The affect of contamination ingesting into a mechanical system can result in failure of bearings, gears and other dynamic parts. Recall from the Hydrodynamic Effect and the Dynamic Sealing Mechanism (Figures 1 and 2) the pumping action under the contact width. If contamination is allowed to reach this point it will naturally ingest into the system. Selecting a radial shaft seal profile that does not allow this to happen is necessary to avoid mechanical failure.
To classify the severity of contamination begin with identifying all potential particle types and sizes. Percentage of cycle exposure should also be considered, defined as the amount of time the seal is exposed to contamination during application. Another variable to consider is the maximum percentage that the seal is submerged. Once all four contamination variables have been identified refer to Table 2 to determine severity level.
Most radial shaft seals are designed to operate under a level 1 or 2 contamination environment. This includes radial shaft seal profiles having a secondary dust lip. This lip provides only minor protection and is often misused in applications. The affect of this additional lip is an increase in underlip temperature and a loss of seal life. When using this profile, it is important to lubricate between the two lips during installation to minimize this effect.
The affect of high percentages of exposure and submergence results in the reduction of avaliable profiles. Severity levels of 4 and 5 require special consideration of lip type, number and orientation. Contact ESP Engineering for design suggestions.
Other important parameters to investigate when dealing with contamination are shaft speed, shaft hardness, duty cycles and down time. Refer to the corresponding sections in this chapter once a contamination level has been chosen before selecting a radial shaft seal profile.
Classification Chart for Ranking the Severity of Contamination:
|Contamination Level||Description||Particle Type||Particle Size||Percent Cycle Exposure||Max. Percent Submerged|
|5||Extreme||Impactment, Slurry Water, Dust, Abrasive Particles||Powdery, Fine, & Large||75-100||100|
|4||Heavy||Dirt, Mud, Water||Powdery, Fine, & Large||50-75||75|
|3||Moderate||Dirt, Splashing||Small / Moderate||25-50||25|
|2||Light||Air Travel, Dust||Small / Moderate||0-25||0|