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Top tips for choosing new oil seals

Although most modern oil seals are manufactured to stand up to all manner of stress, they are not infallible and it is not unusual to find that one or more of the seals on your pumping system has sprung a leak.

The primary cause of external oil leakage from pumping systems, sumps and gearcases are wrong application, wrong selection, bad installation and maintenance practices that are not good enough to ensure sealing systems are in a good state. Luckily, all of these issues are easy to overcome if you have a proper understanding of the available sealing materials, procedures for selecting seals, and the best way to apply maintenance and replacement practices.

There are several variables that must be taken into consideration when choosing oil seals, and a number of things which much be evaluated, including the following:

Shaft speed

It is important to know the maximum allowable shaft speed, along with the kind of fluid that is being sealed and the category of oil seal material, if you want to avoid lubricant leakage.


You also need to know the temperature range of the mechanism the seal is installed in, and you must never allow a seal to be used in a mechanism if it gets hotter than the seal elastomer’s top range.


Most of the commonly used oil seals available in the UK are manufactured to withstand nothing more than very low pressure applications of around 8 PSI or lower. If a higher level of pressure than this is present, or likely to be reached, you will need to take measures to relieve pressure.

Shaft hardness

Seals with a Rockwell hardness of more than 30 will last longer in general. However, if a seal is likely to be exposed to an abrasive contaminant, a seal with a RC hardness in excess of 60 will be needed.

Shaft surface finish

Sealing is most effective when used in conjunction with optimal shaft surface finishes, including ground-off polished shafts with finish marks that are concentric.

Bore and shaft tolerances

Optimum seal performance can be achieved when close bore and shaft tolerances are existent. Vibration and end play can also have a role in optimum performance.


Ensuring that oil seals are continuously lubricated is one of the biggest issues that can help extend their life and ensure that they run optimally. It is also important to use a lubricant, which is of the correct viscosity for the application.

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