 | |
| Illustration 1 | g00502079 |
(1) Hoist and front brake cooling gear pump (2) Hoist screen (3) Hoist screen bypass switch | |
All of the oil from the hoist and front brake cooling gear pump (1) is sent through the two hoist screens (2). Each hoist screen (2) has a hoist screen bypass switch (3). The hoist screen bypass switches (3) will alert the Vital Information Management System (VIMS) of any restrictions in the hoist screens (2). Pump oil from the hoist screens (2) enters the hoist control valve through two hoses.
The pilot oil lines for the hoist proportioning solenoids on the hoist control valve use oil from the parking brake release system.
 | |
| Illustration 2 | g00502080 |
(4) Outlet to the hoist and brake hydraulic tank (5) Test port for the front brake oil cooler relief valve (6) Hoist dual stage relief valve (7) Inlet for pump oil (8) Hoist proportioning solenoid for RAISE (9) Outlet to the rod end of the hoist cylinder (10) Outlet to the front brake oil cooling system (11) Outlet to the head end of the hoist cylinder | |
 | |
| Illustration 3 | g00502081 |
(8) Hoist proportioning solenoid for RAISE (9) Outlet to the rod end of the hoist cylinder (10) Outlet to the front brake oil cooling system (11) Outlet to the head end of the hoist cylinder (12) Hoist proportioning solenoid for SNUB, FLOAT, and LOWER (13) Hoist counterbalance valve (14) Test port for the hoist counterbalance valve (15) Front brake oil cooler relief valve | |
 | |
| Illustration 4 | g00501884 |
(1) Hoist and front brake cooling gear pump (2) Hoist screen (3) Hoist screen bypass switch (4) Outlet to the hoist and brake hydraulic tank (6) Hoist dual stage relief valve (7) Inlet for pump oil (8) Hoist proportioning solenoid for RAISE (9) Line to the rod end of the hoist cylinder (10) Outlet to the front brake oil cooling system (11) Line to the head end of the hoist cylinder (12) Hoist proportioning solenoid for SNUB, FLOAT, and LOWER (13) Hoist counterbalance valve (15) Front brake oil cooler relief valve (16) Pilot oil line from the parking brake release system (17) Screen (18) Orifice (19) Stem (dual stage) (20) High pressure relief valve (21) Low pressure relief valve (22) Directional spool (23) Centering springs (24) Pump oil supply port (25) Signal line (26) Check valve (rod end) (27) Dump spool (28) Two load check valves (29) Hoist and brake hydraulic tank (30) Actuator (31) Hoist cylinder | |
Oil flows through two lines from the hoist and front brake cooling gear pump (1). This oil flows through hoist screens (2) and into pump oil supply ports (7). This oil combines inside the hoist control valve. Two load check valves (28) protect the pump from reverse oil flow from the lines for the hoist cylinders.
Front brake oil cooler relief valve (15) limits the pressure in the lines to the front brake oil coolers. Front brake oil cooler relief valve (15) will vent oil to the hoist and brake hydraulic tank (29), when the pressure in lines (10) is too high.
Hoist counterbalance valve (13) prevents cavitation of the hoist cylinders. If the load shifts suddenly and the hoist and front brake cooling gear pump (1) cannot supply enough oil to the hoist cylinders (31) for pressure compensation, the pressure in the head end of the hoist cylinders (31) will drop. Hoist counterbalance valve (13) will shift if the pressure in the head end of the hoist cylinders (31) drops below the cracking pressure. The counterbalance valve is not adjustable.
Pump oil also flows through dump spool (27) to hoist dual stage relief valve (6). If either low pressure relief valve (21) or high pressure relief valve (20) is opened, dump spool (27) will release pump oil to the front brake oil cooling lines. Low pressure relief valve (21) is set at a lower relief setting than high pressure relief valve (20). A signal line to stem (19) closes low pressure relief valve (21) while hoist proportioning solenoid (8) for the RAISE position is energized.
HOLD Position
In the HOLD position, neither of the hoist proportioning solenoids are receiving current. All of the pilot oil is blocked in actuators (30). Centering springs (23) hold directional spool (22) so that lines (11) to the head end of the hoist cylinders (31) are blocked by directional spool (22). A small notch in directional spool (22) connects the lines to the rod end of the hoist cylinders (9) with the front brake cooling oil.
Because no signal oil is sent to stem (19), the pump oil is open to low pressure relief valve (21). The pressure will not increase enough in order to open low pressure relief valve (21). The directional spool (22) is in a position that allows all of the oil to flow to the front brake cooling system. The maximum pressure in the lines to the front brake cooling system is controlled by front brake oil cooler relief valve (15). If the front brake oil cooler relief valve (15) opens, the oil will vent through line (4) to the hoist and brake hydraulic tank (29) .
RAISE Position
In the RAISE position, hoist proportioning solenoid (8) is receiving a current of 1.9 amperes. Pilot oil in the actuator (30) for hoist proportioning solenoid (8) is allowed to drain to the hoist and brake hydraulic tank (29). Pilot oil in the actuator (30) for the hoist proportioning solenoid (12) will now push directional spool (22) to the left. When directional spool (22) moves, the pump oil that is coming through port (24) flows through load check valves (28), to lines (11), and to the head end of the hoist cylinders (31) .
Load check valves (28) will block the pump pressure until the pump pressure is higher than the pressure in the hoist cylinders. Load check valves (28) also prevent reverse flow into the pump port.
Some of the oil is also sent as signal oil through signal line (25) to stem (19) and to hoist counterbalance valve (13). The signal pressure shifts stem (19) so that low pressure relief valve (21) is blocked. This allows all of the pump oil that is flowing through dump spool (27) to flow to high pressure relief valve (20). If the oil pressure opens high pressure relief valve (20), dump spool (27) will shift upward and the pump oil will be vented to lines (10) for front brake cooling oil.
 | |
| Illustration 5 | g00502322 |
(13) Hoist counterbalance valve (25) Signal line (32) Spool (33) Passage to directional spool (34) Check valve (35) Passage to the line for the rod ends of the hoist cylinders (36) Passage to the line for the rod ends of the hoist cylinders | |
Signal pressure to hoist counterbalance valve (13) pushes spool (32) in hoist counterbalance valve valve (13) to the open position. In this position, oil from the rod ends of the hoist cylinders can flow from passage (35) and into passage (33), which goes to the directional spool. This oil is routed to lines (10) for front brake cooling oil. If the pressure in the head ends of the hoist cylinders drops below the cracking pressure, spool (32) in hoist counterbalance valve (13) will shift and the flow of oil from the rod ends will be restricted. This keeps oil in the rod ends of the hoist cylinders. Check valve (34) blocks passage (36) due to the spring force.
LOWER Position
In the LOWER position, hoist proportioning solenoid (12) is receiving a current of 1.9 amperes. Pilot oil in the actuator (30) for hoist proportioning solenoid (12) is allowed to drain to the hoist and brake hydraulic tank (29). Pilot oil in the actuator (30) for the hoist proportioning solenoid (8) will now push directional spool (22) to the right. When directional spool (22) moves, the pump oil that is coming through port (24) flows through load check valves (28) and into the lines (9) that go to the rod ends of the hoist cylinders (31) .
Load check valves (28) prevent any reverse flow into the pump port. Pump oil flows past check valve (26), into lines (9), and to the rod ends of the hoist cylinders (31) .
Oil in lines (11) to the head end of the hoist cylinders is vented to the hoist and brake hydraulic tank (29) .
Because no signal pressure is sent to stem (19), pump oil can flow to low pressure relief valve (21). If low pressure relief valve (21) opens, dump spool (27) will shift upward and the pump oil will be vented to lines (10) for front brake cooling oil.
 | |
| Illustration 6 | g00502344 |
(13) Hoist counterbalance valve (25) Signal line (32) Spool (33) Passage to directional spool (34) Check valve (35) Passage to the line for the rod ends of the hoist cylinders (36) Passage to the line for the rod ends of the hoist cylinders | |
Because no signal pressure is sent to the hoist counterbalance valve (13), spool (32) blocks passage (35). Pump oil that is coming into passage (33) pushes check valve (34). This opens passage (36) to the rod ends of the hoist cylinders (31). Oil flows freely through hoist counterbalance valve (13) and to the rod ends of the hoist cylinders (31) .
FLOAT Position
In the FLOAT position, hoist proportioning solenoid (12) is receiving a current of 1.55 amperes. Pilot oil in the actuator (30) for hoist proportioning solenoid (12) is allowed to drain to the hoist and brake hydraulic tank (29). Pilot oil in the actuator (30) for the hoist proportioning solenoid (8) will now push directional spool (22) to the right. Because a smaller amount of pilot oil is allowed to drain from the actuator (30) for hoist proportioning solenoid (12), directional spool (22) does not move all the way to the LOWER position. When directional spool (22) moves, some of the pump oil that is coming through port (24) flows through load check valves (28) and into the passages to the rod ends of the hoist cylinders (31). Load check valves (28) prevent any reverse flow into the pump port.
Oil in lines (11) to the head end of the hoist cylinders (31) is vented to the hoist and brake hydraulic tank (29) .
Because no signal pressure is sent to stem (19), pump oil can flow to low pressure relief valve (21). Because the pressure will not increase enough in order to open low pressure relief valve (21), all of the remaining oil is sent to the front brake cooling system.
| | |
| Illustration 7 | g00502344 |
(13) Hoist counterbalance valve (25) Signal line (32) Spool (33) Passage to directional spool (34) Check valve (35) Passage to the line for the rod ends of the hoist cylinders (36) Passage to the line for the rod ends of the hoist cylinders | |
Because no signal pressure is sent to the hoist counterbalance valve (13), spool (32) blocks passage (35). Pump oil that is coming into passage (33) pushes check valve (34). This opens passage (36) to the rod ends of the hoist cylinders (31). Oil flows freely through hoist counterbalance valve (13) and to the rod ends of the hoist cylinders (31) .
SNUB Position
The SNUB position is activated by the Power Train Electronic Control Module (Power Train ECM). The operator has no control over this position. The SNUB position will slow the rate of lowering the dump body as the dump body nears the frame of the truck. The dump body position sensor will signal the Power Train ECM when the dump body is between 12 degrees and 6.5 degrees from the frame. The speed of lowering the dump body will determine the exact degree. The Power Train ECM will then send a signal in order to move the hoist control valve to the SNUB position.
In the SNUB position, hoist proportioning solenoid (12) is receiving a current of 0.925 amperes. Pilot oil in the actuator (30) for hoist proportioning solenoid (12) is allowed to drain to the hoist and brake hydraulic tank (29). Pilot oil in the actuator (30) for the hoist proportioning solenoid (8) will now push directional spool (22) to the right. This moves the directional spool (22) out of the FLOAT position. When directional spool (22) moves, the oil from the head ends of the hoist cylinders is restricted. This lowers the speed of movement of the dump body.
Oil in lines (11) to the head end of the hoist cylinders (31) is vented to the hoist and brake hydraulic tank (29) .
Because no signal pressure is sent to stem (19), pump oil can flow to low pressure relief valve (21). Because the pressure will not increase enough in order to open low pressure relief valve (21), all of the oil is sent to the front brake cooling system.
| | |
| Illustration 8 | g00502344 |
(13) Hoist counterbalance valve (25) Signal line (32) Spool (33) Passage to directional spool (34) Check valve (35) Passage to the line for the rod ends of the hoist cylinders (36) Passage to the line for the rod ends of the hoist cylinders | |
Because no signal pressure is sent to the hoist counterbalance valve (13), spool (32) blocks passage (35). Pump oil that is coming into passage (33) pushes check valve (34). This opens passage (36) to the rod ends of the hoist cylinders (31). Oil flows freely through hoist counterbalance valve (13) and to the rod ends of the hoist cylinders (31) .