VALVE AS-BRAKE 3218318 - Caterpillar

Lower Operation
When the bulldozer lift control lever is moved to LOWER position, lift valve spool (18) moves to LOWER position. Lift cylinder oil (head end) goes through lift valve spool (18) and becomes signal oil. The signal oil goes through shuttle valves (17) and (12) to unloading valve (8) and margin stem (7) of inlet valve group (1). Unloading valve (8) moves completely to the left and pump oil pressure increases.The pump oil now opens load check valve (16). The oil goes around lift valve spool (18) and out bulldozer lift control valve (19) to the head ends of lift cylinders (28). The cylinder rods extend. The lift cylinders cause the bulldozer to lower.The movement of the cylinder rods pushes the oil out of the rod ends of the lift cylinders. This oil comes into the bulldozer lift control valve and goes around lift valve spool (18). The oil goes through the common tank passages in the lift and tilt control valves, and the inlet valve group on its way back to oil filter (6) and oil tank (5).If the blade is lowered very fast, then quick-drop valves (21) send (divert) rod end oil to the head end of the cylinders to make this happen.When the bulldozer lift control lever is released, the lever and lift valve spool (18) go back to their HOLD positions. The lift valve spool holds the oil in lift cylinders (28). Movement of the cylinder rods stops. The bulldozer blade is held in the lowered position until the bulldozer lift control lever is moved again.Float Operation
When the bulldozer lift control lever is moved to FLOAT detent position, lift valve spool (18) moves into the detent in bulldozer lift control valve (19). The signal oil passage drains around the lift valve spool. The signal oil at unloading valve (8) and margin stem (7) drains back to oil tank (5), through shuttle valves (17 and 12) and the signal oil passage. Implement pump (4) unloads around unloading valve (8). The pump oil pressure is low.The head and rod ends of lift cylinders (28) are now open to the tank passages in the bulldozer lift control valve. Outside forces on the blade control the movement of the cylinder rods.The bulldozer lift control lever must be manually moved out of the FLOAT detent position. There is no kickout for FLOAT position.Bulldozer Tilt Circuit
Tilt Right Operation
When the bulldozer tilt control lever is moved to TILT RIGHT position, tilt valve spool (14) moves to TILT RIGHT position. Tilt cylinder oil (rod end oil) goes through tilt valve spool (14) and divides. This oil is now signal oil. Some of this oil goes to the spring chamber of priority flow control valve (10). The valve moves toward the left. The remainder of the signal oil goes through shuttle valve (12) and to unloading valve (8) and margin stem (7) of inlet valve group (1). Unloading valve (8) moves completely to the left and the pump oil pressure increases. Margin stem