Strategies and Devices for Parametric Testing of Radial Lip Seals

Radial Lip Seal Function and Kinematics

Function: Separates a contained liquid from the external environment while transmitting continuous rotational movement about its axis of symmetry. Tolerates, without leakage, low-amplitude perturbations in the remaining five degrees of freedom.
Shown: Deflected cross-section ...

The Physics of Radial Lip Seals


Governing Equation

Measurable Quantity Scaling Law
(Rule of Thumb)
Typical Range
Hydrodynamic Pumping Reynolds: flow, cc/min (q)   0.05 - 1.00
Radial Load Hoop Stress:
line force, lb/ circumf in (l)   5 - 25
Eccentric Load   force, lb (We)   <2Dl
Static Leakage Molecular Scale Laminar Viscous Flow flow, cc/hr Viscosity on scale of molecular length 10 X normal 0 - 0.01

Why Do Parametric Testing?

Parametric Testing Devices and Strategies

Test Device

General Description Measurement Domain Output
Hydrodynamic Pumping Rig Device measures volume, as level change in a sight glass, pumped against a specified head in a specified time interval. Time, fluid volume, pressure, fluid temperature, rotational speed, counterface diameter Pumped volume as a function of time, fluid viscosity (temperature), speed, and head, normalized by counterface diameter.
Radial Load Fixture Split mandrel equipped with load cell measures force to compress halves. Force, time, counterface diameter Radial load (lbs per inch of curcumference) as a function of time, max load, min load after specified time, decay rate.
Eccentric Load Rig Bearing-mounted counterface capable of specified radial displacement and load measurement. Force, time, radial displacement, angular location Max eccentric load curve as function of angular location.
Static Leakage Fixture Pressurized cavities, each equipped with a sight glass, measure contained fluid volume change over time, without rotation. Time, fluid volume, pressure, temperature Volume change over a specified interval as a function of time. Volume change is corrected for pressure, temperature, and trapped air volume.

Hydrodynamic Pumping Rig

Radial Load Fixture

Eccentric Load Rig

Static Leakage Fixture

Results — Seal Characterization

Results — Seal Characterization (continued)

Results — Seal Characterization (continued)

Results — Seal Characterization (continued)

Results — Seal Characterization (continued)