GB908133A - Fluid-operated telescopic devices - Google Patents

Abstract

908,133. Percussive drills. DOWTY MINING EQUIPMENT Ltd. March 21, 1961 [Dec. 31, 1959], No. 44440/59. Class 124. [Also in Group XXIX] A fluid-operated telescopic device for a rock drill comprises a cylinder 2 having a piston 4 mounted on a rod 5 so that the area of the piston at the rod end is substantially less than the area at the opposite end, passage means having a pressure inlet 12 adapted to be connected to a source of fluid pressure and leading to the piston-rod end of the piston and a fluid exhaust 13 leading to the opposite end of the piston, a first fluid flow restrictor between the ends of the piston and a second fluid flow restrictor 17 in part of the passage means, at least one of the restrictors being controllable for varying the fluid flow through the passage means and therefore the pressure drop across the piston, whereby the resultant force acting on the piston is variable both in direction and magnitude. The first restriction may consist of an axiallymovable tapered rod in a bore through the piston, the clearance formed by the space between the piston and cylinder, or radial or axial grooves in the bore of the cylinder. The rod end of the piston is connected by the annular space 10 between a tube 8 and the hollow piston-rod 5 to a chamber 11 connected to the pressure inlet 12, and the other side of the piston is connected by the tube 8 to a chamber 9 having a passage 15, which is controlled by a needle valve 17 and forms the second restriction, connected to the exhaust 13. The valve 17 is axially adjustable by a pin 22 connected to a sleeve 19 axially movable by a nut 18 screw-threaded to the housing 6 of the valve. The device may serve as a strut for a rock drill and at one end be fitted with a socket 1 for a spiked foot and at the other end have a male bayonet fitting 25. When the valve 17 is closed, the pressure on opposite sides of the piston will be substantially equal and, because of the differential areas, the device will expand. When the valve 17 is fully open to permit a flow of fluid, the pressure drop across the piston will cause the pressure on the rod end of the piston to be greater than that on the other so that the device closes. Settings of the valve between the fully open and fully closed positions will determine the direction and force exerted by the device. The bore of the cylinder may be stepped so that the clearance between the piston and cylinder varies according to the position of the piston to vary the speed, or to stop, the piston. A further valve may be provided to control the resistance to the flow of fluid to suit fluids of different viscosities.