Why is the Azimuth Joint Loose (swings back and forth) when Hydraulics are Turned off?
This is a common and normal reaction of a servo controlled actuator. A servo valve has an internal spool that we can simplify by saying that it has 3 positions. When it is perfectly centered it blocks all 4 ports; Pressure, Return, C1 (azimuth right), and C2 (azimuth left). When it is not perfectly centered, it connects Pressure to C1 and return to C2, or Pressure to C2 and Return to C1, depending on which side of center the spool comes to rest when hydraulics are turned off. In addition, the hydraulic solenoid valve is designed to open the manipulator pressure circuit to the return circuit when the valve is closed. This prevents high ambient pressure from being trapped in the manipulator if the hydraulics are turned off at depth and the manipulator is brought to the surface, and also provides compensation pressure to the circuit if the arm is taken to depth with hydraulics off. Therefore, if the hydraulics is turned off and the servo valve spool is not perfectly centered, any movement
