92TS bid for freedom at Epping.

Last week aparently? Having been away that week I got this fed back to me this evening. Suspect it happened as one of the fixed reds had a stores label fluttering away on it in the breeze.

Anyone shed some light???

A bit like the D Stock with total brake failure about a week ago...

Right through the reds ? Does this mean the ATO programmer will get tested for drink and drugs ?

I can't remember if this was one of the runs I programmed. They've not come to test me yet!

Its 12 years since I looked at a D stock schematic , however, from what I recall the symptoms are plausible

Either way , its not a total loss of brakes as the Emergency can still be applied by at least 8 different ways in the cab.

Can I presume the trains aren't fitted with something similar to a BROMS brake on a bus? They work in a way that if the air pressure is too low, the main brakes kick in and won't allow movement until pressure has built again and the BROMS brake is released.

Exactly how it works on buses, so I presume the same would be installed on trains as a fail-safe, making total loss of brakes impossible.

No, they are , this is a fundamental Safe braking practice and is required by RSPG part 2F. For older trains with ECEB this has typically been achieved by a pressure switch , in the case of D stock this is one of the three tripcock pressure switches. For the older trains this was achieved by a balancing pressures in an auxiliary reservoir.

For Newer metro trains such as S stock and 09TS with EP 2002 brakes , things get more interesting, this is a so called mechatronic smart braking system. The system controls WSP on a bogie basis and can monitor the pressure in a separate Brake Supply Reservoir for each bogie. All of the control units are connected by a CAN bus and the system can redistribute effort and decide what to do in the event of failures of the system, the electronics is really in control. The Emergency is still hardwired and works on the energise to release principle.

The "broms" brake, broms is the Swedish word for brakes! Fitted to Volvos, Scanias and the like, it;s the same as the sping loaded parking brake on other buses; a spring loaded parking brake is released by sufficient air pressure being available.

Modern trains have a similar system with a spring-loaded parking brake, first fitted to the 508/313/455 etc. I'm not familiar with later systems so can't comment. On the older stock, it was, as norbitonflyer says, a system of balancing either air or vacuum. In either system, loss of air or vacuum causes the brakes to apply.

On the old Westinghouse air brakes, it is possible to lose the brake if the driver makes more than 3 applications in quick succession, so this brake took some skill on the driver's part. The vaccum brake was unlikely to run out of vacuum (on a steam loco); on a diesel or electric loco, the exhauster could fail, but very unlikely. In either event, admission of atmospheric ait into the vac cylinder would cause the brakes to apply. Vacuum holds the brake off!

We also had handbrakes on old stock, could be useful as a last-ditch attempt, but only at low speed.

Having said all that, there was an instance on a heritage railway recently where there was a mechanical failure of the vac brake on one coach when the brake rodding broke. The train stopped quite safely, defective coach taken out of service, train continued!

That doesn't alter the fact that on a slippery rail, a common occurence at this time of year, trains sometimes don't stop where the driver or the computer wants it to! Leaves on the line and all that.

Presumably on the latest stock, if you shut the unit down, remove control key etc. the thing ought to stop somehow, hopefully before it finds the immovable object.

I don't have the same qualifications as singaporesam, but am a member of the Institute of Road Transport Engineers and the Society of Engineers, and an end user of the above mentioned products!! It's a pity the designers don't consult the end users when the product is being designed.

I'd have thought a total brake failure is a millions to one chance; whereas a brake malfunction i.e. spurious WSP activity as it came to be known is far more common!!

The nearest I've heard of total brake failure was on the ECML in Deltic days. I'd helped prep a loco for a train; approaching Darlington the driver applied the brake, nothing. Loco brake was ok. To cut a long story short, the train went through the paltform as some excess speed, knocked a DMU out of the way that was leaving the northern bay platform, and ended up heading toward Bishop Auckland.

The inquiry found an object had caused a brake cock between the loco and the first coach to be isolated, hence loco brake only! Not my fault guv. The brake test at KX was ok.