PUMP GP-PS-BSC-V 10R4714 - Caterpillar

Quick-Drop Valve (D6D Only)
There is a single quick-drop valve that works for both blade lift cylinders. The valve allows the dozer blade to drop very fast. It will also let the operator apply down pressure on the blade when it is on the ground.
When the main control valve for blade lift is moved to the RAISE position, oil flow goes in passage (8) through orifice (9) and out through passage (7) to the rod end of the lift cylinders. A small amount of oil goes through passage (1) and fills spring chamber (2) behind plunger (3). The pressure of this oil adds to the force of the spring which keeps plunger (3) and valve (6) against the stop. When valve (6) is against the stop, head end passage (4) is closed to the flow of oil being sent to the rod end of the cylinders. Oil from the head end of the cylinders comes in through pasage (4) and out through passage (5) to the main control valve.
When the main control valve for blade lift is moved to the FLOAT (detent) position, the weight of the blade sends oil from the rod end of the cylinders through the quick-drop valve and back to the main control valve. As the oil goes through orifice (9) a pressure increase is caused in the rod end circuit. This pressure increase pushes against valve (6) causing the valve and plunger (3) to move against the force of the spring. Return oil from the rod end of the cylinders can now flow through the open valve and add to the flow of oil from the main control valve to the head end of the cylinders. This will allow the blade to drop very fast.
Movement of the lever for blade control to the LOWER position lets the blade move down slowly without quick-drop valve action. In this case, the oil flow from the rod end of the cylinders is not enough to cause a pressure increase large enough to move valve (6) and plunger (3). All of the oil from the rod end goes back to the main control valve. Only the pressure oil from the main control valve goes to the head end of the cylinders.
QUICK-DROP VALVE
1. Small passage. 2. Spring chamber. 3. Plunger. 4. Passage to head end of blade lift cylinders. 5. Passage to main control valve (head end). 6. Spool. 7. Passage to rod end of blade lift cylinders. 8. Passage to main control valve (rod end). 9. Orifice.