Steam Overview

Steam vehicles are propelled by steam pressure. Steam typically gets built up in a large onboard pressurized boiler containing water, heated by a coal-burning firebox. Smoke and hot air from the firebox pass through the boiler through a cluster of tubes, heating up the water around them, before getting released through a blast pipe at the other end of the boiler.

The steam that accumulates in the boiler can be admitted to cylinders, with pistons tied to the wheels via a mechanical connection. This propels the vehicle. With every cycle, after pushing the pistons in one direction, the steam gets released outside through the blast pipe. This creates a vacuum pull in the firebox, drawing fresh air into it, further boosting the fire.

Water and coal are sometimes carried in a secondary unit, called the tender. Coal is transferred to the firebox by manual shoveling, whereas water is transferred to the boiler using a device called the injector. An adequate amount of water must be maintained in the boiler at all times, else it could lead to catastrophic failure.

Firing up a steam engine from scratch is very costly and can take a very long time. In Derail Valley, the startup process is sped up when the vehicle is stationary, simulating it being done in the most fuel efficient manner, until the boiler pressure reaches about 80% of its maximum capacity. The time scaling is there to drastically reduce waiting, but can be adjusted by a difficulty setting titled Steam Startup.