Vande Bharat/Train-18 — Brake System — EMU and MEMU / Metros Notes

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Train-18 uses the ESRA (Evolution) brake system from Knorr-Bremse — a modular, bogie-oriented brake control architecture. Since it's bogie-controlled rather than coach-controlled, there are 2 Brake Control Units (BCUs) per coach, each independently controlling a single bogie.

BCU Core Functions

Service brake and emergency brake.
Brake pressure limitation based on train load.
A pre-defined pilot pressure (Cv) for the relay valve, used as fallback if the load pressure input fails.

Direct Brake (Electro-Pneumatic)

A microprocessor-based Brake Control Electronics unit (B26 - BCE) performs local brake control — receiving and interpreting brake demand signals plus other train-lined signals to control the EP brake system, providing linear brake response proportional to demand.

Compressed air for the friction brake is tapped from the Main Reservoir equalizing pipe (MR - A07), monitored by pressure switch B07.
B07 connects to the propulsion interlock circuit — if MR pipe pressure is insufficient, the car physically cannot move.
The EP converter (B03.A) turns the electric friction-brake demand into a proportional pre-control pressure, using a charging magnet valve and a venting magnet valve, continuously corrected against a pressure transducer (B03.J) reading.

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Exam Focus — Isolating Cocks & What Each Disables

Cock B04 isolates the ENTIRE BCU (B03) — meaning one whole bogie. Cocks B04/1 and B04/2 isolate only the direct EP brake specifically — under this condition, only the indirect BP (brake pipe) brake remains available on that unit. Cock B01.3 releases brake cylinder pressure for one complete bogie. Getting the scope of each cock right (whole-BCU vs direct-brake-only vs pressure-release) is exactly the kind of distinction real exams test.

Brake Pipe Controlled Brake (Automatic Indirect Brake)

This is the fallback mode — used if the electro-pneumatic direct brake fails, or during rescue operations by a recovery train/locomotive. The driver's brake valve (type FB11, D01) controls Brake Pipe pressure. BP is normally charged from the Main Reservoir Pipe through a pressure-reducing valve (D06) and held at a constant 5 bar. If BP pressure drops below 4.6 bar, the distributor valve (B02.b41) automatically applies the first brake step by increasing the relay valve's pre-control pressure.

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Important Caution — Car Builder's Safety Obligation

Explicitly: the car builder must ensure the train cannot start traction if MR pressure is low (enforced via pressure switch B07), and must ensure isolating cocks (B04, B04/1, B04/2) are correctly positioned — with necessary performance restrictions applied — before a train with closed cocks is put into service.