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James Schroeder

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  • James Schroeder
    Participant

    We had simular concerns on a new coker built in 2007.  We used Rotork actuators with MODBUS actuation from the DCS.  The interlocks are not done through the MODBUS.  We take valve postion contacts off the actuator and sent a descrete signal to the valve to the ESD input.  This allows the valve to be locked out and can not be operatored from the MODBUS or from the local station.  The only way to operate the valve when it is locked out is to engage the clutch and operate the handweel.  The clutch has a key lock and chain on it so the operator must involk a lockout/tagout procedure to operate the valve.  This requires a management signoff to do.
     
    Our concern was the same.  Operators were reluctant to accept valves where the power could not be turned off..  Their concern was that someone could operate the wrong valve locally if the valves were not powered down when not being operated.  They were convinced this was acceptable only after we brought in a demonstration valve actuator and show them how it would work.
     
    As a side note we have had some problems with the MODBUS.  Occasionally the valve will freeze and can not be operated from the DCS.  The only way to get it to work is to cycle power to the valve actuator.  We are studing this issue to see how extensive it is.

  • in reply to: Switch Valves Operation #6657

    James Schroeder
    Participant

    We just started up a new 4 drum coker.  The switch valves are Velan valves that are actuated from the DCS.  We had problems making them work because the valves rely on limit switches to determine the valve position.  Because the valves can travel 360 deg the feed back through the MODBUS interface is not reliable.  We doubled up the position switches and fixed the tolerances and they have been working pretty well.  (For about 3 months).  The valves are actuated by the operator in the control room.  They are not typically monitored in the field while they are moving.

  • in reply to: Automatic deheading on top #7686

    James Schroeder
    Participant

    What actuators have you supplied with your De-hedding valves?  Have yor ever supplied BLAC actuators?  What actuator was used on the Un-heading valve?

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