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Frictional performance of an O-ring type seal at
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the commencement of linear motion
Results of investigation into the relationship between friction in the O-ring type seal
and gauge pressure at the commencement of linear motion of a shaft are presented and
discussed. A number of different O-ring materials were studied and the lowest friction
under dry conditions was found to be produced by a PTFE-encapsulated silicone seal.
The effect of~i number of lubricating fluids on friction in the seal was also studied and the
results obtained are included.4888
Keywords: O-ring seal; dry friction; lubricated friction; friction coefficient
1. Introduction
For applications such as rotary process pumps in chemical and petrochemical
industries or compressors in the offshore oil exploration industry, a seal is a vital
element for reliable and safe operation.
A seal is basically a device for closing a gap or making a joint fluid-tight. When
sealing takes place between surfaces that have relative movement, e.g. rotation of a
shaft relative to a housing, the seal is of a dynamic type. The majority of dynamic
seal types in general use can be classified as contact seals. The other category of
dynamic seals is usually referred to as clearance seals because they operate with
positive clearance. They are usually called mechanical face seals or rotary shaft
seals. Successful operation depends on achieving the right conditions at the inter-
face, i.e. the faces themselves must be separated by a thin film of the fluid con-
tained.
The rotary shaft seal is mainly used in pumps and compressors. A reliable
operation of the seal is especially important for compressors used to circulate
high-pressure natural gas extracted from the North Sea [1-3]. The principle of
operation of the so-called dry gas seal is the balancing of aerostatic and aerody-
namic forces to provide a stable, minimal running clearance. The Department of
Mechanical Engineering, Brunel University has been involved in the develop-
ment of a new type of dry gas seal [4]. A schematic diagram of the dry gas seal is shown in fig. 1. It consists of two faces. The dynamic face is held rigidly to the
drive shaft by the dynamic carrier and locking sleeve. The static face is free to
move axially with retaining three springs and O-ring arrangement. The axial
freedom is required to allow for the gap between seal faces to be established
under given operating conditions.
The O-ring seal prevents pressurised gas escaping behind the static face. The
retaining springs force the static and dynamic faces to be in contact until the cor-
rect operating pressure across the face is reached and separation of the faces
occurs. Typically, on start up of a compressor the seal faces are in contact with
one another due to the action of the retaining springs. Any clearance between
the two faces at this point of compressor operation would lead to an unaccepta-