PSV interlocking

Sorry I came after a long weekend.

In the HP steam service, in situations where to be in line with API area limitation, it is necessary to distribute the capacity with multiple valves to achieve the relieving capacity needed. Where such 20 PSV collectively are used to discharge in which one is left as spare.  So to ensure all 19 valves are open, the interlocking is applied and simple carseal open is not used. Actually for plant operators CSO is easier. But when situation arises where it is only channelized to a diff. PSV and not really meant for maintenance, CSO does not perfectly suit.  Yes we can reduce the number of PSV considering the specialized ASME sectionwise highcapacity PSVs, but it is left to the discretion of the safety engineer. But the pressure in the need of the valve dimensions for the piping layout group is forcing the safety to adopt this API config. solution where the dim. is already available in the standardized form and can still proceed in layout engg while awaiting for the order being placed.

As only one is accounted as a spare out of the 20, all of equal capacity lined up parallelly, I am afraid if any backpressure would develop, as the margin of all put together is equal to one PSV capacity minimum, even if one fails the remaining 18 would still take care of. This multiple distribution is better off than fewer in such failure cases and to ensure least chattering happening.

Regards,
Kannan
Germany.


On Oct 8, 2008, at 4:41 AM, kannan.sundaram@linde-le.com wrote:

> Additionally, where in some cases where a network of 20+ PSVs are
> interlocked the CSO does not serve the purpose.
Just for my own curiosity, how do guarantee that a PSV can operate
independently if it's interlocked with 19 others. I was always taught
to avoid like the plague the possibility that the operation of one
valve might interfere with the operation of another. What sort of
situation requires 20 interlocked safety valves? How do you avoid a
circumstance where one of the valves might put a back pressure on one
or moe of the others?

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