What is the most cost effective design for high purity gas manifold system (long runs with numerous branch tees and valves)?

Until recently, the answer for high purity systems would have been to use integrated valves (combined tee and branch valve) welded to sections of tubing.  Recently, several companies have developed a more cost effective solution, savings ~ 20% of installed cost, utilizing “pulled” tees and small branch valves.  For example, formerly for a 2 inch manifold with ¾” branch valves,   integrated valves would be machined from stainless steel bar stock that was ~ 2 inch wide, 2 inch tube stubs would be welded to the machined tee and a ¾” valve machined into the same block of stainless steel.  With “pulled” tees, a ¾” branch tee is formed in a 20 foot length of tubing wherever needed and relatively inexpensive ¾” valves are welded to the branch.

A “pulled” tee is formed by drilling the tube wherever a tee is required, then inserting a mandrel into the hole and pulling it out in such a way as to pull some metal into a small tee collar.  The collar is machined so that a tube stub or valve can be welded to it.

There is a slightly larger “deadspace” as compared to integrated valves but testing by this expert has shown that the cleanup time (moisture reduction) is only negligibly longer.

Similar cost savings can be achieved using this concept for Process Cooling Water systems and low purity gas systems where manifolds are often “stick built” with reducing tees and valves.

For further information, refer to the article: Reducing Welds with Pre-fabricated Assemblies and Weld-free Couplings and Fittings (Gases and Instrumentation International online magazine, Jan/Feb 2011).

Ralph Cohen, P.E., who provided this information, is an engineering consultant to customers for gas systems components and HVAC, specializing in semi-conductor and other industrial manufacturing facilities.   He has over 30 years in the field, and continues problem solving for clients through his consultancy.    More information on Ralph’s project work, publications, etc. can be found here RalphCohenConsultancy or call 971-227-8989.

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