the bail assembly 10 illustrated in fig1 includes a rectangular frame assembly 12 having opposed top and bottom members 13 and 14 and opposed vertical side members 15 and 16 . head bails 18 and 19 are slideably connected between the top and bottom members 13 and 14 so as to be movable towards and away from the vertical side members 15 and 16 . a yoke assembly 25 is pivotally mounted to an extended portion of the frame member 15 and includes a yoke member 24 having opposed ends 26 and 27 which are linked to the respective upper end portions of the head bails 18 and 19 by link members 21 and 22 such that upon rotation of the yoke assembly about its pivot point 28 , the link members move the head bails 18 and 19 inwardly or outwardly so as to be able to clamp on the neck of a beast . a holding arm 29 and a sleeve 30 are loosely fitted around the yoke member 24 and are connected to pivot point 28 so as to allow pivotal movement between the sleeve and the yoke arm . an operating handle 31 is rigidly connected to the sleeve 30 . the bail assembly also includes a hydraulically operated holding assembly 35 pivotally connected at one end to the holding arm 29 of the yoke assembly 25 and at the other end pivotally connected to a mid portion of the frame member 16 through holes 36a and 37a respectively . the holding assembly 35 includes an outer cylindrical wall 40 having an upper end cap 41 and a piston rod 42 slidably and sealably engaged within the outer cylindrical wall in a lower portion thereof so as to form a fluid chamber between the upper end cap 41 and the piston face of piston rod 42 . a ` j ` seal 43 is positioned at the piston rod end of the cylinder to prevent the ingress of contaminants such as dust . a control means 44 is arranged in a mid portion of the chamber so as to divide it into a locking chamber 36 on the piston rod side of the control means 44 and a fluid reservoir 46 on the other side . the control means 44 includes a one - way ball valve 47 arranged to allow fluid flow from the fluid reservoir to the locking chamber but to prevent flow in the reverse direction unless the ball valve 47 is manually held in the open position . for this purpose there is provided a shaft 48 extending at one end through the upper end cap 41 and at the other end slidably engaging with the ball valve 47 so as to be able to move the ball valve to an open position when the shaft 48 is depressed , and wherein fluid may flow from the locking chamber to the reservoir . the upper end of the shaft 48 is encapsulated in a shaft cap 49 attached to the upper end cap 41 to prevent the shaft 48 from becoming disengaged from the ball valve 47 . the shaft is maintained in a non - engaged position by a spring 50 located between the shaft cap 49 and the end cap 41 . the shaft 48 may be engaged at its upper end by an engaging portion 31a of the operating handle 31 which is arranged to depress the shaft 48 upon initial pivotal movement of the operating handle about the pivot point 2 thereby opening the ball valve 47 . the fluid reservoir 46 can be charged with fluid through filling cap 51 positioned at an upper end thereof . the filling cap includes a vent to atmosphere which may be closed to prevent ingress of moisture when the hydraulic holding assembly is not in use . the upper end portion of the outer cylindrical wall 40 is connected to a mounting portion 36 suitably adapted for pivotal connection to the yoke assembly 25 whilst the lower end of piston 42 includes a mounting portion 37 adapted for pivotal connection to the frame member 16 . in use , the head bails 18 and 19 are moved towards the side members 15 and 16 to enable the neck of a beast to be accommodated therebetween . the operating handle 31 is then pivoted to pivot the yoke assembly 25 in a direction causing opposing movement of the link members 21 and 22 which slide the head bails 18 and 19 towards each other wherein they clamp against the neck of the beast . while the link members 21 and 22 are moving the head bails towards each other the holding arm 29 coincidentally moves the outer cylindrical wall 40 of the hydraulic assembly 35 upwardly thereby extending the holding assembly . as the hydraulic holding assembly 35 begins to extend , the ball valve 47 opens and allows fluid to flow into the locking chamber 36 from the vented reservoir 46 as the holding assembly extends . as rotation of the yoke member 24 ceases the ball valve 47 closes to prevent fluid returning from the locking chamber to the reservoir so that the yoke assembly cannot be rotated in the reverse direction by movement of the head bails 18 and 19 thereby holding them in any desired engaged position against the neck of the beast . to release the beast from the bail assembly , the operating handle 31 is rotated in a reverse direction wherein initially an engaging portion 31a of the operating handle contacts the upper end of shaft 48 and forces it downwardly to open the ball valve 47 so that fluid may return to the reservoir from the locking chamber as illustrated in dashed line in fig2 . as the operating handle is forced further in a reverse direction , the yoke 25 pivots and the oil is forced out of the locking chamber by the piston rod 42 . coincidentally the head bails 18 and 19 move apart . it is preferred that the head bail assembly 60 illustrated in fig4 and 5 include head bails 61 , 62 connected to opposed support posts 63 by concertina type hinge linkages 64 . these linkages include respective pairs of straight outer links 65 connected to brackets at the front of the support posts 63 and cranked inner links 66 connected rigidly at their inner ends to the head bails 61 , 62 . the respective pairs of outer links are rigidly connected to upright members 67 so as to maintain the upper and lower ends of the head bails parallel . as illustrated the hinge links support and guide the head bails for movement between their engaged and disengaged positions , the upper guide members 68 only restraining longitudinal movement of the bail members . furthermore in their disengaged positions the linkages 65 , 66 protrude laterally only a short distance from the outer faces of the support posts 63 . it will be appreciated that the bail assembly 60 is demountable for supply in knocked - down form whereby the members of the bail assembly may be packaged into a relatively small package . for this purpose the opposed support posts 63 are rigidly interconnected at their upper ends to longitudinally spaced laterally extending bars 68 which form guides for upward extension 70 of the head bails . the bars 68 have upper and lower bolt connections 72 providing moment transfer about respective longitudinal race axes 71 between the support posts 63 . the bottoms 73 of the posts 63 are non - rotatably bolted to a lower bail member 74 by laterally spaced bolts 75 such that hinge pivots 76 extending from the front of the posts 63 remain in a fixed orientation to enable the concertina type hinge members to hinge across their front faces . one support post 63 is provided with a lower mounting 77 for the holding means 78 and an upper pivotal mounting 79a for the translation mechanism 79 which operates the bail link members 80 , it being understood that the operation of the bail assembly 60 is by the mechanism described in relation to fig1 to 3 . in order to maintain ruggedness in the assembled bail assembly in use , the guide bars 68 are pre - assembled as a rigid parallel frame bolted at its outer end to the front face of the posts 63 and the lower bar 74 is a flat bar through bolted through widely spaced pairs of bolt apertures formed on mounting wings welded to the lower ends of the posts 63 . it will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as is defined in the appended claims .
a bail assembly including bail members moveable between operative engaged positions and a disengaged position ; bail actuating structure for quickly moving the bail members between the operative engaged positions and the disengaged position , and holding devices for holding the bail members at any selected operative engaged position . preferably the holding device is a selectively releasable self locking hydraulic cylinder assembly which includes adjustable holding device , a locking chamber associated with the adjustable holding device which may be filled to lock the adjustable holding device , control structure for controlling flow of fluid to and from the locking chamber , and actuating structure for selectively actuating the control structure .