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Emerald Group Publishing Limited
Copyright © 2000, MCB UP Limited
Keywords Greene Tweed, Sealing, Pumps, Valves
According to Greene Tweed the problem of creating and maintaining effective sealing on pumps and valves used in cryogenic applications has been overcome. The company reports that this has been achieved with a new design of seal which uses customised PTFE material, and twin coil springs to ensure seal force integrity.
Cryogenics is an important process, as it makes possible the large-scale production of oxygen and nitrogen for commercial and industrial processes. It also facilitates the transport of liquefied natural gas. Without cryogenics nuclear research would lack liquid hydrogen and helium for use in particle detectors and for the powerful magnets required in large particle accelerators.
The nature of cryogenic applications, involving both the production and transportation of gases, inevitably involves the use of pumps and valves. Until recently the problem has been to maintain sealing of these components at the very low temperatures and high pressures which the process demands.
Conventional designs of seal used for this purpose consist of a symmetrical PTFE jacket energised with a single coil spring. According to Greene Tweed the problem with this construction is that differential shrinkage of material on the OD and ID often occurs. This, they claim, causes the coil spring to collapse and compromises the sealing. Worse still, the fact that the jacket material has not got a memory means that the seal deformation is often permanent, resulting in failure of the pump or valve.
The company considers that it has addressed all of these problems with its new seal, which is a further derivative of its MSE range. Based on a new optimised range of materials within Greene Tweed's high-performance Avalon range, the new variant MSE seal is custom designed for each application.
Details available from: Greene, Tweed & Co. Ltd. Tel: +44 (0) 115 986 6555; Fax: +44 (0) 115 986 6235.