Kubota ZD21N-EC Workshop Manual page 193

ZD21N-EC, ZD21-EC, ZD28-EC, WSM
Overloaded
(1) Spool
(2) Control Valve Adaptor
If the pressure in the circuit exceeds the relief valve setting pressure (3.14 to 3.73 MPa, 32 to 38 kgf/cm
540 psi), the relief valve (4) opens to release pressure-fed oil.
Then, oil flows to the hydrostatic transmission through the R port (3) and control valve adaptor (2) as shown in the
figure.
Down
(1) Valve Cover
(2) Spool
(3) Valve Body
(4) Orifice
When the control lever (7) is set to "DOWN" position, the spool (2) moves to the left to form a lowering circuit.
Therefore, oil in the lift cylinder is forced out by the weight of the mower and returns to the hydrostatic transmission to
lower the mower as shown in the figure.
Oil, pressure-fed from the hydraulic pump, goes through the clearance between the valve body (3) and spool (2),
and then flows to the hydrostatic transmission through the R port (8) and control valve adaptor (5).
(3) R (Return) Port
(4) Relief Valve
(5) Control Valve Adaptor
(6) Relief Cover
(7) Control Lever
(5) P (Pump) Port
(6) C (Cylinder) Port
(8) R (Return) Port
(9) P (Pump) Port
(10) C (Cylinder) Port
4-M5
HYDRAULIC SYSTEM
A: To Hydrostatic Transmission
2
, 455 to
A: To Hydrostatic Transmission
B: From Lift Cylinder
KiSC issued 09, 2006 A