Locking devices.

Very interesting note from Surve on CSO/C.

May be it would also be interesting to discuss on interlocking devices also at this point of time.

To the extend I have come across I would classify as below.

1) The normal valve locking devices which are used to have the valve locked in open or closed position on an individual basis.
2) The interlocked valve system where a group of valves are kept in open or closed position to achieve one or multiple different stream flow conditions in a chemical process.
3) The interlocked valve system where a group of valves in the upstream and downstream of one or group of Pressure Safety Valves for safety reasons.
4)  The interlocked valve system where a group of valves are kept in open or closed position and interlinked with electronic locking keys to obtain a swing in production of a plant like a switch between LLDPE to HDPE production based on the market demand and sales conditions.
5) The completely integral electronic interlocking system of valves to obtain a swing which are more sensitive and time framed.

The devices ranges from normal padlocks, integral locks in the valve design itself, external retrofit locking device and electronic locking devices using position sensors in campanion with MOVs.

The interlocking at times may involve as high as 30 different valves in one single network.

I find some companies apply the individual locking devices for PSVs, which is really not a safe solution. I feel the interlocking is required for PSVs so that even accidently the valves are not locked in wrong positions.  Moreover the Master keys are in the control of the plant manager and are obtainable only with proper authorisation for changing any of the valve positions. This is the same concept of CarSeal. This is one reason why we find very less engg. companies are prefering to have the above locking devices rather than the CarSeals.

The logics of locking operation are to be part of the Plant operating manual in my opinion. But rarely implimented.

Members who have used locking devices and systems for other purposes are also requested to share.

With regards,
Kannan