Abstract: A telescopic prop for use in mine workings extends and retracts over three stages. The prop has an outer main base member 1 with respective first, second and third concentric inner members 2, 3, 4 disposed one within another. The first inner member has a piston 6 in which is arranged a non-return valve 23 which normally shuts off communication between a working chamber 20 associated with the first and base members and the working chambers 22, 27, 29 pertaining to the other members. A plunger 24 is provided to open the non-return valve when the first inner member is nearly fully retracted inside the base member so that after retraction of this stage the other stages can be retracted. The second or intermediate member also employs a piston 9 which is connected via a rod 13 with an auxiliary piston 15 disposed in a working chamber associated with the uppermost third member.

Abstract: A fluid actuator where an outside cylinder envelopes an inside cylinder producing four chambers, two for the power stroke and two for synchronization, for application where two or more cylinders are to drive a single load such that all cylinders advance at the same rate by cross plumbing synchronizing chambers. The combination is provided with valve means which opens at the end of each stroke to realign the actuators.

Abstract: In a press with two parallel, spaced apart multiple-acting cylinders that have their respective pistons connected to end portions of a beam to which a bending or forming tool is secured, the cylinders are respectively fed from effectively separate pressure fluid sources providing equal pressures and flow rates. For synchronization of piston extension through an initial rapid advance, the chamber of each cylinder that is normally pressurized for retraction of its piston is connected in feedback relation to the pressure fluid source for the other cylinder, so that fluid expelled from a leading cylinder augments the fluid supply to the lagging one. The system further comprises a pair of sensors, one for each beam end, and a synchronizing bleed-off valve for each sensor.

Abstract: A method and apparatus are disclosed for displacing a crane lift hook and hook cable to follow the relative vertical motion between a crane and a loading deck such as occurs between floating vessels and a fixed crane. In the method, the hook cable is paid out or reeled in to maintain the hook a substantially constant distance from the deck in order to facilitate loading or unloading of cargo from the hook. The apparatus for achieving the method includes a vertically displaceable sheave over which the lift cable is reeved, a power ram to displace the sheave, and motive means operating the power ram. Preferably, the power ram is subjected to a constant upward pneumatic force to provide at least a portion of the force for displacing the moveable sheave upwardly to reel in the cable, such as in response to an upward heave of the deck relative to the crane.

Abstract: Triple action piercing structure comprising an outer cylinder, an inner cylinder, a shaft and radially extending piston means operable between the inner and outer cylinders for providing a plurality of separate pressure chambers between the inner and outer cylinders, specific, simple and efficient passage means for passing a pressure medium into and exhausting the pressure medium from the pressure chambers to produce relative axial movement between the inner and outer cylinders at a particularly high pressure for cylinders of predetermined diameter to facilitate piercing of large diameter openings in thick hard workpieces.

Abstract: A triple action welding gun for welding airport runway concrete reinforcing mesh or the like comprising an outer cylinder, an inner cylinder, a shaft and radially extending piston means operable between the inner and outer cylinders for providing a plurality of separate pressure chambers between the inner and outer cylinders, and means for passing into and exhausting from the pressure chambers a pressure medium to produce relative axial movement between the inner and outer cylinders wherein extension of the welding gun is accomplished at a particularly high pressure for cylinders of predetermined diameter to facilitate welding of large diameter reinforcing rods.