SELECTION OF STANDARD DESIGN
Selection of an oil seal design is dependent on whether the operating conditions exceed the limits of the design. The three operating parameters that mainly affect the design's ability to function are eccentricity, pressure, and shaft speed. In this section, these limits are reviewed.
I “S” and T LIP DESIGN
Table I illustrates standard seal designs, beginning with "S" and 'T1 lip symbols for general nonpressure applications.
The "S" design is a single lip oil seal with a garter spring to provide a consistent radial load against the shaft.
The "T'design uses the same primary lip configuration, with an auxiliary dust lip to provide effective light duty dust exclusion. Below is a table listing approximate limits of the "S" and "T" lip designs.
SHAFT DIAMETER |
HITRILE LIP MAXIMUM CONTINUOUS SHAFT SPEED |
MAXIMUM CONTINUOUS PRESSURE |
MAXIMUM TOTAL ECCENTRICITY |
General |
3.500 rpm |
5 psi |
.020" |
.500 |
8.000 rpm |
5 psi |
.004" |
1.500 |
7.000 rpm |
5 psi |
.006” |
2.500 |
4.500 rpm |
5 psi |
.010" |
3.500 |
3.800 rpm |
5 psi |
.013” |
4.500 |
2.750 rpm |
5 psi |
.017” |
NOTES:
Higher shaft speeds possible using high temperature materials such as polyacrylate, silicone or fluoroelastomer. Slightly higher continuous pressure possible for shaft speeds below 200 ft../min.
Total eccentricity consists of two components, shaft runout and shaft-to-bore misalignment (shaft offset). The eccentricity is determined as follows:
Shaft Centerline Rotation Path
de=Dynamic Eccentricity
Combine the two results for maximum eccentricity in which the seal lip must follow to function effectively. As eccentricity increases or shaft speed increases, it becomes more difficult for the lip to follow.The "V" and "K" type designs are low cost seals designed primarily for retention of grease or similar viscous fluids. The "V" type is a single lip seal. The "K" type has an auxiliary lip for light dust exclusion.
SHAFT DIAMETER |
MAXIMUM SHAFT SPEED |
MAXIMUM COHTIHUOUS PRESSURE |
MAXIMUM TOTAL ECCENTRICITY |
General |
2.000 rpm |
4 psi |
.005” |
.500 |
4.000 rpm |
4 psi |
.003” |
1.500 |
3.000 rpm |
4 psi |
.005” |
2.500 |
2.300 rpm |
4 psi |
.006” |
3.500 |
1.700 rpm |
4 psi |
.008” |
4.500 |
1.400 rpm |
4 psi |
.010” |
NOTES: Higher eccentricity is allowable if maximum shaft speed is reduced.
In comparison with the "S" and "T" lip design, the major reduction in design limits of the "V" and "K" type is the result of the absence of a garter spring. However, for grease applications where lubricant's ability to flow is reduced, these nongarter spring seals are very cost effective designs to use.
Ill “WP” LIP DESIGN
The "WP" design was developed as a dust wiper (scraper) for reciprocating applications such as hydraulic cylinder rods.
As a result, the operating limits for the design are slightly different from "V" and "K" types.
Maximum shaft motion is linear velocity of 200 ft./min. (IM/sec)
Maximum pressure capability is 4psi (.28 Kg/cm2). Stroke length should be limited to 78 inches (1.98 m) maximum.