There are plenty of different sealing solutions to choose from, including radial and axial shaft seals, hydraulic and pneumatic seals, and, in some cases, customized machined seals. But without properly understanding the operating conditions that your sealing solution faces, you can’t be sure that it will deliver reliable, safe performance. Typically, sealing solutions are selected due to the influence of particular factors like type of movement, temperature and pressure range, and fluid media. Let’s look at some of the functional aspects you should consider when choosing a seal.
1: Grease and oil retention
Modern sealing solutions aim to retain grease. Many lubricants have high viscosity, and using a non-loading sealing lip design or V-ring can be sufficient. However, more demanding applications may require a spring-loaded radial shaft seal, as they use higher pressure and seal more tightly. Oils, particularly those with low viscosity, are more difficult to retain. Where oil is standard, spring-loaded seals are an option. When considering hydraulic applications, spring-loaded seals are normally not used. Certain sealing materials, such as PTFE, require an energizer to compensate preload loss due to creeping.
2: Contaminant exclusion
If contaminants are a main concern during operation, the sealing solution can be installed with the lip outwards to keep debris away from components and lubricant where it is required. In more challenging, highly contaminated environments, there may be a secondary protective device, such as an axial shaft seal or a solution with additional dust lips. V-rings typically provide good protection for these type of applications like conveyor solutions in the mining sector, which face highly contaminated environments. These sealing solutions are often used as secondary protective measures against contaminants and would not be suitable for oil retention, for example.
3: Retention and exclusion
For some applications, it is equally critical to retain lubricants and exclude contaminants. In this situation, an auxiliary lip is key. This lip offers an extra protective barrier against debris while enabling the seal to retain grease and keep bearings functional and safe. In hydraulic systems with linear motion, sealing systems, consisting of several elements, are typically used. Combining a wiper to protect from contamination ingress with sealing systems for pressure control and retention. Where more extreme conditions are present, metal face seals can offer increased protection due to their greater robustness. Despite this, it is important to make sure that the sliding velocity of mating surfaces falls within the permissible range.
4: Separating liquids
Certain applications, such as rotary distributors in excavators, must prevent two or more liquids from coming into contact with each other. There are two standard ways of achieving this. The first approach is using two separate seals where two lips face in opposite directions to act as a barrier. Alternatively, you can use a double-seal lip. Both of these variants may be spring-loaded so they offer reliable protection. Alternatively, double-acting designs without a spring are an option. They use a polymeric energizer instead. Examples of these types of seal are the R09 and R10 series of machined seals from SKF.
And that’s it for part one of the series on seal selection. For more information about choosing the right sealing solution for different operating conditions, please visit the SKF website. In the next part, we will cover circumferential and rotational speed, pressure differentials, space limitations, and installation restrictions.