An auto drain valve is a device installed in the compressed-air system of a locomotive or train (often on the main reservoir(s) or air-reservoirs / moisture separators) that automatically removes (discharges) accumulated moisture / condensate (and sometimes oil or dirt) from the air system.
Main Purpose of Auto Drain Valve
To automatically remove water, moisture, oil and dirt from air reservoirs and pipelines in the air brake system.
Key Functions of Auto Drain Valve
| Function | Description |
| Automatic Removal of Water & Moisture | Drains accumulated condensate from MR and reservoirs without manual intervention. |
| Discharges Oil & Dirt Particles | Expels compressor oil traces, dust and impurities mixed with air. |
| Maintains Clean & Dry Air Supply | Ensures brake system air remains moisture-free for reliable operation. |
| Prevents Choking of Brake Pipes | Avoids blockage inside BP/FP lines caused by sediment or moisture. |
| Protects Brake Valves & Components | Reduces wear or malfunction of C2N, A9, SA9, Relay Valve, Control Valve etc. |
| Avoids Freezing in Winter Conditions | Prevents ice formation inside pipelines and cylinders. |
| Improves Overall Brake System Efficiency | Clean air = faster brake response + reduced maintenance issues. |
| Continuous & Timely Draining | Works automatically whenever water level or pressure threshold is reached. |