QUESTION 30

How do you mount and cable dual servovalves?

ANSWER

Depending on how the servovalves are mounted on the actuator will determine if the servovalves are in or out of phase with each other.

Servovalves must be phased properly to ensure that they control the actuator travel; i.e. positive command results in positive actuator travel.

When you install or replace a servovalve you need to check the valve polarity.  The easiest way is to put the system into displacement control and change the command.  If the actuator follows the command the valve is phased correctly.  However, if the actuator fails to move or moves to the other end cap, the servovalve is phased backwards.

Servovalve cables are produced with the first and second servovalve either in phase or out of phase.   All of the control packages allow for the phase to be reversed but it essentially reverses output of the valve driver so you need to be careful when you install a servovalve cable.  Just because it fits, don’t assume it’s correct.   Check to see how the servovalves are mounted on the manifold.   If they are mounted in the same plane the valves are in phase (Figure 1).   

Figure 1 – Same plane in phase mounting 

However, if they are mounted 180 degrees from each other, they are out of phase (Figure 2).

Figure 2 – 180 degrees out of phase mounting

Table 1 – Cable selection for dual servovalves

Figure 3 - Cable diagram 572555 (In phase)

Figure 4 – Cable diagram 572554 (Out of phase)