Typical system operating parameters:
Temperature: 68º F – 185º F (20º C – 85º C)
Pressure: 0-87 psig (0-6 bar)
|It’s important to know and understand that the process conditions within any hygienic system greatly influence the type of valve construction required to provide proper operation of the system for the control of bioburden. It is also important that the owner/end-user understand that the degree of contamination risk changes depending on the valve type selected, how it is installed, and how the valve/system is sanitized.|
Valve sealing systems are clearly defined within ASME BPE by two designations:
» Sliding seals are used within valves such as mix-proof, butterfly, and O-ring shaft sealed single-seat stem valves. These can be considered high risk due to the possibility of contaminants being drawn into the fluid stream or can trap contaminants within the valve in the open or closed position.
» Non-sliding seals are used within diaphragm valves and single seat stem type valves that incorporate a diaphragm to provide a stem seal. These can be considered a low risk due to no internal components other than the sealing membrane making contact with the process fluid. The non-sliding sealing systems also prevent the process fluid from being exposed to atmospheric contaminants.
Commonly used valve seal polymers are FKM, EPDM, PTFE, and modified PTFE classes that are FDA conforming and have been certified to be USP Class VI by a third-party testing lab.
The valves should not incorporate any areas in which fluid becomes trapped. This would not facilitate free-draining when installed in the proper orientation. Following the manufacturer’s installation recommendation for any valve is important in order to achieve the optimum characteristics for the reduction of dead leg areas within the valve. The BPE standard also provided guidance to minimize hygienic union connection within a hygienic system and incorporate welded construction wherever possible.
Typical Methods of Valve/System Sanitization:
» Increase in fluid temperature through a heat exchanger
» SIP (Steam In Place)
» UV unit
1) System Pressure
» The operating pressure of the system should be taken into consideration if it is expected to operate above the typical system pressure of 87psig (6 bar) in order to ensure that the correct actuator is used, especially with a non-sliding seal type diaphragm valve.
2) Seal Material Compatibility
» Compatibility of seal materials should be evaluated if the use of SIP and/or ozonation will be introduced into the system as a method of sanitization. SIP elevated temperatures above the typical system temperature 185º F (85º C) and ozonation degrading seal materials can both have an adverse effect on valve performance.
If there are conditions present within the system that fall outside of the typical operating parameters, the valve manufacturer should be consulted during the selection process (valve type & sealing materials) in order to prevent premature valve failure after installation.
Valve Materials Of Construction:
Valve bodies and other internal process contact components are typically made of 316/316L and equivalent materials (CF3M, CF8M, etc.) are the most commonly used due to their corrosion-resistant properties. Other materials might be used, but these are the most common.
The standard internal surface finish of process contact areas within hygienic valves is 20Ra mechanically polished (BPE code SF1), however, the surface finish to be used is dependent upon the requirements of the owner/user.
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