Patent GB-395037-A (GB)
Title: Improvements in or relating to pneumatic and like tools
IPC: B25D9/16
Filed: 1932-01-13
Abstract: 395,037. Percussive tools. ARTHUR, J. and HOLMAN BROS., Ltd., Camborne, Cornwall. Jan. 13, 1932, No. 1074. [Class 124.] In valve gears of the type described in Specification 349,912 wherein the supply to the cylinder ends is controlled by a disc valve with an axial extension of smaller diameter which is subject to fluid pressure and which valve is reversed partly by compression and partly by fluid pressure, a fluid-actuated exhaust lift valve is provided to relieve the forward or the forward and rear cylinder ends. In the construction shown in Figs. 1 and 2, the compressed air passes by passage 9, recess 10, ports 11, 12 and annular recesses 13, 14 to the seats of the valve, and through orifice 15 to the cavity of the valve. An auxiliary exhaust valve 2 is arranged in a rear box 6. The compressed air passes over the rear seat 17 to the forward end of the cylinder. The exhaust from the rear of the cylinder passes through ports 22, 25 and passages 23, 24. Compression acts on the front of the main valve when the port 25 is passed by the rear of the piston. When the forward edge of the piston uncovers port 22, the rear face of the main valve is released to atmosphere. The valve is moved to the rear, Fig. 2. The piston is driven forward, and the rear end of the cylinder exhausts through ports 25, 22 just before the blow. The pressure on the small end of the main valve moves it to seat 28. Both forward and rear faces of the auxiliary valve communicate with the forward end of the cylinder, and also with recess 18 by ports 29, 30, 31, 19, 20, 21. The area of the forward face exposed to pressure in the ports or channel 29a is slightly greater than the area exposed to pressure in port 30, When compressed air is admitted to recess 18 by the main valve 1, valve 2 is forced rearwardly and closes ports 30, 46. The compression in front of the piston during the working stroke takes the line of least resistance, the auxiliary valve is moved forwardly and ports 30, 46 are connected. The diameter of the port 15 in the small end of the valve and of the cavity determine the speed of the piston. In a modification, the small end of the valve works in a chamber with a restricted supply. In a modification of this construction, the valve has a slightly smaller passage therein as well which provides a leak into the cylinder during the forward stroke. A modification is described wherein the auxiliary valve also relieves pressure in the rear end of the cylinder at least during part of the return stroke. In the construction, shown in Fig. 7, the main valve is formed to work around an extension of the cylinder. In the position shown, air passes to the forward end of the cylinder by passages 50, 57, 58, 56 and acts on the rear face of the auxiliary valve 2 and closes the exhaust port 53 communicating with a seating 52 and passages 54, 60. When the forward end of the piston 3 passes port 60, the forward cylinder end exhausts. The pressure in ports 11 and the compression reverses the valve. When the forward moving piston passes port 60, the valve is again reversed. During the forward stroke, the valve 2, rearwardly seated, releases the compression. The forward area of the valve is slightly less than the rearward area, but the fluid, taking the line of least resistance, exhausts across the front face of the valve from recess 63 to ports 53, 54, 55. The handle is locked in position by a toothed ring 70 which engages teeth on the adjacent surface of the handle, is splined to the cylinder, and is held by a spring ring 73. The exhaust outlet has a deflector 80 which is held in position by a spring.