330D, 336D and 340D Excavators Hydraulic System – Boom Hydraulic System

Boom Raise (High Speed)

A BOOM RAISE operation at high speed is accomplished when the oil delivery from both idler pump (27) and drive pump (28) is supplied to the head end of boom cylinders (1) . Boom l control valve (19) and boom II control valve (16) operate during the high speed operation. A BOOM RAISE operation at low speed is accomplished when the oil delivery from only drive pump (28) is supplied to the head end of boom cylinders (1) . During the low speed operation, boom l control valve (19) operates alone.

The oil delivery from drive pump (28) flows through parallel feeder passage (17) in main control valve (11) to boom l control valve (19) . The oil delivery from idler pump (27) flows through parallel feeder passage (8) in main control valve (11) to boom II control valve (16) .

When the joystick for the boom is moved to the full BOOM RAISE position, the pilot oil flows from pilot control valve (22) through pilot line (24) . The pilot oil flow then divides into two flow paths. Part of the pilot oil flows through pilot line (21) to port (7) of main control valve (11) . The remainder of the pilot oil flows through pilot line (23) to port (20) of the main control valve.

A portion of the oil in pilot line (23) also flows through pilot line (25) to the pressure reducing valve for boom priority (26) . During a combined operation of BOOM RAISE and STICK IN, BOOM RAISE and STICK OUT, or BOOM RAISE and BUCKET CLOSE the pilot oil flow to the pressure reducing valve for boom priority (26) causes the boom circuit to receive oil flow priority. This flow allows the boom to raise at a high speed.

The pilot oil flow from port (20) shifts spool (35) of boom l control valve (19) against the force of spring (33) . The oil delivery from the drive pump in parallel feeder passage (17) flows through load check valve (14) , passage (31) , passage (34) and port (30) to boom drift reduction valve (5) . The oil delivery from the drive pump shifts valve (4) in boom drift reduction valve (5) to the right. The oil delivery from the drive pump then flows through line (3) to the head end of boom cylinders (1) .

Note: For more information on the boom drift reduction valve, refer to Systems Operation, “Boom Drift Reduction Valve”.

The pilot oil flow in port (7) of boom II control valve (16) shifts spool (38) against the force of spring (37) . The oil delivery from the idler pump in parallel feeder passage (8) now flows through passage (36) , passage (39) , check valve (13) and flows out of port (15) to line (10) . The oil delivery from the idler pump combines with the oil delivery from the drive pump at boom drift reduction valve (5) . The combined pump oil flows through passage (12) and line (3) to the head end of boom cylinders (1) .

Note: The swing priority valve does not affect the boom II control valve.

Return oil from the rod end of boom cylinders (1) flows through line (2) to boom l control valve (19) . The oil then flows through passage (32) , return passage (18) , return passage (9) , and return line (6) to the hydraulic tank.

Boom Raise (Low Speed)

When the joystick for the boom is moved less than half of the travel distance for BOOM RAISE, low pilot oil pressure is supplied to boom l control valve (19) and boom II control valve (16) .

When the boom is raised at a low speed, boom l control valve (19) opens and boom II control valve (16) remains closed. The force of spring (33) in boom l control valve (19) is less than the force of spring (37) in boom II control valve (16) . Because of the low pilot oil pressure, boom l control valve (19) will open and boom II control valve (16) will remain closed.

The oil delivery from drive pump (28) now flows to the head end of boom cylinders (1) . Without the oil delivery from idler pump (27) , the cylinder rod movement slows down when the boom is raised. The low speed operation of the boom is performed.

Boom Priority

During combined operations of BOOM RAISE and STICK IN, the pilot oil pressure from the pilot control valve for the boom (22) activates the pressure reducing valve for boom priority (26) . The pressure reducing valve for boom priority (26) causes oil flow priority to the head end of the boom cylinders (1) during this combined hydraulic operation.

When the joystick for the stick is moved to the STICK IN position, a portion of the pilot oil from the pilot control valve for the stick (41) flows through the pressure reducing valve for the boom priority (26) to the stick II control valve (40) . As the joystick for the boom is moved farther from the NEUTRAL position during a BOOM RAISE operation, pilot oil pressure from the pilot control valve for the boom (22) increases. This gradual increase in pilot oil pressure causes the spool in the pressure reducing valve for the boom priority (26) to shift gradually.

A portion of the pilot oil that flows to stick II control valve (40) from the pilot control valve for the stick (41) is routed to the hydraulic tank. The pilot oil pressure that acts on stick II control valve (40) decreases. Stick II control valve (40) shifts toward the NEUTRAL position. The amount of oil flow from the main pumps to the stick hydraulic circuit decreases. This change of routing causes a greater portion of the oil flow from the main pumps to flow to the head end of the boom cylinders (1) .

Since the pilot oil pressure from the pilot control valve for the boom (22) directly corresponds to the amount of movement or position of the joystick, a gradual change to boom priority occurs. Thus, boom priority is controlled by the position of the joystick for the boom and boom priority automatically activates when the joystick reaches a certain position during a BOOM RAISE operation.

The above information describes the condition of BOOM RAISE and STICK IN. During any combined function of BOOM RAISE and STICK IN, BOOM RAISE and STICK OUT, or BOOM RAISE and BUCKET CLOSE, the pressure reducing valve for boom priority allows priority flow to the head end of the boom cylinders by reducing pilot pressure to the stick l, stick II, or bucket control valves.

ReferenceFor more information concerning boom priority, refer to Systems Operation, “Pilot Hydraulic System”.

Boom Lower

During a BOOM LOWER operation, the oil delivery from only drive pump (28) is supplied to boom cylinders (1) through boom l control valve (19) . Boom l control valve (19) operates alone. Boom II control valve (16) is not operational in the BOOM LOWER operation.

The BOOM LOWER operation contains a regeneration circuit. When the joystick for the boom is moved to the BOOM LOWER position, orifice (43) in boom l control valve (19) and boom regeneration valve (41) are operational in the boom hydraulic circuit. The return oil flow from the head end of boom cylinders (1) flows through boom regeneration valve (41) to the rod end of the boom cylinders. The boom regeneration valve is described later in this section.

When the joystick for the boom is moved to the BOOM LOWER position, pilot oil from pilot control valve (22) flows through pilot line (52) . The pilot oil flow then divides into three flow paths. Part of the pilot oil flows through port (46) to boom l control valve (19) . Part of the pilot oil flows through port (42) to boom regeneration valve (41) . The remainder of the pilot oil flows through pilot line (53) of boom drift reduction valve (5) .

Since the pilot oil pressure has caused the spool in boom l control valve (19) to shift against the force of spring (33) , the oil delivery from the drive pump that flows through center bypass passage (45) is restricted by orifice (43) . The negative flow control pressure in negative flow control line (44) decreases. The drive pump upstrokes because of the negative flow control operation.

ReferenceFor more information concerning the negative flow control operation, refer to Systems Operation, “Negative Flow Control System”.

The pilot oil flow from port (46) shifts spool (35) in boom l control valve (19) against the force of spring (33) . The oil delivery from the drive pump in parallel feeder passage (17) flows through load check valve (14) , passage (49) and port (32) . The oil delivery from the drive pump then flows through line (2) to the rod end of boom cylinders (1) .

The return oil from the head end of boom cylinders (1) flows through line (3) into boom drift reduction valve (5) . Since valve (48) is shifted by the pilot pressure from pilot line (53) , passage (49) is open to drain line (50) . The return oil pressure shifts valve (4) to the right. The return oil in line (3) enters passage (51) .

A portion of the return oil flows into port (30) of boom l control valve (19) . The return oil flow is restricted by orifice (40) . The return oil pressure in passage (51) increases. Most of the return oil flows through boom regeneration valve (41) . The return oil is now supplied to the rod end of the boom cylinders through line (2) .

Boom Regeneration Valve

The boom hydraulic circuit contains a regeneration circuit. This regeneration circuit allows the return oil from the head end of the boom cylinders to be supplied to the rod end of the boom cylinders during the BOOM LOWER operation.

When the joystick for the boom is moved to the BOOM LOWER position, pilot oil flow from the pilot control valve (boom and bucket) enters pilot port (42) . Spool (58) in the boom regeneration valve shifts downward. The return oil from the head end of the boom cylinders flows through passage (59) and through the throttling slots on the spool for the boom regeneration valve to check valve (57) . Check valve (57) opens and the return oil flows through passage (56) . The return oil from the head end of the boom cylinders in passage (56) combines with the oil delivery from the drive pump. This combined oil now flows to the rod end of the boom cylinders.

The oil delivery from only the drive pump is used for the BOOM LOWER operation. Since the boom regeneration valve supplies return oil from the head end to the rod end of the boom cylinders, more efficient use of the oil delivery from the drive pump is achieved during a BOOM LOWER operation.