Page 268 - The Tribology Handbook

yrinths, brush seals and throttling bushes B22

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I 104
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Q
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,Q 103
d

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10
1 10 100 1000 10 000
CLEARANCE, pm

Figure 22.4 Effect of clearance and viscosity on mass flow leakage from a bush seal with length equal to
perimeter (if perimeter = k x length then multiply leakrate by k)

Mass flow rate (M) through the clearance ofa bush seal: Materials
ph3 A$ Bush and shaft may sometimes rub; therefore compatible
M = 9.4 x 10-8- gmlh bearing materials should be selected. Segmented bushes
11L are commonly made of carbon-graphite and may run on a
shaft sleeve ofcentrifugally cast bronze (90% Cu, 10% Sn)
where p = density, kg/m3 when sealing water. The life of such a combination could
h = clearance, pm be 5-10 years if abrasives are not present. Other suitable
Ap = pressure differential, bar materials for the sleeve or shaft include carbon steels, for
D = mean diameter, mm more severe conditions nitriding or flame hardening is
Ns recommended, and stainless steel. In the latter case a
q = dynamic viscosity, - compatible babbit may be used to line the bush.
m’
L = leakage path length, mm
B22.3