Question: Air Brake System - Relay valve, and Spring brake valve (Balanced position)

Here's a pic for reference:


Lets say the system builds air pressure to cut out. I push in the PP-1 valve. Air from the double check valve flows to the PP-1, then out to the SR-1. The air enters the SR-1 supply port, out the delivery port and flows to the R-14 relay valve service port. The signal air pressure at the service port depresses a piston in the R-14 and the R-14 opens a supply port. The open supply port allows air from the aforementioned double check valve line (emergency line) to flow into the spring brakes. Now they are released.

My question is: Would both the SR-1 and R-14 be in a balanced position (hold) at this point? Would air pressure in both valves be equal above and below, neither inlet or exhaust open?

 

Where would an Air regulator be plumbed to and what is an Air regulator? I'm assuming it's to "regulate air". But why is it necessary?

And how do spring brakes contain "hold off" air pressure? I assume it's through the balanced position of the valve. But... not sure.

 

Yeah, I understand that part. But what confuses me is how exactly the air stays in there once its sent by the PP valve to the Spring Brakes. Not sure what's keeping it there, I'm assuming constant air pressure from the PP valve once you push it in?

Here's a R-12 Relay valve that is in the "off" position. No signal air pressure above it from the treadle valve.



R-12 "on" position. Signal air pressure from treadle valve opens a supply port. Air flows from primary tank to supply port in the R-12 and out the delivery port to the Service Brake Chambers.



"Balanced" position. Air pressure equalizes above and below so no air is being sent to brakes, and no air is being exhausted at the exhaust port. So basically your holding the treadle valve at the same position. Brakes are being held.


I'm thinking the same thing happens with the R-14 valve that operates the Spring Brakes in that diagram I uploaded. The push pull valve puts the relay valve in a balanced position and the Spring Brakes are released, and air is kept inside. Make sense? Maybe?