What will happen to air pressure in the train air brake system if all the main reservoir drain cocks are left open?

When all the main reservoir drain cocks are left open in the train air brake system, the air pressure will gradually reduce to zero. This occurs because the open drain cocks allow the compressed air in the reservoir to escape uncontrollably into the atmosphere. As air is released, the pressure within the reservoir cannot be maintained, leading to a decrease in pressure until it is fully depleted. This scenario highlights the importance of ensuring that drain cocks are closed when not in use to maintain proper air pressure within the braking system, which is crucial for the effective operation of the train's braking function. Maintaining sufficient air pressure is vital for the safety and functionality of the train's air brake system.