GB484213A - Improvements in or relating to pneumatic percussive tools - Google Patents

Abstract

484,213. Valve - gear for percussive tools. BROOM & WADE, Ltd., and BROOM, H. Nov. 4, 1936, No. 30058. [Class 122 (ii)] In a pneumatic tool, particularly a pneumatic road breaker, with a plate distributing- valve and a pair of co-operating cylinders of different diameters, a plate valve of annular form works in an annular chamber surrounding the head of the cylinder of smaller diameter, controls the admission, and is operated by fluid pressure. The piston has two heads 7, 3 separated by a reduced portion 8. The lower head 3 controls the exhaust 6 towards the bottom of the cylinder. Blocks 12, 13 with a liner through which the small piston passes are spaced above the cylinder 9 and are separated by rings 14, 15. The space 16 houses a ring- shaped, plate, lift valve 17. A chamber 18 to which air is supplied by a lever-operated, spring- pressed valve 20, is arranged above the cylinder. Passages 24, 25 in the block 13 supply air to the spaces between the blocks. The space 16 is connected to the forward cylinder-end passage 28 by a V-shaped conduit 26. Similarly a V-shaped conduit in the lower ring 12 connects the space between the rings 13, 14 and the chamber 16. Further valve-controlled conduits 31, 32 extend from the chamber 16 to the lower cylinder. A conduit extends from below the rings 14, 15 to a groove in the cylinder 9. When air is supplied to the piston placed as shown in the Figure, the piston is raised until the exhaust is again opened. The cylinder compression raises the valve. Air then acts upon the small end and the annular area of the piston and effects the power stroke. When the lower end of the piston 7 passes above the groove 38, air passes by grooves 24, 33, 34 to the cylinder 5 to assist the stroke. When the exhaust 6 is opened, the valve is reversed. In a modification, the valve moves oppositely relative to the piston to that shown. The cylinder 9 has another groove communicating with the lower side of the valve so that fluid is passed to the lower side of the piston to build up pressure to effect the reversal before the end of the power stroke. The valve and seat may be of curved or conical formation.