US3749860A

US3749860A - Sealed limit switch

Info

Publication number: US3749860A
Application number: US00213936A
Authority: US
Inventors: R Crepeau
Original assignee: Allen Bradley Co LLC
Current assignee: Allen Bradley Co LLC
Priority date: 1971-12-30
Filing date: 1971-12-30
Publication date: 1973-07-31
Anticipated expiration: 1990-07-31
Also published as: CA976588A

Abstract

An oil tight limit switch has an operating head mountable upon a body for the switch mechanism so that an opening in the head bottom faces an opening in the top of the switch body. An intermediary member sits in the two openings to serve as a partition between the interiors of the head and the body. A rockable camshaft is journaled in the head with an outer end protruding therefrom to mount an operating lever. A cam is keyed on the inner end of the camshaft to engage a reciprocally movable cam follower that extends through the intermediary member into the interior of the switch body. Rocking of the camshaft rocks the cam to impel the cam follower downward, actuating the switch. An O-ring seal is seated in the top surface of the switch body, or alternatively in the bottom surface of the operating head, to encircle a peripheral portion of the intermediary member and seal the intermediary member with the operating head and also with the switch body.

Description

United States Patent [191 Primary Examiner-Herman J. Hohauser Attorney--Arthur H. Seidel et al.

Crepeau [4 July 31, 1973 SEALED LIMIT SWITCH [75] Inventor: Robert G. Crepeau, Greendale, Wis. [57] ABSTRACT [73] Assgnee: u Company M'lwaukee An oil tight limit switch has an operating head mountable upon a body for the switch mechanism so that an [22] Filed: Dec. 30, 1971 opening in the head bottom faces an opening in the top of the switch body. An intermediary member sits in the PP 213936 two openings to serve as a partition between the interiors of the head and the body. A rockable camshaft is 52 us. Cl. 200/47 jeumeled in the heed with an outer end protruding 5 11 int. Cl. 'II01h 3/16 therefrom to mount an Operating lever- A eem is keyed 581 Field of Search 200/47, 153 K, 153 T, on the inner end of the eemeheft to engage a p 53 p; 74/29, 30 cally movable cam follower that extends through the intermediary member into the interior of the switch 5 References Cited body. Rocking of the camshaft rocks the cam to impel UNITED STATES PATENTS the cam follower downward, actuating the switch. An O-ring seal is seated in the top surface of the switch body, or alternatively in the bottom surface of the oper- 3252345 5/1966 X ating head, to encircle a peripheral portion of the inter- 31512I422 5/1970 Aslan 200/47 ux median member and the intermediary member with the operating head and also with the switch body.

9 Claims, 8 Drawing Figures PAImImJuLanm v ,7 9, 50

sum

2 or 2 INVENTOR ROBERT G.CREPEAU ATTORNEY SEALED LIMIT SWITCH BACKGROUND OF THE INVENTION Electrical limit switches are used in a wide range of industrial control applications such as governing limits of machine travel, controlling automatic processes, and actuating signal and safety devices. They are characterized by an enclosed body housing identical switch contacts, from which body an operating shaft emerges to be moved by some exterior force. The shaft may be rockable about its axis, or of a plunger type translatable along its axis, and a movement imparted to the shaft causes actuation of the associated electrical switch contacts.

One form of limit switch, to which the present invention is particularly directed, is the so-called oil tight limit switch, in which there is a main switch body housing the electrical switch contacts upon which is mounted a smaller housing termed an operating head. It is from the head that the operating shaft protrudes, and inside the head there is mechanism for translating shaft motion into a vertical, reciprocating motion that can be applied to the switch elements inside the main body. There usually is some form of seal between the interior of the operating head and the interior of the main body to impede oil, greases and contaminants that may be in the head from migrating into the region of the switch contacts.

A particular advantage of the use of a separate head in some limit switches is that it can be mounted in any one of several positions angularly around the vertical axis of the limit switch. Thus, the operating shaft may be directed forward of the switch, or sidewardly to either side of the switch, or rearwardly of the switch. A variety of external actuators, which are to operate the limit switch, can thus be accommodated.

Another advantage of the use of a separate head is that lubricant for the operating shaft and the mechanism it operates within the limit switch for developing a vertical motion applied to the contact elements can be isolated from the interior of the main body. External oils and liquids, such as machine tool coolants, can be better excluded than in a construction where the operating shaft enters the switch body interior in the same region in which the switch contacts are located. Nevertheless, it has been a problem in limit switches with separate operating heads to provide a seal to prevent against contaminants from entering into the switch, and also to contain the lubricant in the operating head while still providing efficient transmission of the actuating force without undue friction on the moving parts. Certain operating heads have contained a diaphragm placed between the interior of the head and the interior of themain switch body to isolate one from the other. Although this design provides an effective seal, there is some undesirable diaphragm action that occurs when the diaphragm is moved back and forth with the switch actuating movement. Other switches have utilized an O-ring disposed between the head and the switch so that together they form a sealed body to the outside, but such construction does not isolate lubricant in the head from the switchv body. It is these problems to which the present invention is directed.

SUMMARY OF THE INVENTION The present invention relates to limit switches having operating heads mounted on switch bodies and it more particularly resides in a switch having a hollow head with an open bottom that sits upon and closes over the open top of a main switch body and in which there is an intermediary member that functions as a partition between the head and body. A reciprocally movable element extends through the intermediary member, with a seal around its circumference, to transfer motion into the main switch body, and a seal is also disposed in a position sealing off an interface between the switch body and intermediary member from an interface between the head and the intermediary member, and also from an interface between the head and body.

In sealing off the interior of the operating head from the interior of the switch body some means must be included for transmitting motion from inside the head to inside the switch body. It is desirable that the mechanism in the head includes some cam type motion between the operating shaft that introduces motion into the head and the element that transmits vertical motion into the main switch body. For good cam design utilizing line contact between the cam elements, there must be some manner of aligning the cam element that delivers vertical motion into the switch body with the cam element that moves with the operating shaft. In a preferred form of the present invention this is achieved by provision of a cam follower that extends through an intermediary partition that separates the head from the main body. A keyed association between the follower and intermediary partition insures constant alignment of these parts, and the partition is also keyed into a preset position with the head, to thereby align the caming elements. Thus, regardless of the position in which the head is mounted on the main body, the internal operating parts retain their alignment with one another.

The invention also teaches a unique seal for the intermediary member. This member has a crosswise dimension less than that of the operating head and main switch body, so that it is seated inside the head and body. It is seated in such manner that at the peripheral regions of the member there are established interfaces between the member and the head and between the member and the body. There is also an interface between the head and body where the head rests upon the body. A single seal is then disposed at the juncture of the three interfaces to seal each from the others. An oil tight condition for the interior is thus established.

It is an object of this invention to provide a limit switch head that utilizes a cam and a cam follower motion converting assembly to transmit movement of an operating shaft to the associated switch contacts.

It is a further object to provide a shaft operated limit switch head with an interior that is sealed from the switch contacts that it is to actuate.

It is another object to provide a shaft operated limit switch head that forms with a main switch body an oil tight assembly.

It is still another object to provide a shaft operated limit switch head that may be mounted on its associated switch body in various positions to thereby increase the flexibility of its usage.

The foregoing and other objects and advantages of the invention will appear from the following description. In the description reference is made to the accompanying drawings, which fonn a part hereof, and in which there is shown by way of illustration, and not of limitation, specific forms in which the invention may be embodied. Such embodiments do not represent the full scope of the invention, but rather the invention may be employed in a variety of embodiments, and reference is made to the claims herein for interpreting the breadth of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view in elevation of a lever operated limit switch embodying the invention,

FIG. 2 is a fragmentary view on an enlarged scale in section taken through the plane 2-2 indicated in FIG.

FIG. 3 is a fragmentary view in section taken through the plane 3-3 indicated in FIG. 2,

FIG. 4 is a view of a cam shown in FIG. 3 which is depicted in a second of three alternative keyed positions,

FIG. 5 is a view of the cam of FIGS. 3 and 4 in its third keyed position,

FIG. 6 is a fragmentary view in section similar to FIG. 2 showing an alternative embodiment,

FIG. 7 is a top view of the switch body of FIG. 1 taken through the plane 7-7 indicated in FIG. 2, and

FIG. 8 is a perspective view of a cam follower forming a part of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, FIG. 1 is a front view that shows a limit switch with a switch body 1 upon which is mounted a switch operating head 2. The construction of the switch mechanism within the hollow interior of the switch body 1 is not a part of the present invention, and only the top of an actuator 3 and a return spring 4 of a switch mechanism are shown to explain the cooperation between parts of the invention and the mechanism housed within the body 1. The operating head 2 has four vertical walls and a flat top to give it a rectangular appearance, and it is secured to the switch body 1 by a set of four mounting bolts 5.

Referring now to FIG. 2, the head 2 has an integral hub 6 projecting from its front wall which has a throughbore 7 leading from the exterior to the hollow interior of the head 2. A movable camshaft 8 is journaled in a bushing 9 fitted in the hub 6, and the rear end of the shaft 8 is journaled in a second bushing 10 fitted in the head back wall opposite the hub 6. The shaft 8 has a complex configuration to mount and engage various operating components within the head 2. Beginning at the left in FIG. 2, the front end of the shaft 8 protrudes from the bushing 9 to mount an operating lever 11 that is fast upon the shaft 8, so that a tilting motion of the lever 11 will produce a corresponding rocking movement for the shaft 8. Inward of the lever 11, the shaft 8 has a land 12, and spaced from the land 12 is a bearing portion 13 fitted within the bushing 9. Between the land 12 and the bearing portion 13 is a sleeve 14 that provides an oil tight seal for the shaft 8. The specific construction of the sleeve 14 is not a part of this invention, but rather is the separate and distinct invention of Roy E. Wilson for which separate application for a patent may be made. Further, other types of dynamic seals may be substituted therefor.

Immediately adjacent the bearing portion 13, the shaft 8 is milled to form a notch 15 which is beneath a spring retaining pocket 16 in the interior of the head 2. A spring assembly consisting of a coil spring 17 seated in a sliding sleeve 18 is disposed in the pocket 16, with thespring 17 being partially compressed to force the sleeve 18 downward against the notch 15, biasing the shaft 8 in a normal angular position, as shown in FIG. 2. In addition, the sleeve 18 acts as an abutment in the notch 15 to prevent outward axial movement of the shaft 8.

To the right of the notch 15 is a truncated equilateral key portion 19 cut on the shaft 8, as seen most clearly in FIGS. 3, 4 and 5. A cam 20 has a key-way 21 that conforms to the shape of the key portion 19 for mounting thereon. Referring back to FIG. 2, beyond the key portion 19 is the rear end of the shaft 8, which is journaled in the bushing 10. A partially compressed cam spring 22 encircling the rear shaft end is interposed between the cam 20 and the bushing 10 to hold the cam 20 on the key portion 19.

Referring again to FIGS. 3, 4 and 5, the cam 20 has a pair of lobes and may be keyed on the shaft 8 in any one of three positions to engage a reciprocally movable cam follower 23 having an elongate body portion, as shown in FIG. 8. Affixed on the lower end of the follower 23 is an alignment cap 24, notched to form a set of four radially extending dogs 25. The upper end of the cam follower 23 terminates in a convex cam engaging apex 26 positioned directly beneath the cam 20, so that the follower 23 extends downward with a bearing fit through an intermediary member 27, seated in the open bottom of the head 2, as shown in FIGS. 2 and 3.

The intermediary member 27 is generally circular with a collar 28 protruding radially from the upper part thereof. The bottom portion of the member 27 has four downwardly extending teeth 29 which define notches into which the dogs 25 of the cam follower 23 fit. There is a central bore 30 in the member 27 through which the cam follower 23 extends, and the collar 28 of the member 27 loosely seats in the bottom opening of the operating head 2. The bottom opening has a stepped, circular seat 31 to receive the collar 28, and the top surface of the member 27 has a niche 32 (see FIG. 2) and a circular recess 33. The niche 32 mates with an alignment rib 34 in the wall of the head 2 to orient the member 27 with respect to the head 2. A felt washer 35 is seated in the recess 33 and is held in place by a retaining ring 36. The washer 35 snugly encircles the body portion of the follower 23 to serve as a seal between the follower 23 and the intermediary member 27. The dogs 25 and teeth 29 are not uniform in width and as a result, the intermediary member 27 and cam followers 23 will mate only when the dogs 25 are matched with conforming notches between the teeth 29. The follower 23 is thereby aligned by the member 27 so that the follower apex 26 transversely engages the cam 20 to normally fit into an arcuate gap between the lobes of the cam 20.

The lower portion of the cam follower 23 and the bottom of the intermediate member 27 are designed to protrude from the bottom of the operating head 2, extending into a stepped opening in the top of the switch body 1 as shown in FIGS. 2 and 3. The switch body 1 has a hollow interior in which the switch mechanism resides, and the cam follower 23 sits atop an actuator 3 for the switch mechanism. A return spring 4 biases the actuator 3 into an upper position.

The collar 28 of the intennediary member 27 overlaps the opening of the switch body 1 and rests on the top surface thereof to serve as a partition between the interiors of the body 1 and the head 2. With the member 27 positioned as thus described, the exterior sidewall of the collar 28 and the sidewall of the seat 31 in the operating head 2 form an interface 43. Similarly, a second interface 44 is formed by the bottom surface of the collar 28 and the top surface of the switch body I. These two interfaces 43, 44 meet at a common juncture with a third interface 45 formed by the bottom surface of the head 2 seating on the top surface of the body I. A circular channel 46 is precisely located in the top surface of the body I to receive an O-ring 47 that un derlies the periphery of the member 27 and seals each of the

interfaces

43, 44 and 45 from one another at the point of their common juncture. In this way, the O-ring 47 serves the dual purpose of sealing the operating head 2 and the switch body I together as a sealed unit, and also completing a seal isolating the interior of the head 2 from the interior of the body 1. FIG. 7 illustrates the manner in which the O-ring 47 lies in the channel 46 to surround the member 27 seated in the open top of the body 1. Mounting holes 48 for the bolts 5 are also shown. The holes 48 are positioned so that the operating head 2 may be secured on the switch body 1 in any one of four angular mounting positions.

The placement of the member 27 above the O-ring 47 is not crucial to the integrity of the seal between the

interfaces

43, 44 and 45. Satisfactory sealing may also be achieved by a second embodiment of the invention, as shown in FIG. 6, wherein an intermediary member 49 is seated in a switch body 50 so that its top surface is level with the top surface of the body 50. A cam follower 51 is directed through a central bore 52 in the member 49;, with its lower end resting on the switch actuator 3 and its upper end in engagement with the cam 20. The side of the cam follower 51 is grooved as at 53 to receive a key 54 in the bore 52 for preventing cam follower rotation and maintaining the follower 51 in proper alignment with the cam 20. A recess 55 is formed in the upper surface of the member 49 and a felt washer 56 is seated therein to encircle the follower SI, forming a seal between the follower 51 and the member 49. The washer 56 is held in place by a retaining ring 57.

A circular channel 58 is precisely located in the bottom surface of an operating head 59 to receive an O- ring 60 overlying the upper peripheral edge of the member 49. The O-ring 60, similar to the O-ring 47 of the first embodiment,also serves as a seal between three interfaces. There is an interface 61 formed by the bottom surface of the head 59, and the top surface of the body 50, a second interface 62 formed by the bottom surface of the head 59 and'the top surface of the intermediary member 49, and a third interface 63 formed by the upper sidewall of the intermediary members 49 and the sidewall of the opening in the body 50. All three of these interfaces are sealed from one another by the strategic location of the O-ring 60. Thus, the second embodiment provides essentially the same type of sealing as does the first embodiment.

With the above structures in mind, the operation of the operating head 2 will now be described assuming that a switch actuating stimulus is applied to the operating lever II. Since both forms of the present invention operate basically the same, only the operation of the first embodiment will be described. Upon application of an actuating stimulus the lever 11 will be tilted in a clockwise or counterclockwise direction depending upon the direction of the stimulus. The stimulus must be sufficient to overcome the biasing of the shaft 8 provided by the sliding sleeve 18 and the spring 17 since tilting of the lever rocks the camshaft 8. Rocking of the camshaft 8 cants the floor of the notch 15 to one side forcing the sleeve 18 upward to increase compression of the coil spring 17. The cant of the shaft 8 is limited because the sleeve I8 cannot be fully accepted into the pocket 16. Therefore, at its limit of movement into the pocket 16, the sliding sleeve 18 acts as a stroke limiting abutment.

The cam 20 rocks in correspondence with the camshaft 8 and, as shown in FIG. 3, either clockwise or counterclockwise rocking of the cam causes one of the lobes of cam 20 to engage the cam follower apex 26. This engagement impels the cam follower 23 downward, thereby forcing the switch actuator 3 downward to actuate the switch.

When the actuating stimulus on the operating lever 11 is relaxed the compression of the coil spring 17 returns the camshaft 8 and the cam'20 to their normal positions. Upon disengagement with the lobe of the cam 20 the cam follower 23 and the switch actuator 3 return upward to their normal positions by the return spring 4. During its vertical travel the cam follower 23 is restricted from rotating due to the interlocking between the teeth 29 of the intermediary member 27 and the alignment cap dogs 25. Hence, the cam follower apex 26 remains transversely aligned with the cam 20.

To increase the flexibility in usage of the operating head 2, the cam 20 may readily be changed from its position as shown in FIG. 3 to either of the keyed positions shown in FIGS. 4 and 5. With reference to FIG. 2, such change is performed simply by sliding the cam 20 toward the rear end of the camshaft 8 to disengage the cam from the key portion 19 and thereby compress the cam spring 22. The cam 20 may then be rotated to one of its other keyed positions and thereafter mounted back on the key portion 119.

By positioning the cam 20 on the key portion 19, as shown in FIG. 4, only clockwise motion of the cam 20 will bring one of the lobes of the cam 20 into engagement with the cam follower 23 to force the follower downward, because the rocking limit of movement of the shaft 8 is not sufficient to produce such engagement through counterclockwise motion.

In FIG. 5 the cam 20 is mounted in its third keyed position in which only counterclockwise motion of the camshaft 8 will bring one of the lobes of the cam 20 into engagement with the cam follower 23 to produce switch actuation. Thus, the present operating head 2 can be utilized in applications where it is desired to actuate the switch by either or both clockwise and counterclockwise movement of the operating lever 11. This capability increases the operational flexibility of the structure, so that it may be utilized in a variety of ways.

The flexibility of use of the present invention is enhanced by the sealing of the operating head 2 when it is mounted on an associated switch body 1. Through the utilization of the sleeve 14 and the O-

rings

47 or 60, the operating head 2 and the switch body 1 form an oil tight unit that may be employed in a variety of atmospheres. The efiectiveness of the seal is maintained for any angular position of the operating head 2 with respect to the switch body 1. Further, the intermediary member 27 provides an excellent bearing for the cam follower 23, while at the same time functioning as a tight partition and a means for assisting the cam follower 23 with the cam 20 on the operating shaft regardless of angular orientation of the operating head 2. The disclosed structure also provides a limit switch with a minimum of operating parts for translating motion from within the operating head to within the main switch body, so that it is both oil tight and employable for many types of application.

l claim:

1. In a switch actuating mechanism for a switch having a switch body in which switch contacts are housed, an operating head seated upon the switch body that can be disposed in a number of angular positions about an axis passing through the body and the head, an operating shaft protruding from the head at an angle to said axis adapted to mount an external lever arm which can be shifted to produce an actuating motion of the shaft, and a cam member within the head mounted on the shaft to move therewith, said switch body having an open top and said head having an open bottom closing over the top of said body, the combination therewith of:

a separate intermediary member interposed between the open bottom of said head and the open top of said switch body forming a partition between said head and said body, such intermediary member having a central bore leading from within said head to within said body;

reciprocally movable cam follower extending through said central bore of said intermediary member with a bearing fit, such cam follower thereby being movable with respect to said intermediary member; and separate seal in engagement with the periphery of said intermediary member that seals such member with said head and also seals such member with said switch body.

2. A mechanism as in claim 1, wherein said head has a bottom surface resting upon an upper surface of said switch body in an interface relation therewith; said intermediary member has a crosswise dimension less than those of said head and said body to fit within the interface of the head and body, and such member is seated in a recess of at least one of said head and said body to have an interface with said head and another interface with said body, the three interfaces meeting at a common juncture; and said seal being disposed at said juncture to seal off each interface from the other interfaces.

3. The combination of claim 1 wherein the top surface of said intermediary member has a niche and a rib protrudes from said operating head to mate with said niche, aligning said intermediary member with said head.

4. The combination of claim 3 wherein said cam follower has a lower end portion notched to form a number of dogs and said intermediary member has a toothed portion that interlocks with said dogs of said follower to align said follower with said cam.

5. In a switch mechanism for a switch having a switch body in which switch contacts are housed, an operating head seated upon the switch body, an operating shaft protruding from the head at an angle to an axis passing through the body and the head and adapted to mount an external lever arm which can be shifted to produce an actuating motion of the shaft, and a cam member within the head mounted on the shaft to move therewith, said switch body having an open top and said head having an open bottom closing over the top of said body, the combination therewith of:

a separate intermediary member interposed between the open bottom of said head and the open top of said switch body forming a stationary partition between said head and said body, such intermediary member having a bore forming a bearing leading from within said head to within said body, and also having a peripheral portion that has an interface with both said head and said body;

a reciprocally movable cam follower extending through and having a bearing fit with said bore for reciprocation with respect to said intermediary member; and

a seal in engagement with the periphery of said intermediary member that seals such member with said head and also seals such member with said switch body.

6. In a switch actuating mechanism for a switch having a switch body member in which contacts are housed, an operating head member seated upon the body member, an operating shaft protruding from the head member at an angle to an axis passing through the body member and the head member and adapted to mount an external lever arm which can be shifted to produce an actuating motion of the shaft, and a cam within the head member mounted on the shaft to more therewith, said body member having an open top and said head member having an open bottom, the combination therewith of:

a recess formed in the opening of one of the head and body members;

a separate intermediary member with an upper portion having a peripheral collar that seats in said recess of one of the head and body members and overlaps the opening of the other member to form a stationary partition between said head and body members, such intermediary member having a bore leading from within said head member to within said body member;

reciprocally movable cam follower extending through said bore of said intermediary member with a bearing fit; and separate seal in engagement with the periphery of the collar of said intermediary member that seals such member with said head member and also seals such member with said body member.

7. A mechanism as in claim 6, wherein said recess is formed in the opening of the head member so that the collar of the upper portion of said intermediary member overlaps the opening of said body member, and said seal is located in the top surface of said body member.

8. A mechanism as in claim 6, wherein said recess is fonned in the opening of the body member so that the collar of the upper portion of said intermediary member overlaps the opening of said head member, and said seal is located in the top surface of said head member.

9. The combination of claim 6 wherein said cam follower is centrally positioned with respect to the top of said switch body member, and said operating head member is mountable on said body member in a plurality of angular positions.

Claims

1. In a switch actuating mechanism for a switch having a switch body in which switch contacts are housed, an operating head seated upon the switch body that can be disposed in a number of angular positions about an axis passing through the body and the head, an operating shaft protruding from the head at an angle to said axis adapted to mount an external lever arm which can be shifted to produce an actuating motion of the shaft, and a cam member within the head mounted on the shaft to move therewith, said switch body having an open top and said head having an open bottom closing over the top of said body, the combination therewith of: a separate intermediary member interposed between the open bottom of said head and the open top of said switch body forming a partition between said head and said body, such intermediary member having a central bore leading from within said head to within said body; a reciprocally movable cam follower extending through said central bore of said intermediary member with a bearing fit, such cam follower thereby being movable with respect to said intermediary member; and a separate seal in engagement with the periphery of said intermediary member that seals such member with said head and also seals such member with said switch body.

5. In a switch mechanism for a switch having a switch body in which switch contacts are housed, an operating head seated upon the switch body, an operating shaft protruding from the head at an angle to an axis passing through the body and the head and adapted to mount an external lever arm which can be shifted to produce an actuating motion of the shaft, and a cam member within the head mounted on the shaft to move therewith, said switch body having an open top and said head having an open bottom closing over the top of said body, the combination therewith of: a separate intermediary member interposed between the open bottom of said head and the open top of said switch body forming a stationary partition between said head and said body, such intermediary member having a bore forming a bearing leading from within said head to within said body, and also having a peripheral portion that has an interface with both said head and said body; a reciprocally movable cam follower extending through and having a bearing fit with said bore for reciprocation with respect to said intermediary member; and a seal in engagement with the periphery of said intermediary member that seals such member with said head and also seals such member with said switch body.

6. In a switch actuating mechanism for a switch having a switch body member in which contacts are housed, an operating head member seated upon the body member, an operating shaft protruding from the head member at an angle to an axis passing through the body member and the head member and adapted to mount an external lever arm which can be shifted to produce an actuating motion of the shaft, and a cam within the head member mounted on the shaft to more therewith, said body member having an open top and said head member having an open bottom, the combination therewith of: a recess formed in the opening of one of the head and body members; a separate intermediary member with an upper portion having a peripheral collar that seats in said recess of one of the head and body members and overlaps the opening of the other member to form a stationary partition between said head and body members, such intermediary member having a bore leading from within said head member to within said body member; a reciprocally movable cam follower extending through said bore of said intermediary member with a bearing fit; and a separate seal in engagement with the periphery of the collar of said intermediary member that seals such member with said head member and also seals such member with said body member.

8. A mechanism as in claim 6, wherein said recess is formed in the opening of the body member so that the collar of the upper portion of said intermediary member overlaps the opening of said head member, and said seal is located in the top surface of said head member.