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.