Leak-free high temperature valves and manifolds
14 June 2016
The E Series valves and manifolds from AS-Schneider are now available with sealing made of graphite enabling their use at temperatures of up to 550 degrees Celsius.
The international standard EN 61518 / IEC 61518 describes the flange connection between the manifolds and the pressure transmitters. It also lists the temperature limits of these connections as 80 degrees Celsius for PTFE sealing and 120 degrees Celsius for graphite sealing. The temperature limit of 120 degrees Celsius refers to the limits which are applicable for the transmitter. The limit for the flange connection itself can be dimensioned higher according to the pipeline standards.
"There are many users who require significantly higher temperature limits than 120 degrees Celsius for their manifolds," said Markus Häffner, head of Design & Development at AS-Schneider.
AS-Schneider supplies the E Series valves and manifolds with either PTFE or graphite sealing. PTFE becomes very soft at high temperatures causing the pressure of the process medium to press the plastic into the existing cavities. In addition, PTFE has a much higher thermal expansion coefficient than steel. This results in the sealing ring being expanded more than the housing causing it to flow into the existing gaps. "If the connection cools down again, the extruded PTFE no longer bounces back leading to a loss in tension of the sealing ring and thus a risk of leakage.
With graphite, it is different: The carbon does not show any appreciable deformation even with extreme temperatures providing a durable, leakage-free flange connection.
AS-Schneider was able to demonstrate the reliability of the material in laboratory trials which showed that the graphite does not extruded even at 350 degrees Celsius. The flange connectionalso remains stable after the test.
The maximum possible operating temperature is 550 degrees Celsius. The user, however, is responsible for ensuring that the flange connection including the bolts can withstand the process requirements such as pressure, temperature and chemical load.
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