I imagine that many will recognize the item in the attached pictures as a Westinghouse B-3 oil cup. We need two of these for a compressor that we're overhauling and, although I do realize that they can be bought from Backshop Enterprises, this isn't an option for us. Quite apart from the question of whether something that consists of just four quite straightforward parts (including the cap) can really be worth USD1,463.12 (each), this kind of money isn't in our budget.

So thoughts have turned to a DIY solution. We do have two body castings that a member of our group made for an unrelated project some time ago, so if we can get the functional parts right we'll have cups that not only work but also look right.

Does anybody have any experience with the innards of these cups? I do have a diagram in a Westinghouse booklet and understand the principle of operation. And I've also the cup shown in the pictures. It's required elsewhere and is therefore not available, but it does allow for some reverse engineering.

My key questions at this point are

1/. Is the stem a force fit in the body or is it screwed into the body? I suspect the former but am reluctant to try forcing the stem out (from the bottom) until I've confirmed this.

2/. Just how wide is the annular opening between the stem and the sleeve that is pressed onto it? This dimension appears to be the "magic ingredient" of the whole design (and the precision required the only thing that, IMHO, could possibly justify the price).

Any help would be much appreciated.

- John

We have long since given up on getting the stock arrangement to meter the oil feed reliably, and have all of ours fitted with a .013 drilled orifice in the joint at the base of the cup. Very reliable, and each cup uses about 1/2 of its capacity in a day's running.

This doesn't surprise me. The Westinghouse booklet says that "a good grade of standard locomotive saturated steam valve oil should be used in the air cylinders", and I can't see how any annular opening, no matter how small or cleverly sized, can possibly appropriately meter the flow of both such an oil and the much less viscous air oils that I think most people use these days. Overfeeding would seem to be inevitable.

I take it that you leave the rest of the cup alone (i.e. that your orifice in the base is an addition to the existing stem and sleeve rather than a replacement for them)?

I've attached a scan of the drawing in the Westinghouse booklet. "e" is the magic annular opening that is supposed to perfectly meter the flow of oil. If the drawing is accurate, the stem (3) is in fact pressed into the body (2) and there's no way of pressing it out. One would have to somehow pull the stem out (possibly this is the purpose of the groove about half way up the sleeve (4)?). Needless to say, the text is coy about the dimensions of "e" and openings "c" and "d", but it strikes me that if one knew these dimension there isn't anything here that would be very hard to manufacture. In particular the stem and sleeve are just plain turning jobs (with a bit of cross drilling).

This is just a reservoir that dribbles oil into the steam line, correct?

https://www.grainger.com/product/GRAINGER-APPROVED-Reducer-Coupling-1XKU4

Combine that with a 2 inch plug, and screw bushings/pipe/tube nipples in the bottom as required for your output line. Run a pipe tap on the reverse side into the threads on the INSIDE of the coupler or bushings, lightly, just enough to get a hex plug to thread in. Drill the magic 13 thousandths hole into the hex plug.

There are also some nipples/bushings with both internal AND external threads, so the same end could be used as say male 3/4 or female 1/2, universal fit. Even less machining required.

Actually it drips oil into the air cylinders, but this is a detail apart from the fact that, while the compressor is running, these obviously experience pressure fluctuations.

At one point I thought that perhaps the design cleverly exploited these to somehow "pump" oil through the restricted passageways, but looking at the patent description I see that I was mistaken.

The whole point of the stem and sleeve arrangement is evidently just to allow the reservoir to be refilled while the compressor is operating without the possibility of oil being blown in one's face. Otherwise the whole thing does seem to amount to a reservoir with a restricted opening at the bottom. And, as you suggest, something such is not hard to knock together.