Discussions

[derekmorton]

Gents,

The previous discussion was an attempt to show that people here do not understand Westinghouse brakes.
The issue comes up because of a crash, but was and is not an attempt to lay blame.

Westinghouse brakes rely on stored air in cylinders.
These cylinders have seals, seals are not perfect and leak over time.

This is the reason that handbrakes are always applied when trains are parked, Westinghouse brakes cannot be relied on after an hour or so.

Some people think that you have to apply air to get the brakes off, this is not the case.

http://www.smex.net.au/Reference/AutoAir02.php

This diagram shows a 2 way valve that removes all air from a car so it can be "loose shunted/switched"
When the car has all air removed it can be moved by an engine without hoses connected but has NO brakes.

As an ancient switchman I used this 2 way valve every day in my job.

[CRQ5508]

I learned something from it, admittedly as one of those people who didn't fully understand how the air brake system works. I understood the basics of it, but not to that extent, so, thank you for the link(s).

[MCDemuth]

The previous discussion was an attempt to show that people here do not understand Westinghouse brakes.
The issue comes up because of a crash, but was and is not an attempt to lay blame.

Yeah, I don't understand why it was locked.

Westinghouse brakes cannot be relied on after an hour or so.

The 30 year old space shuttles could stay in the vacuum of space for days, even weeks, with out losing air, and that included the seals around the cabin windows...& what about the space stations that have been up there for years?

And yet the best technology human kind has been able to create, improved upon, expanded, ETC for the railroad, a mode of transportation that has been around for over 150 years, is one that will only allow for a train to maintain brake pressure for just one hour???

This is way to disturbing to hear!

If one hour is the best we can do, Somewhere in most manuals, there has to be some notation noting this.

I find that way just way to difficult to believe! The best train braking systems in the world can not be this fragile.





More information about how railroad brakes work may be found here:

https://en.wikipedia.org/wiki/Railway_air_brake

[derekmorton]

Space shuttles are maintained far better than railway cars.
Space shuttles are not reliant on pistons in cylinders.

Why do you think ALL railways have regulations about handbrakes?

[slipperman]

Hi Derek,
Many thanks for the information on air brakes; it's been most enlightening! Like many others, I'd considered modern brakes as fail-safe, period. I'd never even studied how they worked, but now understand why they can never be used as a long term brake and why hand brakes are so important.

Cheers,
Ged

[E444.005]

I have a question:
In the lapped position of the control valve (that, I finally understand, in effect allows for different pressure in the cylinder and in the reservoir , thus allowing brake gradualilty) does the auxiliary reservoir charge in any way?

Thank you

Fabio

[markus1996]

May I add, that according to the description of of the figure derekmorton provided a link to, this is just a Close representation of how a real westinghouse System works. The Major difference between the mentioned figure and the real Thing, is the triple valve.

So, according to www.railway-technical.com, the figures should look like this:



Click Picture to get to the Viewer, and then click it again to view it as a separate page. For full size, then click it one more time (Internet Explorer)

According to what Al Krug tells at railway-technical.com, there´s no Advantage in keeping break pipe pressure constant, as this pressure is in no way linked to the brale cylinder when the brakes are applied. Prove me wrong, that´s just what I read out of this article.

Yours, markus

[derekmorton]

I have a question:
In the lapped position of the control valve (that, I finally understand, in effect allows for different pressure in the cylinder and in the reservoir , thus allowing brake gradualilty) does the auxiliary reservoir charge in any way?

Thank you

Fabio

Hi Fabio,

Single pipe system
When the brake is lapped, I expect that the brake pipe pressure is less than normal, in which case the Aux reservoir is at a higher pressure than the brake pipe, so not charging.

[E444.005]

Thank you Derek, so if I understand well, no matter if have an active locomotive or not coupled with the train if this remains "lapped".
I'm asking because I'm a bit more used with a design like this



Where:

SA= auxiliary reservoir, SC= "command (reference?) reservoir, CG brake pipe
Posizione di marcia= running / brake relased, Posizione di frenatura = appling brake, posizione neutra di frenatura= lapped position.
In this, one pipe, design the auxiliary reservoir is not use for brake pipe reference, so, if I understand well, it can be manteined at a pressure egual or higher of the pipe.

[derekmorton]

Hi Fabio,

http://ptv.vic.gov.au/assets/PTV/PTV%20docs/VRIOGS/Vol-1-Section-1-Part-A.pdf

Shows a simple picture of a wagon brake system.
As you may see, any loss of air from the brake pipe, will move the triple valve slide and allow the auxiliary reservoir to apply the brake.

ps: The auxiliary reservoir cannot be higher that the brake pipe else it will move the triple valve and apply the brake.

[E444.005]

Thanks again!

"ps: The auxiliary reservoir cannot be higher that the brake pipe else it will move the triple valve and apply the brake. "

I agree with triple valves, but with the "distributor" shown in the picture? Note that there are two reservoirs: one for pressure reference and one for air acuumulation.

[rdamurphy]

Another "must read" article on air brakes...

http://www.railway-technical.com/brake2.shtml

Robert

[Keystoneaholic]

Great link, Robert. That even made complete sense to me!

Thanks.

Rob.

[ragtimer]

I posted that link on the original thread.First thing I said was "read Al Krug's article on air brakes" or similar words.Whatever air brake system you are using,unless handbrakes are applied if the air supply to the train is cut by whatever reason,eventually the train brakes will leak off.

[Vince]

I posted that link on the original thread.First thing I said was "read Al Krug's article on air brakes" or similar words.Whatever air brake system you are using,unless handbrakes are applied if the air supply to the train is cut by whatever reason,eventually the train brakes will leak off.

Sorry but that turns out not to be the case;
All The brakes will eventually leak off, bleed down and release even if the engine is connected and running. Why?
Because the air tanks and brake cylinders on the cars are NOT recharged with the brakes applied.

Please remember that brakes are APPLIED by a train air line REDUCTION, NOT pressurized as some folks here are thinking. And a 'reduced pressure' air line simply cannot keep the brakes applied.

The brakes are held applied only as long as there is pressure in each cars air tank, the same tank that is recharged when the brakes are released and the train air line is pressurized. Do not confuse this car air resevour tank with the cars brake CYLINDERS! They apply mechanical force through the brake rigging/shoes only as long as there is sufficient pressure in the cars air resevour.

Remember that the train line is emptied when brakes are fully applied and you can't recharge anything to keep brakes applied from an empty air line.
As soon as the brake cylinders leak off over some amount of time, then no brakes.

That's why it's against the operating rules on every railroad to park a train with air only.

The single train line air pipe has TWO purposes it does in life:
1. APPLIES train brakes (by triggering the triple valve in each car) when air is RELEASED from the air line.
and
2. RECHARGES the train cars air resevours to RELEASE the train cars brakes.

The above applies to a SINGLE PIPE (Westinghouse) air brake system only! Used on US freight.
Twin pipe air found on passenger equipment operate differently, a completely different system. Don't confuse the two types.

Enjoy!