This valve type is electrically operated, 2-stage servo directional control valve.
The valve consist of an electro-mechanical governor (torque motor) , which is only electrically working part in valve device.
It controls hydraulic-mechanical amplifier , which controls hydraulically main control piston.
Electric parts are 2 pcs covernor coils
They can be measured with ohm-meter
Type of signal Analog
Nominal current per coil..... 30mA
Resistance per coil.............. 85Ω
further testing you need hydraulic test devices and hydr. pressure source.
You can imagine this valve as hydraulic push-pull amplifier.
input is electric current to coils and output is hydraulic flow,
and testing objects are offset, dead band, gain plus flow and gain minus flow , gain linearity.
4/3 servo directional control valve with mechanical position feedback
Operation of the servo system can usually be tested with the auxliary equipments,
when all devices and components are installed on the machine
by removing the automatic control input circuits and replace this wiring to manual control system for testing.
This requires a very good understanding of control principle and working devices.
(In this activity, I will not give further instructions for safety reasons)