45 - 7
Section D
9803/3280
Section D
45 - 7
Issue 1
Precision Control (Servo)
A403930
1 2 3 4
Hydraulic symbol
P T
5
9
8
6
7
11
T
P
Basic System Operation
Joystick Controllers - Description
The joystick controllers operate as direct operated pressure
reducing valves and consist of a hand control lever, four
pressure reducing valves and the housing. Each pressure
reducing valve consists of a control spool, control spring,
return spring and a plunger.
In neutral the control lever
5
is kept in the central position by
the return spring
8
. Service ports
1
,
2
,
3
and
4
are connected
to the tank port
T
via gallery
11
.
When the control lever
5
is operated, plunger
9
pushes
against return spring
8
and control spring
7
. The control
spring
7
moves the control spool
6
down-wards and closes
the connection between the relevant service port and the
tank port
T
. The service port is connected to the pressure
port
P
via gallery
11
.
The control phase begins when the control spool
6
has
found its balance between the force of the control spring
7
and the force which results from the hydraulic pressure in the
selected port.
The interaction of the control spool
6
and control spring
7
enables the plunger
9
to produce pressure proportional to
the position of the control lever
5
.
Full Pressure
Pressure
Servo
Neutral
Exhaust
Cavitation
Lock Up
A390630
Key to Oil Flow & Pressure