Mechanical connection between the moving parts of a fluid power control device and the moving part of the device to be controlled for the purpose of .
Example: Two stage servo valve with flapper-nozzle system: here, a feedback spring (tube) is stretched while the valve control spool is being deflected until a balance is established between the spring force and the hydraulic force on the end of the valve control spool (Figure M 3).
Figure M 3: Mechanical feedback for the flapper-nozzle system