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A Guide to using Vacuum Brakes on Steam Engines

By Will Cook (aka nigelgresley), Copyright ©2002 - 19 May 2002

Please bear in mind that the following is intended to aid the operation of MSTS locos which operate on vacuum brakes, and therefore might not reflect real working practise.

Stopping Steam Engines is yet another art in itself and when I've seen firemen drive a steam loco for the first time, it's invariably what they've had most trouble with.

The brake handle in MSTS is rather cumbersome as it takes a lot of time to move it from 100% released to even 10% apply. What I find best for someone using vacuum brakes for the first time in the context of MSTS is to put the brake into 10 or 5% released.

Simply put, vacuum brakes use vacuum to keep the brakes off. When there is a vacuum throughout the continuous brake pipe that runs the length of the train then the brakes are released and you can move the train easily.

When fully released the brake gauge will show 21in. this gauge shows the amount of vacuum in the brake pipe.

You may be wondering how this vacuum is so easily created, well on the locomotive there is the small ejector, one end of which is attached to the brake pipe, the other end is attached to another long pipe which can be seen running along the side of the boiler to the smokebox.

The small ejector uses steam from the boiler to pass along the pipe into the smokebox and as the steam is moving quite fast it creates a vacuum behind it, this draws all the air from the brake pipe and creates the vacuum which releases the brakes.

The brake level normally has about 3 positions, released, running, apply. You will also see that the vacuum brake gauge in the cab has two sides to it, when the brakes are off (i.e. a vacuum in the brake pipe) both sides show 21in. However if you start to apply the brake you will see that the left hand needle will fall. The left hand needle indicates the amount of vacuum in the brake pipe so as you put the brakes on it falls. As for the three positions of the brakes handle, they do more or less what they say. Released takes off the brakes (creates vacuum), Apply puts them on (returns pressure to atmospheric) and Running holds the amount of vacuum in the brake pipe where it is.

Now on to the methods of actually stopping a train. Whilst running along, you will probably have your brake lever somewhere in the released position. If you want to stop at a station I would usually start braking about 1 mile from the station (speed and load dependant).

First I would move the brake out of the released position to 100% running, then I would very gradually move the brake into 1 or 2% apply, there is a tendency here for some people to gain an "all or nothing" syndrome and whack the brake into 100% apply, totally destroy the vacuum and stop the train rather faster than they had wanted. It is important to keep in mind that at no point during my braking for a station to I intend the brake gauge to read 0in, as this would be an emergency brake application. Normally I would watch the gauge go down to about 15in and then I'd move the brake lever into about 95% running, sometimes the brakes may start to come off (i.e. an increase in vacuum in the brake pipe) when the handle is in the running position, if this happens just put the handle into 1 or 2% apply and get the needle back to 15in again.

I would continually assess the rate at which my train was slowing down, the next step would usually be to get the needle down to 10in using the above of putting the lever into the apply position only about 1 or 2 %. I would continue to apply/decrease the amount of braking in order to stop where I want to - don't forget you can always take the brakes off totally and open the regulator a bit, for this purpose I always wind the cut-off into 75% forward as I begin the braking procedure, so that I don't have to open the regulator too much.

Braking is dependant on three variables:

Load: can affect your braking, i.e. it will be harder to stop with 350tons of coaches all going at 70mph behind you than 2 coaches doing 30mph.

Incline: The loco travels faster downhill, so more brakes may need to be applied in order to stop in the right place.

Speed: If you are going at 90mph it will be harder to stop than if you are going at 15mph, this is closely linked in with the load variable, as they both provide momentum behind the loco.

The key is to bear the above in mind when assessing how quickly you are going to stop.

Another key is to just 'dip' into the apply section of the brake by 1 or 2%,

as the more percentage the faster the brakes will go on and before you know where you are you are in an emergency brake application. It might not look good but it is often better to crawl into a station at 3 or 4 mph rather than overshoot it!

The assessment of the above variables will get better with experience and then you'll be able to stop the train on a two-pence piece!

Air brakes work opposite to vacuum brakes, i.e. they rely on pressurised air in the pipe to keep the brakes off, but again they rely on atmospheric pressure in the pipe when they are on. This is for the reason that if the train parts (eg. a non-planned decoupling), then the brake pipe will be separated also. Atmospheric pressure then will fill the pipe and put the brakes fully on. With air brakes the running position is usually called the lap position and they are also easier in operation though they are not very applicable to British steam. Air brakes were used extensively on continental and American steam locos, they are also used elsewhere in the world for steam.

The only default MSTS loco which operates on air brakes is the 380.

Compiled by

Will Cook 2002 (revdscook@btinternet.com)



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