Air Brakes - What Goes Where?

[D869]

This may be a dim question but I've spent a long time building models of vacuum braked wagons and none at all doing air braked vehicles.

I don't have a good understanding of how the various components of an air braked wagon fit together so I thought I'd try to figure it out. The snag is (of course) that this stuff is usually buried in shadows. Drawings are of some help but the usual side elevation of a wagon collapses everything into two dimensions.

The diagram below is my best guess at the arrangement for a Charles Roberts ferry tank of mid-1960s vintage (Bromine in this case). This is based partly on a GA drawing, partly on photos and partly on bits and pieces of other wagons that I've used to fill the gaps.

The bits that are not clear on the drawings are the cranks that run horizontally across the wagon chassis, the lateral position of the various cranks on the main cross shaft, plus anything that is obscured by something in front of it and finally of course... how the whole lot fits together.

The moving parts are in red. The brake levers are not shown and I've also left off the (clasp) brake shoes and yokes. The extra crank on the cross shaft connects via a linkage (not shown) to the brake standard on the end platform.



So am I barking up the wrong tree or is this anywhere near close?

Have I missed an obvious source of info that will provide a nice picture showing how this stuff goes together?

Some questions...

1. I think that the actuating cylinder is double ended but other vehicles have single ended ones. Is this plausible?
2. As far as I can see with my speculative layout, the handbrake only works on one axle. Is this plausible?
3. What is the long thin cylinder that looks a bit like a shock absorber? Does it really belong on the linkage to the furthest axle or should it be somewhere else? Why is it only shown at one end on the GA drawing?

 

It may be that my guess at the layout is completely wrong but hopefully someone can help me to make it right.

Regards, Andy

[The Bigbee Line]

Not a bad first stab.

 

The long thing is the slack adjuster (wagons without one have pinhole adjustment, look at all the holes in minfit brake gear.)

 

The cylinder will be single ended.

 

Joints will be pinned.

 

What is the wagon number?

 

I'm sure I can find some stuff to post that will help.

 

Good luck

[D869]

Ernie,

 

There's a photo of one here plus another in the same gallery.

 

http://www.rmweb.co.uk/community/index.php?/gallery/image/32505-tank-slide-84-12-29-749-0-001-bromine-dow-chemical/

 

I'm interested in them at an earlier stage when owned by Associated Octel. An example number from 1971 (in Dave Larkin's PO wagons book) is 21 70 078 5 244-5

 

BTW, Roberts also did Chlorine and Ethylene Dibromide tanks for Octel to a very similar design, just with bigger tanks. I suspect that the brake layout is not unique to the Octel vehicles, but I don't have details of other examples.

 

Regards, Andy

[jonhall]

This is a screw handbrake, but levers are similar.

 

J

[D869]

That's excellent thanks Jon. I think this is a very similar layout. The Roberts vehicle just has some extra 'V' hangers and cross shafts for lever handbrakes (as well as the screw handbrake on the end platform).

 

I'm thinking that the transverse lever has a fixed pivot mounted on the end of the cylinder.

 

And one slack adjuster does the job for the whole wagon?

 

I'll have a bash at re-jigging my drawing later on.

 

Regards, Andy

[The Bigbee Line]

Andy,

Try these, like Jons it is for a wagon without side handbrakes.

To work out what's happening, look for the pins and where the force of the brake cylinder will act.

Good luck

[D869]

Thanks Ernie.

 

I think between your drawings and Jon's I now have a pretty clear idea of how this stuff fits together.

 

... and now I have the answer in four languages.

 

Vielen Dank, Merci, Grazie.

[D869]

Here is the modified drawing. I've used blue for the tension spring.

 

Thanks again to Jon and Ernie.

[Adam]

Another thank you to all concerned; I can now indulge my detail fetish on my clayliner tank - I'm not used to AB wagons either... The basic underfeame, with detail variation, is common to just about every AB fitted 15' wb tank built from the mid-60s onwards (erroneous shorthand: TTA). You're planning on doing all that in 2mm? Wow. That Bromine tank looks an interesting prototype too.

 

Adam

[D869]

Hi Adam,

 

Normally I tend to stick to the bits that can be seen but in this case I will probably do an etch (with 3d prints for the lumpy bits) so I tend to feel more compelled to 'get it right' before paying money to get things produced. On a more positive note, using CAD to draw fiddly bits that 99% of people will never see seems less like hard work than cutting them out of metal or plastic.

 

Associated Octel traffic throws up several types of interesting vehicle and stories (e.g. most people are surprised to hear that there was a chemicals factory in the far west of Cornwall). Be careful though or you might get hooked

 

Regards, Andy

[Adam]

Hooked? To brake gear detail? Too late Andy, far, far too late.

 

EDIT: for evidence of this sad affliction: http://www.rmweb.co.uk/community/index.php?/topic/37002-adams-em-workbench-backwards-from-a-bda-to-bogie-bolster-d/

 

Adam

[D869]

I'm sure that there are other people who can provide more detail than me but my limited understanding (err... Wikipedia I think) is that BR chose the two pipe system for freight vehicles initially and that more recently this has fallen from favour. The buffer beam of the Roberts bromine tank had two air pipes from new in the late 1960s plus a vacuum pipe (which I think was just a through pipe because no vacuum cylinder is visible).

 

There were of course pre-nationalisation companies that used air brakes, so BR's decisions are not the 'dawn' of UK air braking but I have not looked back that far in time.

 

Regards, Andy

[Torr Giffard LSWR 1951-71]

Andy,

 

The Enginemen's Manual, a BR publication available from secondhand book dealers is excellent for informing enthusiasts of all manner of railway related subjects such as this.

 

Dave

[45125]

Its a distrubutor not a triple valve. The twin pipe system should allow a much faster response of the distrubutor as it does not have to charge the aux reservoir up. The propgation rate of the brake pipe is sped up as it does not have to do two jobs.

 

The resevoir pipe on some freight vehicles was removed simply to save money as someone though it was not need. Many newer wagons are twin pipe as trains get longer the faster brake response is required. 

 

Some of the trials with the longer trains on single pipe found that the brake was still hard on at the rear whilst more than half the train was released.

 

Al Taylor

[Fat Controller]

Twin-piped wagons dropped from favour when more and more ferry-vehicles, equipped with only a single pipe, started appearing in Speedlink services. Just one of these wagons, would be enough to render the twin-pipes useless, so the second pipe started to be removed from many of the BR fleet, and PO wagons used in air-braked mixed services. I have noted twin pipes on several recent types used in block trains- perhaps we are seeing a resurgence..

Speaking to some RfD drivers, they reckoned it could take between five and ten minutes to release the brakes on a long freight.

[Torr Giffard LSWR 1951-71]

...hence the flow meter gauge on class 60s...giving the driver a good idea of the rate of release of the brakes along the train and helping him not to damage the wagons by pulling against brakes still applied.

 

Dave