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25/07/2016

What you need to know about radial lip seals

Pepijn Swarte

In many of Lagersmit’s sealing solutions the radial lip seal is the corner stone and at the heart of the sealing system. These lip seals are clamped in bronze housing parts and run on a corrosion resistant liner. In most cases multiple radial lip seals are applied in various arrangements to provide a reliable and cost effective system which fits the application best. For decades the radial lip seal is the most important building block in the design of the rotating shaft sealing system. These sealing solutions have found their way in many areas of industry like marine propulsion equipment, dredge equipment and tidal turbines.

The seal

The function of the seal is twofold: the exclusion of water, contaminants, dirt, dust etc. from entering the equipment on one hand and the prevention of leakage of fluids from inside the equipment to the environment on the other hand. The fluid pressure which can be sealed when using a radial lip seal is typically low, e.g. a few bars at maximum. Allowable shaft speeds are in the range of a few hundred revolutions per minute in case of a propulsion equipment application.

 

Figure 1: A singe radial lip seal assembled in its housing

The radial lip seal

A radial lip seal generally consists of an elastomeric lip with an asymmetric tip geometry. In most cases a metal garter spring is added, see Figure 2. After assembly of the lip seal on to the liner the elastomeric lip seal is in a pre-stressed state on the liner surface due to the difference in outer liner diameter and inner lip seal diameter and due to the garter spring. Due to the deformation of the tip of the seal a small contact area exists between the surfaces of the lip and the shaft. The width of the contact zone depends on the pressure difference over the seal and the lip seal compound. The sealing action under non-rotating and under rotating shaft conditions takes places within this small contact zone.

 

The reliability and service life of a radial lip seal is influenced by many factors, like lip seal geometry and compound, temperature, type of lubricant, shaft misalignment and run-out. In order to develop and provide a reliable sealing system Lagersmit focuses on the type of application and takes the corresponding environmental factors into account that may influence proper functioning of the seal. This way a suitable sealing solution is granted.

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