GB758181A - Improvements in steam engines - Google Patents

Abstract

758.181. Steam engines; valve gear. DOBLE, A. May 29, 1952 [April 10, 1951], No. 8294/51. Classes 122(1), 122(2), 122(3), 122(4) and 122(5). [Also in Groups XIII and XXIX] In a compound steam engine of the Woolf type comprising a high pressure piston 70 and a low pressure piston 65 interconnected to reciprocate together, valve means 33 to admit steam to the high pressure cylinder 17 and a poppet valve 39 to transfer steam from the high pressure cylinder to the low pressure cylinder 11, means are provided to equalize the pressure on both sides of the high pressure piston at the end of its working stroke and during the power stroke of the low pressure piston. The lower end of the high pressure cylinder is connected by a passage 26 with a valve chamber 27 communicating by a port 29, controlled by the valve 39, with the low pressure cylinder and by a duct 31 with the high pressure steam inlet port 32 controlled by the valve 33 whose stem 34 is aligned with and abuts an auxiliary exhaust valve 49 actuated, with the valve 33, through a member 36 by a cam 37 on the camshaft C and when open connects the low pressure cylinder to exhaust via passages 30 and 48. The transfer valve 39 is operated by a cam 44 through a member 42 slidable in a guide 43. The high pressure cylinder liner 16 forms an annular space 25 with the cylinder head 19, which space 25 is open at its upper end and communicates at its lower end with ports 75 in the liner 16 and a duct 74 leading to the low pressure cylinder. The ports 75 are uncovered by the piston 70 at the end of its working stroke, i.e. in the position shown in Fig. 1 and steam is admitted to the clearance space 72 above the piston to equalize the pressures thereon and also to the passage 30 via a duct 74 to act on the underside of the valve 39 and reduce the force exerted by the cam 44 to open the valve. During the working stroke of the low pressure piston which follows, the pressures on the high pressure piston 70 will be substantially balanced since the valve 39 remains open and the piston 70 will uncover ports 75 on its downward stroke. Exhaust from the low pressure cylinder occurs when the piston 65 uncovers an exhaust port 78 in the cylinder wall; any residual condensate in the cylinder being exhausted through the auxiliary valve 49. The port 78 and passage 48 may be connected to a condenser. The high pressure and low pressure pistons are connected to a common crosshead 63 and the high pressure piston rod 68 passes through a labyrinth gland 69 cooled by boiler feed water. circulated through a duct 83, space 81 and a duct 82 to a port 20 in the high pressure cylinder 17 and thence around a helical passage 22 in the liner 16, being finally discharged at the outlet port 21. The engine may be braked by closing the throttle and supplying high pressure steam to the low pressure cylinder through a port 79. The crankcase space is maintained under vacuum by a separate suction pump. Several units such as shown in Fig. 1 may be arranged in line. The cam 37 is of axially variable form and the camshaft C is axially adjustable to vary the cut-off under means responsive to both steam pressure and engine speed. High pressure steam is supplied through a conduit 116, Fig. 3, to one side of a piston 119 slidable in a cylinder 118 and connected to one end of the camshaft C which it urges to the left against the action of a spring 121 and the force due to the pressure of liquid pumped by a positive displacement pump 126 driven from the engine crankshaft and acting on a piston 122 slidable in a cylinder 123 and connected to the other end of the camshaft. Increase in engine speed thereby gives an earlier cut-off period whilst increase in steam pressure results in a later cut-off. The camshaft is provided with reversing cams 131 and 132 and in order to reverse the engine a handle 145, connected with slide valves 138 and 134, is pulled to the left from the position shown so that steam still flows to the cylinder 118 through a passage 140 in the valve 138 whilst the pressure in the cylinder 123 is released through a pipe 136 and a passage 135 in the valve 134. Consequently, the camshaft is moved to the right to bring the reversing cams 131, 132 into use.