320C Excavator Hydraulic System – Boom Drift Reduction Valve

The boom drift reduction valve is placed in the boom circuit between the main control valve and the boom cylinders. When the joystick for the boom is in the NEUTRAL position, the boom drift reduction valve stops oil leakage from the head end of the boom cylinders. Stopping oil leakage prevents boom drift.

Boom Raise



Illustration 1 g01042907

Boom drift reduction valve (BOOM RAISE)

(1) Passage

(2) Valve

(3) Spring

(4) Spring chamber

(5) Passage

(6) Port

(7) Port

(8) Port

(9) Passage

(11) Spool

(15) Port

(16) Boom drift reduction valve

When the joystick is moved to perform a BOOM RAISE operation, pilot oil is not sent from the pilot control valve to port (15) of boom drift reduction valve (16). Spool (11) does not shift.

The oil flow from the boom II control valve enters port (6) of the boom drift reduction valve. The oil flow from the boom I control valve enters port (7) of the boom drift reduction valve. The combined oil flow from ports (6) and (7) flows into passage (1). As the oil pressure in passage (1) increases, valve (2) shifts against the force of spring (3). The oil in spring chamber (4) flows through passages (5) and (9) to port (8). The oil delivery in passage (1) now flows through port (8) to the head end of the boom cylinders.

Boom Lower



Illustration 2 g01043156

Boom drift reduction valve (BOOM LOWER)

(1) Passage

(2) Valve

(3) Spring

(4) Spring chamber

(5) Passage

(6) Port

(7) Port

(8) Port

(9) Passage

(11) Spool

(12) Passage

(13) Drain line

(15) Port

(16) Boom drift reduction valve

(18) Port

(20) Spring chamber

(21) Plug

When the joystick is moved to perform a BOOM LOWER operation, pilot oil is sent from the pilot control valve to port (15) of boom drift reduction valve (16). Spool (11) shifts downward until the spool contacts plug (21). Passage (9) to spool (11) is blocked. The oil in spring chamber (4) flows through passage (5), the passage in spool (11), spring chamber (20), passage (12), port (18) and drain line (13) to the hydraulic tank.

The return oil from the boom cylinder head end enters port (8). Since the pressure in spring chamber (4) is low, the oil in port (8) shifts valve (2) against the force of spring (3). The return oil from the head end of the boom cylinders flows through port (8), passage (1), port (7) and the boom I control valve to the return passage.