GB190816686A - Improvements in Fluid Pressure Engines, especially Percussive Machines such as Rock Drills. - Google Patents

Abstract

16,686. Mauss, W. Aug. 8. Rock drills.-A percussion tool having leakage holes for curtailing the rearward stroke of the piston as described in Specification No. 27,496, A.D. 1906, is provided with a differential piston 4, which is subjected to constant pressure of the fluid entering at ports 7, and contains a differential valve 10, the face 11 of which is constantly subjected to fluid pressure through a port 13. The valve face 12 is connected alternately with the two ends of the cylinder by means of passages 15, 16, a recess 14, and a by-pass 24. During the reciprocation of the valve, the forward end of the cylinder is connected to the exhaust through a passage 22, valve chamber 18, ports 20, and the piston-rod bore 17, and with the inlet through passages 22, 21, and a valve chamber 19. With the piston in the right-hand position, the valve is held to the right by the pressure on the face 11. When the piston moves to the position shown in Fig. 1, the fluid pressure, passing through the passage 15, acts on the face 12 to reverse the valve rod and admit fluid to the forward end of the cylinder. On the return of the piston, the port 21 is closed, and air in the forward end of the cylinder is worked expansively until exhausted through ports 22 or 23. During the expansion in, or exhaustion of the air from, the forward end of the cylinder, the pressure on the valve face 12 is reduced, and the valve is reversed by the pressure acting on the face 11. In a modified form of valve, shown in Fig. 2, the valve face 26 is constantly subjected to the pressure of fluid which enters by the passage 21, and the face 12 is decreased in area to effect a rapid reversal of the valve. In a further modification, the groove 14 and by-pass 24 are dispensed with, the ports 16, 15 are replaced by a port 16<a>, and the valve faces 11, 26 are made equal in area. The reversal of the valve at the end of the forward stroke is effected by its momentum. In a modified form of the valve, shown in Fig. 3, the port 16, Fig. 1, is dispensed with, the port 21 is brought near the piston head, and a small port 27 is provided through the valve to relieve the face 12 of pressure after the piston passes the by-pass 24. A leakage hole 28, Fig. 1, which is opened aiter the cut-off takes place, is led into the piston-rod bore. The size of the hole 28 is such that the leakage has little effect when the piston is reciprocated normally, but, when the movement is retarded, the escape reduces the pressure in the front part of the cylinder sufficiently to enable the valve to be reversed and the piston to be driven forward.