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| Illustration 1 | g00886796 |
Hydraulic Schematic for Swing Boom (1) Swing cylinder (2) Line (head end of swing boom cylinder) (3) Line (rod end of swing boom cylinder) (4) Swing boom control valve (5) Pilot line (swing left) (6) Main relief valve for swing boom and blade (7) Return line (8) Pilot line (swing right) (9) Pilot supply line (10) Pilot control valve (11) Pilot manifold (12) Return line (13) Pilot supply line (14) Line (supply oil from swing boom pump) (15) Pilot pump (16) Pilot supply line from pilot pump (17) Return line (18) Hydraulic tank (19) Swing boom pump (20) Load check valve (21) Manifold (22) Center bypass passage (23) Return passage | |
The swing boom is used to dig in locations that prevent the upper structure from swinging. The main components of the swing boom are listed below.
- Pedal
- Pilot control valve
- Main control valve
- Swing boom control valve
- Swing boom cylinder
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| Illustration 2 | g00842086 |
Control pedal for swing boom (24) Control pedal (25) Footrest | |
Under the right footrest, the hydraulic control is bolted to the cab floorplate on the right side of the travel levers/pedals. The hydraulic control consists of control pedal (24) and the pilot control valve (10) below the control pedal.
Only when the pedal is depressed, the hydraulic system of the swing boom is supplied with oil.
Depressing the pedal to the left allows pump oil to flow to the head end of the swing boom cylinder. This causes the swing boom to swing left. Depressing the pedal to the right allows pump oil to flow to the rod end of the swing boom cylinder. This causes the swing boom to swing right.
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| Illustration 3 | g00842064 |
Control Pedal and Pilot Control Valve (24) Control pedal (26) Rod (27) Seat (28) Spring (29) Spring (30) Port (return oil to hydraulic tank) (31) Stem (32) Passage (33) Passage (34) Port (pilot oil pressure) (35) Port (36) Port (37) Passage (38) Passage (39) Passage (40) Stem (41) Spring | |
When pedal (24) is depressed to the right, the pedal pushes down on rod (26) and seat (27) against the force of spring (28) and spring (29). Stem (31) is moved downward, and the stem opens passage (37) to passage (32) .
As passage (37) is opened, pilot oil from port (34) flows through passage (32) and through a drilled passage in the stem (33). The oil leaves through port (35). The oil enters the swing boom control valve. The pilot oil then shifts the spool in the swing boom control valve.
The shifted spool allows pump oil to flow to the swing boom. The spool also forces the pilot oil at the front of the swing boom control valve to flow back to the pilot control valve and to port (36). The pilot oil pushes up on stem (40) and spring (41). When the pressure is high enough, stem (40) moves up against the force of spring (41), and passage (38) opens to passage (39). This allows pilot oil in port (36) to go through the drilled passage in the stem. The oil flows through passage (38) to passage (39). The pilot oil flows out of port (30) to the drain. When the pilot oil pressure decreases, spring (41) moves the stem (40) downward, and passage (38) to passage (39) closes.
The same operation happens in reverse order when the pedal is depressed to the left. The pilot oil flows from port (36) of the pilot control valve. The spool of the swing boom control valve shifts and the valve of the swing boom drains.
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| Illustration 4 | g00889186 |
Front Lines of Swing Boom (1) Cylinder (2) Line (head end) (3) Line (rod end) (4) Swing boom control valve (42) Port (head end for swing left) (43) Port (rod end for swing right) (44) Swing boom | |
Supply oil flows out of port (42) when the spool shifts to the right. The oil flows through line (3) to the rod end of the swing boom cylinder. When the spool shifts to the left, oil flows out of port (43). The oil flows through line (4) to the head end of the swing boom cylinder.