Speed change
1. Neutral condition
2.Hydraulic oil flow from supply line opens shuttle ball and flows to the speed change valve.
There is no pilot oil pressure from travel speed solenoid valve. The speed change valve move to the right
because of spring force and make passage between the supply line and the bottom side of piston. And the
top side of piston is connected to the drain line through internal hole of speed change valve.
So the axis angle decreases and machine travels at high speed condition.
3.While the machine travels at high speed condition, according to the travel load increment, pressure at
the speed change valve is increased. Due to the sectional area A is larger than sectional area B, the suply
pressure is applied to the ring area (A B). When the supply pressure reaches to the setting pressure of
spring, the speed change valve moves to the left and and make passage between the supply line and the
top side of piston. And the bottom side of piston is connected to the drain line through internal hole of
speed change valve.
So the axis angle increases and machine travels at low speed condition.
Picture text:
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