Three-pipe Automatic Air Brake

[hexagon789]

Reading the British Rail Mark 2 Coaches book by Michael Harris I recently acquired, I was intrigued by a reference in Chapter 12: Mark 2 the world over, which refers to the intial batch of Mark 2b coaches Northern Ireland Railways obtained for use on The Enterprise service as being fitted with Westinghouse Three-pipe Air braking. After a little digging it seems this system was standard in Northern Ireland from the 50s until 1981 on coaching stock and some DMUs such as the Class 70 and 80 DEMUs.

My question is what is the difference between three-pipe and two-pipe air brakes. I'm familiar with the advanages of the Twin-pipe automatic air brake over the single-pipe system but cannot find any reference online to whether there are any advantages with the three-pipe system.

Essentially - what was the "third" pipe for, did it give an advantages or even disadvantages over the Twin-pipe system and why does it seem to only have found favour in Northern Ireland and for a relatively short period at that?

Any answers/suggestions would be welcome.

 

[hexagon789]

Doesn't matter any more, I've found out how the 3-pipe differs to the 2-pipe air brake and that the 450 Class had the standard UIC 2-pipe air brake not the NIR Westinghouse 3-pipe system.

 

[GW43125]

Doesn't matter any more, I've found out how the 3-pipe differs to the 2-pipe air brake and that the 450 Class had the standard UIC 2-pipe air brake not the NIR Westinghouse 3-pipe system.

I'm quite interested now, could you post an insight or a link please?

 

[hexagon789]

I'm quite interested now, could you post an insight or a link please?

The two-pipe UIC air brake consists of a brake pipe (red) and a main reservoir pipe (yellow).

The NIR 3-pipe system consists of:

The Straight Air Pipe (Green)
The Main Reservoir Pipe (Yellow)
The Emergency Pipe (Red)

The straight air brake is controlled by the Driver's brake valve operating the brakes on each vehicle by means of a relay valve admitting air from the auxiliary reservoir (charged at 100 psi) to the brake cylinders.

In the case of the NIR system fitted to the Class 80s, electro-pneumatic (EP) assistance was provided by a micro-switch on the Driver's brake valve in circuit with a magnet valve on each vehicle, causing air to be admitted immediately and simultaneously on each vehicle from the auxiliary reservoir to the brake pipe when a brake application is made.

For the EP system fitted to the 80s, there is no EP release of brakes and as with other such systems the isolation of the EP system simply means the brakes are slower acting.

The emergency brake pipe controls the emergency brake (as you might imagine), the emergeny pipe charges the emergency reservoir on each vehicle to 70 psi and is operated by the Driver's brake handle being placed to Emergency, operation of the Driver's Safety Device, Guard's Emergency Valve or Passenger Communication Apparatus.

Unlike the two-pipe system which is compatible with the single-pipe, indeed the two-pipe system can be operated as a single-pipe system if necessary, the three-pipe is compatible with neither.

I'm not knowledgeable enough to say exactly what advantages the 3-pipe system offers, perhaps another member of this forum might provide such insight, but the obvious difference is the addition of the Emergency Brake Pipe it would seem.