308C CR Excavator Hydraulic System – Boom Drift Reduction Valve

Illustration 1 g00865473

Boom drift reduction valve

(1) Poppet

(2) Passage

(3) Drain passage

(4) Spool

(5) Piston

(6) Port

(7) Spring chamber

(8) Valve

(9) Spring

(10) Passage

(11) Passage

(12) Port

(13) Boom I control valve

(14) Return passage

(15) Boom drift reduction valve

The description of the boom drift reduction valve during boom lower operation is explained below.

When the control lever is moved to the BOOM LOWER position, pilot oil from the pilot control valve enters boom I control valve (13) through port (12). Pilot oil shifts the stem downward. Return oil for the boom cylinder head end goes through passage (10) to boom drift reduction valve (15). Boom drift reduction valve (15) opens in the following manner.

  1. Pilot oil from port (6) shifts piston (5) and spool (4) to the left against the force of spring (9). Passage (2) in spool (4) and poppet (1) connects with drain passage (3) .
  1. The oil in spring chamber (7) flows through passage (2) to drain passage (3). Oil pressure in spring chamber (7) becomes low.
  1. Oil pressure in passage (10) opens boom drift reduction valve (15) downward.

Boom drift reduction valve (15) is shifted downward. This allows the flow of return oil in passage (10) to return through passage (11) to return passage (14).