General
In December 2019, modifications were made to the compressed-air system and brake system of the UHN.
For model 437.421, the modified compressed-air system and brake system has been installed by special request to vehicles with code B89 (low-pressure brake system) already since July 2017.
As part of the modification, the following factors have changed:
Changes to the compressed-air system
The previous high-pressure-capable compressed-air drier was replaced by the "AirProcessing Unit (APU)" air supply unit.
The system pressure of the air pressure provision was reduced from 18.3 bar to 10 bar.
The pressure regulators are omitted in the air pressure provision in front of the service brake. As a result, the system pressure of the service brake increases from 8.3 bar to 10 bar.
Modifications to the brake system
Omission of the automatic load-dependent brake controller (ALB controller).
Control of brake force at rear axle via electronic brake force limitation function (EBLF).