Page 266 - The Tribology Handbook

Labyrinths, brush seals and throttling bushes B22

PLAIN BUSH SEALS
Fixed bush seal Rigid floating bush seal

Leakage is limited by throttling the flow with a close- Alignment of a fixed bush can be difiicult but by allowing
fitting bush-Figure 22.1. some radial float this problem can be avoided (Figure
22.2)
BEARING MAlERIAL LEAKAGE DEPENDS ON
COMPATIBLE WITH (CLEARANCE)' AND
SHAFT (ECCENTRICITY )*
I

'0' RING

Figure 22.2 Bush seals with radial float
Figure 22.1 Typical fixed bush

Leakage catleulation

The appropriate formula is indicated in Table 22.1 for
laminar flow conditions. For an axial bush with an
incompressible fluid, Figure 22.3 can be used in both
laminar and turbulent regions.

I
Table 22. Bush seal volumetric leakage with laminar flow
q = volumetric flow ratelunit pressure
gradientlunit periphery Fluid incompressible Fluid compressible*
q absolute viscosity

2.rra(PS - Pa)
Q= . q m3/s or in3/s
(a - b/

c3 . (a - 6) c3 (Q - 6) (P, + Pa)
4=- - 4=-,-
RADIAL BUSH 127) a1og,a 247 a pa
b
* For Mach number < 1.0, i.e. fluid velocity < local velocity of sound.
t If shaft rotates, onset of Taylor vortices limits validity < 41.3 (where v = kinematic viscosity).

622.1