Selecting Clean Valves

Pristine processing, where high purity and contamination control are extremely important, is a familiar concept for pharmaceutical production and microelectronics fabrication. Increasingly, it is also an issue for the manufacture of agricultural and fine chemicals, and in environmentally sensitive processes. Regardless of the application in the chemical process industries (CPI), the approach to valve selection when clean processing is involved is very different from that taken when purity requirements are not as stringent, or are nonexistent.

Compared with other applications where valves are used, clean processes typically have three major distinctions:

• Different types of valve are used
• More valve are used
• More valves are actuated and
  automatically controlled

An assortment of valves
In contamination-sensitive processes, the first step is to select valves that do not harbor trace amounts of contaminants, and are easy to clean. In the pharmaceutical industry, for instance, the diaphragm valve is generally regarded as the only choice for a generalpurpose valve in process fluid applications. Why? Because it has no crevices or recesses to harbor contaminants, and, when open, it exposes only smooth, gently curved surfaces that are easily cleaned. When closed, it squeezes product out, so as not to trap significant amounts of residue in the valve body. There are no sharp corners that are difficult to wash out, and there are no seams in which material can collect.

Is the diaphragm valve it then? Not necessarily. The diaphragm valve is one of a handful of valve types for which there is a 3A sanitary standard. 3A - nicknamed after the three milk associations that developed the first sanitary-piping standards back in the 1920s, and now merged under the International Assn. of Food Industry Suppliers (IAFIS; McLean Va.) - has adopted voluntary Sanitary Standards and Accepted Practices for the dairy industry. Other industrial sectors - beverage and pharmaceutical, for example - use these standards as well. Of the more than 70 standards and practices currently in place, 10 pertain to valves, including the following types:

• Diaphragm valves
• Check valves
• Ball valves
• Plug valves

The standards for these different valve types share a requirement for smooth surfaces and cleanability. All of the valves must be self-draining when properly installed, have no sharp angles, and have no threads to contact product. Manufacturers with valves that meet sanitary standards may submit them to the 3A Symbol Council, which will then decide whether to authorize the use of the registered 3A symbol on the valve.

Pristine processing, where high purity and contamination control are extremely important, is a familiar concept for pharmaceutical production and microelectronics fabrication. Increasingly, it is also an issue for the manufacture of agricultural and fine chemicals, and in environmentally sensitive processes. Regardless of the application in the chemical process industries (CPI), the approach to valve selection when clean processing is involved is very different from that taken when purity requirements are not as stringent, or are nonexistent.

Compared with other applications where valves are used, clean processes typically have three major distinctions:

• Different types of valve are used
• More valve are used
• More valves are actuated and
  automatically controlled

An assortment of valves
In contamination-sensitive processes, the first step is to select valves that do not harbor trace amounts of contaminants, and are easy to clean. In the pharmaceutical industry, for instance, the diaphragm valve is generally regarded as the only choice for a generalpurpose valve in process fluid applications. Why? Because it has no crevices or recesses to harbor contaminants, and, when open, it exposes only smooth, gently curved surfaces that are easily cleaned. When closed, it squeezes product out, so as not to trap significant amounts of residue in...