Control Valves and Eccentric Reducers

[Gator]

For steam service, bottom flat reducers upstream of control valves are recommended to minimize the possible accumulation of condensate and sediment.

Is the same configuration preferred for other fluids as well?

One other reason for FOB (flat on bottom) reducers in control stations with up and downstream block valves is that drains can be installed on the reducers (one for fail-open, two for fail-closed), but I've heard that welding olets or half-couplings to the "flat" side of reducers can cause problems.

Paul

Piping Design Central

 

[dtn6770]

Eccentric reducers with the flat side up are typically use upstream of pump suctions to prevent the accumulation or trapping of vapor/gas at the top of piping.

 

[Gator]

Thanks.

At

http://www.eng-tips.com/viewthread.cfm?qid=149171&page=10

there is a thread about reducers in pump suctions (I think there's also at least one other), but I'm referring to their use upstream of control valves and at control stations.

 

[dtn6770]

http://www.documentation.emersonprocess.com/groups/public/documents/book/cvh99.pdf

The two editions before the above contained two ISA illustrations that show concentric rducers on both sides fo the CV, with what appears to be drain piping atached to them.

As a general practice, irrespective of the service, piping should be designed to accomodate for low point drains. I'm familiar with using eccentric reducers, flat side down, in steam (condensate) distribution (collection) headers for the reason you described but I'm not familiar with that logic carrying over to control valve station piping.

Expanding on the distirbution and collection headers; there are other practices specifically geared at minimizing liquid accumulation and (really) the eventual hammering that comes with it. Lines should be sloped and have requent "boots" that collect and trap out condensate. Again these practices are employed with long(er) runs of pipe. If all that's done correctly upstream of your control station you shouldn't need to worry much; concentric or eccentric...just have the drains installed at the lowest point and consider trapping on both sides of the valve.

 

[zdas04]

Gator,
References to eng-tips.com threads in the format thread407-149171 are much easier for people to follow. You can get this thread number at the top of the thread and then copy/paste it.

David