The vacuum pump is so hard to RxR I feel a need to inform all of a glitch I found in the Cummins Forum pictorial and instructions. The seal directions and picture of the seal coming out are WRONG!  They show and explain that the dust seal side of the seal faces the vac pump. The cummins instructions say that the spring side of the seal should face the vac pump. The spring side of the seal always faces the area to be sealed.

hmmmm,    in a vac pump...  not so sure  about this!

 

the lip seal   is  pointed  so  the  pressure differences  within a  pump,  either  vacuum or pressure,  cause the lips to  'bite down'  when  there is  a  pressure difference...  making for a better seal.

 

so in a vac pump..  wouldn't the  lip seal  be pointed  so  outside  atmosphere  (high pressure)  would be   helping the seal  do it's job?    

 

you are right,  when it comes to  keeping oil in, or water in...   lips  face the  material to be kept  'in'...    but  on   a  pressure  situation,   atmosphere  will be higher  and  always  seeks  low pressure...  blowing through  seal lips  pointed backwards  would be  easier.

Edited August 5, 201411 yr by rancherman

Key word is "Dust" seal, there are many applications where lip seals are used as a dust seal and the spring side faces to the outside of a compartment versus in as would be the normal case if it was to be used as an oil seal. It has been many years since I have done a vacuum pump reseal so without seeing pics of it I can't say what is right or wrong in the pics.

 

In fact there are many cases where lip seals are installed lip side out of compartments that get greased so the grease can ooze past the seal lip and the seal keeps moisture and dust out but while being greased prevents them from being pushed out as the seal won't hold pressure and will allow the grease to purge past the lip.

The cummins bulletin that comes with the seal page 3 fig 7 says to put the dust lip side away from the vac pump. Good point about the vacuum. So why does the oil want to blow out of the vac pump?

Vacuum pump is lubed by oil