Komatsu PC88MR-10 Shop Manual page 171

Arm regeneration circuit
When cylinder bottom pressure is higher than the head pressure (during hydraulic drift, etc.)
Function
During the arm "IN" operation, if head pressure (A) of arm cylinder (1) is higher than bottom pressure (B)
and the arm drifts hydraulically, regeneration circuit (a) increases the oil flow to the bottom side to increase
the cylinder speed.
Operation
If the arm drifts hydraulically during the arm "IN" operation, head pressure (A) of arm cylinder (1) is higher
than bottom pressure (B).
A part of the return oil on the bottom side flows through the notch of arm spool (2) to regeneration circuit
(a) and opens check valve (3).
Then, the above oil flows from check valve (3) to the bottom side of arm cylinder (1) to increase the arm IN
speed.
PC88MR-10
(PC88MR-L911-040-K-00-A)
10 Structure and function
Control valve
10-93