Slide Seal Ring for the Water Pump – Small Part; Great Importance

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Water pumps from febi

Modern commercial vehicle engines must work efficiently. More power and fewer emissions is the name of the game. In terms of design, however, the performance limits of the materials that are used are reached. Pressures and temperatures in the engine can reach high values. As a result, modern engines must be cooled down more efficiently. This function is performed by the cooling system – especially the water pump.


Besides the bearing package, the most important and most sensitive component is also the smallest. We are talking about the slide seal ring, which cannot be seen from the outside, but whose filigree technology deserves closer examination. The slide seal ring is located on the water pump shaft and serves as a seal between the water pump bearing and the coolant.

Qualitative Differences

It consists of many parts, some of them rotating, some standing. Sealing is ensured by sliding the sealing surfaces of both rings (sliding ring and counter ring) against each other under the pressure of a spring. The seal ring pairs are made of high-quality and wear-resistant materials such as silicon, graphite, or ceramics. If savings are made in regard to the quality of materials, the life expectancy of the mechanical seal is considerably shorter. This is also one reason why water pumps can be similar in appearance, but very different in quality.

In order to ensure that the mechanical seal functions continuously throughout its entire service life, constant lubrication and cooling between the two rings is necessary. This is achieved by means of a lubricating film which forms between the two pairs of slide seals during rotation. This lubricating film of 1-2 μm should always be there to reduce friction and dissipate heat.

Leaks Can Be Normal

It is normal for a certain amount of leakage to escape between the seal ring and the counter ring. However, this is very small and can still evaporate in the pump. Some coolant can also enter the free space behind the slide seal ring and exit at the drainage hole. This is normal in small quantities, especially after initial assembly, and does not constitute a reason for complaint. Some pumps are equipped with small evaporation containers where the coolant is collected and held in the pump until it has evaporated.

A permanent coolant leakage at the leakage hole, on the other hand, is a sign of a defective slide seal ring and thus a leaking water pump.

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