PURPOSE: To prevent the occurrence of cavitation, by a method
wherein oil chambers across a cylinder to support a load are
communicated to oil chambers across a compensation cylinder to
which a means to exert a spring force in any displacement of a
piston is mounted, and a ratio between the areas ot
corresponding oil chambers of the one of the two cylinders is
coincided with that of the other. CONSTITUTION: Oil chambers A
and B across a tilt cylinder 1 are communicated to an
accumulator 2 through check valves 13 and 14. With the check
valves 13 and 14 forcibly opened by means of a handle 15, the
piston ot the cylinder 1 is displaced to an arbitrary position,
and is fixed in a closed state. A compensate cylinder 3 is
partitioned into oil chambers C and D on both sides by means of
a piston 21, a spring force is exerted in any displacement of
the piston 21 through the forces of springs 29 and 30, and the
oil chamber C is communicated to the A and the oil chamber D to
the B. An effective sectional area is set so