GB811485A - Improvements in pneumatic jacks - Google Patents

Abstract

811,485. Pneumatic jacks. REGIE NATIONALE DES USINES RENAULT. May 2, 1957 [May 3, 1956], No. 14091/57. Class 8(2). [Also in Group XXVI] A double acting pneumatic jack which normally assumes a central position and to which it is automatically returned after a working stroke in either direction comprises main pistons 18, 19, Fig. 1, having extension sleeves 22, 23 connected together by a sleeve 25 and secured to the actuating rod 4, and non-connected secondary pistons 20, 21 slidable within liners 14, 14<SP>1</SP> and also having extension sleeves 28, 29 in sliding engagement with sleeves 22, 23 either inside or outside thereof and capable of being displaced by an adjacent main piston ; the outer faces of pistons 18, 19 forming with the cylinder ends chambers 12, 13 having ports 9, 91 normally connected to the exhaust outlets of control valves (not shown) but when connected to a compressed air outlet of one or other of the valves provide the pressure necessary to effect a working stroke 50 whereas the faces of the secondary pistons 20, 21 remote from their sleeves 28, 29 form with the cylinder liners a chamber 43 having a port 42 connected to a constant supply of compressed air which serves to return the appropriate secondary piston and hence the connected main pistons to the dead centre position after the appropriate port 9, 9<SP>1</SP> has been connected to exhaust. In operation and on pressurising say chamber 13, the secondary piston 21 is displaced to the left by piston 19 whilst secondary piston 20 is held stationary by its abutment against a shoulder 30 of liner 14. On connecting chamber 13 to exhaust the constant pressure in chamber 43 acting against the piston 21 returns it and the connected main pistons to the dead centre position. In a modification the actuating rod 57, Fig. 2, connected to the main pistons 54, 55 extends through a slot 58 midway of the cylinder wall and the secondary pistons 64, 65 slide in liners 62, 63 and the sleeves 67, 68 thereof slide within the sleeve connecting the main pistons 54, 55. To effect a working stroke 80 the chamber 76 is pressurised, and the main pistons together with secondary piston 64 is moved to the left, whereas secondary piston 65 is held against a shoulder 81 of liner 63. On connecting chamber 76 to exhaust, the constant pressure in connected chambers 69, 70 returns piston 64 to its former position together with the main pistons 54, 55.