GB1449020A - Multistage hydraulic telescopic lifting jack - Google Patents

Abstract

1449020 Telescopic jacks MONTANHYDRAULIK GmbH & Co KG 12 Oct 1973 [2 Nov 1972] 47824/73 Heading F1D A telescopic jack comprises a cylinder 11, a piston 121 slidable in the cylinder 11 and carrying a cylinder 12, a piston 131 slidable in the cylinder 12 and carrying a cylinder 13, and ports 116', 118' in the wall of the cylinder 11 for co-operation with passages 123, 124 in the piston 121 in a manner which causes extension of the cylinder 12 followed by extension of the cylinder 13. To extend the jack, the cylinder 11 is pressurized through an inlet 113' and a non-return valve 114. Pressurization of the cylinder 11 extends the cylinder 12, fluid in the annular chamber 112 behind the piston 121 flowing to exhaust through the port 116' and a line 116. At the end of the stroke of the cylinder 12, fluid in the cylinder 11 flows into the cylinder 12 via the port 118' and the passage 123 now aligned therewith. This causes the cylinder 13 to extend, fluid in the annular chamber 122' behind the piston 131 flowing to the exhaust line 116 via a port 133 in the cylinder 13, a tube 124' fixed to the piston 121, the passage 124, and the port 116'. Retraction is effected by reversing the lines 113, 116 whereby pressure in a control line 117 opens the valve 114. Initially pressure in passages 124, 124' retracts the cylinder 13 until the piston 131 uncovers a port 126, thereafter the annular chamber 112' is pressurized first via the port 126 and subsequently directly from the port 116', whereby the cylinder 12 retracts.