A mechanism for controlling the position of a movable member and for locking it in any desired position comprising a hydraulic displacement device movable with the member and a slide valve hydraulically connected to the displacement device to control {HEAD ~ flow} of liquid to or from {TAIL ~ the device} 
A mechanism for controlling the position of a movable member and for locking it in any desired position comprising a hydraulic displacement device movable with the member and a slide valve hydraulically connected to the displacement device to control { HEAD ~ flow } of liquid to or from { TAIL ~ the device }
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