air gap size recommendations

I need some help designing this part.

I have a .8661 diameter shaft. What should the clearance be between it and the stationary housing I am making. Gap will be fed compressed air for an air/gas seal. the length of this seal area along the shaft is about .315. There will be a groove in the middle of this length to allow the air to distribute evenly.

I have a drawing from the parts list, but no dimensions.

Housing supports rotary union for CTS.

I am thinking .002 per side.

Assuming that this is just a seal and not a bearing, I would be looking at other design factors. The overall tolerance on this shaft's position in the hole. You need to make the hole large enough so it does not come in contact. Also the amount of air you are willing to supply. Be bigger the gap, the greater the air loss. And what the differential pressure will be between the two sides of the hole/seal. And what, if any limit is there to the amount of air that can be admitted to the enclosed side of the seal.

I suspect a large range of gaps could work. If this is an original design on your part, then you may need to experiment to find the best gap size. If it is for a replacement part, I would try to measure the OEM part.

It is not "my" design. I am copying what it should be from the Parts book.I never had the original.

It is just a seal. But it has to stay dry and it will see liquid.

It is open to atmosphere on one side. The leakage on the other side is used to motivate liquids down a drain. Drain line is about 4 inches long.