Colonel Leon Junior Train Controller

Location:
I have a few questions regarding brakes. Thanks to all who can answer them. CL

  • The brakes sound identical between the Sydney S sets, Sydney K sets, XPT carriages (not the power cars) and the Melbourne Comeng sets. Sorry if the Comeng/XPT makes this not suitable for this sub-forum. So, do the stated trains use the same brakes?
  • I believe that the Tangaras have two braking modes; one that is the air brakes and utilises chopper control and one that is the disk brake and is used when loco hauled. Is this true? Are there any other trains that have multiple braking modes?

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  sunnyyan Station Staff

^ The T sets have two brake modes, automatic and electropneumatic (E/P). Not sure what that means, but I think the automatic mode takes longer to release the brakes. As seen in this video:

https://www.youtube.com/watch?v=PFYxt7SiVXs
  Colonel Leon Junior Train Controller

Location:
Yes, I'm not sure why they would use the disk breaks on a trainee driver.
  seb2351 Chief Commissioner

Location: Melbourne
Automatic = Westinghouse brake, all trains have this brake. A reduction in brake pipe pressure means the brakes apply.

EP = An electronic signal is sent to each brake unit, where a change in main resivour pressure applies the brakes.

Disk brakes are used on the motor carriages, as there is less room for the standard brakes that you normally see due to the regen braling equipment.

Disk brakes and normal caliper style brakes have no difference in train handling if your a trainee or not.

Feel free to PM if you require further information
  gordon_s1942 Deputy Commissioner

Location: Central Tablelands of NSW
Interurban and Suburban sets used the E/P system because its faster in both its application and release.

It one sense it works just like the hydraulic brakes on your car, apply pressure to the pedal and you get an application depending on how far you press the pedal.
In the early Interurban's circa 1958, right behind the driver on a panel were 2 large black Relays that were associated with the EP system.
They were quite noisy when activated that you could easily hear them in the Guards compartment with the Driver's door closed.

For some reason they were labeled N  and K  and were subsequently nicknamed 'Nock and Kirby' which at the time was a major department store in Sydney.
Why the N & K designation or the nickname I have no idea.
  stront Junior Train Controller

Tangaras have three braking systems - EP and Auto, as described by Seb, and electric/regenerative, where the motors act as brakes and return electricity to the overhead or to resistor banks. Four if you count the spring parking brakes.

Every train since tangaras have had disc brakes for the simple reason that they are low maintenance. Tread brakes are high wearing, and also wear wheels out faster, and overheat more easily. They have some advantages (such as cleaning water and oil off the wheel) but discs are better from an engineering standpoint. Main disadvantage from driver's point of view is that in inclement weather they're more likely to slide as nothing clears crap off the wheels.
  gordon_s1942 Deputy Commissioner

Location: Central Tablelands of NSW
Not long after the Interurban services were introduced, one Sydney bound unit failed to stop and collided with stop blocks on the end of Platform 14 I think it was at Central Station.

It was of course a major talking point because at the time, the EP system in use was considered as you would today a set of Disc Brakes and would stop the train on a 5 cent coin.

I spoke to the Driver of that Train months later and he said those at the inquiry wanted to know why he didnt apply the 'Regen Braking System' when it became obvious the Train wasnt stopping.
He said they had difficulty understanding that firstly it would not work under a certain speed and it was not a BRAKE in that context  as all it did was  cause the Motor to generate power which in turn slowed the motor down but would not stop it.

This was long before the introduction of wheel slips and electronics fitted to the Trains of today.

Another lesser point was that 'Regen' then was NOT to be 'selected' in the Sydney Metro area as the system was not designed to dissapate any loads generated.
  tazzer96 Deputy Commissioner

Any regenerative brake is linked to the speed at which its travelling.  Its similar to an airbrake/spoiler on a plane or F1 car.  Its useless at 10km/h, but at high speeds it is much stronger than even the high quality disc brakes.
  YM-Mundrabilla Minister for Railways

Location: Mundrabilla but I'd rather be in Narvik
Any regenerative brake is linked to the speed at which its travelling.  Its similar to an airbrake/spoiler on a plane or F1 car.  Its useless at 10km/h, but at high speeds it is much stronger than even the high quality disc brakes.
tazzer96
Question
  KRviator Moderator

Location: Up the front
Generally speaking, regen or dynamic braking produces most braking effort at moderate speeds then begins to drop off as road speed increases, though the newer AC loco's will peak around 38kph then have an essentially flat curve until around 0.5-1.5kp/h. Loco's with 'extended range' dynamic braking can use it down to around 2kp/hr, though it is not overly effective at those speeds. Above this magic number, which is different for each loco type but usually around the 40kp/hr mark, the braking effort diminishes significantly. For heavy locomotives with decent adhesion, you can expect around 250kn braking effort solely with the independent brake fully applied, but using dynamic braking can easily exceed this number at over 800kn for some AC types. This is enough of a risk for limits to be placed on using DB exclusively with significant tonnages behind empty wagons, as the risk of derailment is high. In ARTC territory, you cannot use DB exclusively for controlling the speed with more than 2,000 tonnes behind an empty wagon, for example.

The top chart below shows the 82 Class, with the individual peaks and troughs showing how the loco transitions through the different braking connections based on road speed. Particularly with AC equipment operated light engine, once the DB has loaded up, you need to be restrained or holding on, or it will easily put you into the windscreen. The second chart - and apologies for taking a photo of my laptop screen - shows two identical loco's, one AC, one DC, with the different dynamic braking curves.




  normw Junior Train Controller

Conventional air brakes require a reduction in brake pipe pressure by the driver's brake valve, which must be propogated to all the vehicles of the train. The air exhausts from the brake pipe through a port in the driver's valve, which means vehicles towards the front of the train brake sooner than towards the rear, which makes for tricky train handling on long trains.

EP Brake

With EP braking (used on fixed length trains like EMU's, DMU's) electric circuits are energised through the entire train length (typically via the jumper connections), resulting in the air brakes being released. When the driver applies the brake the electric circuits are de-energised in sequence, causing activation of the brake equipment on each vehicle at the same time, resulting in reduced or no 'run-in' and carriage jostle.

Red Rattlers had a single step EP, the electric feed passing from the drivers brake valve then (via a special jumper coupling) to every carriage in the set, to a terminating plug at the end of the last carriage. The brake handle would be moved towards the application position, the bakes on each car would start to apply; when sufficient braking effort had been attained, by moving the brake handle back towards release, the EP wire would energise again and keep the brake effort at that level.

Newer trains have three (or more?) wires, all energised when the brake handle is in release. As the brake handle is moved towards full application, switches in the driver's brake unit open and close in a binary sequence, and does not need to be moved back towards release to set a partial application of the brakes.

111  Release
110
101
100  Half brake effort
011
010
000  Emergency (The train separating has the same effect)

I could guarentee all suburban rolling stock (Tangaras onward) would have some form of EP brake.

I know of no locomotives in Australia having support for EP brake, since freight trains are longer than the electric circuits would allow, but locomotive-hauled passenger trains (like RUB sets and I-P style cars that already had electrical jumpers between cars) would have benefited from EP, and I've read of at least one U.S. steam locomotive class having it.

Long freight trains that utilise mid-train or rear locomotives (or via a control truck such as Locotrol), can initiate a brake pipe reduction on the remote locomotives (as noted in the following message by KRviator) when the driver (on the lead loco) operates his brake valve; this speeds up activation of brakes from the rear of the train and helps to minimise 'run-in' . This isn't really a form of EP since it only allows brake pipe reductions on the locomotives of the train, but it does provide similar benefit and trains of 1.5 km possible with a single crew.

ELECTRIC BRAKING

Electric forms of braking have locomotive or train traction motors switched to function as generators, being driven by the forward movement of the train. As already noted here, this means that at low speeds or standstill there is no braking force, and hence it cannot hold a train on a grade.

Diesel-electric locomotives are usually fitted with dynamic brake. In this form the electical energy generated by the traction motors is disipated in on-board resistor banks cooled by a (usually noisy) electrically-driven fan. The driver can control the amount of power generated, but once the maximum power is reached, control systems automatically ensure the maximum is not exceeded, regardless of how fast the train goes.

Electric locomotives and EMU's can optionally have regenerative brake or possibly synchronous braking.

In regenerative braking, power generated by the traction motors is supplied back to the overhead wire, and could be used by other electric trains in the same section. If there were no electric trains in the section the power was disipated in large resistor banks at the sub-stations.

The original single-deck interurbans (and possibly the double-deckers) had a 'blended' brake system such that if the driver applied the brakes at high speed, regenerative braking would commence first, then, as the train slowed to the point where regenerative braking was less effective, it would switch off automatically and allow the conventional EP air braking system to bring the train to a stand.

46/85/86 class locomotives had regenerative braking selected and controlled solely by the driver.

I never worked on or saw circuit diagrams for Tangaras or later so cannot say if any of them support(ed) regenerative brake. From what I've noticed in recent years, the resistor banks in substations have been removed, which suggests regenerative braking may have been phased out altogether. Someone who knows is welcome to comment on this point.

WHEEL BRAKES

Regardless of wether brakes are activated be brake pipe reduction or EP, air is made available to one or more pistons to push brake shoes on to friction surfaces that absorb the forward energy of the train.

Clasp brakes press brake shoes onto the wheel tread of each wheel, two shoes per wheel. The brake shoes in this configuration kept the wheel surface free of scale, which is useful for electric trains and EMS's that need to get electric current back to the substation. If a wheel locked up under high braking it could produce a small flat spot on the wheel tyre face. Cast iron brake shoes could be sometimes used to wear off these small flats, obviating need for wheel turning.

Disc brakes have the advantages of larger brake surface and likely ease of access for maintenance, and does not cause heating of the wheel rims under high-speed braking, resulting in better wheel life.
  KRviator Moderator

Location: Up the front
You'll find most locos these days that are fitted with an electronic air brake are capable of also being fitted with ECP brakes, Rio Tinto, FMG and Roy Hill run ECP on their Pilbara trains nudging 2500m long, and it is in use on a good portion of the coal trains running about NSW as well.

In saying that, that is ECP, not EP braking, though there wouldn't be much limiting 3-wire EP brakes if an operator wanted to. However there is not much to be gained vs full ECP, other than a reduced setup time prior to departure but there are several downsides to EP-braked freight trains that ECP avoids.

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