A 1 X 4 Machined From Block Divert Diaphragm Valve
Carrying on with our series of posts about various valves types used throughout the high purity process industry, today we’ll address a nuanced segment of a valve type we’ve already discussed: the sanitary diaphragm valve. In our 60 years in the high purity process industry, Holland has come to fully appreciate the challenges multi-product biopharmaceutical manufacturing facilities can present. In today’s manufacturing facilities, there is not only a need to direct process flow from one operation to the next, but also to allow flexibility of directing flow to any one of several identical operations. This problem is only further complicated when CIP and SIP systems are fully automated, causing a large increase in the overall number of valves required.
Before getting too far into the advantages of valve assemblies, it is important to remember that the ASME BPE standards many pharmaceutical companies abide by dictate that high purity water systems, clean steam systems, fermentation, and filtration systems be designed to meet a length to diameter ratio of 2:1. L is defined as the length of the dead leg extension measured from the ID wall normal to the flow pattern. D is the nominal size dimension of the extension of a valve or instrument. The 2:1 ratio is not an absolute requirement, but good GMP and design practices set this as the goal. By targeting this ratio, we limit the areas for bacterial entrapment and increase system cleanability, as well as drainability.
To meet the challenges of maintaining the 2:1 L/D ratio, manufacturers have introduced products into the market that incorporate multiple valve bodies known as valve assemblies. Valve assemblies use a series of two or more valves prefabricated valves with specific arrangement and orientation to fit a particular process requirement. Using valve assemblies minimizes the distance between valves. This is not only a “cleaner” design, but also maximizes the premium manufacturing space available. Integral construction and careful orientation also allow for proper slope of all lines and complete system drainage by minimizing system dead legs.
Probably the most common type of valve assembly is the sterile access and GMP valve assembly type. The two assembly types are typically used for simple process diversion and sampling. Sterile access valves commonly feature the main valve mounted in the horizontal while the main valve of the GMP valve is mounted in the vertical.
In an effort to further reduce dead legs and meet the increasing demand to shrink the overall envelope of valve assemblies, sanitary diaphragm valve manufacturers developed the block body. The top entry, weir type diaphragm design allowed valve designers to start machining multiple valve weirs into a single block of stainless steel. The further reduced the dead legs created by multiple valves and made for a much smaller dimensional envelop, something that sanitary skid manufactures were demanding. Today there are many variants on the block body sanitary diaphragm valve, all designed to meet specific needs.
The ITT ISG Block Valve
An interesting new valve brought to market by ITT is the ISG valve. The ISG valve combines the GMP and sterile access valve into one sanitary block assembly. This is achieved by providing the purge or secondary valve machined into the main block. By simply rotating the assembly, one block can provide three process fabrication orientations. This integral valve assembly reduces contact surfaces and hold up volumes.
Another commonly used valve type is the point of use valve. Instead of mounting a two way valve at the outlet of a tee, creating a process compromising dead leg, a zero static point of use valve incorporates a weir into a tube or U bend. When closed, fluid passes through the tube and there is virtually no dead leg between the weir and the tube. When the valve is opened, process fluid crosses the weir and is discharged. Point of use valves allow process fluids to be transferred, sampled, drained, or diverted. The most common type of zero static valve is the ITT ZSBT or ZSBBT. Both valves serve the same purpose and are identical in dimensions, the difference being the ZSBBT having a faceted body and the ZSBT valve having a non-faceted valve body.
The ITT ZSBBS Body
A couple of variations of the zero static valve are the zero static sample valve and the zero static valve with downstream purge. These valves function similarly and as their names would suggest. They feature a second valve machined integrally into the main valve body. The ZSBBS valve allows for sampling of process fluid prior to opening the main valve while the ZDP valve allows for sterilization of the fluid path prior to opening of the main valve. The difference between the two is where the secondary valve is located in regards to the main valve weir.
Other types of block body valves include divert and mixing valves, ported tank bottom valves, sterile barrier valves, and block and bleed valves. We’ll focus more on the nuances of these valves in a later post. When approaching your process challenges, it is important to remember that total cost of ownership cannot be calculated by material cost alone. Installation and ongoing operation costs must be taken into account when evaluating total cost of ownership. When these factors are taken into consideration, the high initial cost of block body valves is offset by reduced installation costs, space savings, and improvements in operational efficiency. If you have any questions about your next application or would like more information on standard as well as custom valve assembly options, contact a Holland Sales Engineer today.