Sanitary connection to the process with in-line diaphragm seals

In the manufacture of pharmaceuticals and food, safety in production and the prevention of any risks to patients and consumers is a top priority. In the chain of all process components within a plant, measurement technology plays a key role. Edited by Greg Rusznyak, marketing manager, WIKA South Africa 

Measurement technology delivers process-specific information, which enables high-quality production. For this, the safety and hygienic requirements in the design of the measuring instruments and the connection of the sensors to the production plant must be optimally fulfilled in terms of ease of cleaning. 

The connection of pressure measuring instruments to the process is ideally performed by means of diaphragm seals with hygienic connections. Diaphragm seals separate the pressure measuring instrument, pressure sensor or pressure switch from the medium and ensure a process connection that is either free of dead spaces or where dead spaces are reduced to a minimum. 

The isolation is achieved by means of a flexible metal diaphragm. The internal space between the diaphragm and the pressure measuring instrument is filled completely with a fluid. The process pressure is transmitted by the elastic diaphragm into the fluid and from there to the measuring instrument.

Hygienic design  

The hygienic design of plant components in contact with products is an essential prerequisite for avoiding microbiological contamination, and with that, ensuring product quality. 

As part of the overall hygienic concept of a plant, the measuring instruments used must comply with special requirements on material, surface quality, process safety, connection engineering and cleanability in the scope of the CIP process. 

Materials

Austenitic stainless steel is used as a standard material for wetted areas. In the pharmaceutical industry and in the food and beverage industry, SS316L (1.4404) and SS316LMo (1.4435) grades are preferred. Stainless steels are inert to most foods and pharmaceuticals, while also offering good corrosion resistance to disinfectants and cleaning agents. 

Surfaces

An important aspect in the cleaning of a plant using CIP/SIP processes is the quality of the surfaces in contact with the process medium. To enable the easy cleaning of the measuring instruments and to prevent biofilms, the wetted surfaces must be passive and free from microscopic flaws. 

In addition to the surface topography, the surface roughness is an important  criterion for cleanability. In the standards, such as EHEDG Doc. No. 8, ‘Hygienic equipment design criteria’, a roughness of Ra < 0.8μm is sufficient for normal cleaning processes. For sensitive biotechnology processes, surfaces with a lower roughness are needed, eg Ra < 0.38µm per ASME BPE. 

In-line diaphragm seal

The in-line diaphragm seal is perfectly suited for manufacturers with flowing media. With the seal being completely integrated into the process line, measurements do not cause any turbulences, corners, dead spaces or other obstructions in the flow direction. The measured medium flows, without obstruction, through the in-line diaphragm seal. This results in an additional self-cleaning of the measuring chamber. The in-line diaphragm seal is installed directly into the pipeline. 

WIKA’s model 981.51 in-line diaphragm seal is designed for ultra-pure steam systems, aseptic plants as well as the pharmaceutical and biotechnology industries. The diaphragm seals can withstand the cleaning vapour temperatures occurring in the SIP processes and thus ensure a sterile connection between the medium to be measured and the diaphragm seal. 

Mounting of the diaphragm seal to the measuring instrument may be made via a direct connection, for high temperatures via a cooling element or via a flexible capillary. 

The availability of the diaphragm seals for common pipe standards and nominal widths simplifies integration into already existing pipe cross-sections. 

Contact Wika South Africa for more information.