Abstract: A multiple mode hydraulic piston assembly employing a regenerative hydraulic circuit which when incorporated in the piston of a hydraulic cylinder and assembled with a pressureized hydraulic source through appropriate piping and valving, will sequentially permit, restrict, and block liquid flow through the piston and will thus extend its piston rod in multiple force modes, namely a low force rapid extension mode, a moderate force rapid extension mode, and a high force extension mode. In response to fluid pressures within the cylinder chamber the multiple mode piston assembly automatically changes operational modes. First bi-directional flow is provided between opposing chambers, then uni-directional flow is provided from the rod end to the back end chamber, and finally flow between the chambers is blocked. A modified embodiment provides a free motion mode wherein a modest external force can displace the piston in either direction.

Abstract: Liquid fluid pressure applied to a piston causes advancement thereof at a rapid rate until an external resisting load applied to the piston rod exceeds a predetermined value producing a corresponding increase in the pressure within the opposing pressure chambers to which the piston is exposed. Bi-directional flow, conducted between the opposing chambers during rapid piston movement, is automatically blocked by a differential circuit pressure operated piston valve to cause a rapid increase in the differential pressures acting on the piston, and an increase in the value of the external piston rod load with a corresponding decrease in its rate of movement in the same direction. A modified embodiment permits the piston rod to act under pressure and with a force in both the extending and retracting phases of the stroke with the same rapid extending rate until the external resisting force is encountered.

Abstract: A bolt assembly for supporting a mine roof or the like is disclosed having a yieldable coupling means at least at one end to allow controlled sagging of the rock to prevent exceeding the elastic limit of the bolt. An expandable anchor may be provided at the other end. The coupling means includes a collar having a die movable along deformable threads of the bolt when the rock load increases. This relative movement provides relief thereby assuring against the bolt becoming excessively tensioned. The die deforms the threads by coldflow extruding and flattening action against the crest of the threads. This action forms a frictional holding interface between the bolt and the collar and maintains substantially constant tension in the bolt. A nut on the collar transmits the supporting force to the rock face. A removable cap nut may be threaded onto the bolt to properly pre-position the parts and transmit torque to the anchor during installation.