Sterile diaphragm valves for food processing and beverage industry

In June 2006, GEMÜ's metal diaphragm valve sealing system was awarded EHEDG certification. The key to any diaphragm valve is the seal provided by the diaphragm. It separates the medium from the actuator and, at the same time, ensures that the valve body is externally sealed. The medium only comes into contact with the diaphragm and the valve body. This is a crucial argument for using diaphragm valves, particularly in sensitive sterile processes.

GEMÜ's diaphragm valves and the diaphragm seat have certain features that make them particularly suitable for sterile applications. To achieve a good seal with minimal deadlegs one needs to examine the whole system, comprising valve body, diaphragm and actuator. With the actuator, it is particularly its stroke and the compressor to which the diaphragm is fixed that needs to fit the diaphragm exactly. For example, if the stroke selected is too large to achieve an intended, high kv value, the diaphragm will suffer mechanical overload and therefore fail early. The diaphragm's fixing to the compressor is also vital. Apart from the tiny diaphragm size 8 attachment method, GEMÜ only uses a threaded pin to fix the complete size range. In any switching situation and unlike a bayonet attachment, this provides well-distributed power transmission from the com-pressor to the diaphragm and ensures that the contact between the two components is secure.

To ensure that the valve body is well sealed at the valve seat, the contour of the valve body weir has to be optimally matched to the diaphragm and the compressor. A secure seal with a long service life can only be provided when all three contours are optimally matched with one another. GEMÜ's diaphragms have a sealing rib in the flow to achieve a defined sealing surface.

For good external sealing, all the valve bodies are fitted with a defined sealing bead which provides a reliable, well-defined seal to atmosphere. The potential deadleg in the ringshaped gap between the diaphragm and the valve body is therefore considerably reduced. The compressor shape was improved even further specifically to meet the EHEDG certification requirements. Geometrically, the valve body and diaphragm are arranged in such a way that any incorrect diaphragm assembly can be ruled out.

The production costs for this extra sealing bead on the valve body are significant. However, our experience with customers over the last 20 years has shown that higher costs have a positive knock-on effect in terms of system safety and availability. The secondary sealing surface that occurs behind the sealing edge because the actuator presses the diaphragms against the body is not required for external sealing. By carefully matching all the components with one another, the service life and cycle duties have also been significantly improved. Depending on the medium and application, over 10 million cycle duties are now being achieved in beverage industry filling processes.