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Rotary Sealing Considerations
Pressure-Velocity 6.1
An important factor in the design of
rotary seals is the “pressure-velocity” or
PV limit. The PV limit is defined as the
product of the system pressure and the
surface velocity of the dynamic portion
of the hardware. This factor is very
useful in estimating seal life. If the PV
limit is exceeded, a seal may wear at a
rate greater than desired. The PV limit
should always be considered when
designing a dynamic seal. Charts 6.1
and 6.2 show the boundary between
mild wear and severe wear for both lip
seals and anti-rotation,
spring-energized seals as a function of
the PV limit.
6.2 Other factors may also contribute to
seal wear in rotary systems. These
factors include surface finish,
temperature, lubrication and media
abrasiveness. As a general rule, the
better the surface finish the longer the
seal will last when exposed to identical
conditions. In high temperature
applications, both the pressure rating
and PV limit are reduced. Often in this
type of system, application of a coolant
will increase the life of the seal. In the
case of abrasive fluid media, material
selection becomes very important.
Lower fill PTFE materials will wear at a
greater rate than higher fill materials.
Some non-PTFE materials such as
UHMW-PE exhibit better wear
characteristics. Keep in mind when
using non-PTFE material that friction
may increase and most materials are
not as chemically compatible as PTFE.
Click here to view Anti-Rotation Seal Descriptions Click here to view Lip Seal Descriptions |
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