Abstract:
Disclosed is a pneumatic actuator which includes a housing comprised of two halves and having at least two passages defined therethrough, including a “loop” groove defined in an inner peripheral wall of the housing into which a seal member is inserted. A rotary piston is rotatably received in the housing. The piston has a top and a bottom with an intermediate wall connected there between, and an actuating shaft extending through the housing, which is rotated by movement of the rotary piston. The seal member extends into the housing and is in contact with the top and bottom of the rotary piston all the times. The rotary piston moves free of contact with the interior surface of the housing and this one seal member provides a seal for the joint created between the halves of the housing, the chambers of the housing as well as the actuating shaft. Movement of the piston is effected by air pressure and return motion of the piston can be air driven or spring assisted.

Description:
[0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 09/597,268, filed on Jun. 20th, 2000, which had been a continuation of U.S. patent application Ser. No. 09/287,261, filed on Apr. 7th, 1999, which had been a continuation of PCT/CA 97 / 00736 , and this application is also a continuation of PCT/CA00/00373. 
     
    
     
       FIELD OF INVENTION  
         [0002]    The present invention is concerned with the field of valves and actuators and relates to a pneumatic actuator. More particularly, the present invention is an improved pneumatic actuator, which includes a rotary piston that reciprocates within a housing.  
         BACKGROUND OF INVENTION  
         [0003]    [0003]FIG. 1 shows a conventional pneumatic valve actuator which includes a toothed shaft  10 , an actuating shaft  20  extending through the toothed shaft  10 , two piston members  30  each having a rack member  301  engaged with the toothed shaft  10 , and a plurality of springs  302  biasedly disposed between an inner side of a housing  40  and the piston members  30 . In operation, the pneumatic valve actuator operates on the basis of cycles of air movement. At the beginning of a cycle air under pressure enters the interior of the housing  100  via two holes  41  to push the piston members  30  from a starting position away from each other to a fully separated position (as illustrated in FIG. 1) such that the toothed shaft  10  is rotated in a counter-clockwise direction by the movement of the two rack members  301  and the springs  302  are thereby compressed. By virtue of the rotation of the toothed shaft the actuating shaft  20  is also rotated. The rotation of the actuating shaft  20  is utilized for some other function (not shown). When the piston members  30  reach the fully separated position air entry into the housing is stopped, and the two holes  41  are opened to vent the housing at which time, the springs  302  push the piston members  30  back to the original starting position and thereby the toothed shaft  10 , and correspondingly, shaft  20  are rotated in a clock-wise direction. When the piston members reach the starting position, one cycle will have been completed. During operation, the force of pressurized air in the housing  100  causes leakage at the positions where the toothed shaft  10  and/or the actuating shaft  20  extend through the housing  40  (not shown in FIG. 1). Depending upon the construction characteristics and materials used in the valve, as well as the amount of pressure, even after using such actuators for a short period of time leakage can occur. Furthermore, the interior surfaces of the housing  40  and contact and sliding surfaces of the rack members  301  must be manufactured precisely to ensure that the rack members  301  slide smoothly along the inner surfaces of the housing  40  all of which increases the cost of manufacturing.  
           [0004]    Another commonly used pneumatic valve actuator is illustrated in FIGS. 2 and 3. The actuator is disposed between a return spring  7400  and a valve  7200  with a shaft  6200  extending through the return spring, the actuator and the valve so that when pressurized air is injected into the actuator, the shaft is rotated to operate the valve.  
           [0005]    The actuator includes a casing, including an upper casing  6010 , a lower casing  6020  and a vane member  6400  which is received between the upper and lower casing. The upper and lower casing are connected by bolts  6030  along flanges extending from each of the upper and lower casing wherein the lower casing has two passages  6800  defined therein so that pressurized air can be injected from the air pump and into the passages. The shaft rotatably extends through the upper casing and the lower casing and securely extends through the vane member. A seal member  6600  is disposed to the vane member so that the piston member is reciprocally moved within the casing by pressurized air entering the casing through the passages. The shaft is co-rotated with the vane member so as to control the actuator between an open and closed position. A return spring means  7400  including a spring coil  7600  is disposed above the actuator casing in accordance with a requirement to automatically return the shaft to its starting position once the pressurized air is stopped, thereby returning the vane member to its original position.  
           [0006]    The seal member tends to become quickly worn out because the seal member slides along an inner surface of the casing whenever the piston moves. Furthermore, the inner surface of each of the upper and lower casing must be machined smooth to prolong the life of the seal. The return means including the coil spring and the machining of the inner surface of the casing results in the whole assembly being quite expensive.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention avoids the above-noted problems of the prior art by providing an improved pneumatic actuator comprising a simpler, cost efficient piston, spring, and seal assembly.  
           [0008]    Accordingly, the present invention provides a pneumatic actuator comprising a housing having an inner surface, a piston having an exterior surface and disposed within the housing, a shaft connected to piston, and a seal simultaneously engaging each of the exterior surface of the piston, the inner surface of the housing, and the shaft, and defining first and second chambers within the housing. The first chamber can be substantially isolated from the second chamber. The seal can further include aperture means for receiving the shaft. The exterior surface of the piston can be movable relative to the seal. The seal can immovably reside in a groove formed within the inner surface of the housing. Movement of the piston from a static condition to an operative condition can be effected by fluid pressure. The actuator can further comprise resilient means for biasing the piston towards a static condition. The resilient means can have a first end and a second end, the first end engaging an inner surface of the housing within the second chamber, and the second end engaging the piston, and could include a leaf spring. The actuator can be operatively connected to a valve to effect movement thereof.  
           [0009]    In another aspect, the present invention provides a pneumatic valve actuator comprising a housing, a piston, moveable between a stable condition and an operative condition, a seal for effecting sealing between the piston and the housing, and defining first and second chambers within the housing, and resilient means disposed within the housing for biasing the piston towards a static condition. The first chamber can be substantially isolated from the second chamber. The resilient means has a first end and a second end, the first end engaging an inner surface of the housing within the second chamber, and the second end engaging the piston. The actuator can be operatively connected to a valve to effect movement thereof.  
           [0010]    In yet another aspect, the present invention provides a pneumatic actuator comprising a housing, a piston having an exterior surface, means to introduce fluid pressure into the housing to effect movement of the piston, and a seal for effecting sealing between the piston and the housing, and defining a first chamber and a second chamber within the housing, the seal engaging the exterior surface of the piston in a substantially fluid tight arrangement in response to fluid pressure in the first chamber. The seal can have a surface exposed to fluid pressure within the first chamber, the fluid pressure acting upon the surface to effect a substantially fluid- tight engagement between the seal and the exterior surface of the piston. The surface of the seal is other than perpendicular relative to an axis defined by the exterior surface of the piston. The actuator can be operatively connected to a valve to effect movement thereof.  
           [0011]    In a further aspect, the present invention provides a pneumatic valve actuator comprising a housing, a rotary piston having at least atop, a bottom and a peripheral wall, sealing means, wherein the sealing means is cooperatively arranged with the housing and the piston such that the sealing means is in contact with the top, bottom and peripheral wall of the piston and the housing and thereby defines a first and second chamber within the housing, means for effecting movement of at least a portion of the piston from the first chamber into the second chamber and back into the first chamber, such movement comprising one cycle of the piston, means for transferring movement of the piston to a further device, wherein the housing is comprised of two halves and the sealing means is securely received in a groove which is formed upon joining the halves of the housing, the groove defines a loop on an inside wall of the housing where the halves join, the sealing means comprising a single loop of sealing material, and wherein the sealing material is selected from the group comprising Viton, Buna N™ or polyurethane.  
           [0012]    According to a further aspect of the present invention there is a pneumatic valve actuator comprising a housing having a first half and a second half each half containing at least one passage defined therethrough and communicating with the interior and exterior of the housing, a groove defining a loop in an inner wall of the housing and formed when the halves are joined, a first and second hole defined perpendicularly through the housing, the first and second holes located in alignment with each other and communicating with the groove, a rotary piston having a top, a bottom, a peripheral wall connected between the top and the bottom, and at least one intermediate wall connected perpendicularly between the top, the bottom and the peripheral wall, and further having two engaging holes perpendicularly defined through the top and bottom, wherein the two engaging holes each are defined by a rectangular periphery and the actuating shaft has a rectangular cross section, a seal member securely received in the groove on the inner wall of the housing, two seal member holes defined through the seal member and located to communicate with the first hole and second hole wherein the sealing means is cooperatively arranged with the housing and the piston such that the sealing means is in contact with the exterior of the piston and the housing and thereby defines a first and second chamber within the housing, means for effecting movement of at least a portion of the piston from the first chamber into the second chamber and back into the first chamber, such movement comprising one cycle of the piston, an actuating shaft rotatably extending through the first hole, the two seal member holes, the two engaging holes and the second hole, wherein the rotary piston is fixedly connected to the actuating shaft, the actuating shaft imparting movement of the piston to a further device.  
           [0013]    According to another aspect of the present invention, there is a pneumatic actuator comprising a housing having an inner surface, a piston having exterior and interior surfaces and disposed within the housing, the piston having a first position and a second position, whereby the piston is urged from the first position to the second position by fluid pressure, a shaft connected to the piston, and resilient spring having a first end and a second end, the first end abutting against the inner surface of the housing and the second end fixedly connected to the shaft, for urging the piston from the second position to the first position, wherein the first end comprises a roller disposed against the inner surface of the housing. The shaft includes lever arms for imparting kinetic energy from the piston to the spring means, the lever arms disposed against the interior surface of the piston. The shaft comprises a two-part construction, each part having a hub with a lever arm extending from the hub and each part rotatable about an axle. The axle is a two-part axle. The piston further includes opposing first and second interior surfaces having opposing first and second recesses respectively for retaining the two-part axle, and wherein each of the hubs includes throughbores for receiving the two-part axle therethrough. The two-part axle is spring-loaded by a spring means disposed between each part of the two-part axle for urging each part of the two-part axle against the first and second recesses.  
           [0014]    According to a further aspect of the present invention there is a pneumatic actuator comprising a housing having an inner surface and defining a chamber, a piston having exterior and interior surfaces and disposed within the housing, the piston having a first position and a second position, whereby the piston is urged from the first position to the second position by fluid pressure, a shaft connected to the piston, a spring support member extending from the inner surface of the housing, resilient spring having a first end, and a second free end, the first end connected to the shaft, the second free end extending outwardly from the shaft and into the chamber, and the second free end being biassed against the spring support member. The first end of the resilient spring can be secured to the shaft.  
           [0015]    Other advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a top plan view, partly in section, of a conventional pneumatic actuator;  
         [0017]    [0017]FIG. 2 is a perspective view of a pneumatic actuator comprising a conventional control means and a spring return;  
         [0018]    [0018]FIG. 3 is an exploded view of the pneumatic actuator of FIG. 2;  
         [0019]    [0019]FIG. 4 is an exploded view of a pneumatic actuator in accordance with the present invention;  
         [0020]    [0020]FIG. 5 is a side elevational view, partly in section, of a pneumatic actuator in accordance with the present invention;  
         [0021]    [0021]FIG. 6 is a top plan view, partly in section, of the pneumatic actuator to illustrate how the torsion spring works when the rotary piston is actuated;  
         [0022]    [0022]FIG. 7 is a top plan view, partly in section, of another embodiment of the pneumatic actuator to show the rotary piston is actuated by air-flow without the torsion spring;  
         [0023]    [0023]FIG. 8 is a top plan view, partly in section, of another embodiment of the pneumatic actuator to show the rotary piston is actuated by air-flow without the torsion spring;  
         [0024]    [0024]FIG. 9 is a side elevation view, partly in section, of the piston assembly and spring assembly of the actuator in FIG. 10;  
         [0025]    [0025]FIG. 10 is a top plan view, partly in section, of another embodiment of a pneumatic actuator of the present invention;  
         [0026]    [0026]FIG. 11 is an exploded view of the piston assembly and the spring assembly of FIG. 9;  
         [0027]    [0027]FIG. 12 is a side elevation view, partly in section, of a valve which is operatively connected to an embodiment of a pneumatic actuator of the present invention;  
         [0028]    [0028]FIG. 13 is a top plan view, partly in section, of another embodiment of a pneumatic actuator of the present invention;  
         [0029]    [0029]FIG. 14 is a side elevation view, partly in section, of the embodiment illustrated in FIG. 13;  
         [0030]    [0030]FIG. 15 is an exploded view of the housing piston assembly, and seal of the embodiment illustrated in FIG. 13; and  
         [0031]    [0031]FIG. 16 is an exploded view of the piston assembly and the spring assembly of the embodiment illustrated in FIG. 13.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    Referring now to the drawings and initially to FIGS. 4 through 6, one embodiment of a pneumatic actuator according to the present invention comprises a housing  50 , a rotary piston  70  and a seal  60 .  
         [0033]    The housing  50  is composed of two halves, first half  151  and second half  152 , combined with fastening means  501  and has at least two airway passages  51 , 57  (see FIGS. 6 and 7) defined therethrough which communicate between an interior  55  and exterior of the housing  50 . A retaining groove  52  is defined on an inner side wall of the housing  50  to receive a seal  60  therein. The complete retaining groove is conveniently formed when the two halves of the housing  50  are fastened together by fastening means  501 . When the first half  151  and the second half  152  are joined with piston  70  and seal  60  disposed therein, the housing  50  includes first chamber  1511  and second chamber  1512  which are substantially isolated from each other by piston  50  and seal  60 .  
         [0034]    The housing  50  further includes a first aperture  54   a  and a second aperture  54   b , or two “holes”, both of which pass through walls of the housing  50  and are located in alignment with each other to receive an actuating shaft  80  therethrough.  
         [0035]    The seal  60  forms a band and is securely received, and immovably resides in the groove  52  and (see FIGS. 4, 5,  6  and  7 ) forms a complete loop around the interior side walls of the closed housing  50 . The seal  60  can be made of any appropriate sealing material such as polyurethane, Viton™, or Buna N™. The placement of the seal  60  into the groove is conveniently achieved by fastening the two halves of the housing  50  together. A portion  602  of the seal  60  extends into the first chamber  1511  of the housing  50 . This portion of the seal incorporates pressure assisted seal technology to ensure complete contact between the seal  60  and the exterior of the piston  70 , as further described below. First and second apertures  62   a  and  62   b , or two “holes”, are defined through the seal  60  and located to communicate with the first housing aperture  54   a  and the second housing aperture  54   b  respectively.  
         [0036]    The piston  70  has a top wall  71 , a bottom wall  142 , a peripheral wall  701  connected between the top wall  71  and the bottom wall  142 , and an intermediate wall  702  joining the top wall  71 , the bottom wall  142  and the peripheral wall  701 . The piston can be open on one side such that the interior of housing  50  communicates with second chamber  1512  for facilitating the use of a biasing means to bias piston  70  to its static condition, as described below. The piston  70  receives an actuating shaft  80  through first aperture  72   a  and second aperture  72   b , or two “engaging holes”, provided in top wall  71  and bottom wall  142  respectively. Each of the first aperture  72   a  and second aperture  72   b  can have a rectangular periphery, although any shape which is capable of engaging an actuating shaft  80  of corresponding shape is within the scope of the present invention. The actuating shaft  80  has a first base portion  81  (see FIG. 4) having a splined sleeve  810  so as to receive a splined shaft  90  to which other mechanisms can be connected.  
         [0037]    A cylindrical second base portion  82  extends axially from the first base portion  81 , and the actuating shaft  80  extends axially from the second base portion  82 . In one embodiment, the shaft  80  is rectangular although any shape corresponding to the shape of the first aperture  72   a  and second aperture  72   b  is within the scope of the present invention. When assembled, (see FIG. 5) the first base portion  81  is received within and provides seating for housing  50 . The second base portion  82  extends through the first aperture  62   a  and provides seating for the exterior surface of piston  70 . The actuating shaft  80  extends through the first piston aperture  72   a  and second piston aperture  72   b , seal aperture  62   b , and housing aperture  54   b . Sleeve  83  is received in second housing aperture  54   b  and second seal aperture  62   b , and is seated on the exterior surface of piston  70 . Sleeve  83  receives shaft  80  and, therefore, spaces shaft  80  from the side walls of each of housing aperture  54   b  and seal aperture  62   b.    
         [0038]    Referring to FIG. 4, a tubular sleeve  73  having a passage  731  defined therethrough is mounted on the actuating shaft  80  and located between the top wall  71  and bottom wall  142  of the piston  70 . In one embodiment, the passage  731  is defined by a tubular periphery. Referring to FIG. 5, when assembled, it can be seen that the rotary piston  70  rotates in unison with actuating shaft  80 . According to one embodiment, a torsion spring  85  is mounted on the sleeve  73 . The torsion spring  85  winds around sleeve  73  and has a first extending portion  801  thereof contacting against an inner surface of the intermediate wall  702 . The torsion spring  85  further has a second extending portion  802 , extending from piston  70  and contacting against an inner side of the housing  50  in second chamber  1512 . First extending portion  801  is joined to second extending portion  802  by intermediate portion  803 .  
         [0039]    Referring now to FIGS. 4 and 6 it can be seen that an effective seal is created by the seal  60 . Inner surface of seal  60  engages the exterior wall of piston  70  and outer surface  604  (FIG. 4) engages housing  50 . More particularly, seal  60  contacts the top  71  and the bottom  142  of the piston  70  while the central portion  63  contacts the peripheral wall of the rotary piston  70 . A portion of the seal  60  directly opposite the central portion (not shown in FIG. 4) is shown in cross-section in FIG. 6 and  7  as  640  and this portion  640  is in contact with the extended wall portion  720  of intermediate wall  702 . As well, the apertures in the seal  60  contact the piston where the shaft parts  82 ,  83  are located. In this respect, an effective seal is created between chambers  1511  and  1512 . By virtue of this same arrangement, an effective seal is created between actuating shaft  80  and first chamber  1511 , and between housing  50  and its external environment.  
         [0040]    In summary, one seal provides all of the sealing necessary to provide two substantially isolated chambers  1511  and  1512 .  
         [0041]    As can be seen in FIG. 6, the contact between the seal member and the external surface of the piston  70  creates an effective seal and provides two chambers  1511  and  1512  thereby making it possible for air pressure to rise in chamber  1511  which provides a driving force for movement of the piston  70  into chamber  1512 . As such, the exterior surface of piston  70  does not engage housing  50 . Advantageously, the inner walls of the housing  50  do not need to be manufactured precisely and machined smooth because the rotary piston  70  does not contact the inner walls, only the seal. All that is required is that the walls of the piston  70  be smoothed, which from a manufacturing cost perspective is significantly easier to do and therefore significantly less costly.  
         [0042]    In another embodiment illustrated in FIGS. 9, 10 and  11 , a spring  200  maybe provided to bias piston  70  towards a static condition, such condition being further described below. A two-part hub  206 , comprising upper and lower parts  206   a  and  206   b  is provided to fix one end  208   a  of spring  200 . In this respect, each of upper and lower parts  206   a  and  206   b  include recesses  206   c  and  206   d  for receiving the first end  208   a  of spring  200 . Each of upper and lower hub parts  206   a  and  206   b  rotate about spring-loaded two-part axle  212 . Further, each of the hub parts  206   a  and  206   b  include bores extending therethrough for receiving each member of the two-part axle  212 . Two-part axle  212  has upper and lower members  212   a  and  212   b  which are biased by spring  214  towards recesses  215   a  and  215   b  inside piston  70  and are retained therein.  
         [0043]    The second end  208   b  of spring  200  is substantially fixed in space relative to housing  50  by armature  210  so that substantially all energy imparted to spring  200  is transferred to first end  208   a . Armature  210  includes first and second ends  210   a  and  210   b . First end  210   a  is coupled to second end  208   b  of spring  200 . Second end  210   b  includes a roller  211  which is disposed against an inner wall of second chamber  1512  of housing  50  for reducing friction load as armature  210  moves in response to a reduction in diameter of the spring  200  as spring  200  is placed under tension.  
         [0044]    To impart kinetic energy from piston  70  to the spring  200 , upper and lower drive arms  218   a  and  218   b  are coupled to upper and lower hub parts  206   a  and  206   b  respectively. Each of upper and lower drive arms  218   a  and  218   b  are disposed against inner walls of piston  70 . As piston  70  rotates, kinetic energy is imparted to each of drive arms  218   a  and  218   b , which consequently transfers kinetic energy to hub parts  206   a  and  206   b , whereby kinetic energy is finally transmitted to the first end  208   a  of spring  200 .  
         [0045]    In the embodiment illustrated in FIG. 9, stub shafts  216   a  and  216   b  are integrated with piston  70 . In turn, devices can be operatively connected to either of stub shaft  216   a  or  216   b , to thereby be actuated by the actuator of the present invention.  
         [0046]    In another embodiment illustrated in FIGS.  13 - 16 , a pneumatic actuator is shown also having a two-part coil spring  400  for biasing piston  70  towards a static condition. Coil spring  400  includes an upper spring part  400   a  and a lower spring part  400   b . In association with each upper and lower spring parts  400   a  and  400   b , a pair of two-part bushings  406   a  and  406   b  is provided for spacing spring parts  400   a  and  400   b  from each other and from the inner wall of piston  70 . In this respect, upper and lower parts  406   a  and  406   b  include slots  406   c  and  406   d  for receiving the first end  408   a  of the spring part  400   a  or  400   b . The first end  408   a  extends through slots  406   c  or  406   d  and is keyed to shaft  80  within groove  81  formed therein. In this respect, inner portion of spring parts  400   a  and  400   b  rotate with shaft  80 .  
         [0047]    Shaft  80  extends through opposing and aligned throughbores  54   a  and  54   b  formed in piston  70 . Retaining clips  420  and  422  are provided to prevent axial movement of shaft  80  to piston  70 . Retaining clips  420  and  422  are fitted upon corresponding shoulders formed on the surface of shaft  80 . When fitted on their corresponding shoulders, retaining clips  420  and  422  extend outwardly from the shoulders and are interposed between flanges  424  and  426 , provided on respective bushings  406   a  and  406   b , and inner wall portions  428  and  430  of piston  70  proximate respective throughbores  54   a  and  54   b . In this respect, retaining clips  420  and  422 , acting in concert, substantially prevents axial movement of shaft  80  relative to piston  70 . Shaft  80  can further be operatively connected to a valve stem  432 .  
         [0048]    The second outer end  408   b  of each of spring parts  400   a  and  400   b  extends outwardly from shaft  80  and into chamber  1512 , where it is freely supported by spring support member  410 . Spring support member  410  is mounted on and extends from an inner wall of chamber  1512 . Spring support member  410  has a distal end  412  having a surface comprising an antifriction sleeve. Distal end  412  has a first side surface  414  and a second side surface  416 , both extending from an inner wall of chamber  1512  connecting to distal end  412 . Each of spring parts  400   a  and  400   b  proximate their respective second outer ends  408   b  is biased against distal end  412  of spring support member  410 . Ends  408   b  are configured to move radially relative to the spring support member  410 . In the embodiment illustrated in FIG. 13, distal end  412  is rounded to minimize frictional losses when spring parts  400   a  and  400   b  move across the surface of distal end  412  in response to rotation of piston  70 . Spring parts  400   a  and  400   b  proximate second outer ends  408   b  move across the surface of distal end  412  in response to rotation of shaft  80 . Second outer ends  408   b  are bent for facilitating installation of respective spring parts  400   a  and  400   b.    
         [0049]    Referring to FIG. 12, an embodiment of the pneumatic actuator may be operatively connected to a valve  300  for effecting movement of valve  300  between static and operating conditions. In this respect, shaft  80 , which is engaged to piston  70 , can include a splined sleeve  81  for receiving a spline shaft  90  which is coupled to valve  300 . Rotation of piston  70 , therefore, effects movement of valve  300 . It is understood to those skilled in the art that any other conventional means by which the movement of the piston  70  can be transferred to a further device is within the scope of the present invention.  
         [0050]    The sealing arrangement will now be explained with reference to FIGS. 4, 10, and  12 . The seal  60  comprises a continuous band having an outer surface  604  and an inner surface  606 . The outer surface  604  engages housing  50 . In this respect, an outer retaining ring  608  extends radially from and coextensively with the outer surface  604 , and is keyed or anchored within groove  52  of housing  50 . In this respect, groove  52  acts as a keyway having opposing locking shoulders  52   a  and  52   b  for locking or anchoring the outer retaining ring  608  within the keyway or groove  52 . The inner surface  606  engages piston  70 . In this respect, portion  602  has an inner retaining ring  610  extending radially from and coextensively with the inner surface  606 , and projecting into the first chamber  1511 . The outer retaining ring  608  is joined to the inner retaining ring  610  by web  612 . The inner retaining ring  610  has an outer surface  614  and an inner surface  616 . The inner surface  616  engages the exterior surface of piston  70 . The outer surface  614  faces first chamber  1511  and is disposed such that outer surface  614  is not perpendicular to an axis defined by the exterior of piston  70 . In this respect, any fluid in chamber  1511  will tend to exert forces on outer surface  614  such that a substantially fluid tight seal is formed between inner surface  616  and the exterior of piston  70 .  
         [0051]    In one embodiment, the piston  70  can be constructed to provide biasing means for biasing the piston  70  towards a static condition and in the general direction of first chamber  1511 . Unlike the elaborate external return means of the prior art illustrated in FIGS. 2 and 3, or a multiplicity of linear coil springs as illustrated in the prior art of FIG. 1, the torsion spring  85  can be designed to be installed inside the piston  70 . After adding one revolution (clockwise) of preload, the helical portion of the torsion spring  85  (see FIG. 6) will relax against an extended wall portion  720  of the piston  70  making the assembly safe for handling while it is being installed between the two halves of the housing  50 . As the housing halves are tightened together the helical portion will be forced clockwise about another  30  degrees adding more preload. This now removes the arm  802  from contact with the extended portion  720 , of the piston  70 .  
         [0052]    In operation, a complete cycle of the piston  70  starts when pressurized air is allowed into the housing  50  through passage  51  (passage  57  is open to atmospheric or reduced pressure) into first chamber  1511 . By virtue of the air pressure, the rotary piston  70  rotates from a static starting position to an actuated midcycle position as shown by phantom lines in FIG. 6. The rotary piston  70  completes the cycle upon release of air pressure into chamber  1511  by rotation back to the static starting position condition as shown by solid lines in FIG. 4 by virtue of the energy stored in the torsion spring  85 . This rotation is transferred to any external device connected to the rotary shaft  80 .  
         [0053]    [0053]FIG. 7 shows another embodiment of an actuator valve of the present invention which differs from the embodiment in FIG. 6 by the absence of a torsion spring. In operation, a complete cycle of the piston  70  starts when pressurized air is allowed into the housing  50  through passage  51  (passage  57  is open to atmospheric or reduced pressure) in the first chamber  1511 . By virtue of the air pressure in chamber  1511 , the rotary piston  70  rotates from a static starting position to an actuated midcycle position as shown by phantom lines in FIG. 7. The rotary piston  70  completes the cycle by rotation back to the starting position as shown by solid lines in FIG. 7 by virtue of the introduction of pressurized air via passage  57  (passage  51  is open to atmospheric or reduced pressure) into second chamber  1512 .  
         [0054]    [0054]FIG. 8 shows a further embodiment of an actuator of the present invention. As in the embodiment shown in FIG. 7, there is no torsion spring. In this embodiment, however, intermediate wall  702  is disposed such that it contacts an intermediate part of the peripheral wall  701  of the piston  70 . The arrangement of this intermediate wall is such that in operation, a complete cycle of the piston  70  starts when pressurized air is allowed into the first chamber  1511  of the housing  50  through passage  51  (passage  57  is open to atmospheric or reduced pressure) and by virtue of the air pressure the rotary piston  70  rotates from a static starting position to a midcycle position as shown by phantom lines in FIG. 8 The rotary piston  70  completes the cycle by rotation back to the starting position as shown by solid lines in FIG. 8 by virtue of the introduction of pressurized air via passage  57  (passage  51  is open to atmospheric or reduced pressure) into second chamber  1512 .  
         [0055]    Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.