GB1285150A - Improvements in or relating to hydraulic lifting apparatus - Google Patents

Abstract

1285150 Shovelling machines SOC ANON POCLAIN 16 June 1970 [18 June 1969] 29088/ 70 Heading E1F [Also in Divisions B8 and Fl] A jib arm 2 Figure 1 is lifted about a pivot 3 carried by a fixed structure 1 by extension of a hydraulic jack 4 having its rod end pivoted at 7 to the jib 2 and having its cylinder end pivoted at 8 to an element 5 which is itself pivoted at 6 to the structure 1 and is actuated by a hydraulic jack 9 pivoted thereto at 11 and pivoted to the structure 1 at 10; supply of fluid to one or other end of jack 9 being determined by the fluid pressure required to extend jack 4 and hence arm 2 whereby under light load jack 9 is retracted so that element 5 assumes the position shown in broken line the jack 4 extends at high speed whereas under heavy load jack 9 is extended so that element 5 assumes the position shown in broken line and the jack 4 extends less quickly. To extend jack 4 under light load a 3-way valve 13 Figure 2 is moved to the left to connect a pump 12 to a supply line 16 having a branch line 18 leading to a spring-biassed piston 19 at one end of a 3-way slide valve 20 which is urged by its spring 21 so as to connect a pump 22 to the rod end of jack 9 which thus swings element 5 to the full-line position. When the extending jack 4 becomes loaded the pressure in line 18 overcomes spring 21 and valves 20 connects the pump 22 to the head end of jack 9 which is thus extended and so swings element 5 to the broken line position. To lower the jib arm 2 valve 13 is moved to its extreme right position whereon lines 16, 18 are connected to a reservoir 15 and jack 9 is retracted so that element 5 assumes the full line position and jack 4 retracts at high speed. In a modification adjustment of jack 9 and hence of elements 5 effected over a range of pressures in the head end 4a Figure 3 of jack 4 is effected by a pressure pick up 37 comprising a spring- biassed piston 38 subjected to fluid pressure in the feed line 29 of extending jack 4. At low pressure a rod 42 of piston 38 pivots a lever 43 counter-clockwise about 11 to move a 3- way valve 34 to the left and thus connects a branch 32 of a supply pressure line 32 to a line 35 to retract jack 9; fluid being exhausted from 9b through a line 36 valve 34, a line 33, check valve 49 a valve 50 held open by pressure in line 32 and a return line 30. Retraction of jack 9 pivots lever 43 clockwise about an axis 44 and thus returns valve 34 to the closed position whereon lines 32, 33 are blocked by valves 48, 50. An increased pressure in line 29 thence in line 40 extends rod 42 which pivots lever 43 clockwise about 11 which moves valve 34 to the left to connect line 32 to chamber 9b thereby extending jack 9 and hence pivoting element 5 clockwise until such time as the lever 43 recloses valve 34 whereon element 5 is held fixed.