# Brakes

## Brakes

Locomotive and Train Brakes There are three types of brakes used in railway operations: the Air Brake, the Steam Brake and the Vacuum Brake. Steam Brake (steam locomotives only): steam brakes are used only on steam locomotives and their tenders. Steam brakes use the steam from the locomotive’s boiler to generate the braking force that […]

## Reuleaux Diagram

How to construct a Reuleaux Diagram Whilst the exact movements of a locomotive’s valves are indeterminate because of the angularity effects of both connecting rods and eccentric rods, a close approximation of its valve events can be found through constructing a Reuleaux diagram in which the angularities are ignored. Porta used these as a first […]

## Clearance Volume

Cylinder Clearance Volume The clearance volume of a cylinder (often presented as a percentage term) is that part or proportion of the cylinder volume that is not swept by the piston. It is therefore the volume (or proportion of total volume) taken up by the steam passages and cylinder-head cavities – i.e. the volume contained […]

## Steam Chest

Steam Chest The steam chest (or steamchest) is the “reservoir” for collection of steam as it passes between the superheater header and the inlet port to the cylinder. The advantage of a large steam chest (as is the advantage of any reservoir) is that fluctions in pressure as the steam passes from the steamchest into […]

## Balancing & Hammer Blow

Dynamic Augment or Hammer Blow Hammer Blow or “Dynamic Augment” is a dynamic force imposed through the driving wheels and onto the railway track resulting from the rotation of out-of-balance weights that are attached to the driving wheels for the purpose of counteracting the horizontal inertia forces resulting from the “to-and-fro” motion of the reciprocating […]

## Snifting, Drifting, Bypass and Herdner Valves

Snifting, Drifting, Bypass and Herdner Valves Snifting, Bypass and Drifting Valves were commonly used as a means of preventing negative pressures occurring in the cylinders of a locomotive during “drifting” or free-wheeling. If a negative pressure does occur, it will immediately result in combustion gases and solid particulates being sucked down from the smokebox through […]

## Valves, Valve Gear etc

Valve Gear and Valve Events This page covers (very briefly) a number of topics related to valves. These come under the following headings: Valve types Valve ports Valve events Predicting valve events Valve travel Lap and Lead Lead Lap Purpose of steam lap Purpose of exhaust lap Attention is also drawn to separate pages as […]

## Motion

Motion A locomotive’s “motion” consists of the reciprocating and rotating parts incorporated in its drive and in the operation of its valve gear as shown and described below:     Drive components of the Motion: Pistons and rings; Piston rods; Cross-heads, Cross Head Arms, and Small Ends; Connecting Rod and Big Ends; Coupling Rods. Valve […]

## Simple/Compound

Simple and Compound Expansion The term “Simple Expansion” refers to the single use of steam in powering a steam engine. “Compound Expansion” refers to the multiple uses of steam in powering a steam engine. In a “simple” engine, the steam enters the cylinder at high pressure, expands as it pushes the piston through its stroke, […]

## Rolling Resistance

Locomotive and Train Resistance A locomotive’s tractive force is required to overcome the resistance to motion of both locomotive and train. When the tractive force is greater than the resistance, then the train will accelerate in accordance with Newton’s law of motion: Force = Mass x Acceleration or Acceleration = Force ÷ Mass.  If the tractive […]