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| Illustration 1 | g01589033 |
(1) Service brake pedal (2) Brake control valve (3) roller | |
Disengaged Position
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| Illustration 2 | g01596343 |
View from bottom of the machine Service brake pedal in the DISENGAGED position (4) Piston (5) Tank port (6) Outlet to service brakes on the front axle (7) Passage (8) Drain port (9) Cavity (10) Lower valve spool (11) Tank port (12) Outlet to service brakes on the rear axle (13 ) Cavity (14) Spring (15) Supply port for the accumulator for service brakes on the rear axle (16) Lower valve spool passage (17) Passage (18) Upper valve spool passage (19) Supply port for the accumulator for the service brakes on the front axle (20) Upper valve spool (21) Spacer (22) Ball (23) Retainer (24) Spring (25) Spring | |
When the service brake pedal is in the disengaged position, the front and the rear service brakes are drained to the tank. Oil flows from the service brakes through outlets (6) and (12). The oil flows through passages (7) and (17) into the tank return ports (5) and (11) .
Partially Engaged Position
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| Illustration 3 | g01596354 |
View from bottom of the machine Service brake pedal in the PARTIALLY ENGAGED position (4) Piston (5) Tank port (6) Outlet to service brakes on the front axle (7) Passage (8) Drain port (9) Cavity (10) Lower valve spool (11) Tank port (12) Outlet to service brakes on the rear axle (13 ) Cavity (14) Spring (15) Supply port for the accumulator for the service brakes on the rear axle (16) Lower valve spool passage (17) Passage (18) Upper valve spool passage (19) Supply port for the accumulator for the service brakes on the front axle (20) Upper valve spool (21) Spacer (22) Ball (23) Retainer (24) Spring (25) Spring | |
When the brake pedal is depressed, the roller on the pedal assembly pushes piston (4) downward. Piston (4) applies a force on springs (25) and (24). The force of springs (25) and (24) moves retainer (23) and ball (22). Movement of retainer (23) and ball (22) causes upper valve spool (20) to move away from the seat in spacer (21) .
The movement of upper valve spool (20) causes the movement of lower valve spool (10) and the compression of spring (14). When valve spools (20) and (10) move, oil flow through passages (7) and (9) to tank return ports (5) and (11) is blocked.
This allows pressurized oil from the supply ports (19) and (15) to flow through passages (7), (18), (17) and (16). The oil then flows through passages (6) and (12) in order to engage the service brakes. At the same time, pressurized oil flows through passages (18) and (16) and into cavities (9) and (13). The oil pressure at the service brakes has the same pressure as the oil in cavities (9) and (13) .
Oil pressure in cavity (13) and the force of spring (14) act to balance lower valve spool (10) against the force of the pressure in cavity (9). In the same manner, pressure in cavity (9) creates a force against the bottom of upper valve spool (20). The upper valve spool is balanced by the force of spring (25) at the top of spool (20) .
The force of springs (25), (24) and (14) is balanced by the force that is applied to the pedal. Upward movement of valve spools (20) and (10) causes the supply ports (19) and (15) to be covered. The level of pressure in the valve sections (20) and (19) create a feedback force. The feedback force from the valve spools allows the operator to feel the amount of pressure that is applied to the service brakes.
Valve spools (20) and (10) balance between the tank ports and the ports for the service brakes. This is done in order to maintain the brake pressure until the position of the pedal changes. A change in the pedal position means that more brake pressure or less brake pressure is necessary.
If piston (4) is moved downward in order to apply more compression on springs (25) and (24), valve spools (20) and (10) will move. The valve spools move in order to allow more pressure oil to flow to outlets (6) and (12) to the service brakes. This results in a higher oil pressure in cavities (9) and (13). A higher oil pressure is necessary in order to maintain the balance of valve spools (20) and (10) .
Fully Engaged Position
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| Illustration 4 | g01596395 |
View from bottom of the machine Service brake pedal in the FULLY ENGAGED position (4) Piston (5) Tank port (6) Outlet to service brakes on the front axle (7) Passage (8) Drain port (9) Cavity (10) Lower valve spool (11) Tank port (12) Outlet to service brakes on the rear axle (13) Cavity (14) Spring (15) Supply port for the accumulator for the service brakes on the rear axle (16) Lower valve spool passage (17) Passage (18) Upper valve spool passage (19) Supply port for the accumulator for the service brakes on the front axle (20) Upper valve spool (21) Spacer (22) Ball (23) Retainer (24) Spring (25) Spring | |
When the brake pedal is depressed, the roller that is on the pedal assembly pushes piston (4) downward. Piston (4) applies a force on springs (25) and (24). The force of springs (25) and (24) moves retainer (23) and ball (22). Movement of retainer (23) and ball (22) causes upper valve spool (20) to move away from the seat in spacer (21) .
The movement of upper valve spool (20) causes the movement of lower valve spool (10) and the compression of spring (14). When valve spools (20) and (10) move, oil flow through passages (7) and (17) to tank return ports (5) and (11) is blocked.
This allows pressurized oil from the supply ports (19) and (15) to flow through passages (7), (18), (17) and (16). The oil then flows through passages (6) and (12) in order to engage the service brakes. At the same time, pressurized oil flows through passages (18) and (16) and into cavities (9) and (13). The oil pressure at the service brakes has the same pressure as the oil in cavities (9) and (13) .
Oil pressure in cavity (13) and the force of spring (14) act to balance lower valve spool (10) against the force of the pressure in cavity (9). In the same manner, pressure in cavity (9) creates a force against the bottom of upper valve spool (20). The upper valve spool is balanced by the force of spring (25) at the top of spool (20) .
The force of springs (25), (24) and (14) is balanced by the force that is applied to the pedal. Upward movement of valve spools (20) and (10) causes the supply ports (19) and (15) to be covered. The level of pressure in the valve spools (20) and (10) create a feedback force. The feedback force allows the operator to feel the amount of pressure that is applied to the service brakes.
Valve spools (20) and (10) balance between the tank ports and the ports for the service brakes. This is done in order to maintain the brake pressure until the position of the pedal changes.