IMPLEMENT AND STEERING HYDRAULIC SYSTEM CONTINUED
d. Bulldozer Lift Control Valve (Float)
When pilot control pressure causes the control valve spool to move to the FLOAT position, there is no signal oil
pressure. The chamber is open to the outlet passage. Pilot control pressure enters the signal resolver network at
the passage.The pressure at the passage is the same pressure that is supplied by the pilot signal pressure at pilot
port that is causing the control valve spool to move to the FLOAT position. This causes the pump to maintain
margin pressure over the pilot control pressure. The margin pressure over the pilot control pressure is required in
order to shift the control valve spool to the FLOAT position.
Because of the position of the control valve spool, rod end and head end passages are open to two outlet
passages. Because both ends of the lift cylinders are opened to the tank, the cylinder rods move freely in either
direction. The amount and direction of the force on the blade controls the movement of the blade.
Figure 30. Bulldozer Lift Control Valve (FLOAT).