Electrically controlled fail-safe braking instead of air brake

[eldomtom2]

I was reading the squarewheels website when I came across this description of the 1973 stock:

It was the first stock on the Underground to do away with the Westinghouse Automatic Brake. The latter had provided fail-safe braking using the Train Pipe carrying compressed air which, if exhausted, caused the brakes to apply. Instead of a pipe, this stock has an electric wire which, if de-energised, causes the emergency brakes to apply. This is the round-the-train circuit, into which are connected items of safety equipment such as the tripcock, deadman handle, and emergency brake buttons. This system was adopted on all subsequent stocks.

Is this accurate? If so, what other trains use this system? Where can I find out more about it?

 

[MarkyT]

I was reading the squarewheels website when I came across this description of the 1973 stock:

Is this accurate? If so, what other trains use this system? Where can I find out more about it?

EP (Electro-Pneumatic) brakes were used widely on new electric multiple-unit trains in the UK after WW2.

 

[Ken H]

EP (Electro-Pneumatic) brakes were used widely on new electric multiple-unit trains in the UK after WW2.

but they still had a train pipe which stopped the train, if divided for example

 

[eldomtom2]

EP (Electro-Pneumatic) brakes were used widely on new electric multiple-unit trains in the UK after WW2.

I was under the impression that EP brakes also used an air pipe as with standard air brakes as a backup, though.

 

[TurboMan]

Is this accurate? If so, what other trains use this system? Where can I find out more about it?

It's an EP brake, used on all current multiple units (at least, I can't think of any MU stock that doesn't use it). Put simply, a number of valves in a brake unit on each vehicle open and close using electricity according to the position of the brake controller in the cab to permit varying amounts of air to the brake cylinders; the more valves that are open, the greater the air pressure, and the greater the brake force.

So a combination of electricity and air to apply/release the brakes, hence electro-pneumatic.

The valves are the 'energise to close' type, so if the electrical supply is lost then all the valves open, allowing the maximum amount of air pressure to the brake cylinders, causing the maximum (emergency) brake demand.

== Doublepost prevention - post automatically merged: 5 Feb 2024 ==

I was under the impression that EP brakes also used an air pipe as with standard air brakes as a backup, though.

Older multiple units had both, and the driver could switch between the two, but I don't think there's anything left in operation like that today.

 

[eldomtom2]

Thanks, this is one of the many areas of rail transport where everything online only talks about one country without saying it's doing that.

 

[John Webb]

An early form of electromagnetic emergency braking was used in the original GWR Automatic Train Control system, whereby a valve in the brake system on the loco was held closed by a current from a battery carried on the loco. As the loco passed over the ramp at a distant signal the loco shoe was raised breaking the circuit allowing the valve to open.
If the ramp wasn't energised because the associated distant signal was at 'caution' the valve remained open and a siren (operated by the air entering the brake system) sounded until the driver acknowledged the warning. If he didn't the brakes were applied.
But if the distant signal was at 'clear' the ramp was energised and the valve remained closed, a bell rang and the the brakes were not applied.

 

[contrex]

EP (Electro-Pneumatic) brakes were used widely on new electric multiple-unit trains in the UK after WW2.

LT 1938 stock had EP brakes, as did the LMS units introduced in Merseyside that year. Many of the LT Standard Stock cars were fitted with EP brakes by 1935.

 

[Taunton]

Pioneer was the PCC type of tramcar, devised in the USA in the 1930s, which before WW2 had air brakes and controls, known as "Air-Electrics", but then developed postwar into "All-Electrics", which had dynamic brakes, supplemented to the stop (or if the current failed) by spring brakes released electrically. These were able to run in multiple unit formations, and then some Metro operators, principally Chicago on the L, used the same concept on full trains.

 

[millemille]

Every multiple unit in service in the UK has round train continuity - normally 13 wire - which if broken will cause the brake to apply with an emergency rate demand.

13 wire can be broken by the wire being physically broken - in the event of the train having a break away for example - or by any of the switches or relays directly within the 13 wire circuit - such as emergency stop buttons - or by a separate circuit - door interlock for example - which feeds a relay coil with contacts in the 13 wire (so a loss of door interlock breaks the interlock circuit which causes the coil to de-energise which opens the contacts and which breaks 13 wire and will cause an emergency brake application - when train speed is above the Low Speed Relay threshold speed).

The '73 stock was still braked by the same brake friction brake equipment, what changed was how that brake equipment was activated in the event of an emergency.