You're going to have to give us something more to work with. A photo would go a long way. That being said, if what you are asking about has several air lines going to and from, including to the air reservoir, then I would be inclined to think you are talking about the control valve. Does it look like the following?
(My photo)
If so, than it will probably be either a Westinghouse (now Wabtec) ABDX valve, or a New York Air Brake DB-60. At least, that's what I typically find on modern cars. Wabtec technical information, meaning drawings, is almost impossible to find online. NYAB though has a very comprehensive list of technical documents available on their website, and this includes cad drawings of many of their brake system components. This link should take you to the some examples of DB-60 control valve drawings.
I can't think of what else it might be, but if the item in question is not the control valve, then a photo would be really helpful, if not an absolute necessity.
Jim
