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Steam brakes

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Peter Simpson 102/03/2021 10:07:30
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199 forum posts
9 photos

Hi guy's, this might sound a stupid question. At the moment I'm fabricating the brake parts for my Don Young's BR standard 2 loco. I have made the brake cylinder and majority of other parts. As the diagrams are not obvious. Is steam applied to the cylinder to put the brakes on, or does the return spring keep the brakes on, and the steam release the brakes ?

Nigel Bennett02/03/2021 10:56:06
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395 forum posts
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Steam is applied to the brake cylinder to put the brakes on. No steam = no steam brake. It would be a bit of a pain if the brakes were on with no steam, as you couldn't push the loco along the steaming bays when loading and unloading it from the car!

You need to have a suitable valve fitted so that when you release the steam brake, the exhaust can go somewhere.

Peter Simpson 102/03/2021 11:08:14
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199 forum posts
9 photos

Thanks Nigel, I thought that would be the case, but as I say the plans do not make that area of the loco obvious, just like the total lack of info for the operation of the cylinder drain cocks.

Nigel Graham 205/03/2021 22:48:13
1275 forum posts
17 photos

The inlet and exhaust valves are operated by a single control, which has certainly two and probably three, settings:

ON - the obvious. It sends steam to the brake cylinder to apply the brake.

OFF - closes the steam supply and opens the cylinder to exhaust to the return-spring can pull the brake off.

The third if it is given on your loco's design (as one would hope), is;

LAP - the running position. It trickles steam through the brake cylinder to keep that warm so when the brake is applied, the steam does its stuff and is not just condensed in the cylinder.

I don't know your loco's particular design, but there should be a self-acting valve on the brake cylinder itself to aid the brake coming OFF, and to clear residual steam and condensate. This is closed by the steam pressure when the brake is ON, but opens by, e.g., a light spring, when the brake is off.

On some designs the steam-brake is also linked to the parking hand-brake.

'

What in particular puzzles you about the drain-cocks?

They look more involved than they are thanks to the links that allow all to be worked by one lever, but the main point is that they are all shut or all open fully and together, and that does entail careful fitting so their spindles are all aligned and turn correctly.

The operating lever has only two positions - closed or open.

On miniature locos the drain-cocks are sometimes left to blow down onto the track but for a proper job, as in full-size, they are fitted with pipes that discharge the steam and water horizontally ahead. Just mind bystanders' feet!

In use, they should be open on first starting away with cold cylinders, because a goodly amount of the steam is condensed there and that water has to be removed, not left in the hope of it being ejected from the chimney. On a miniature engine that may only give the driver and passengers an unpleasant shower of hot, oily water but in full size, water trapped in a cylinder can cause very expensive damage to the locomotive. The drain-cocks can normally be closed after quite a short distance - they do after all, waste steam.

The Golden Rule - applying to steam road-vehicles too - is that an engine in steam is parked in mid-gear, regulator closed, brakes on, and drain-cocks open.

Leave the drains open when storing the loco too, with something suitable to catch the oily condensate that almost invariably drips out.

Peter Simpson 106/03/2021 08:03:34
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199 forum posts
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Hi Nigel I have made and fitted the drain cocks, The plans omit all of the details of the valves the method of operation the route of any cable, where the operating lever sits within the cab. I have tried bicycle cable in the past but think a solid rod running in a tube is the best method. I will just have to design a route for the tube.

Nigel Graham 206/03/2021 12:40:48
1275 forum posts
17 photos

Hmmm. I wonder what other details are missing elsewhere?

Anyone else here familiar with the Standard Class layout, and Don Young's interpretation of it?

I don't know the Standard Class 2's specific layout, but the model version should follow full-size practice as far as possible; with some compromises and simplifying necessary for function.

I am surprised that the drain-cock details are missing from the plans. With great respect, have you searched all the drawings carefully? Model-engineering draughts-people tend to scatter small parts around the plan sets to confuse us - a club project within my own society was delayed for a considerable time by a single dimension error compounded by this scattering across many drawings.

So...

By the official BR locomotive driver's manual, the driving controls on the Standard Class are on the left hand side (looking forwards), and the drain--cock lever is low down, close to the cab side, aft of the big structure that holds the reverser hand-wheel.

'

Whatever BR did in detail with the Std Class 2, replicating full-size practice as faithfully as possible means leaving rods-in-tubes and Bowden cables to battery-electric and i.c. loco controls, where they are entirely appropriate.

The drain-cocks on each cylinder are simple plug-cocks, 90º rotation; set with their "handles" pointing downwards, moving 45º either side of vertical.

Their handles are linked by steel bars of mainly rectangular section with the pivot-pins through the thickness not width (for rigidity); one bar linking the drain-cock pair on each cylinder.

This link in turn is connected to its opposite number by a cross-bar, typically in the centre of the links or at their rear end - depending on the individual engine.

The cross-bar is also jointed at the end corresponding to the control layout, to a reach-rod. This is a bar that may be of similar form to the links but possibly a bit beefier and again with its pins through the thickness for rigidity; or it may be of circular section and fitted with clevises.

That reach-rod goes back, sited to clear things like the reverser reach-rod, and might pass through a slot in the spectacle-plate, to its pivot on the lever in the cab. It is usually quite discreetly located, and on some miniature engines (as I don't know your specific design) is under the running-board with the lever working through a slot in the footplate.

As above, the operating-level is low down, close to the cab side-sheet, pivoting on a bracket attached to the footplate, reverser stand, cab side-sheet or other rigid part of the structure. It moves in a plain parallel to the cab side; and the whole mechanism is often set so you pull the lever back to open the drains.

A pair of suitably-arranged stop-pins or a simple quadrant will prevent over-travel of the lever, which would not affect the valves themselves but could risk jamming and perhaps bending the link-work.

'

"...mainly rectangular section"... For neatness rectangular-section links are commonly shaped a bit like the coupling-rods: the areas around the pins being part-circular of diameter a trifle over that of the pivot-pin heads, and wider than the bar in between.

Edited By Nigel Graham 2 on 06/03/2021 12:43:15

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