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Liquid seal developed for gas use

Original article date: September 1999

Developing a concept originally aimed at sealing liquids Feodor Burgmann has introduced a version of the CSR aerodynamic clearance seal for gases and gases containing solids.

The CSR type aerodynamic clearance seal consists of a split carbon graphite restricting ring that is held together by a tension spring around its circumference. Pockets are worked into the inner surface of the ring to generate a radial lifting force under operating conditions. A concentric gap thus forms automatically as the seal lifts off the shaft. Measuring no more than a few um this gap is small enough to keep leakage to a minimum. Good static sealing at standstill is guaranteed because the seal and the shaft are then in contact.

Now manufacturer Feodor Burgmann has launched a further development of this seal with a bi-directional gal lubricated version for gaseous media. It is suitable for all gas conveying machines such as gas turbines compressors turbochargers and turbo pumps. It can also be used with gases containing solid particles of grain sizes up to 10um. Liquid mist or flooding at standstill is withstood without damage as are radial movements of the shaft in the 0.1mm range.

The main advantage of this seal over comparable sealing elements for gases is that it achieves lower leakage rates whilst requiring the same installation space. For example its leakage is up to 50 times less than that of a labyrinth seal. Because a higher pressure differential is possible with a constant leakage rate the seal represents a simple form of differential pressure control for buffer gas systems. It runs together with the shaft but without making contact with it thereby enabling a machine to be shut down under controlled conditions in the event of a malfunction.

The cartridge design makes it easy to install. High sliding velocities are a feature: up to 200m/s cooled – ie with applied differential pressure) and up to 100m/s uncooled (unpressurised).

The operation of the CSR seal is independent of temperature in that the leakage rate remains almost unchanged throughout the entire temperature range (up to 500degC). Good emergency running properties are provided by the carbon graphite.

September 1999

Added on 3 August 2009 at 12:10 pm | Read more fluid control articles