Combination Valve for the Hook
 | |
| Illustration 1 | g00541420 |
Combination valve (hook) (A) RAISE inlet port (B) RAISE motor port (BR) Brake release port (PI) Pilot port (DR) Drain port (1) Manifold (2) Directional valve (3) Pressure reducing valve (4) Counterbalance valve | |
 | |
| Illustration 2 | g00541423 |
Location of the combination valve for the hook winch (5) Combination valve (6) Hook winch | |
Combination valve (5) is mounted to the motor for hook winch (6). Combination valve (5) controls the pressure to the brake release on hook winch (6). Valve (5) also controls the power down pressure for the hook.
When the hook is in the HOLD position, combination valve (5) is not receiving pump pressure. Pressure reducing valve (3) allows brake release pressure from port (BR) to drain through port (DR) and the brake for the hook winch is engaged.
When the pilot control valve for the hook is in the RAISE position, pump pressure enters manifold (1) through port (A). A pilot signal from this oil is sent to directional valve (2) and the spool is shifted. This allows any existing brake release pressure to drain to port (DR). The brake for the hook winch is engaged during the RAISE function. The rest of the oil travels through a check valve in counterbalance valve (4). The oil exits combination valve (5) through port (B). This pressure enters the motor and the hook is raised. The return oil from the motor returns to the boom and hook control valve.
When the pilot control valve for the hook is in the LOWER position, pump pressure enters the LOWER port on the winch motor. A pilot signal from this oil enters port (PI) in manifold (1) through an external line. This pilot signal shifts directional valve (2). This allows a portion of this oil to travel through the spool to pressure reducing valve (3). The pressure of this oil is reduced and the oil is sent to the brake release port on the hook winch. The brake is released. The rest of the oil from port (PI) travels to counterbalance valve (4). Pressure builds up in the motor and port (B) because counterbalance valve (4) blocks port (B). This causes a back pressure in the LOWER port on the winch motor. As pressure builds up in the LOWER port, this pressure is also felt on counterbalance valve (4) through port (PI). Once this pressure reaches the set pressure, counterbalance valve (4) is opened and the return oil from port (B) is allowed to flow through combination valve (5). This allows the winch motor to lower the hook. The pressure in port (B) must be maintained at the set pressure in order to keep counterbalance valve (4) open.
The following sections explain the operating principles of each component of the combination valve.
Directional Valve
 | |
| Illustration 3 | g00469885 |
Directional valve (hook winch) (C) Port (D) Port (E) Port (F) Port (X) Port (Y) Port (7) Chamber (8) Chamber (9) Spring (10) Spring (11) Passage (12) Spool (13) Stem | |
The directional valve is only located in the combination valve for the hook winch motor. The directional valve controls the flow of oil to the pressure reducing valve. This oil controls the brake release in the hook winch.
When the hook control valve is in the HOLD position, ports (D) and (F) are open to port (C). Oil from port (D) drains to port (C). Oil from port (F) travels through passage (11) in spool (12) to port (C). The oil from port (C) travels back to the return manifold. There is no brake release pressure in this position and the brake is engaged.
When the hook control valve is in the RAISE position, a pilot signal enters port (Y) from the supply oil to the hook winch. This signal fills chamber (8). The pressure builds up in chamber (8) and stem (13) begins to move to the left against the force of springs (9) and (10). As stem (13) moves, spool (12) also moves. Port (D) is opened to port (C). This oil travels from port (D) to port (C) and the oil travels to the return manifold. Port (F) is also opened to port (E). Oil travels from port (F) to port (E). The oil from port (E) joins with the return oil from the hook winch. There is no pressure in order to release the brake in this position and the brake is engaged.
When the hook control valve is in the LOWER position, a pilot signal enters port (X) from the supply oil to the hook winch. This signal fills chamber (7). The pressure builds up in chamber (7) and stem (13) begins to move to the right against the force of springs (9) and (10). As stem (13) moves, spool (12) also moves. Port (E) is opened to port (D). Part of the oil pressure from the supply oil to the hook winch is sent through port (E) to port (D). This oil travels to pressure reducing valve (3). The pressure is reduced and brake release pressure is sent to the hook winch. The brake is released. Port (F) is opened to port (C) and the leakage from the pressure reducing valve is allowed to drain to the return manifold.
Pressure Reducing Valve
 | |
| Illustration 4 | g00471116 |
Pressure reducing valve (G) Outlet port (H) Pump pressure port (J) Drain port (14) Adjustment screw (15) Spring (16) Pilot valve (17) Spring (18) Sleeve (19) Orifice (20) Spring chamber | |
The pressure reducing valves reduce the supply pressure to a controllable pressure of 5500 kPa (800 psi) for the brake release on both winches.
Pump pressure enters port (H). The oil passes through a cross-drilled hole in sleeve (18) and the pressure is felt at outlet port (G). This oil also fills spring chamber (20) by passing through orifice (19). The pressures in port (G) and chamber (20) are equal in this state.
As the pressure from port (H) begins to increase, the pressure that is inside of valve (3) also increases. When the pressure rises above the set point of 5500 kPa (800 psi), pilot valve (16) begins to open. This allows the oil in chamber (20) to exit through pilot valve (16) into port (J). The oil that is exiting causes a pressure drop in chamber (20). The oil in chamber (20) cannot be replaced through orifice (19) at a quick enough rate. This pressure drop causes sleeve (18) to move upward. As sleeve (18) moves, port (H) begins to become covered by the sleeve. A large pressure difference between port (G) and chamber (20) causes sleeve (18) to move upward further. This causes port (H) to experience a larger restriction of flow.
Once the pressure in port (G) drops below the set point of 5500 kPa (800 psi), pilot valve (16) closes and the pressure in chamber (20) equalizes. As the pressure increases, the previous process begins again.
Counterbalance Valve
 | |
| Illustration 5 | g00471180 |
Counterbalance valve (K) Port (L) Port (M) Pilot port (21) Adjustment screw (22) Spring (23) Stop (24) Chamber (25) Sleeve (26) Spring (27) Chamber (28) Valve | |
The counterbalance valves control the return oil pressure from the hook winch motor when the load is being lowered. The counterbalance valve restricts the flow of return oil in order to prevent the load from falling when the brake is released. Pressure is required to power down the load in this mode.
When either control valve is in the RAISE position, supply oil to the winch motor enters port (L). This oil travels to chamber (27) and the pressure begins to build up. The pressure in chamber (27) pushes on valve (28). When the pressure overcomes the force of spring (26), valve (28) moves downward. An opening between valve (28) and sleeve (25) is formed. This oil exits through port (K) and the oil travels to the winch motor.
When either control valve is in the LOWER position, pressure from the return oil in the winch motor begins to build up at port (K). This pressure applies a force to a small area on sleeve (25). A pilot pressure from the supply oil to LOWER port in the winch motor also travels to port (M). This oil travels to chamber (24). The return oil at port (K) is blocked until one of the following conditions is met.
- The pressure at port (K) reaches the pressure setting of the counterbalance valve.
- The pressure at port (M) reaches the pilot pressure setting of the counterbalance valve.
- A combination of the two pressures reaches the pressure setting of the valve.
Sleeve (25) moves upward and an opening between valve (28) and sleeve (25) is formed. The oil from port (K) travels through chamber (27) to port (L). This oil travels through the manifold for the combination valve. The oil exits to the return manifold.
The combined pressure must be kept at the set pressure. If the pressure is lower, the return oil cannot flow and the winch motor will not turn.