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Chemical Technology • October 2015
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pressures of 2 to 3 bar. InWFI supply, the pressures can reach
up to 10 bar,” commented Knöbl, comparing applications.
Key starting point – the material
A valve for sterile applications has to do far more than steer
fluids for CIP/SIP cleaning into the right direction. For over 20
years the Luxembourg-based valve manufacturer has been
optimising its SISTO-C series and supplied prestigious proj-
ects with this diaphragmvalve. “Around hundred thousand of
these SISTO-C valves have been installed to date,” said Knöbl.
The valves fulfilled the following requirements:
• GMP Guidelines (Good Manufacturing Practice)
• Food and Drug Administration (FDA) of the USA
• United States Pharmacopeia (USP)
The selected materials were very carefully tested and
their production was precisely documented. To avoid cracks
in the high-alloy stainless steels during orbital welding and to
enable optimum machining processes, the sulphur content
has to be kept within very tight tolerances. Furthermore, an
optimum delta ferrite content is a key requirement in the
pharmaceutical sector. Pharmaceutical valves are often
made from forgedmaterials to ensure high steel homogeneity
and to avoid the risk of cavities in the material. Of course,
this requires the valve to be produced in large batch sizes.
Economically viable production of forging dies can only be
achieved by producing large quantities.
Completely enclosed diaphragm
During the design stage of the SISTO-C series innovative new
paths were explored. A wide range of variants comprising
simple straight-way valves, welded designs and complex
multi-port valve manifolds means that SISTO can offer
customised solutions for every type of application. “If we
combined all of the possible components together, we would
have at least 1 000 different variants,” Knöbl estimated.
The valve series set new benchmarks with its completely
enclosed diaphragm. This is crucial for the high pressure limit
offered by the series. The diaphragm is inserted in a recess
and seated on a small defined surface. The biggest advan-
tage is that it is very robust in operation and has an increased
service life compared with conventional diaphragms. “This
property often influences our customers’ purchase decisions
PUMPS & VALVES
Diaphragm valve in a plant for producing agents