GB1426358A - Hydraulic self-levelling device for a boom-mounted bucket - Google Patents

Abstract

1426358 Fluid-pressure servomotor systems INTERNATIONAL HARVESTER CO 25 April 1973 [2 May 1972] 19635/73 Heading G3P [Also in Divisions El and F2] A control system for maintaining level a boom mounted bucket during raising of the boom is generally similar to that described in Specification 1426357 except that when spool valve port 28, Fig. 2, is opened the fluid from side 31 of bucket ram 20 is exhausted to drain via passages 104, 74 in spool 16 rather than being recirculated through port 30 to the other side of the ram. In addition the system includes a priority valve which prevents accidental rollback of the bucket whilst the boom is within a predetermined height range. In one arrangement, Fig. 3, the priority valve 118 includes a shuttle spool 128 biased rightwards within bore 126 by spring 138 to a position in which the spool interior 138 communicates via ports 130, 120 with line 40 of manual valve 18. A restriction 134 also connects spool interior 138 to port 28 of self levelling spool valve 10. Thus as soon as port 28 opens to drain upon movement of spool 16 of valve 10, the pressure drop across restriction 134 causes shuttle spool 128 to move leftwards to cut-off port 120. Thus accidental operation of valve 18 cannot cause high-pressure fluid to flow through line 40 to rollback bucket ram 20 during the self levelling phase. Fig. 4 (not shown) illustrates a modified priority valve.