For dosing and control tasks in sterile or hygienic processes, plant designers and operators often have to compromise. Conventional diaphragm valves may be easy to clean but the accuracy with which they are able to meet controllability requirements is inadequate. Globe valves, on the other hand, are characterized by high control accuracy but are more difficult to clean.

PD technology (plug diaphragm technology) combines the advantages of both valve types. A cone-shaped diaphragm made of modified PTFE separates the media-wetted area from the actuator. The material PTFE is composed of linear, extremely long carbon chains which are surrounded exclusively by fluorine atoms. They spatially shield the carbon atoms, thereby protecting the molecule from chemical attack – even at higher temperatures. Modified PTFE (TFM™) is even better suited. TFM™ has the same advantages as PTFE, but it also has a denser polymer structure with a lower concentration of pores, which leads to lower permeability and a smoother surface. The GEMÜ diaphragm is therefore suitable for CIP/SIP applications and is also approved by the U.S. Food and Drug Administration (FDA).

The conventional design only allows diaphragm valves to be predominantly used in rough control applications because they do not offer any option for enabling a defined cross-sectional area. The unique PTFE diaphragm, however, can be designed as a parabolic plug. The geometry can be adjusted to set control characteristics. The valve thereby achieves a similar control accuracy to standard control valves with a regulating cone, without the cleaning disadvantages. Due to the so-called lift effect on the spindle, medium is transported into the gland packing with these valves and is not removed during plant cleaning, which can lead to the multiplication of bacteria. Medium can also be deposited in the folds of the bellows, which can be used as actuator seals. Owing to the low-turbulence flow areas, adequate cleaning is not possible or only with increased expenditure.

PD technology, by contrast, hermetically seals the valve body from the actuator and can withstand normal operating conditions. When it is installed, a number of tests show that its tightness during the endurance test is in accordance with DIN EN 12266. The steam sterilization simulation with pure steam at 135 °C also showed no disadvantages in comparison to the conventional diaphragm. In our own sterile test rig, the requirements were even exceeded. Moreover, the valves with PD technology achieved twice as many cycle duties as comparable diaphragm valves (clocking cycle 5 sec. open, 5 sec. closed). The pneumatic control valve 567 BioStar control has been successfully tested on over seven million cycle duties, while the new F40 filling valve has been tested on over ten million.

The following products are based on PD technology or are modified versions:

• Filling valve platform GEMÜ F40, F60
• GEMÜ 567 BioStar control aseptic control valve
• GEMÜ iComLine product range