In the previous posts about the valves used in BioProcess Engineering, the important features of the valves to be used was detailed. The valve satisfying almost all the requirements is the DIAPHRAGM Valve. It is clearly stated in ASME BPE 2002 that the Diaphragm valve is to be used in the product contact areas.
The features of Diaphragm Valve makes it the most suitable & preferred valve for aseptic and sterile operations. The Diaphragm valve has outstanding self draining characteristics. The diaphragm of the valve is the key performance component providing leak tight shutoff between upstream and downstream. The Diaphragm also isolates the top works or actuating parts from the process media. The operating mechanism of a diaphragm valve is not exposed to the media within the pipeline.
The picture explains the section view of the Diaphragm vlave.
The materials commonly used in bioprocess for the diaphragm is EPDM (Ethylene Propylene Diene Monomer)
Good mechanical properties.
Resistant to aging, ozone, oxygen, and ultraviolet radiation.
Good resistance to steam and CIP fluids.
PTFE (Poly Tetra Fluoro Ethylene) is preferred during very high temperatures. Normally PTFE diaphragms are two piece construction. The working surface is PTFE and it is backed with a rubber or EPDM.
Key elements in diaphragm selection: Media compatibility
Temperature of operation
Level of extractables
Resistance to compression
Diaphragm life depends upon:
The nature of the material handled
Temperature & Pressure
Frequency of operation
The Diaphragm valves need to be placed in a angle prescribed by the manufacturer in order to achieve 100% drainability. This is important when the valve comes in the horizontal direction. The angle varies from 15 degrees to 45 Degrees.
With all the aspects of the diaphragm valve, it is clearly understood that it is the most suitable for product contact lines in Bioprocessing.