Komatsu Galeo PC138US-8 Shop Manual page 215

10 Structure, function and maintenance standard
Brake operation at travelling downhill
If the machine is going to run away when trav-
q
eling downhill, the motor idles and the hydrau-
lic pressure at port (C) drops. The pressure of
hydraulic oil that is sent to chamber (G)
through orifice (f) also drops.
When the hydraulic oil pressure in chamber
q
(G) goes below spring (3) reaction force, coun-
terbalance valve (2) starts to return to the left.
The hydraulic oil in chamber (J) tends to flow
q
to port (B) through orifice (h). However, the
back pressure is generated by closing of orifice
(h), controlling the return speed of counterbal-
ance valve (2) to the right.
When ports (D) and (B) are closed and when
q
the hydraulic pressure at port (D) increases, a
resistance is generated in motor rotation to
protect the machine from running away.
Counterbalance valve (2) is moved to the posi-
q
tion where the hydraulic pressure at port (B) is
well balanced with the pressure by the weight
of machine itself and the pressure at port (A).
The motor speed is controlled according to the
pump delivery by controlling the opening of
hydraulic oil output circuit.
PC138US, USLC-8
SEN02550-01
33