drive stroke, the diameter of the area against which the fluid under pressure reacts will be reduced so that a reduced force is applied against the pin of the Scotch yoke mechanism.

Accordingly, it is an object of the invention to provide an improved actuator mechanism for rotating the shaft of a rotary valve wherein the final closing movement of the valve is effected at lower force than is present during the initial movement of the valve shaft.

A further object of the invention is the provision of a valve actuator of the type described which employs a Scotch yoke connection to translate axial movement of the actuator into rotary movement of the valve, the actuator comprising an axially movable bellows including a free end against which fluid under pressure may react, the effective diameter of the free end being a first vaiue during the initial portion of the expanding stroke of the bellows and progressively becoming smaller as the bellows reaches the end of its expanding stroke.

Still a further object of the invention is the provision of a device of the type described wherein the drive bar carrying the drive pin of the Scotch yoke assembly is mounted for reciprocation between two actuator assemblies of the type described, one of which is pressurized in the opening stroke of the valve and the other of which is pressurized to effect the closing stroke of the valve, both such actuator assemblies applying reduced force at the end of the operative strokes thereof, whereby both the final opening movement of the valve and the final closing movement of the valve are effected at reduced forces as contrasted with the initial movements thereof.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is an end elevational view of an actuator mechanism in accordance with the invention; Figure 2 is a horizontal sectional view of the assembly of Figure 1 taken on the line 2-2 of Figure 1.

Figure 3 is a magnified discontinuous section taken on the line 3-3 of Figure 2.

Turning now to Figure 2 of the drawings, the actuator assembly includes a housing 10 rotatably carrying a drive shaft 11, keyed end portion 11' of the latter enabling the same to be operatively connected to shaft 12 of a rotary valve, such as a ball valve or a butterfly valve.

A Scotch yoke assembly Y having a pair of fork elements 13, is keyed to the shaft 11, as by a key member 14. Each of the fork members 13, 1 3 includes bifurcate leg portions 1 5, 1 6, defining therebetween a slot 1 7 for reception of the drive pin assembly 1 8 of the Scotch yoke mechanism.

Optionally, but preferably, a pair of abutment stops 1 9, 20 are formed on the housing 10 extending radially inwardly toward the key member 14, thereby providing limit stops restricting the rotary movement which may be imparted to the shaft 11 to a fixed angular extent, e.g., 900 The drive pin assembly 1 8 is carried on a reciprocable drive bar 21, the assembly including a carrier pin 22 fixed within a transverse apertures 23 in the bar 21. A pair of bearing sleeves 24,25 are rotatably mounted on the portions of the pin projecting from the drive bar 21, the sleeves 24, 25 lying intimately within the slots 1 7 of the fork portions of the Scotch yoke assembly.

The drive 21 is reciprocably movable in the direction of the arrow 26 by an actuator assembly forming the principal advance of the present invention.

More particularly, the actuator assembly comprises a pair of casings 27, 28 fixed to the housing 10 as by machine screws 29. As will be readily recognized from a consideration of Figure 2, the actuator mechanisms encompassed within the casings 27, 28 are preferably identical but operate in opposition to each other, that is to say, when one such assembly is caused to extend, the other one is retracted, and vice versa. Accordingly, a description of one such assembly will suffice.

Within the casing 27 there is mounted a bellows assembly 30, (shown in extended position) which assembly includes a bellows 30A characterized by the ability to expand and contract in an axial direction responsive to the pressure introduced into the interior, the bellows 30A being resistant to substantial radial expansion under pressures of the magnitude encountered. Bellows of the type described are known per se as components of shock absorber mechanisms and generally are comprised of heavy resilient neoprene or like elastomeric substances, resistant to the hydraulic oils or like fluids with which they are contacted. The bellows 30A at each of the pleats 31 thereof, preferably incorporates an annular reinforcing member 32 which limits expansion at the pleat.

The bellows assembly 30 has one end 33 secured to the end wall 34 of the casing 27.

Mounting of the end 33 to the wall 34 is effected by a mounting plate member 35 having inturned end portions 36 encompassing an annular bead 37 at the end 33 of the bellows 30A.

The wall 34 includes a plurality of mounting holes 38. Machine screws 39 are threadedly connected into threaded receiver sockets 40 formed on the plate 35 and defining a leak-proof connection therewith.

Access to the interior of the bellows 30A is provided through aligned apertures 41, 42 in the end plate 34 and plate 35, respectively, in which a nipple fitting 43 is secured, the latter being externally threaded and maintained in position by a lock nut 44 mounted over the projecting threaded portion of the nipple.

The free end 45 of the bellows assembly is, in similar fashion, mounted to a drive plate 48 secured, as by welding, to the end 47 of the drive bar21.

As noted in connection with the end 33 of the bellows assembly, the free end 45 is secured to the plate 48 which has internally threaded receiver sockets 49 for the reception of machine screws 50 which are passed through apertures in the drive plate 48, whereby the drive plate 48, and consequently the free end 45 of the bellows assembly, are rigidly secured to the ends 47 of the drive bar 21.

As best seen in Figure 2, the bellows assemblies disposed within the respective casings 27 and 28 are shown in their limiting positions, the hollows 30A within casing 27 being disposed in its fully extended or elongated condition, and the bellows 30A' in casing 28 being disposed in its fully contracted position. A nipple 43' is provided in the end wall 34' of the casing 28, providing access to the interior of the bellows assembly 30A'.

It will be readily recognized from the above that movement of the drive bar 21 is effected by alternately filling one of the bellows assemblies 30A or 30A' while permitting fluid encompassed within the other bellows to be exhausted either to the atmosphere, where air is used as the motive fluid, or to a reservoir, where hydraulic operation is employed.

A principal contribution of the present invention lies in the ability of the bellows assemblies hereinabove described, when properly coordinated in their strokes to exert on the drive bar a force of the first magnitude, when the bellows extends from the contracted toward the expanded limiting position thereof, and a force of a second magnitude, less than said first magnitude, when the bellows approaches its fully extended position.

Referring now to the bellows 30A' within casing 28, and particularly to the portion or area of the lead end of the bellows 30A' designated by the reference numeral 52, it will be perceived that when it is in collapsed condition, the portion 52 together with plate 48' has an effective area D against which the fluid introduced into bellows 30A' may react, to urge the drive bar 21 to the left. The bellows 30A' is so constructed and arranged relative to the length of the bellows stroke that when the bellows expands toward the end of its stroke, i.e., when the plate 46' abuts against end wall 54', as shown for example on the left side of casing 28, the diameter of the end of the bellows 30A' against which the fluid pressure reacts will be progressively reduced to D'. (See Left Side of Figure 2).

As a result the force reacting against the drive bar 21 will be reduced.

The drive bar 21 passes through aligned apertures 53, 53' in the end plates 54, 54' of the casings 27 and 28, respectively.

The operation of the device will be apparent from the preceding description.

When it is desired to rotate the shaft 11 in such direction that the fork component 13 of the Scotch yoke assembly will be moved tb the solid line (clockwise) position, Figure 2, fluid is introduced into the interior of the bellows 30A (when it is in contracted condition) through fitting 43. The nipple 43 of bellows 30A' is connected either to the atmosphere or to a reservoir. Fluid entering the bellows 30A will cause the same to extend from left to right (Figure 2) carrying the drive bar 21 to the right. The drive bar carrying the drive pin assembly will induce the desired clockwise movement of the shaft 11 through its connection with the fork component of the Scotch yoke.

The force exerted by the drive bar 21 through the drive pin 18 will progressively decrease assuming constant pressure, from the initial or "break away" position of the valve, to its final closed position due to reduction in the area of the end of the bellows with consequent reduction in the force applied to the drive bar 21.

In the illustrative example shown the effective inner diameter D of the bellows when in retracted condition will be, say, 7-3/8". When the bellows is in fully extended condition the inner diameter D' will be say, 6-7/8" or one half inch less. Thus with a pressure of 100 P. S. I., the initial force is 4272 pounds and the final force is 3712 pounds, a difference of 560 pounds.

It will thus be observed that the objective of reducing the force at the terminal ends of the operation of the bellows is automatically achieved in accordance with the present invention.

The final positioning of the valve in its fully opened or fully closed position is preferably dictated by the abutment of the key 14 against either of the abutments 1 9 or 20.

As hereinbefore noted, return movement of the drive bar 21 and consequent reverse operation of the valve is effected by the admission of fluid through nipple 43 into bellows 30A' and the connection of fitting 43 to the atmosphere or to a reservoir, as appropriate.

While the device of the present invention has been illustrated in conjuction with a pair of oppositely acting actuator units operatively connected to a drive bar interposed therebetween, it will be readily recognized that the invention in its broadest context, does not require the utilization of two such devices. More particularly, the principal benefit of the invention may be achieved utilizing a conventional return mechanism in combination with the force reducing bellows device as described in detail above. Under such circumstances, of course, the benefits of reduced force at the end of a stroke are achieved only in one direction.

The automatic force reducing features of the present invention are particularly useful in combination with the Scotch yoke connection in that it is the nature of the Scotch yoke connection, by reason of mechanical advantage to increase the force exerted at the end of the operative stroke, a tendency which is counteracted by the operation of the bellows device.

Claims (12)

1. An actuator assembly for imparting rotary movement to a valve shaft or the like, comprising an elongate casing defining a guideway, a drive bar extending from said casing and shiftable axially relative thereto between retracted and extending limited positions, a Scotch yoke connection interposed between said bar and said shaft for rotating said shaft in accordance with the axial position of said bar relative to said casing, an actuator member in said casing shiftable between contracted and extended limiting positions within said casing, said actuator member including a drive end connected to said bar, means for introducing fluid under pressure to said actuator member to react against the driver end thereof, thereby to extend said member, said actuator member being conformed for progressive reduction of the effective area of the driver end thereof as the actuator member moves from contracted to expanded position, thereby to reduce the extending force exerted by said actuator as the same approaches said extended limiting position.

2. Apparatus in accordance with Claim 1 and including retractor means connected to said drive bar for shifting said actuator member from said extended to said contracted limiting position.

3. Apparatus in accordance with Claim 2, wherein said retractor means comprises a second actuator member disposed in a second casing.

4. Apparatus in accordance with Claim 3, wherein said second actuator member includes means for introducing fluid under pressure thereinto.

5. Apparatus in accordance with Claim 4, wherein said second actuator member is substantially identical to the actuator member defined in Claim 1.

6. A device in accordance with Claim 1, wherein said actuator member comprises a bellows.

7. A device in accordance with Claim 6, wherein said driver end of said bellows comprises a rigid plate secured to said drive bar, and said bellows end includes a flange portion at the end thereof mechanically coupled to said plate whereby upon extension of said bellows, the diameter of the portion thereof secured to said plate will become progressively smaller, thereby reducing the effective area of said driver end and hence the force exerted thereby.

8. Apparatus in accordance with Claim 6, wherein said bellows includes means for limiting radial expansion thereof.

9. An actuator assembly for a rotary valve or the like comprising an elongate casing defining a guideway, a drive bar extending from said casing and axially movable relative thereto between retracted and extended limiting positions, and an operating shaft mounted in laterally offset position relative to said bar for rotation about an axis normal to the axis of said bar, Scotch yoke connection means interposed between said bar and said shaft for rotating said shaft responsive to axial movement of said bar relative to said casing, an actuator member disposed within said casing, said member including a fixed end secured to said casing and a free end, said actuator member comprising a longitudinally extensible bellows member shiftable from a collapsed position to an extended position within said casing, a driver portion at said free end of said bellows, said driver portion being fixed to said bar and being of a first diameter, when said bellows is in collapsed position, means for introducing fluid under pressure to the interior of said bellows to react against said driver portion thereof to extend said bellows, thereby progressively reducing the diameter of said free end thereof against which the fluid under pressure reacts.

10. Apparatus in accordance with Claim 9, and including retractor means connected to said drive bar for shifting said bar in a direction to move said actuator member from said expanded to said contracted position.

11. Apparatus in accordance with Claim 10, wherein said retractor means comprises a casing having a second actuator means in accordance with Claim 9 disposed therein, said second actuator means being arrayed in opposition to the first actuator means.

12. An actuator assembly for a rotary valve substantially as described and as shown in the accompanying drawings.