Air Brakes

Assuming that brakes are fitted throughout the length of the train, there are two main types of actuating systems commonly used:- vacuum brakes and air brakes. This article describes the 'simple' or 'straight air' brake system. 'Simple' in this context means the brakes are applied when pressure is applied to the brake line. i.e. pressure in the line equals the brakes going on. Automatic brakes are the subject of another article.

Although generated and stored at higher pressures, the operating air pressure in the brake line is normally less than 30 lb/sq.inch (psi) (<2 Bar or 200 kPa) for operation. This reduces the air requirements, and provides sufficient power for normal operation without requireing the use of 'high pressure' fittings.

How to get compressed air?

There are several ways to get compressed for use in ride-on trains:

  • On steam operated models, a steam powered air compressor is sometimes used
  • A mechanical pump, driven by the axles or by the motor in petrol powered models
  • An electric pump on battery powered models
  • Charging an air reservoir from the station/workshop industrial size compressor

Compressed air needs to be stored in an on-board tank or reservoir. This air tank usually stores air at a much higher pressure than required for brake applications, and a regulator is used to drop (and regulate) the pressure to the lower operational levels required for brake application. It is usual practice to install a pressure gauge on the brake line to see how much braking effort is being applied. A gauge is also installed on the air tank reservoir.

Basic schematic diagram

The brake line runs throughout the train, and the connector is often marked with a 'B' to signify 'Brakes'. As an option to increase the reservoir capacity, additional smaller reservoirs can be mounted under each car (particularly passenger-carrying cars), and the air line connector is often marked with an 'A' to signify 'Air'.

An air supply is obtained from an on-board compressor, or from filling the reservoir from occasional station stops. The option of having a reservoir tank only, and not have an on-board source of compressed air, is a viable option. In practice, provided the on-board reservoir is of sufficient capacity and not too small, storing air at 80~100 psi and using at 0~30 psi provides sufficient in reserve for severa hours of normal running. The optional additional reservoirs are usually used on each car with this option, and provides air storage proportional to the length of the train. Topping the reservoir(s) up occurs when in the station or servicing area, and usually this is at intervals much less than the maximum. It has proven a very practical and operational solution.

The driver's brake control valve is a commercial plunger type air pressure regulator, modified to operate with a cam rather than the standard screw, and provides fully proportional control of the braking. Alternatively, a simple ball valve can be used, however control is less precise. The stop valves on the car ends can either be a separate valve, or use a self-sealing quick connect air connector.

Air brake connection
Typical inter-car hose connections
using quick connect fittings
 

A system for automatic brakes is available here.