The purpose of the seal is to keep the oil in the housing, if it allows air to come in, it also allows oil to go out. The oil will become hot, generate vapors and build-up pressure. If there is no way to equalize the pressure, it will blow the seal, or splash in the face of the operator/mechanic checking the oil level....

If the machine, whether pump, gearbox whatever, features a breather and there is any concern over moisture intrusion, a dessicant breather can and probably should be used. They can be sized appropriately for inflow/outflow of vapors without allowing moisture and [hopefully] dust or other contaminants.

Good Luck
Dana

It's a good question and I'm not 100% sure of the answer.

I can think of some bad possible effects of breather through the seals: One is any entrained dirt/dust stays in the seal. Another you may have an abrupt change in temperature during in-breathing or outbreathing which may cause condensation in the seals.

I'm not sure if that's the whole story. We just bought a large motor with 55 gallon upper oil reservoir and there is no vent at all on that reservoir. However upper bearing compartment is vented to stator via the shaft/standpipe clearance.

pete,

The response from svanels is exactly as I have always understood it.

Remember you chemistry. Somebody's Law of gases is pressure times volume equals the number of moles of gas times a gas constant times the temperature.

Thus without relief for the gasses, pressure will build-up and eject oil under the seal or blow the seal out if there is enough temperature change.

Gitts (I think) makes a washdown duty oil breather.

Good Luck,

I am working under the assumption that the oil seal itself can breathe (but it is not desireable)

You are working on the assumption that the oil seal itself cannot breathe.

I guess it depends on type of oil seal. The labyrinth oil seals I see on large motors certainly can breathe. I don't picture oil seals being pressure tight like the fluid system seals. But maybe someone can clarify.

It will be pure speculation on my behalf but I would guess that seals (even labirinth type) are not 100% hermetically tight and do allow air in and out.

For critical apllications though a breather with a dessicant will force air movement exclusively via the breather thus eliminating moisture penetration.

Pete,

With the normal lip seals, as the seal leaks and the temperature rises, the flexible components of the seal become brittle and eventually fail, allowing the oozing to become flowing. Most all types of seals will allow air to vent, but with a build-up of pressure and temperature to the force thay they will allow. (I hope that made sense).

In addition, if the seals are allowed to relieve the pressure, what is vented will probably include oil while a breather in the top of the lubricant reservoir will allow mostly gas to escape.

You might ask this same question at Noria's website and get a better explanation.

Hello All,
Debal the purpose of the breather (as others have stated) is to allow for the equalization of pressures between the outside and inside of the unit. Yes you are right the seals will allow the pressure to equalise but on the way out they will take lubricant out and on the way back in they will bring contaminants. So the breather is also supposed to filter out the contaminents. What contaminents you want to filter out will dictate the type of breather you select. There was some discussion regarding seals, and thier purpose, the seal in this pump (if it's a single lip seal) could be positioned to keep in the oil or turned around to keep out the contaminents. There could be 2 single seals configured the same way as previously mentioned or. It could be a double lipped seal and again they could be oriented in opposite directions to keep the oil in and the contamination out. These rubber lipped seals are normally designed to be able to maintain a pressure anywhere between 4-12 PSI, in a housing without a breather. This of course assumes a reasonable shaft finish and the requred dimensions and lubricant viscosity.

hope this helps...

regards.......

Thanks all for clarifying to me about different types of seals. I did not realize before that some oil seals are air tight.

Hello All,
Just a minor point (for clarification) I am not implying that lip seals are air tight. Their ability to hold pressure in an application is a function of the ~6-12 % seal swell from the absorbtion of oil and the physical interface between the rubber lip the oil and the housing/shaft surface. In a new installation the seals will (leak like a basket) so to speak until they get seated....
Sorry for the confusion....

regards.....