10.03
A.1 Servo solenoid valves
A-249
 Siemens AG, 2003. All rights reserved
SINUMERIK 840D/SIMODRIVE 611 digital, HLA Module (FBHLA) - 10.03 Edition
A.1.3 Pilot-controlled servo solenoid valves, sizes 10 and 16
The principle of pilot control is applied in order to control higher flow rates.
A size 10 or 16 directional control valve with suitable control edges is used as
the main stage on the valve spool. Like the piston rod of a cylinder, this stage is
hydraulically clamped and positioned by a size 6 pilot valve
(see Subsection A.1.2).
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.
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 using suitable plugs.
Pilot-actuated 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 mid-
position.
The integral valve amplifier is mounted on the pilot valve assembly and contains
both position control loops. A cable is used to connect the position sensor on
the main stage to the amplifier.
Mechanical
structure
Inlet and outlet of
hydraulic fluid
Valve positions
Valve amplifier
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