HARNESS AS 5I8212 - Caterpillar

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BOOM RAISE
As the joystick is moved to the BOOM RAISE position, pump oil flows from port (A) through port (B) after pushing on check valve (5). The control valve works as a standard check valve. When the joystick returns to the NEUTRAL position, the load will be held by all valve elements in a sealed condition. BOOM LOWER
Pilot pressure comes in the control valve from the pilot valve. The pressure pushes control piston (7) against the spring. When pilot pressure increases, the control piston pushes the ball. The ball then pushes rod (8). The rod lifts poppet (14) off the seat. This allows spring chamber (11) to release pressure to the tank. Now, piston (9) can be pushed against spring force (10). Oil can flow from port (B) to port (A) through orifices of piston (9). Increased pilot pressure allows the opening between port (A) and port (B) to be increased. When pilot pressure is decreased, forces of springs (10) and (15) push the piston backward. Spring (13) closes poppet (14). Piston (9) comes back on the seat. This closes the opening between ports (A) and (B). Oil leaks between piston (9) and the housing in order to refill chamber (11) with oil. This locks piston (9) on the seat and the boom lowering control valve is locked again.
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Flow control valve (16) Nipple (17) Stop nut (18) Spring (19) Washer (20) BoltParallel Cylinders
If two cylinders are working in parallel mode, a flow control valve is installed in the parallel cylinder port of the boom lowering control valve. The flow control valve restricts oil leakage if a connecting hose breaks.Normal Operation (Open Valve)
Spring (18) pushes washer (19) open. Stop nut (17) determines the length of bolt (20), which determines the amount of flow from port (B) to port (A) .Broken Line
A high flow from port (B) to port (A) raises the pressure in chamber (B). This pressure closes washer (19) against the seat and flow is restricted through orifice (D) .