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Table of contents
1 The basic principle of compressed air supply and distribution – the main air
supply pipe
1.1 Compressed air supply
1.2 Distribution – the main air supply pipe
2 The direct acting brake – different kinds of through-brake cocks
2.1 The direct acting brake
2.2 Different kinds of through-brake cocks
3 The indirect automatic brake – the 5 bar main brake pipe – the double-jack valve
3.1 The continuous compressed air brake
3.2 The 5 bar main brake pipe
3.3 The double-jack valve
The basic principle of compressed air supply and distribution – the main
air supply pipe
1.1 Compressed air supply
All pneumatic or compressed air brakes act by pressing the brake blocks or pads against the wheels or
break discs by means of compressed air.
The braking force can be regulated by altering the air pressure.
Each locomotive or motor coach is equipped with a compressor driven by an electric motor. Different
types are in use
Distribution – the main air supply pipe
On passenger trains composed of a locomotive and carriages or motorcoaches, the compressed air is
distributed over the whole length of the train by the main air supply line serving the following purposes:
• supplying the drivers brake valve on a driving trailer
• supplying auxiliaries on passenger carriages with compressed air (door operating gear, pneumatic
suspension, additional brake filling on electro-pneumatic brake systems, etc.)
On freight trains, the compressed air is distributed over the length of the train when it is necessary for the
supply on certain wagons the unloading gear.
Figure 5 shows an example of the compressed air supply on a passenger train.
The direct acting brake
In the case of the direct acting brake, compressed air flows directly into the brake cylinder when the
through-brake cock is manipulated. Since this system is not working automatically in case of breaking
of coupling, it is only in use as an auxiliary brake on locomotives.
The braking force can be regulated by altering the air pressure in the direct acting brake pipe. The
through brake cock lets the compressed of the main air supply pipe into the brake cylinders (fig. 8 and
9).
The 5 bar main brake pipe
All braking devices connected to the main brake pipe will be activated in the following conditions:
• the train driver manipulates the drivers brake valve;
• on a passenger train when a passenger activates the emergency brake;
• in case of a considerable loss of air in the main brake pipe on any vehicle of the train;
• when the main brake pipe is damaged caused by a rupture in a hose or when a derailment
happens and the hoses are uncoupled.
At the ends of the continuous main brake pipe on each vehicle are to be found brake hose couplings
and air cut-off cocks.
The pressure in the main brake pipe is decreasing and the distributors will be activated resulting in an
application of the brakes. The figures 13, 14, 15 and 16 are representing the working principles of a
distributor related to the pressure in the main brake pipe in different circumstances.
The double-jack valve
Since most locomotives are equipped with an direct acting brake and an indirect automatic brake, both
systems using the same brake cylinders, a double-jack valve is needed to separate both systems in
filling the brake cylinders. Figure 17 shows the working of the double-jack valve.
The brake cylinder can be filled with compressed air from the auxiliary air reservoir by decreasing the
pressure in the main brake pipe. In that case the connection between the cylinder and the direct acting
brake pipe is interrupted.
When the direct acting brake pipe is filled with compressed air the connection between the brake
cylinder and auxiliary reservoir is interrupted, the main brake pipe is in that stage on a pressure of 5
bar and only the brakes of the traction unit are applicated.