closed center solenoid valves legal??
 

We're wanting to design using closed center, three position valves, for double acting cylinders. Anyone know if that might be legal?? Also last year I was thinking that we were required to provide one manual ball valve to release the pressure on everything on the robot. Is this still a requirement - I can't seem to find where this requirement is/was documented.

Re: closed center solenoid valves legal??
 

Please section 4.10, R67, R72 and for visual Figure 4-7. That will take care of your pressure vent and many other questions.

As for the centre tap plug that may require a Q&A question.

Re: closed center solenoid valves legal??
 

R67 requires a pressure vent plug.

R78 requires the pressure vent plug to vent ALL stored pressure when actuated.
I don't think a block center valve will dump any upstream air volume unless one of the solenoids on the valve are energized. For this reason, I don't believe this valve will satisfy R78.

Note that when the robot us disabled, all relay outputs are de-energized (causing the valve to center and prevent air from venting).