What is this air brake component?

If it is leaking like that then the middle valve is bad. IF it was leaking only when the park brake was pushed in then you could put your hand on the bottom of the exhaust on that middle valve and the park brakes would slowly start to apply. But if yours is leaking as soon as air builds up then the middle valve is bad. Middle part is the cheapest of the three. Without the part number looking at a similar setup on Freightliner is 325.00 for the whole valve and about 90.00 for the middle part. Sometimes the tag is still on there with a part number.

 

Thanks Smellfunny sounds like you've been around trucks for a while and learned a lot. That pretty much settles it. I'm ordering a new one. Thanks also to MLC Adventures and xsetra for being right from the very beginning. I could have just stopped then, bought a new one and saved us all a lot of time.
By the way xsetra, did you know your handle anagrams as sex rat? Good to know, right? Crazy what I think about when I'm lying under my truck, chasing down air leaks.

 

Final post: Ordered from Volvo dealer in Medford OR (Tec Equipment). $532.80 plus shipping (no sales tax in Oregon). Parts manager, Ray Hayes says there is no rebuild kit.

 

Not sure about anagrams.

Xsetra is just Et Cetera spelled with an X gen, twist.

 

I got the et cetera. Didn't know X gens have their own spelling twists. An anagram is where you rearrange the letters to spell a different word or words. Usually something ironic or funny. Like Sex Rat. Or Extras.