SUPPORT 1281008 - Caterpillar

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 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).
Illustration 2 g00733579
(6) Oil passage to tank
(8) Retainer
(10) Spring
(11) Shuttle valve
(24) Oil passage to tank
(26) Oil passage to 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 passes through the small orifices in shuttle valve (11) and drains to the tank through passage (26). When the oil from passage (6) passes 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.
Illustration 3 g00733585
Position of the shuttle valve with application of an external force
(6) Oil passage to tank
(8) Retainer
(10) Spring
(11) Shuttle valve
(24) Oil passage to tank
(26) Oil passage to tank If an external force is applied to the bail, the flow of oil from the bail cylinder will increase. Oil continues to pass through the small orifices until the pressure increases enough to overcome the spring force of spring (10). Shuttle valve (11) will move retainer (8) to the left in order to compress spring (10). This will open the slots on shuttle valve (11) to passage (26). Return oil is allowed to drain to the tank and the bail is lowered rapidly. This prevents the pressure in passage (6) from rising too high.Pressure Relief Valve
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 passes 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) will unseat poppet (17).When poppet (17) is unseated, the oil in spring cavity (19) is vented 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 is vented past poppet (17), the pressure decreases and poppet (17) is reseated. When poppet (17) is reseated, the oil pressure in spring cavity (19) begins to increase again. The pressure in spring