Patent GB-390637-A (GB)
Title: Improvements in pneumatic percussive tools
IPC: B25D9/14
Filed: 1932-04-01
Abstract: 390,637. Percussive tools. AKTIEBOLAGET ATLAS DIESEL, Sickla, near Stockholm. April 1, 1932, No. 9459. Convention date, May 28, 1931. [Class 124.] A percussive tool is provided with a disc or ring life valve one side of which engages a seat to control the fluid supply to the rear end of the cylinder, the other side of which is constantly supplied with main pressure fluid to actuate the valve, the pressure thereon being reduced on the main piston over-running a passage connected to the valve chamber behind the valve or by means of an auxiliary valve. In the construction shown in Fig. 1, fluid is constantly supplied to the forward cylinder end through passage 16, and alternatively to the rear of the cylinder through an annular passage 12 communicating with the supply through a passage 11 and controlled by a disc lift valve 6 which slides in a chamber 8 communicating with the main supply through a port 14 and with the forward end of the cylinder through a passage 15. With the piston and valve in the upper position and the ports 13 open fluid is supplied to the upper end of the cylinder and drives the piston down. When the port 15 is closed fluid pressure builds up in chamber 8 and closes the valve. The piston is moved by expanding fluid until the port 13 are closed. When, during the return movement of the piston under a restricted supply through port 16, the port 15 is opened, the pressure is reduced on the back of the valve which is reversed by compression towards the end of the stroke. In a modification, shown in Fig. 2, an auxiliary slide valve 20 is provided which controls the admission to the forward end of the cylinder by connecting passages 25, 25 and an auxiliary exhaust from the rear end through passages 28, 27. The valve has differential ends ; the upper end is open to the cylinder through passage 23; the lower end to the atmosphere through passage 27. In the position with raised piston, the supply to the forward cylinder end is closed, and also the auxiliary exhaust. The back of the valve 6 is put to pressure through passages 24, 26 but is open to exhaust through passage 15 ; the main valve is raised. When the descending piston covers passage 15, the valve 6 is lowered, and the descent continues under expanding compressed air until the piston hits the anvil block 19. When the ports 13 are opened the cylinder pressure falls, the valve 20 is raised and opens the auxiliary exhaust and the supply to the forward cylinder end. When the rising piston uncovers passage 15, the pressure above the valve 6 is reduced. When the passage 28 is closed, the compression checks the piston and reverses the main valve. A modification is described wherein a tubular auxiliary slide valve is arranged coaxially with the cylinder bore. Modifications are described wherein the supply chamber 10 is 50 per cent or more of the cylinder volume. A separate storage chamber 31, Fig. 3, may be provided to receive the controlling air which is separate from the connections leading to the valve casing and is only connected to the inlet. In the construction shown in Fig. 6, the top of the chamber is divided into two parts by an annular projection 32 provided with a highly-throttled connection 33. The channel 14 in this case is of ample dimension to fill chamber 8 during the closing of the valve 6. The fall of pressure due to the opening of passage 15 affects the outer annular part only. The projection 32 may be on the back of the valve 6. In this construction, fluid is supplied to the forward passage 53 by a control valve 50 for starting. The valve 50 is afterwards turned to close passage 53 and fully open passage 52. The piston is then returned by cushioned fluid as described in Specification 389,318.