As seen best in FIG. Except when flat 26 is in alignment with one of the latch arms 71, 72, as illustrated in FIGS. Actually, only the longer latch arm 71 is in actual abutment. The shorter latch arm 72 is held just short of abutment by the longer latch arm. Abutment of the longer latch arm 71 against the step 25 prevents the heavy compression spring 55 from shifting the clutch fork 40 pivotally counter-clockwise, as viewed in FIG.
The preferred direction of rotation of sleeve 23 is indicated by the arrow in FIG. Latch arm 71 is now unobstructed and can move forwardly and fork 40 can pivot counterclockwise but both can move for only a very small distance since movement is limited by the second latch arm 72 which has now abutted against sleeve step As rotation of sleeve 23 continues, in the direction of the arrow in FIG.
However, by the time the second latch arm 72 has come into full alignment with flat 26 and is no longer obstructed by step 25, the first latch arm 71 has been cammed up the now inclined slope of the flat 26 and has come to rest on the top edge of the step 25, as illustrated in FIG. Thus, both latch arms 71,72 are now free. The fork 40 is no longer latched and is now free to move pivotally in the counter-clockwise direction and does so in response to the force of the heavy compression spring 55 against the opposing action of the lighter compression springs 75, one of which is attached to each of the latch arms 71, In this manner, clutch 50 is shifted out of handwheel engagement into electric motor engagement.
This is the condition illustrated in FIG. In FIG. Instead, lugs 53 at the right end of clutch 50 are now in lug-on-lug engagement with lugs 27 at the left end of the worm gear sleeve And, since worm gear sleeve 23 is being driven rotationally by motor drive input worm gear 20, the clutch 50 is driven rotationally by sleeve Since clutch 50 is splined to shaft 21, shaft 21 is now driven rotationally.
This drives worm 33 which, being in mesh with output worm gear 30, drives worm gear 30 rotationally. Worm gear 30 is keyed, as by key 31, to output drive sleeve 32 and thus output drive sleeve 32 is driven rotationally. This drives stem nut 35 FIG.
Where the valve operator is a part-turn operator, the amount of rotation of stem nut 35 and valve stem S is limited by the primary positioning limit switches FIG. These switches are operated by the cams which are adjustable on cam shaft Cam shaft is fixed to and rotates with output drive sleeve While the primary position limiting elements are limit switches , mechanical stops 91 are also provided to assure that stem S does not rotate beyond the point desired.
This assurance is provided by the stop lug 90 FIG. When and if stop lug 90 reaches one of the stop screws 91, rotation of stem nut 35 is halted. When rotation of stem nut 35 is stopped, rotation of worm gear 30 is also stopped. However, the motor drive gear 20 is still being driven by the drive worm 17 and worm 33 on output shaft 21 is still being driven rotationally.
The fact that gear 30 is prevented from rotating, while worm 33 is still being driven, causes worm 33 to try to climb up the threads of gear This causes shaft 21 to move to the right, as viewed in FIG.
Movement of shaft 21 to the right moves rack 82 to the right and causes rotation of shaft This shuts off power to the motor M. As has already been described, when the valve operator is in handwheel drive, lugs 64 are in engagement with lugs 52, and manual rotation of the handwheel drives clutch 50 rotationally. Since clutch 50 is splined to output shaft 21, output shaft 21 is moved rotationally. Since the motor drive sleeve 23 is mounted on output shaft 21, there is the possibility that there will be sufficient frictional engagement between the manually actuated shaft 21 and the motor drive sleeve 23 to cause sleeve 23 to move rotationally.
If this should occur, there is a possibility that the flat 26 of step 25 will come into alignment with the latch arms 71, This would release the latch and permit the heavy compression spring 55 to pivot the fork 40 counterclockwise, thereby shifting the clutch 50 out of handwheel drive.
As previously stated, this occurrence is undesirable and would inhibit handwheel operation of the unit. To avoid the possibility described above, the worm and worm gear drive are made self-locking. That is, the pitch angle of the threads of the worm 17 is made sufficiently steep that it is impossible for worm gear 20 to move rotationally unless the worm 17 is being driven.
Since sleeve 23 is keyed to worm gear 20, sleeve 23 cannot rotate even though there is frictional engagement between sleeve 23 and the manually actuated shaft What is claimed is: 1. A valve operator comprising: a. A valve operator according to claim 1 wherein each of said pair of latch arms is L-shaped, having a long leg and a downwardly extending short leg at the outer end of said long leg.
A valve operator according to claim 2 wherein the under surface of each of said downwardly extending short legs is inclined upwardly in the direction of the adjacent leg. In a valve operator; a. Apparatus according to claim 4 wherein each of said latch arms is L-shaped having a long leg and a shorter leg depending from the end of said long leg.
Apparatus according to claim 5 wherein the under surface of each of said short depending legs is inclined upwardly in the direction of the adjacent leg. Apparatus according to claim 4 where said means for rotating said annular step member includes a self-locking input worm set comprising a drive worm and a worm gear, said worm gear being connected to said annular step member, the pitch angle of the threads of said worm being sufficiently steep to prevent said worm gear from moving rotationally unless said worm is being driven.
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