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Block Bodies: A Steady Revolution in Valve Design

One of the hallmarks of the biopharmaceutical industry is constant innovation that supports the industry goal of helping people live longer, healthier lives. These innovations are spread throughout the industry from the science behind new drugs to advancements in processing equipment. Sometimes changes are subtle, other times they are dramatic. One of the subtle changes has been the constant, ceaseless evolution to valve assemblies over the years. These changes have helped improve bioprocessing systems in a number of ways.

To understand block valve assemblies and their evolution, it’s best to start with a look at industry requirements and how they are implemented. In the biopharmaceutical industry, like any other industry, there is a need to constantly innovate. In our case, this innovation is driven by the need for improved yields, lower costs, faster production, and improved safety. One of the most important influences leading to these innovations has been the American Society of Mechanical Engineers Bioprocessing Equipment Standard (ASME BPE), which has been an instrumental part of getting new improvements implemented throughout the industry.

LD ratio
Figure 1. This image shows the 2:1 ratio as defined in the ASME BPE and the "6D rule" from the FDA Guide to Inspections of High Purity Water Systems. Note that the position from which they are measured is different.

For example, when it comes to systems design, one of the improvements highlighted in the ASME BPE is reducing and eliminating dead legs. In the ASME BPE Standard, “dead leg” is defined as:

Block Bleed 1 inch
Figure 2. Block and Bleed assembly –
1” valve with 1/2” bleed

“An area of entrapment in a vessel or piping run that could lead to contamination of the product.”

This is often shown as a length to diameter ratio (L/D). The earliest requirement comes from the FDA Guide to Inspections of High Purity Water Systems, which states:

“…dead-legs as not having an unused portion greater in length than six diameters….”

While very common, this 6:1 ratio has largely been replaced in the biopharmaceutical industry by the L/D ratio of 2:1 or less, as stated in the BPE:

“An L/D of 2 or less is attainable with today’s manufacturing and design technology.”

By switching from the 6D rule to the 2:1 ratio, you can significantly improve the cleanability and sterility of your system. While there are several factors to consider when trying to reduce or eliminate dead legs, the main goal is to reduce the L/D ratio to 2:1 or less. (In Figure 1 you can get an idea of what L/D looks like. This image shows a standard tee fitting.) When it comes to valves, a primary way to reduce the L/D and eliminate dead legs is by building valve blocks.

Deadlegs
Figure 3. Area of entrapment or
dead leg in a welded assembly

A valve block is a group of two or more valves combined into a single assembly. The easiest way to build these is to simply weld the valve bodies together prior to installing them in a system. By having valve blocks built this way at the factory, they can be built in a more compact arrangement while simultaneously reducing or eliminating dead legs. This results in better cleanability and drainability in your system.

The simplest of these types of assemblies is a two-valve assembly. Two-valve block assemblies are most often seen where you need to sample or divert flow. When they are built as assemblies in the factory, they can be built much more compactly. This can reduce or eliminate the dead leg. In addition to making the assembly much more compact, by being factory built, welds can be finished giving cleaner, better drainability. Figure 2 shows a typical block and bleed assembly.

A welded block assembly often has a lower up-front cost, but may have an impact on long-term maintenance and operating costs. Additionally, as highlighted in Figure 3, this type of welded assembly has a short run of tubing between the two seal points. In some cases, this creates a dead leg that may collect leftover product or prevent the area from being properly cleaned.

Block Bleed Machined
Figure 4. Machined Block and Bleed
assembly – 1” valve with 1/2” bleed

The challenge of improving the cleanability and sterility of this type of design has led to a new generation of block and bleed valves. This next step in the evolution of block valve assemblies has continued with the introduction of integrally machined valve assemblies. These assemblies are made by machining multiple valves in a single piece of material. By building assemblies this way, most dead legs are eliminated entirely.

Figure 4 shows this new type of integrally machined block and bleed assembly. As you can see, the dead leg has been eliminated. This has removed an area of entrapment, improved drainability, reduced the number of welds, and improved cleanability. In turn, this can make maintenance easier and reduce operating costs.

One of the greatest assets of valve block assemblies is that they can be configured in countless ways. For example, one of our customers needed to create a six-valve assembly in order to reduce the distance between valves in their system. In the original system design, there were individual valves that were separated by as much as six feet of tubing. We offered several options for different parts of their application.

6 Valve Welded
Figure 5. Six-valve welded block assembly

In one application, we gave them a welded valve assembly that combined valves with 90° and 180° flow paths. As shown in Figure 5, this compact assembly was made of six 1.5” valves and fit in a space 21” x 20” x 14” including pneumatic actuators. This significantly reduced the amount of space required, eliminated a series of unfinished welds, improved cleanability, and enhanced drainability.

In another application, we offered the single-piece machined assembly of six valves shown in Figure 6. This consisted of five 1.5” valves and one 0.5” valve and fit in a space 27” x 26” x 12”. In addition to the benefits of reduced space, improved cleanability, and enhanced drainability, this design also eliminated over a dozen welds and simplified documentation by reducing the number of components in the assembly.

block assembly machined
Figure 6. Six-valve machined block assembly

As you can see, block valve assemblies can be designed to fit your precise needs and give you benefits beyond just saving space or removing dead legs. While improvements like these are just one small part of a bioprocessing system, these types of continuous improvements in design and fabrication help support and advance the bioprocessing industry itself.

Benefits of block valve assemblies:

  • Reduce or eliminate dead legs
  • Minimize hold-up volume
  • Improve cleanability
  • Reduce installation costs
  • Eliminate welds

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