Precontrolled Servo Solenoid Valves - Siemens SINAMICS S120 System Manual

A.3.1.3

Precontrolled servo solenoid valves

The principle of precontrol is applied in order to be able to handle higher flow rates.
Mechanical design
A directional control valve with appropriate control edges at the valve spool is used as main
stage. Like the piston of a cylinder, this stage is hydraulically clamped and positioned by a
precontrol valve.
The position of the main spool is scanned by another position sensor and the corresponding
actual value applied to a second, subordinate position control loop.
Hydraulic fluid intake and discharge
The control fluid can be supplied and removed either internally via ports P and T or, as often
is the case in practice, externally via additional ports X and Y. The unit is converted over
using suitable plugs.
Switch settings
Precontrolled servo solenoid valves have only three stepless-transition valve positions.
The 4th fail-safe position is omitted. If the supply voltage is disconnected, the spring force of
the main spool causes the valve to assume an indifferent middle position.
Hydraulic Drive
System Manual, 04/2015, 6SL3097-4BA00-0BP1
Appendix
A.3 Hydraulic
247