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| Illustration 1 | g01333260 |
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(1) Service brake pedal
(2) Brake control valve (3) Rod | |
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| Illustration 2 | g03551737 |
| (1A) Limit switch to activate the brake lights | |
Brake control valve (service) (2) controls the flow of pressurized oil. When service brake pedal (1) is depressed, rod (3) actuates the service brake control valve. The position of the brake pedal causes a specific pressure at the service brakes. As the position of the pedal changes, the pressure at the service brake also changes. There is a limit switch located at (1A). When the brake pedal is activated, the brake pedal activates limit switch (1A). The limit switch will send an electrical signal to the brake lamps causing the brake lamps to turn on.
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| Illustration 3 | g01333272 |
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View from bottom of the machine Service brake pedal in the DISENGAGED position (4) Piston (5) Tank port (6) Outlet to left service brakes (7) Passage (8) Drain port (9) Cavity (10) Lower valve spool (11) Tank port (12) Outlet to right service brakes (13 ) Cavity (14) Spring (15) Supply for the right brakes (16) Lower valve spool passage (17) Passage (18) Upper valve spool passage (19) Supply for the left brakes (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 right and the left service brakes are drained to the tank. Oil flows from the service brakes through outlet (6) and outlet (12). The oil flows through passage (7) and passage (17) into the tank return port (5) and tank return port (11).
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| Illustration 4 | g01333294 |
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View from bottom of the machine Service brake pedal in the PARTIALLY ENGAGED position (4) Piston (5) Tank port (6) Outlet to left service brakes (7) Passage (8) Drain port (9) Cavity (10) Lower valve spool (11) Tank port (12) Outlet to right service brakes (13 ) Cavity (14) Spring (15) Supply for the right brakes (16) Lower valve spool passage (17) Passage (18) Upper valve spool passage (19) Supply for the left brakes (20) Upper valve spool (21) Spacer (22) Ball (23) Retainer (24) Spring (25) Spring | |
When the brake pedal is depressed, the rod on the pedal assembly pushes piston (4) downward. Piston (4) applies a force on spring (25) and spring (24). The force of spring (25) and spring (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 spool (20) and valve spool (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 port (15) and supply port (19) 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 passage (16) and passage (18) 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 spring (25), spring (24) and spring (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 section (20) and valve section (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 spool (20) and valve spool (10) balance between the tank ports and the ports for the service brakes. This balancing 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 spring (25) and spring (24), valve spool (20) and valve spool (10) will move. The valve spools move in order to allow more pressure oil to flow to outlet (6) and outlet (12) to the service brakes. This results in a higher oil pressure in cavity (9) and cavity (13). A higher oil pressure is necessary in order to maintain the balance of valve spool (20) and valve spool (10).
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| Illustration 5 | g01333318 |
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View from bottom of the machine Service brake pedal in the FULLY ENGAGED position (4) Piston (5) Tank port (6) Outlet to left service brakes (7) Passage (8) Drain port (9) Cavity (10) Lower valve spool (11) Tank port (12) Outlet to right service brakes (13) Cavity (14) Spring (15) Supply for the right brakes (16) Lower valve spool passage (17) Passage (18) Upper valve spool passage (19) Supply for the left brakes (20) Upper valve spool (21) Spacer (22) Ball (23) Retainer (24) Spring (25) Spring | |
When the brake pedal is depressed, the rod on the pedal assembly pushes piston (4) downward. Piston (4) applies a force on spring (24) and spring (25). The force of spring (24) and spring (25) 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 port (19) and supply port (15) to flow through passage (7), passage (18), passage (17) and passage (16). The oil then flows through passage (6) and passage (12) in order to engage the service brakes. At the same time, pressurized oil flows through passage (18) and passage (16) and into cavities (9) and (13). The oil pressure at the service brakes has the same pressure as the oil in cavity (9) and cavity (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 spring (14), spring (24) and spring (25) is balanced by the force that is applied to the pedal. Upward movement of valve spool (10) and valve spool (20) causes the supply port (15) and supply port (19) to be covered. The level of pressure in the valve spool (10) and valve spool (20) create a feedback force. The feedback force allows the operator to feel the amount of pressure that is applied to the service brakes.
Valve spool (10) and valve spool (20) balance between the tank ports and the ports for the service brakes. This balancing is done in order to maintain the brake pressure until the position of the pedal changes. A change in the pedal position means that less brake pressure is necessary.