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.

Use caution while learning how your brakes work, and watch out for the following:
  1. 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.
  2. It is not possible to partially release brakes that have been applied. Closing the train brake control valve will effectively cause all brakes on all cars to be entirely released. To control train speed, it may be necessary to re-apply the brakes by opening the train brake control valve again, which leads to:
  3. The brake reservoirs on each car are only charged with compressed air when the brakes are in the released state, and this process takes a while. 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.


Each locomotive carries 2 duplex gauges, with a red needle and a black needle. Ignore the vanilla printed legend; each gauge is calibrated to indicate 10 bar at full travel.

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.

Brake Valves

This mod contains both self-lapping and manually lapped 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.

Independent valves are always self-lapping. At the minimum position, it operates in "bail-off" mode, completely deactivating the locomotive brakes irrespective of the setting of the main train brake. For normal operation, move the independent valve one notch from the minimum. At this setting the locomotive brakes will follow the main train brake setting, as in vanilla Derail Valley.

For the main train brake (aka automatic brake), DE2 and SH282 locomotives carry the older manually lapped valves by default, but can be given the more modern self-lapping valve via a mod setting. Similarly, the DE6 carries a modern self-lapping valve by default but can be changed to the manual valve via a setting.

Manually lapped 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.
  • Lapped: 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.


  • 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: 1 (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 / 5
  • Car reservoir recharge speed: how quickly the reservoirs on each car recharge from the train brake pipe when the brakes are released. Default: 2
  • Triple valve type: plain (1872-1900) or K-Type (1900-1950). The K-Type responds more slowly than the plain, but gives much more consistent results from the front to the back of a train.
  • 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: 0.2
  • 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: 1 bar


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