What is this air brake component?

After two spray bottles of soapy water, I finally found my air leak. It's coming from the bottom center of the component pictured. In case it it not pictured, it is located between the frames in front of my single axle. It's three units. The center unit is the one leaking air. The center unit has a big air hose going into it and the two side units have hoses coming out and going to the rear air brakes. Here are my questions:
1. What is it?
2. Can I buy a rebuild kit for it?
3. Where can I buy a rebuild kit?
4. If I have to buy a new one, where can I get that?
Truck is 2011 Volvo VNM single axle D11 Volvo engine.

20220424_111135 by careycal64 posted Apr 24, 2022 at 11:26 AM

20220424_111124 by careycal64 posted Apr 24, 2022 at 11:26 AM

 

Thanks! I hope someone can tell me how to fix it without replacing it. I would bet these puppies are above my pay grade.

 

Well. That's not too bad. Is that new OEM, refurb or China? Probably the best idea is to replace it. But it seems like overkill when it is probably just a gasket or an o-ring. This is my first personally owned semi. I've been doing my own mechanicking for years but never on a semi. I'm all ears on where to go for parts. The places I've found seem limited in both information and even the parts themselves. I guess I could just contact a Volvo dealer. There's one in Medford. Tec Equipment I think.
Thanks for the info, xsetra.

 

With the parking brake on, idling at 1,000 rpm it leaks all the time. It leaks while the air is coming up and still in the red zone. There's a round socket or collar on the bottom center about 1.5 to 2 inch diameter. Inside this there is another smaller collar with a rubber disk dust cover. If you fold that down you can see a filter screen so this must be an overflow valve. It doesn't leak. The leak is coming from the inner rim of the larger collar around the large circlip holding it all in place.
I think MLC Adventures will turn out to be right and I just need to replace it. I hope xsetra's price estimates are close.
Two more pics. One before spraying soapy water, one after.

20220424_175610 by careycal64 posted Apr 24, 2022 at 6:24 PM

20220424_175641 by careycal64 posted Apr 24, 2022 at 6:24 PM