Push-Pull Control Valve in BAIL LOWER Position
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| Illustration 1 | g00792231 |
(1) Valve spool (2) Passage to the rod end of the bail cylinder (3) Line relief valve (4) Passage to the head end of the bail cylinder (5) Oil passage to the hydraulic tank (6) Oil passage to the hydraulic tank (7) Cavity (8) Retainer (9) Passage to the hydraulic tank (10) Spring (11) Shuttle valve (12) Passage (13) Orifice (14) Passage (15) Piston (16) Spring (17) Poppet (18) Valve (19) Spring cavity (20) Spring (21) Orifice (22) Check valve (23) Inlet passage from the pump (24) Oil passage to the hydraulic tank (25) Oil passage to the hydraulic tank (26) Oil passage to the hydraulic tank | |
The push-pull solenoid valve is normally in the BAIL LOWER position when the valve is not activated by the bail control switch. The push-pull solenoid valve is activated when the switch is moved to the BAIL RAISE position.
When the push-pull solenoid valve is in the BAIL LOWER position, oil is sent to cavity (7) and valve spool (1) is shifted to the left. Pump oil enters the valve through passage (23) and passes through check valve (22). The oil moves through passage (12) around valve spool (1). From valve spool (1), oil flows through passage (4) to the head end of the bail cylinder. This extends the rod in the bail cylinder and this lowers the bail. This oil also passes through orifice (21) and into spring cavity (19). The pressure of this oil acts on poppet (17).
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| Illustration 2 | g00733579 |
(6) Oil passage to the hydraulic tank (8) Retainer (10) Spring (11) Shuttle valve (24) Oil passage to the hydraulic tank (25) Oil passage to the hydraulic tank (26) Oil passage to the hydraulic tank | |
Rod end oil is returned through passage (2) to passage (6). The oil from passage (6) moves shuttle valve (11) to the left against retainer (8). Return oil flows through the small orifices in shuttle valve (11) and drains to the hydraulic tank through passage (26). When the oil from passage (6) flows through the small orifices in shuttle valve (11), the restriction of the orifices meters oil flow from passage (6). The small orifices control the speed of the bail as the bail is lowered.
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| Illustration 3 | g00733585 |
Position of Shuttle Valve with Application of External Force (6) Oil passage to the hydraulic tank (8) Retainer (10) Spring (11) Shuttle valve (24) Oil passage to the hydraulic tank (26) Oil passage to the hydraulic tank | |
If an external force is applied to the bail, the flow of oil from the bail cylinder increases. Oil continues to flow through the small orifices until the pressure increases enough to overcome the spring force of spring (10). Shuttle valve (11) moves retainer (8) to the left in order to compress spring (10). This opens the slots on shuttle valve (11) to passage (26). Return oil drains to the tank and the bail lowers rapidly. This prevents the pressure in passage (6) from rising too high.
Pressure Relief Valve
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| Illustration 4 | g00720232 |
(12) Passage (14) Passage (15) Piston (16) Spring (17) Poppet (18) Valve (19) Spring cavity (20) Spring (21) Orifice (26) Oil passage to tank | |
At the same time as oil is entering passage (2), oil also enters orifice (21) and flows into spring cavity (19). When the oil pressure in spring cavity (19) overcomes the force of spring (16), the oil pressure in spring cavity (19) unseats poppet (17) .
When poppet (17) unseats, the oil in spring cavity (19) vents to the tank through tank passage (26). The pressure in passage (12) causes valve (18) to shift downward. This blocks the flow of oil from passage (23) to passage (12) .
As the oil vents past poppet (17), the pressure decreases and poppet (17) reseats. When poppet (17) reseats, the oil pressure in spring cavity (19) begins to increase again. The pressure in spring cavity (19) in addition to the force of spring (20) causes valve (18) to shift upward and oil flows from passage (23) to passage (12) .
Line Relief Valve
Line relief valve (3) protects the lines, the bail cylinder and the push-pull control valve when external forces are applied to the bail. When two machines are connected, the movement may cause high pressure to develop in the bail cylinder.
When the bail control switch is in the BAIL LOWER position, the pump oil flows through passage (12) to passage (4). The oil flows from passage (4) to the head end of the bail cylinder. When the front machine raises, or the rear machine drops, there is excessive pressure in the head end of the cylinder. When the pressure reaches the pressure setting of line relief valve (3), the line relief valve opens. This relieves the excess pressure to the tank through passage (5) .
Push-Pull Control Valve in BAIL RAISE Position
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| Illustration 5 | g00718835 |
(1) Valve spool (2) Passage to the rod end of the bail cylinder (3) Line relief valve (4) Passage to the head end of the bail cylinder (5) Oil passage to the hydraulic tank (6) Oil passage to the hydraulic tank (7) Cavity (8) Retainer (9) Passage to the hydraulic tank (10) Spring (11) Shuttle valve (12) Passage (13) Orifice (14) Passage (15) Piston (16) Spring (17) Poppet (18) Valve (19) Spring cavity (20) Spring (21) Orifice (22) Check valve (23) Inlet passage from the pump (24) Oil passage to the hydraulic tank (25) Oil passage to the hydraulic tank (26) Oil passage to the hydraulic tank | |
When the bail control switch for the push-pull solenoid valve is moved to the BAIL RAISE position, the solenoid valve shifts. This causes oil in cavity (7) to be directed to the hydraulic tank. The force of the springs causes valve spool (1) to move to the right. Pump oil enters passage (23). This oil flows through check valve (22). The oil flows through passage (12) and through valve spool (1). The oil enters passage (2) and flows to the rod end of the bail cylinder. The bail raises. Return oil from the head end of the bail cylinder flows through passage (4) into passage (5) and from passage (5) to passage (9) .
The pressure of the oil in the rod end of the bail cylinder increases and this pressure is felt in passage (2) and passage (12). As the oil pressure in passage (2) increases, oil flows into passage (14). The pressure of the oil in passage (14) shifts piston (15) to the right, which compresses spring (16) .
At the same time, pressure oil flows through orifice (21), through spring cavity (19) and against poppet (17). When the pressure on poppet (17) is greater than the pressure in passage (14) and the force of spring (16), poppet (17) unseats. This pressure is greater than the pressure that is needed to unseat poppet (17) when the bail control valve is in the BAIL LOWER position.
Pressure Relief Valve
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| Illustration 6 | g00720232 |
Position of Pressure Relief Valve During Pressure Relief (12) Passage (14) Passage (15) Piston (16) Spring (17) Poppet (18) Valve (19) Spring cavity (20) Spring (21) Orifice | |
If the pressure in spring cavity (19) exceeds the pressure that is needed to unseat poppet (17), oil from spring cavity (19) vents to the hydraulic tank. When the oil in spring cavity (19) vents to the hydraulic tank, the pressure in passage (12) causes valve (18) to shift downward. This blocks the flow of oil from passage (23) to passage (12) .
As oil vents past poppet (17), the pressure in spring cavity (19) decreases and poppet (17) reseats. When poppet (17) reseats, the oil pressure in spring cavity (19) increases again. The oil pressure in spring cavity (19) causes valve (18) to shift upward and oil again flows from passage (23) to passage (12) .
Line Relief Valve
When the bail control switch is in the BAIL RAISE position, the pressure to line relief valve (3) is not great enough to cause line relief valve (3) to open.