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.
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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.
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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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