WO2000073687A1

WO2000073687A1 - Improved pneumatic valve actuator

Info

Publication number: WO2000073687A1
Application number: PCT/US2000/014349
Authority: WO
Inventors: David E. Cain
Original assignee: Fmc Corporation
Priority date: 1999-05-27
Filing date: 2000-05-24
Publication date: 2000-12-07
Also published as: GB2363626B; AU5043800A; GB0125155D0; GB2363626A

Abstract

A fluid dampened pneumatic actuator (10) has a housing (12) defining a pneumatic chamber (70) and a dampening chamber (72), with a fluid being located within the dampening chamber (72). A piston (60) is movable within the housing (12) and separates the pneumatic chamber (70) and the dampening chamber (72). An actuator stem (68) is fixed to the piston (60) and extends from the actuator housing (12) for connection with a linearly movable valve element. A pneumatic supply (69) is in communication with the pneumatic chamber (70) and delivers pressurized pneumatic fluid to the pneumatic chamber (70) for piston (60) and actuator stem (68) movement.

Description

IMPROVED PNEUMATIC VALVE ACTUATOR

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to valve actuators, particularly to linear valve actuators used for valves for oilfield applications. The invention also concerns pneumatic actuators for mechanical devices other than valves. More particularly, the present invention concerns a pneumatic actuator for imparting linear movement to a valve stem responsive to application of pneumatic pressure and for dampening valve actuator movement to prevent pressure induced slamming of the valve or other actuated device to which the actuator, actuator stem is operatively connected.

Description of the Prior Art

Pneumatic actuators connected to gate valves in oilfield flow lines can, under some circumstances, cause a problem in the operation of the gate valve. A valve stem, which is attached to a gate or other valve element is attached to a piston of a pneumatic valve actuator. Compressed gas acts against the piston thereby moving it linearly within an actuator housing chamber. When initial valve stem movement causes initial opening of a gate valve, the pneumatic energy of the compressed gas imparting force to the piston of a valve actuator rapidly increases as the valve cracks open, because the friction between the gate and seat of the valve in the closed position is greatly reduced or even eliminated as the valve cracks open and differential pressure across the gate member of the valve becomes minimal. As a result of the low friction, the valve gate and the stem are free to be accelerated to the completely

open position by the piston and actuating stem of the valve actuator. The rapid opening movement of the gate and stem caused by the action of the compressed gas of the actuator often causes the gate to accelerate and then impact, i.e., slam into the internal structure of the bonnet or body of the valve. This sudden stop or slamming of the gate member against the bonnet or body structure of the valve results in a significantly large impact force, which may damage the valve. It is desirable therefore to provide a pneumatic, linear actuator mechanism that minimizes the potential for slamming of the valve gate within the valve body, especially under conditions where friction between the gate and seats of a valve is suddenly reduced during initial opening of the valve. Objects of the Invention It is a principal object of the invention to provide a novel improved pneumatic actuator for valves and other linearly actuatable mechanical devices which develops a damping action for slowing the opening movement of the valve mechanism in order to avoid damage to the valve by slamming during opening;

It is another feature of the present invention to provide a novel improved pneumatic actuator utilizing a fluid, such as a fluid or a gas which is metered through a flow restriction and dampens or slow pneumatic pressure induced movement of the actuator piston and stem so that a condition of slamming at the end of the actuator stroke does not occur;

It is also a feature of the present invention to provide a novel improved pneumatic actuator having an internal resilient cushioning element which may be contacted by the actuator piston or stem and serves to provide a cushioning effect to minimize the potential for actuator damage by slamming;

SUMMARY OF THE INVENTION The objects and features of the invention identified above, along with other features and advantages of the invention, are incorporated in an improved pneumatic valve actuator of the type which includes a closed chamber having a piston disposed therein which is coupled to the valve stem of the valve. Pressurized air or other gas, referred to herein as "air", is applied to one side of the piston. A return spring on the other side of the piston resists motion of the piston caused by the force of air pressure on the other side of the piston. When the air pressure is removed or lowered below the piston return force of the spring, the return spring causes the piston to move to the closed position and the valve to move to a fail closed position, assuming that the valve is of a reverse acting gate design. The principal improvement of this invention is the incorporation of a motion restriction device with the pneumatic valve actuator and the valve system for the purpose of controlling the rate of piston and valve movement and minimizing any potential for actuator induced slamming of the valve mechanism due to friction changes of the valve mechanism.

According to a first alternative embodiment of the invention, the piston chamber of the prior art pneumatic actuator is fluid filled with the spring. A second fluid filled chamber is provided which acts against a second spring resisted piston. An orifice restriction between the first and second fluid filled chambers slows the flow of fluid between the two chambers and thereby slows the movement of the piston in the first chamber and the valve stem. The gate speed and acceleration of the valve are significantly restricted, and the damage to the valve is mitigated.

According to a second alternative embodiment of the invention, the piston chamber of the prior art pneumatic actuator is sealed with the exception of one or more orifice restrictions in the chamber. As the piston is actuated, air in the piston can only escape via the orifice restriction. This design retards the acceleration of the value stem and the piston of the actuator. A rubber spring in the actuator housing chamber is positioned to face the piston and serves to mitigate piston impact with the internal wall structure of the actuator housing during the opening of the valve or other device being actuated. BRIEF DESCRIPTION OF THE DRAWINGS

The objects, advantages and features of the invention will become more apparent by reference to the drawings which are appended hereto and wherein an illustrative embodiment of the invention is shown, of which:

Figure 1 is a sectional view of one embodiment of a valve actuator embodying the principles of the present invention and including a fluid filled piston chamber and a fluid motion restriction device;

Figure 2 is a sectional view of a fluid dampened actuator mechanism representing an alternative embodiment of the invention and illustrating a particular fluid motion restriction device suitable to inhibit acceleration of the valve stem to which the actuator is attached; and

Figure 3 is a sectional view illustrating another alternative embodiment of the present invention incorporating a sealed pneumatic chamber opposite the actuator piston and with one or more orifices to restrict escaping air upon operation of the actuator and with a rubber spring to resiliently stop movement of the piston during actuation. DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Referring now to the drawings and first to Fig. 1, an actuator mechanism for linear actuation of a valve or other similarly actuated device, is shown generally at 10 and incorporates an actuator housing shown generally at 12. The housing 12 has an end wall 14 from which extends a tubular wall 16 defining an internal wall surface 18 of cylindrical configuration which defines a piston chamber 20. A piston 22 is located for movement within the piston chamber 20 and has a peripheral seal 24 establishing sealing relation with the internal wall surface 18. The piston 22 partitions the piston chamber 20 and defines variable volume gas chamber 26 and a variable volume fluid chamber 28. An actuator stem 30is disposed in fixed relation with the piston 22 and extends in sealed relation through a central opening 32 of the end wall 14. For actuating movement of the piston 22, air or other actuating gas is introduced into the variable volume gas chamber 26 via a gas supply conduit 34 which is in communication with a gas supply passage 36 of the end wall 14. When the actuator is utilized for controlling movement of a valve mechanism, the actuator stem 30 is coupled to the valve stem of a gate valve or other linearly actuated valve for controlling the flow of fluid through oilfield flow lines. Within the piston chamber 20 is located a compression spring 38 which serves as a return spring for returning the piston and actuator stem, for example, to a normally closed position for a gate valve. The variable volume fluid chamber 28 is sealed and is filled with a dampening fluid 40, either fluid or gas. A fluid motion restriction device 42 is provided which defines a flow restriction in communication with the variable volume fluid chamber 28 and restricts pressure induced fluid flow from the variable volume fluid chamber when the valve is just opened and slows the valve stem from opening too rapidly when air or other gas pressure is introduced into the variable volume gas chamber 26 via a gas supply conduit 38 connected with a gas supply passage 40 of the end wall 14. Alternative One of the Invention Referring now to Fig. 2, an alternative embodiment of the present invention is shown having a fluid filled chamber from which a dampening fluid is metered through a flow restriction, with the metered fluid passing into a second chamber having a spring urged free piston which returns the dampening fluid to the fluid filled chamber when the actuating force of the actuator has been depleted. In this case, the fluid motion restriction device is in the form of a second piston and piston chamber where one side of the second piston is sealed for accepting fluid, the other side of the second piston being exposed to the atmosphere. As shown in Fig. 2 a fluid dampened actuator mechanism is shown generally at 50, having a first actuator housing shown generally at 52 and being defined by an end wall 54 and a tubular wall 56 defining an internal cylindrical piston sealing surface 58. A primary piston 60 is movable within an internal actuator chamber 62 defined by the actuator housing walls 54 and 56 and a second housing end wall 64. The primary piston 60 is provided with a peripheral piston seal 66 of any suitable character which maintains a seal between the primary piston and the piston sealing wall surface 58 of the tubular wall 56. An actuator stem 68 which, in the case the actuator mechanism is a valve actuator, may be referred to as a valve stem, is fixed to the primary piston and extends in sealed relation through the end wall 54 of the actuator housing. The actuator stem 68, in the case of valve actuators, imparts linear opening movement to the gate member of the valve when pneumatic pressure is introduced via a gas supply inlet conduit 69 into the actuating chamber 70 of the housing. The actuating chamber 70 is separated from a fluid filled chamber 72 by the primary piston 60. A piston return spring 74 is located within the fluid filled chamber with one of its ends seated on the second housing end wall 64 and the opposite end disposed in force transmitting relation with the primary piston 60. When the force of gas pressure acting on the primary piston 60 diminishes below the return force of the return spring, the primary piston 60 will be moved to the left as shown in Fig. 2. In the case of gate valves, this return movement of the piston 60 will typically cause the actuator stem 68 to move the valve gate member to the "safe" or "fail closed" position. If the gate member is arranged for "fail open" positioning, this piston movement will cause the gate member to be returned to its open position.

The second housing end wall 64 is typically connected to the tubular housing wall 56 by stud and nut connectors 76 or by any other suitable means of connection. The second housing end wall 64 also defines a wall or partition of a second piston housing shown generally at 78 and being defined by a tubular housing wall 80 to which is connected an end wall 82. The second housing end wall 64, tubular housing wall 80 and end wall 82 cooperate to define a secondary chamber 84 having a cylindrical piston sealing wall surface 86. A secondary piston 88 is movable within the secondary chamber 84 and is provided with a peripheral piston seal 90 which seals the secondary piston to the piston sealing wall surface 86. The secondary piston thus partitions the secondary chamber 84 into a secondary fluid chamber 92 and a return spring chamber 94. The return spring chamber 94 is in communication with the atmosphere via an atmosphere port 96 in the end wall 82 and contains a secondary return spring 98 having ends bearing respectively against the end wall 82 and the secondary piston 88. An orifice restriction device 100 is provided in the second housing end wall 64 as shown and serves to restrict the flow of liquid from the liquid filled chamber 72 into the secondary liquid chamber 92 of the secondary piston housing 78 when pneumatic pressure is introduced into the actuating chamber 70 and acts to force the primary piston and the actuating stem 68 to the right, as shown in Fig. 2 for displacement of liquid from the liquid filled chamber into the secondary liquid chamber 92. During such liquid displacement, the pressure of liquid acting on the secondary piston causes yielding of the secondary return spring. The force of the secondary return spring is sufficient to return the liquid through the orifice restriction 100 to the liquid filled chamber 72 when the force of gas pressure on the primary piston 60 has sufficiently dissipated to permit movement of the primary and secondary pistons by their return springs.

It should be noted that the actuating chamber 70 is identified as having a volume Vi and that the secondary liquid chamber 92 is also identified as having a volume Vi. The meaning of this is that the volume of liquid displacement caused by pneumatic pressure actuated movement of the primary piston results in equal volume displacement of liquid from the liquid filled chamber 72 into the secondary liquid chamber 92, though clearly the linear distances of piston movement will be different due to the differences in the sizes of the pistons. The secondary fluid return spring 98 normally causes the volume Vi of liquid of the second chamber to be of the same volume as that for the volume of air pressure at the head of the primary piston 60. The orifice restriction 100 provides restricted fluid flow from the liquid filled chamber 72 into the secondary liquid chamber 92. Where pneumatic pressure is applied to the head of the primary piston 60, liquid is forced via the orifice restriction 100 from the primary chamber 72 into the secondary chamber 92. Motion of the primary piston 60 and the actuator stem 68 connected thereto is slowed due to the orifice restriction and due to the retarding force of both fluid return springs 74 and 98 acting on the primary and secondary pistons. When air pressure is removed from the head of the primary piston, the spring of the primary liquid filled chamber 72 forces the piston and valve stem outwardly, typically to the normally closed position of a gate valve. As a result, the fluid return spring of the second piston forces liquid from the secondary liquid chamber 92 into the primary liquid filled chamber 72 via the orifice restriction 100. Alternative Two of the Invention

Referring now to Fig. 3, there is illustrated an actuator mechanism generally at 110 having an actuator housing shown generally at 112. The actuator housing is defined by an end wall 114 to which a tubular wall 116 is attached or with which the tubular wall 116 is integral. A mounting plate 118 is fixed to the tubular wall 116, such a by means of mounting bolts 120 and is sealed to the tubular wall 116 by a circular plate seal 122. The mounting plate 118 is provide with a mounting projection 124 which is adapted for fitting relation with the bonnet of a valve or a structural component of any other device to which the actuator is to be mounted.

A piston 126 is movable within the actuator housing and is provided with a peripheral seal 128 which maintains sealed relation of the piston with a cylindrical internal wall surface 130 of the tubular wall 116. The piston 126 is mounted in sealed relation on an actuator stem 132, with a piston retainer 133 maintaining the piston seated against a shoulder of the actuating stem. An upper, reduced diameter portion 135 of the piston stem projects through a stem passage 132 of a tubular stem seal retainer 136. One or more stem sealing elements 138 are retained within internal seal receptacles of the stem seal retainer and serve to maintain a seal between the actuator housing and the actuator stem during actuating and return movement of the actuator stem. The upper section 135 of the actuator stem projects from the end wall 114 of the actuator housing and serves as a visual indicator of the position of the piston 126 as well as accommodating the distance of piston and actuator stem movement during the actuating and return strokes of the actuator mechanism.

At the lower, mounting projection or structure 124, there is defined in internal seal flange 142 which retains an actuator stem seal 144 having sealing engagement with the cylindrical surface 146 of the actuator stem. The internal seal flange 142 and a cylindrical wall section 148 of the actuator mounting structure also defines a spring receptacle within which the lower end of a piston return spring or springs 150 are located. The upper ends of the return springs 150 are disposed in force transmitting relation with the piston 126. The return springs, in absence of air pressure within the actuating chamber 152 between the head surface 154 of the piston maintain the piston seated against the internal piston stop 156. The end wall 114 of the piston housing is provided with an air inlet fitting 158 connecting an air supply conduit 160 in communication with the actuating chamber 152.

Air pressure is applied to the head surface 154 of the piston for piston and actuating stem movement by injection of pressurized air or other gas into the actuating chamber. The injected air or gas may be supplied by a pilot valve, responsive to a particular pressure condition or it may be supplied simply by controlling a manually actuated valve in the air supply system. Typically the compressed air maintains the piston in a condition compressing the return springs so that shut-off of the actuating air will permit the return springs to shift the valve actuating mechanism and the valve associated therewith to a desired "safe" condition, typically the closed position in the case of gate valves.

To prevent slamming of the actuator mechanism and the valve being actuated thereby during opening valve movement, the mounting plate 118 is provided with an orifice fitting 162 which is received by an internally threaded section 164 of a gas transfer passage 166 in the mounting plate. The orifice fitting 162 defines a plurality of restricted passages through which fluid is metered from the sealed chamber 166 below the piston 126. Thus, when the friction of the gate of a valve with its seats suddenly decreases as the gate is being opened, the volume of air being displaced from the sealed chamber 166 is caused to flow through the flow restriction provided by the multiple orifices of the orifice fitting 162. The piston and valve stem and thus the valve gate being actuated thereby will thus move in controlled manner to an actuator position where the gate valve is fully open, with the slamming activity that can occur if flow of fluid from the chamber 166 were not restricted. The mounting plate 118 is also formed to define a dove tail-groove 168 or any other resilient spring mounting groove or structure. A resilient spring 170, typically of circular configuration, defines a dove-tail connector which is received within the dove-tail groove and serves to retain the resilient spring in its proper position with respect to the mounting plate. When the piston 126 has been moved linearly, nearly to its maximum extent, it will come into contact with the resilient spring 170 and will be cushioned thereby. This

cushioning feature functions in concert with the fluid metering feature of the invention to ensure against gas pressure induced slamming of the actuator mechanism or the valve or other device being actuated thereby.

In view of the foregoing it is evident that the present invention is one well adapted to attain all of the objects and features hereinabove set forth, together with other objects and features which are inherent in the apparatus disclosed herein.

As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its spirit or essential characteristics. The present embodiment is, therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.

Claims

I CLAIM:

1. A fluid dampened pneumatic actuator, comprising:

(a) a housing defining a pneumatic chamber and a dampening chamber; (b) a fluid being located within said dampening chamber;

(c) a piston being movable within said housing and separating said pneumatic chamber and said dampening chamber;

(d) an actuator stem being fixed to said piston and extending from said housing;

(e) a pneumatic supply being in communication with said pneumatic chamber and delivering pressurized pneumatic fluid to said pneumatic chamber for piston and actuator

stem movement; and

(f) a fluid motion restriction device being in communication with said dampening chamber and restricting pneumatic pressure induced flow of fluid from said dampening chamber for dampening movement of said piston and actuator stem.

2. The fluid dampened pneumatic actuator of claim 1, wherein said fluid motion restriction device comprising:

(a) a discharge passage being defined in said housing and being in communication with said dampening chamber; and

(b) a restriction element being in flow controlling relation with said discharge passage and defining at least one restricted passage restricting piston induced discharge flow of fluid from said dampening chamber through said discharge passage to dampen movement

of said piston and actuator stem to prevent slamming movement thereof.

3. The fluid dampened pneumatic actuator of claim 1, wherein said fluid motion restriction device comprising:

(a) a discharge passage being defined in said housing; and

(b) a restriction element being in flow controlling relation with said discharge passage and defining at least one restricted passage restricting piston induced discharge flow of fluid from said dampening chamber through said discharge passage to dampen movement of said piston and actuator stem to prevent slamming movement thereof;

(c) a secondary fluid chamber being in communication with said restricted passage of said restriction element and receiving fluid displaced from said dampening chamber;

(d) a secondary piston being movable within said secondary fluid chamber by fluid displaced from said dampening chamber; and

(e) a secondary return spring being disposed in force transmitting relation with said secondary piston and urging said secondary piston for displacement of fluid from said secondary fluid chamber into said fluid chamber upon dissipation of fluid displacement pressure within said dampening chamber and said secondary fluid chamber.

4. The fluid dampened pneumatic actuator of claim 1, comprising: a return spring being disposed in spring force transmitting relation with said piston and actuator stem and returning said piston and actuator stem to a predetermined position upon dissipation of pneumatic pressure within said pneumatic chamber.

5. The fluid dampened pneumatic actuator of claim 3, wherein:

(a) a secondary housing being located adjacent said housing and defining a secondary chamber therein

(b) said secondary piston partitioning said secondary chamber into a secondary fluid chamber and a spring chamber;

(c) said secondary housing having a vent port communicating said spring chamber with the atmosphere

6. The fluid dampened pneumatic actuator of claim 1, comprising:

(a) a secondary housing being located adjacent said housing and having a common wall with said housing;

(b) said fluid motion restriction device being located in said common wall and establishing fluid restricting communication between said dampening chamber and said secondary housing; and

(c) a secondary piston being movable within said secondary housing by pressure of fluid displaced from said dampening chamber.

7. The fluid dampened pneumatic actuator of claim 1, comprising:

(a) a vent port in said housing communicating said dampening chamber with the atmosphere; and

(b) a mechanical dampening element being located for cushioning said piston when said piston is moved to its full pneumatically actuated extent within said housing.

8. The fluid dampened pneumatic actuator of claim 7, comprising: said mechanical dampening element being an elastomer spring.

9. The fluid dampened pneumatic actuator of claim 8, comprising:

(a) said housing having an end wall defining a circular undercut spring groove; and

(b) said elastomer spring being received within said undercut spring groove with a portion thereof projecting beyond said end wall toward said piston for cushioned contact by said piston.

10. A fluid dampened pneumatic actuator, comprising: (a) a housing defining an internal chamber;

(b) a piston being movable within said internal chamber and partitioning said internal chamber into a pneumatic chamber and a dampening chamber;

(c) a fluid filling said dampening chamber an actuator stem being fixed to said piston and extending from said housing for connection to a mechanism to be actuated;

(d) a pneumatic supply being in communication with said pneumatic chamber and delivering pressurized pneumatic fluid to said pneumatic chamber for piston and actuator stem movement; and

(e) a fluid motion restriction device being located in said housing and defining at least one restricted passage in communication with said dampening chamber and restricting pneumatic pressure induced displacement flow of fluid from said dampening chamber for dampening pneumatic pressure induced movement of said piston and actuator stem.

11. The fluid dampened pneumatic actuator of claim 10, comprising:

(a) a discharge passage being defined in said housing; and (b) a restriction element being in flow controlling relation with said discharge passage and having at least one restricted passage therein restricting piston induced discharge flow of fluid from said dampening chamber through said discharge passage to dampen movement of said piston and actuator stem to prevent slamming movement thereof;

(c) a secondary housing defining a secondary fluid chamber being in communication with said restriction element and receiving fluid displaced from said dampening chamber; and

(d) a secondary piston being movable within said secondary fluid chamber by fluid displaced from said dampening chamber.

12. The fluid dampened pneumatic actuator of claim 10, comprising: (a) a primary return spring being disposed in spring force transmitting relation with said piston and actuator stem and returning said piston and actuator stem to a predetermined position upon dissipation of pneumatic pressure within said pneumatic chamber; and

(b) a secondary return spring being in force transmitting relation with said secondary piston and moving said secondary piston in a direction displacing fluid from said secondary fluid chamber to said dampening chamber upon dissipation of fluid pressure within said secondary fluid chamber.

13. The fluid dampened pneumatic actuator of claim 12, wherein:

(a) a secondary housing being fixed to said housing and defining a secondary chamber therein

(b) said secondary piston partitioning said secondary chamber into a secondary fluid chamber and a spring chamber; and

(c) said spring chamber having a vent port communicating said spring chamber with the atmosphere.

14. The fluid dampened pneumatic actuator of claim 10, comprising:

(a) a secondary housing being located adjacent said housing and having a common wall;

(c) a secondary piston being movable within said secondary housing by pressure of fluid displaced from said fluid filled chamber.

15. The fluid dampened pneumatic actuator of claim 10, comprising:

(a) a vent port in said housing communicating said dampening chamber with the atmosphere; (b) a return spring being located within said dampening chamber and applying spring force to said piston to return said piston to a predetermined position within said pneumatic chamber upon dissipation of pneumatic pressure therein; and

(c) a mechanical dampening element being located for cushioning said piston when said piston is moved by pneumatic pressure to its full extent within said housing.

16. The fluid dampened pneumatic actuator of claim 15, comprising: said mechanical dampening element being an elastomer spring.

17. The fluid dampened pneumatic actuator of claim 16, comprising:

18. A fluid dampened pneumatic actuator, comprising: (a) a primary housing defining an internal chamber;

(b) a piston being movable within said internal chamber and separating said internal chamber into a pneumatic chamber and a dampening chamber;

(c) a fluid filling said dampening chamber

(d) an actuator stem being fixed to said piston and extending from said housing for connection to a mechanism to be actuated; (e) a pneumatic supply being in communication with said pneumatic chamber and delivering pressurized pneumatic fluid to said pneumatic chamber for piston and actuator stem movement;

(f) a secondary housing being located adjacent said primary housing; (g) said fluid motion restriction device being in fluid restricting communication between said dampening chamber and said secondary housing;

(h) a secondary piston being movable within said secondary housing by pressure of fluid displaced from said fluid filled chamber; and

(i) a fluid motion restriction device having at least one restricted passage therein restricting pneumatic pressure induced displacement flow of fluid from said dampening chamber to said secondary fluid chamber for dampening pneumatic pressure induced movement of said piston and actuator stem.

19. The fluid dampened pneumatic actuator of claim 18, comprising:

(a) a primary return spring applying spring force to said piston for returning said primary piston to a predetermined position upon dissipation of pneumatic pressure; and

(b) a secondary return spring applying spring force to said secondary piston for displacement of fluid from said secondary housing into said dampening chamber responsive to dissipation of pneumatic pressure induced fluid pressure within said secondary housing.

20. The fluid dampened pneumatic actuator of claim 19, comprising: A resilient spring element being disposed for cushioning of said primary piston upon

pneumatic pressure induced movement thereof to its full extent.