Asahi/America Inc.

Nov. 20, 2007
Diaphragm Valve's Three-Layered Construction Provides Safety

Asahi/America Inc., a manufacturer of engineered, thermoplastic fluid handling systems, presents the 3-piece design Teflon diaphragm valve. Supplied on Asahi’s Type-14, Type-15, and Type-G diaphragm valves, this design provides safety and protection against harsh chemicals.  This three-piece diaphragm is a standard feature on all Asahi Teflon diaphragm valves. The 3-piece design Teflon diaphragm provides extra safety by creating a gas barrier that prohibits leakage associated with other diaphragm designs. These diaphragm valves are suited for use in a wide variety of applications including water and waste water treatment and chemical processing.

The diaphragm is made up of 3 separate layers which perform 3 specific functions. 

The first layer is the "wetted" part of the diaphragm.  This is the only part of the diaphragm that comes in direct contact with the media. This is the white layer of Teflon.  Teflon has excellent chemical resistance properties, however it is a permeable membrane which means it allows vapors to pass through it.  Teflon also has no elastomeric properties or "memory".  This means that once the Teflon has been tightened to a specific torque value, when that torque value is reduced, the Teflon will not expand back to its original dimension.

The second layer is a unique thin opaque layer of Polyvinylidene Fluoride abbreviated as PVDF.  PVDF is a more dense plastic material and prevents the migration of vapors in applications where off-gassing can occur.  As the vapors pass through the permeable Teflon membrane they hit the next layer which is PVDF.  The PVDF acts as a “Vapor Barrier” and will not allow the vapors to pass, thus trapping any vapors down in the cavity of the valve. 

Third is a layer of black rubber EPDM.  EPDM is an elastomeric material and when it backs Teflon, it allows for a lower sealing torque requirement by providing elasticity to the Teflon and PVDF layers.   Bonnet to body bolt torques are reduced as well as handwheel effort when cycling the valves closed.