Hyundai HX130LCR Manual page 116

Counterbalance operation
④
Counterbalance operation is required to decelerate slowly the hydraulic motor while absorbing
inertia force.
In case the hydraulic oil is gradually decreased from pump to VB port, the drive shaft of hydraulic
motor tends to rotate faster than that matched to the volume of oil supply.
Consequently, the pilot chamber pressure on MB to VB side decreases and the spring (33) force
moves the spool (31) leftwards towards neutral position.
Therefore, the area of passage from MA to VA becomes smaller and the pressure on MA side
rises due to increased resistance in the passage and the motor receives hydraulic braking effect.
If the motor rotates slower than that matched to the volume of supplied oil, the pilot chamber
pressure on VB port increases, and spool (31) moves rightwards to enlarge the area of passage
from MA to VA. Therefore the braking effect becomes smaller and the rotational speed of motor
is controlled to correspond to the volume of supplied oil.
In order to give stable counterbalance operation, the restrictors (34) are set in the pilot chamber
to damp the spool (31) movement.
The parking brake is released during pressure adjusting action of the spool (31).
DR
DR
MB MA
MB MA
VB
VA
VB VA
125LCR2TM32
2-72