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Need an Innovative Way to Eliminate Dead Legs?

Try a Block Body

In the biopharmaceutical industry, the need to innovate is driven by the need for improved yields, lower costs, faster production, and improved safety. When it comes to systems design, one of the improvements is reducing and eliminating dead legs.


Dead legs are typically defined in terms of a length to diameter ratio (L/D).

Initially, the FDA Guide to Inspections of High Purity Water Systems defined the L less than “6D rule” (on right). Later, the ASME BPE defined the L less than 2:1 ratio (on left). (Note that L is measured differently in the two definitions!)

While very common, the 6:1 ratio rule has largely been replaced in the biopharmaceutical industry by the L/D ratio of 2:1 or less. By switching your standard from the 6D rule to the 2:1 ratio, you can significantly improve the cleanability and sterility of your system. A primary method used to reduce the L/D and eliminate dead legs is to build valve blocks.

A valve block is a group of two or more valves combined into a single assembly. There are two ways to build a valve block:

  • Weld two or more valves together
  • Machine two or more valves from a single piece of material

Welded assemblies are less expensive!

The easiest way to build a valve assembly is to simply weld the valve bodies together in a compact arrangement prior to installing them in a system.

A welded block assembly often has a low up-front cost, but since this type of welded assembly has a short run of tubing between the two seal points, the resulting dead leg might collect leftover product or prevent the area from being properly cleaned.

Dead Leg area called out

Welded Block and Bleed Assembly with area of entrapment (dead leg) highlighted.

No Dead Leg in welded block and bleed valve

Machined Block and Bleed Assembly – A 1-inch valve with 1/2-inch bleed.

Machined valved assemblies are cleaner! 

The second choice for creating valve assemblies is by machining multiple valves from a single piece of material. Although it is more costly, building valve assemblies this way eliminates most dead legs entirely.

This new type of integrally machined block and bleed assembly has removed an area of entrapment, improved drainability, reduced the number of welds, and improved cleanability.

Countless configurations are possible!

Valve block assemblies can be designed to address specific needs. For example, one of our customers asked us to create a six-valve assembly to reduce the distance between valves in their system. Another customer needed a sterile sampling assembly to replace an existing assembly that needed to be more easily cleaned and sterilized.

Block valve assemblies can be designed to fit your precise needs and give you benefits beyond removing or reducing dead legs:

  • Fit into smaller spaces or save space
  • Minimize hold-up volume
  • Improve cleanability
  • Eliminate welds

Find out more about our Block and Bleed Assembly valves at, or contact our outstanding customer service department at 800-882-3886.

Best wishes,


ASEPCO – Thinking Ahead – Saving You Time, Saving You Money, and Improving Your Products.

Phone: 800.882.3886


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