Derail Valley
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About this mod

A realistic simulation of railway air brakes, based on commonly-used Westinghouse Air Brake Company (WABCO) equipment.

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This mod changes the way train brakes behave to adhere more closely to real-life equipment. It supports multiple variations of brake valves for the engineer's use in the locomotive, and multiple equipment variations on individual cars that control their response to the engineer's inputs. Use caution while learning how your new, more realistic brakes work.

A freshly spawned locomotive or car has no brakes until it has been connected to a locomotive with a running compressor and the brake reservoir charged with compressed air. This makes coupling to these cars quite challenging, and I recommend installing the Hand Brake mod to help hold cars in place while coupling.

The brake reservoirs on each car are depleted each time the brakes are applied, and take time to recharge from the brake pipe. Repeatedly applying and releasing the brakes without taking sufficient time between applications can exhaust the supply of air in the car reservoirs, leading to brakes that work poorly or not at all. Watch out for letting your train runaway!

You can adjust the realism and difficulty via mod settings, accelerating how quickly the system responds to make it easier to drive the train safely.

I highly recommend combining with the Heads-up Display mod until you get a feel for how the various brake system components respond to different situations and control inputs.

Car Control Valves
This mod supports several kinds of car control valves:
  • Westinghouse "plain triple" control valves (1872): These are single release valves. An increase in pressure in the brake pipe will entirely release all brakes on all cars. Fast reacting, but suitable only for short trains.
  • Westinghouse "Type K" control valves (1903): Single release valves that are less responsive than the plain triple, but have additional features that make them more consistent on longer trains. They also have an emergency mode that triggers when the brake pipe pressure is rapidly reduced.
  • Knorr Bremse "KE" control valves (1955): These are graduated release valves where brake cylinder pressure is directly controlled by brake pipe pressure, similar to vanilla DV. They do not have an emergency mode, and may not be reliable on very long trains.


Each locomotive carries 2 duplex gauges, with a red needle and a black needle. Each gauge is calibrated to indicate 10 bar at full travel. I recommend using the Super Gauges mod with these alternative textures for the gauge faces.

Brake pipe gauge:
  • Black needle: The current pressure in the locomotive brake pipe, connected to the rest of the train. Over time this will follow the current pressure in the equalizing reservoir. Normally 5 bar when the brakes are released or recharging.
  • Red needle: The current pressure in the locomotive brake cylinders, directly indicating stopping power for the locomotive only. 0 bar when fully released and approximately 3.5 bar under full brake application.

Aux res gauge:
  • Black needle: The current pressure in the equalizing reservoir. Controlled by the main train brake valve, and determines the target pressure for the train brake pipe.
  • Red needle: The current pressure in the main reservoir. Normally 8 bar.

Engineer's Brake Valves

This mod contains both self-lapping (Type 26L) and manually lapped (Type 6ET) brake valves. Self-lapping valves use a "service zone," where valve position determines the air pressure put in the brake pipe. Manually lapped brake valves provide positions to increase, decrease, and maintain the current pressure in the brake pipe, and the engineer must observe the gauges and manipulate the valve accordingly to reach the desired pressure.

By default, DE2 and SH282 locomotives carry the older manually lapped valves, but can be given the more modern self-lapping valves via a mod setting. Similarly, the DE6 carries a modern self-lapping valves by default but can be changed to the manual valves via a setting.

Self-Lapping Brake Valves

Pressing Shift-B while in the cab will activate the "bail off" mode, releasing the independent brakes while leaving the brake pipe and train
brakes at the current setting.

Manually Lapped Brake Valves

The manually lapped train brake valves have 4 positions:
  • Running: restores pressure in the equalizing reservoir and brake pipe to full, releasing the brakes and slowly recharging the auxiliary reservoirs on all cars.
  • Lap: holds current equalizing reservoir pressure.
  • Apply: slowly releases pressure from the equalizing reservoir at a constant, gradual rate.
  • Emergency: releases pressure from the brake pipe as rapidly as possible.

The manually lapped independent brake valves have 5 positions:
  • Release: releases pressure from the locomotive brake cylinders, releasing the brakes.
  • Running: applies and releases the locomotive brakes according to the pressure in the brake pipe, matching the behavior of freight car triple valves, including auxiliary reservoir recharge rates.
  • Lap: holds current pressure in the locomotive brake cylinders, neither releasing nor applying brakes when brake pipe pressure changes.
  • Slow Apply: slowly adds pressure to the locomotive brake cylinders at a constant, gradual rate, increasing brake force.
  • Quick Apply: rapidly adds pressure to the locomotive brake cylinders up to a set maximum pressure.


While coupling and uncoupling from cars you will frequently drain the brake pipe, leading to the brakes on the cars applying in the emergency position. It can be quite time consuming to need to hook up a locomotive to charge the brake pipe and release the brakes, so cars are equipped with a manual brake release mechanism. To use it, stand on the car and hold down Shift-B on the keyboard for a few seconds.


  • Train brake control valve type for DE2, SH282, and DE6. Defaults: DE2, SH282: unchecked; DE6: checked.
  • Locomotive air compressor production rate. Default: 0.03
  • Locomotive brake application/release speed: how quickly the locomotive brakes respond to changes in brake pipe pressure and/or the independent brake control valve. Defaults: 10 / 10
  • Locomotive brake pipe recharge speed: how quickly the locomotive brake pipe is recharged from the main reservoir when the train brake is released. Default: 20
  • Train brake pipe balance speed: how quickly changes in pressure in the locomotive brake pipe propagate down the length of the train to other cars. Default: 4 (Set to 10+ to make it easier to drive very long trains.)
  • Car brake application/release speed: how quickly brakes on each car respond to changes in brake pipe pressure in that car. Defaults: 2 / 10
  • Car reservoir recharge speed: how quickly the reservoirs on each car recharge from the train brake pipe. Default: 4
  • Triple valve type: plain, K-Type, or Knorr KE.
  • K-type triple pipe drain rate: the proportion of air the K-Type triple takes from the brake pipe when applying the brakes. Larger numbers set the brake harder and faster, but make precise control more difficult. Default: 0.1
  • K-type triple retarded release rate: the modifier on how quickly cars release their brakes when there is a large increase in brake pipe pressure. Slows down the rate at which cars near the locomotive release their brakes to better synchronize with cars farther from the locomotive. Default: 0.5
  • Return spring strength: the minimum pressure necessary in the brake cylinders for any braking force to be applied. Lower values make brakes apply more quickly but take much longer to fully release. Default: 0.5 bar


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