Butterfly valve for corrosive media
February 2011
Valves, Actuators & Pump Control
Gemü has introduced a new range to complement its lined butterfly valve portfolio. The new 490 series is fitted with a TFM liner and PFA-encapsulated stainless steel disc as standard. The design of the valve, and especially the liner, the shaft seal and backing, has been optimised to reduce actuation torques while providing increased sealing, service life and reduced probability of failure.
Why TFM instead of PTFE
TFM is a further development of the classic PolyTetraFluorEthylene (PTFE) material. The properties of PTFE have been improved even more in this second generation to include:
* High resistance to chemicals that allows universal usage.
* Gas permeability is significantly less than with conventional PTFE. This means that less medium diffuses through a TFM seal with the same material thickness as PTFE.
* Cold flow properties with TFM are significantly lower than with PTFE. A significantly lower plastic deformation of the material therefore results at the same mechanical stress, which means that the liners remain dimensionally stable for longer.
* Surface quality of TFM is considerably improved in comparison to PTFE. The smoother surfaces reduce mechanical friction and therefore wear.
The backing
The backing behind the liner consists of two parts. Both backing parts are fully inserted in the space between the body and the TFM liner and centred with the shaft bushing. The backings are sufficiently strong in design, so that their flexibility is better transferred to the TFM liner. At the same time, the tolerances of the backings have been further reduced and the greater accuracy leads to improved mechanical properties. The backing is also designed in such a way that it resists larger deformations with permanent elasticity. The side play between the backing and liner is so great that no negative stresses can be transferred when compressing the liner between the flanges. These design measures also result in a further reduction in the torque and hence a longer service life of the liner.
The spindle seal
The spindle seal has also been optimised further. The transition from shaft disc to liner is positive and edge-free in design. Every shaft bushing has dual protection against overload, so that the valve fulfils the leakage in the Technical Guidelines on Air Quality Control VDI 2440 paragraph.
General technical data
Gemü 490 is available in sizes DN 40-1000. A wafer design and a lugged version for end-of-line duty are the body design options, with body material available in GGG 40.3, stainless steel 316 L and cast steel as standard. (Special materials are available on request for both wafer and lugged bodies.) The maximum operating pressure is 10 bar at DN 40-600 and 6 bar at DN 650-1000 and the temperature limits are -20 to 200°C.
The valves are available with manual (497), pneumatic (491) and motorised (498) operators. The pneumatic actuators can be fitted with pilot valves, electrical position indicators and positioners for easy integration into automated systems. Smaller operators can be used due to the reduced torque which results in lower purchase and operating costs.
Areas of application
The TFM liner of the butterfly valve provides a very high resistance to chemicals, while the butterfly disc is made from stainless steel or PFA-encapsulated stainless steel. Thus the valves can be used in all applications where corrosive liquids and gases must be controlled. For instance:
* Chemical industry.
* Mining and metal extraction.
* Steel works.
* Treatment of highly corrosive waste waters.
* Treatment and distribution of ultra-pure water in pharmaceutical installations and in the semiconductor industry.
ATEX compliant versions can be provided for explosion endangered areas of group II, zones 0, 1, 2 or 20, 21 and 22.
For more information contact Keith Hedges, Gemü Africa, +27 (0)11 462 7795, [email protected], www.gemue.de
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