HST Brakes

TrainBotherer · 26 May 2018

Evening all,

Why does the brake controller need to be in emergency to allow the system to charge the main res?

Thank you

RailUK Forums

Kneedown · 27 May 2018

TrainBotherer said:
Evening all,

Why does the brake controller need to be in emergency to allow the system to charge the main res?

Thank you

At my depot we never have to start them from cold, but as far as I am aware it doesn't have to be?
The compressors are continually running from engine start, and so constantly charging the main res. If you were to energise the cab with the parking brake applied that would result in air loss, but we have a switch to prevent that.
It is important however, (with parking brake applied obviously) when joining a set that has been stood for some time, to place the brake controller to the running (release) position for a period of not less than 5 minutes. This is to ensure that the distributors are fully charged with sufficient air to supply the brake cylinders.

TractiveEffort · 27 May 2018

The right answer is it doesn’t. But, if it’s having air issues putting the brake into emergency stops the brakes ‘lapping’ and using MR to do so, as well as keeping up BP pressure due to air loss via leaks. Also if starting up from being stood a while, it lets the MR build first, before charging the brake system.

Kneedown · 27 May 2018

TractiveEffort said:
Also if starting up from being stood a while, it lets the MR build first, before charging the brake system.

We just use the brake test switch to prevent air loss via the applied parking brake.

TractiveEffort · 27 May 2018

The brake test switch has no effect on the service brake system, which is what consumes the most air. All the brake test switch does is put a feed on the park brake ep valve, to close it, as well as having contact in the circuit to PCR to prevent taking power with the park brake on.

Kneedown · 27 May 2018

TractiveEffort said:
The brake test switch has no effect on the service brake system, which is what consumes the most air. All the brake test switch does is put a feed on the park brake ep valve, to close it, as well as having contact in the circuit to PCR to prevent taking power with the park brake on.

Yep. But unless you operate it, once you put your key in with the parking brake applied you'll soon lose your main air via the ep valve, is what i'm getting at.

smiffy9373 · 27 May 2018

You don't have to, but by placing the brake into emergency you are only charging the main res. Any other position you will be charging the main res and the brake pipe so it takes longer.
Should there be a problem with the brake pipe you will have 7+ bar of air escaping through the leak making it easier to find a problem when you try and charge the brake pipe.
If you try charging the main res not in emergency the compressors will feed a leak in the brake pipe directly at a much lower pressure making it very difficult to hear where the leak is.

Kneedown · 27 May 2018

I can certainly see the logic there as a fault finding technique. It's not something we currently train Drivers to do as a matter of course during start up and prep though.

SPADTrap · 28 May 2018

smiffy9373 said:
You don't have to, but by placing the brake into emergency you are only charging the main res. Any other position you will be charging the main res and the brake pipe so it takes longer.
Should there be a problem with the brake pipe you will have 7+ bar of air escaping through the leak making it easier to find a problem when you try and charge the brake pipe.
If you try charging the main res not in emergency the compressors will feed a leak in the brake pipe directly at a much lower pressure making it very difficult to hear where the leak is.

This is what I was taught when I learned HST recently. They're an amazing train!

TractiveEffort · 28 May 2018

smiffy9373 said:
You don't have to, but by placing the brake into emergency you are only charging the main res. Any other position you will be charging the main res and the brake pipe so it takes longer.
Should there be a problem with the brake pipe you will have 7+ bar of air escaping through the leak making it easier to find a problem when you try and charge the brake pipe.
If you try charging the main res not in emergency the compressors will feed a leak in the brake pipe directly at a much lower pressure making it very difficult to hear where the leak is.

You’ll never have more than 5.2 bar in the brake pipe (overcharge is blanked off on HST), so whoever told you you could have 7+bar escaping from the BP is wrong.

SPADTrap · 28 May 2018

TractiveEffort said:
You’ll never have more than 5.2 bar in the brake pipe (overcharge is blanked off on HST), so whoever told you you could have 7+bar escaping from the BP is wrong.

Probably a typo. I read 5.2 when I read the OP.

Kneedown · 28 May 2018

TractiveEffort said:
You’ll never have more than 5.2 bar in the brake pipe (overcharge is blanked off on HST), so whoever told you you could have 7+bar escaping from the BP is wrong.

I think what Smiffy was getting at, was if there was a leak in the brake pipe, then the more chance of hearing and locating it with full main res pressure, than with depleted tanks. That's how I read it anyway.

TractiveEffort · 29 May 2018

Kneedown said:
I think what Smiffy was getting at, was if there was a leak in the brake pipe, then the more chance of hearing and locating it with full main res pressure, than with depleted tanks. That's how I read it anyway.

The brake supply is a protected supply, whilst it is fed from the MR, the MR pressure is irrelevant in determining BP leaks.

Kneedown · 29 May 2018

TractiveEffort said:
The brake supply is a protected supply, whilst it is fed from the MR, the MR pressure is irrelevant in determining BP leaks.

But surely, if a brake pipe leak occurs while travelling along with the brake controller in "Run", the E70 will attempt to charge the brake pipe until the LOMAG operates and applies the brake fully? Therefore, the more main air available, the more time available to pinpoint a leak before the LOMAG intervenes?
My procedure would be brake controller to full service and PB on while attempting to ID leak. If I couldn't find it before LOMAG intervened i'd build up the main res supply again and pick up the ID where I left off.

Bornin1980s · 30 May 2018

Another question; I've heard that the HSTs had the first digitally controlled brakes on a British train. Do they still use the original circuits?

hexagon789 · 30 May 2018

Bornin1980s said:
Another question; I've heard that the HSTs had the first digitally controlled brakes on a British train. Do they still use the original circuits?

They have a standard UIC twin-pipe aura brake. This is supplanted by an E70 brake unit in each power car. When the driver makes a brake application an electric signal is sent from the driver's brake controller to the E70 brake unit in the rear power car with the result the brakes apply from both ends of the train more or less simultaneously.

The InterCity 225s and Mk3 DVTs also have these units. This system is not like modern Electro-Pneumatic systems as the coaching stock is not fitted and the system does not release the brakes from both ends only applies them.

HST Brakes

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