You guys beat me to it. Now if you really want to get into the small details on them which I'm sure you do there are actually several types of brake systems.
D22 is the old style which was used in the streamliner era and heavyweight era which has to get a COT&S every three calendar years. It is also a very heavy system compared to the more modern 26C.
26C is the new system that Amtrak and the commuter railroads use. In addition to being lighter weight it is valid for four years between inspections.
There is also ADBX which I've heard is valid for six years but I honestly don't know much about that one to talk about it.
When you do a COT&S you must take all of the valves off the car, send them into be inspected most PV Owners go to Pittsburgh Air Brake (PABCO), or Mutli-Service. They will then clean, and oil your valves which you then have to reinstall. You also send the cylinders in as well.
Now a railroad like Amtrak, MARC, or any other company probably has a shelf in their shops that has all of the components needed to do a COT&S in just about a day. Private Car Owners you remove the stuff in a day or two, send it in wait a few weeks and reinstall it unless you have a back up set on the shelf.
Once you've reinstalled the valves and cylinders you then get an inspector to come out with a single car tester who will pump the cars system full of air from a air compressor and test the cars brakes. If it passes and you hope and pray it does the inspector then stencils the car with the location, date, and initials of the inspector. So my car has COT&S 3/21 BH, BEE to denote who did the work, when, and where. The date is 3/21 for March of 21, BH is Bill Harman, and BEE is Beech Grove.
Now to add more complexity the hoses also have to be changed out as well. Hoses that see light are to be changed every 8 years, while hoses in the shade are every 16 years. The only hoses you have that see light are your end hoses. Then there are three other types of hoses that are in the shade. Now Amtrak and commuter cars also have an additional set of hoses for Main Reservoir that powers the toilets, water system, and doors. You can circumnavigate that actually off your brake line which is acceptable in some cases. However Amtrak prefers that you have a MR on your car to operate on Amtrak.
Brakes are fun. I just took the 26C Bracket off a Superliner when I went to Beech Grove a few weekends ago to check on my car and did it for a friend of mine who bought some superliners. Surprisingly for a wrecked, and unused superliner the valves still held air for over 10 years.
