I don't know about this type of brake. I guess that you said that the Westinghouse brakes had no graduated release. On North American railroads, only passenger equipment has graduated release. Once an application is made, it can partially be reduced. Our locomotives with the 26 and 30 brake valves sometimes have a 3 position cutout valve. The two cut in positions are passenger and freight. The passenger position increases equalizing and brake pipe pressure as the handle is moved toward release. If the locomotive's brake valve is cut into passenger position with direct release cars (wagons), if the Engineer (driver) even bumps the handle toward the release position, the brake pipe pressure will increase. ANY increase in B. P. pressure will totally release the brakes of any cars with direct release control valves on them. Freight will not release the brakes until the handle is fully in release.
I don't know about European brake systems, but again using North America I will explain retainers. Retainers hold pressure in the brake cylinders when the brake valve has gone into the release mode, and will charge the cars' reservoirs. This was used more in the old days before pressure maintaining brake valves. Engineers (drivers) would make a reduction of the brake pipe. Train leakage would then keep drawing down the B. P. pressure. Eventually, he would need to release the brakes and charge it back up. The retainers kept the brakes applied while he was doing that. The retaining valves are on the cars, and had to be applied by the train crew. They are still used in modern times, if a locomotive's brake valve is defective, and will not maintain an application. Another use is in a train with a "kicker". This is a car in the train which goes into emergency, with a service application. It causes a chin reaction, with the whole train going in emergency. On a hill, in this case, retainers are set up, and the train is pulled to the bottom.
