A couple of steam technical questions please

[Sassanid]

Hi again - I am well and truly getting sucked (pardon the pun) into the science of steam, but I have a couple of questions please.

What is cut off? Usually shown as a percentage.

What is the firebox crown and why did they sometimes collapse - usually killing someone on the footplate in the process?

How did the locomotives get water from "troughs"?

And finally please can someone recommend a good book that actually explains precisely how a steam train works? I am struggling with most of the technical terminology. It is like an alien language - and I have a HNC in Mechatronics which included a unit in hydraulics.

Many thanks in advance if anyone can help.

[Bullhead]

I can only answer the water trough one without referring to books. Water troughs, as their name implies, were very long troughs placed in the four-foot and kept filled with water from a lineside supply. I presume they were heated too, or the P.Way were employed on ice-breaking duties during winter.

As a train requiring to take water approached the troughs (whose presence was notified to the crew by a special sign - see http://www.railsigns.co.uk/sect25page1/sect25page1.html) the fireman would lower a scoop which fitted into the trough. The scoop was forward-facing, and the momentum of the train was such that it would force the water up the scoop. The water would then cascade down from a specially shaped dome into the tender tank. Hopefully the fireman would then raise the scoop from the trough before the train reached the end!

This picture (by me) shows the tender dome on an Ivatt 2MT 2-6-0 at Bridgnorth:



If you have a recent Bachmann LNER Pacific, look underneath the tender - you'll see the scoop modelled between the wheels.

This link takes you to an excellent shot of "Jeanie Deans" taking water from Bushey (LNWR) Troughs: http://www.scienceandsociety.co.uk/pr/9 ... 321459.jpg

The British Transport Film "The Elizabethan" (available on a DVD compilation of fantastically atmospheric films, also including A3 and D49 Fest "This is York") contains spectacular footplate and lineside footage of an A4 taking water from troughs. The fireman gets quite wet and anyone with the windows open in the first coach might well have, too. Interestingly, I believe that some of the early steam heat-equipped BR diesels (40s, Deltics) were fitted with water scoops.

For your other queries a quick reference to Wiki offered a couple of answers, though I don't know if these are detailed enough.

[Sassanid]

Thanks Bullhead - that is great.

I have just ordered "How Steam Locomotives Really Work" by A J GoldFinch so hopefully that will help on the technical front. I will check out Wiki though and another website I have just found -

http://ukhrail.uel.ac.uk/glossary/

Best,
Andrew

[Colombo]

Sassanid

You ask about the firebox crown.

The firebox of a conventional or Stevensonian locomotive is a steel or copper box inside the boiler with water on the outside and the fire inside. The front of the firebox is the tubeplate. So the firebox is surrounded by water. It is braced by stays which are rivetted inside the firebox and outside the boiler shell. If the stays corrode away, the firebox can collapse, and yes, the resulting boiler explosion can be fatal to the crew and anybody else near enough to be affected. There is a legal requirement for a thorough system of regular boiler inspections to ensure that this does not happen.

It is important that the top of the firebox is covered by water at all times to keep it relatively cool, as it will be damaged by the heat of the fire if it is not. As a "safety device" it is usual to fit fusible plugs into the top of the firebox. If the water level in the boiler falls and these become exposed, they melt due to the heat of the fire and the resulting in-rush of steam and water into the firebox will put out the fire and also scald the crew if they are in the cab. This preferable to a boiler explosion, but hardly a fail safe device in my opinion.

When locos are descending gradients facing downhill, the water in the boiler flows towards the front, and under these conditions the firebox can suddenly become exposed. It is therefore important that the fireman ensures that the water level in his gauges is high before descending a steep gradient. It is normal for locomotives operating steeply graded branch lines like the KWVR or the NYMR to face uphill to reduce the risk of this eventuality. This is just another of the fireman's many responsibilities and there is no fail safe device because you cannot switch a coal fire off.

Colombo

[CVR1865]

Sassanid

This leaves me with cut off. Put very simply it refers to the injection of steam into a cylinder. The higher the cut off say max 60% then steam is being injected into the cylinder for 60% of the stroke. Thus max cut off is used to pull away and then the cut off is reduced once you pick up speed. Or atleast that was how i was taught to drive steam engines.

In modern steam locomotives, LNER built for example the steam will be injected to compress and retard the piston, so the cut off is set, i believe, at a lower maximum than for an older type such as Rocket. Oh and you shouldn't coast in max cutoff very bad for the valve gear.

Simon

[Sassanid]

Those are excellent explantations. Thank you both for taking the time

[sirbrian]

Bullhead suggests that the fireman could pull the scoop out of a water trough when sufficient water had been taken. This was not the case in practice. Once the scoop had been lowered into the water in the trough it was impossible to lift it out. The scoop was held down by water pressure acting against the moving scoop until the locomotive had passed the end of the trough, at which point the scoop could be raised.

Locomotive crews knew by experience when to lower the scoop in proportion to the amount of water that was needed to fill the tender. Locomotive crews always preferred to fill the tender from the troughs rather than from the facilities at the stations because this took time. Frequently, sufficient time was not available at station stops, especially if running late. It was always policy to keep the tender as full as possible all the time, so often only a top-up was taken at each trough.

The action of picking up water from the trough gave a strong retarding effect to the locomotive, so full power was required and a high initial speed, such as 70 mph minimum. In consquence, the speed would drop by about 20 mph during the water pick-up operation.

There was never any problem with water freezing in the troughs. There was a steady stream of locomotives picking up water. The only problem with the trough system was that it took time to re-fill the trough after a locomotive had picked up water, so a locomotive crew could never be quite sure that water would be available at a particular trough. For this reason, locomotive crews always liked to keep the tender full for the entire trip, even right to the end of the trip.

Perhaps I should add that my comments given above are related mostly to many cab rides on LMS and BR Standard locomotives on the former London Midland Region. The technology was the same for other locomotives, so I do not think the practices would have been significantly different.

Sir Brian (30782)

[Bullhead]

The scoop was held down by water pressure acting against the moving scoop until the locomotive had passed the end of the trough, at which point the scoop could be raised.

How come the scoop didn't knock the end out of the trough, then? Was the trough tapered upwards towards the end somehow?

There was never any problem with water freezing in the troughs. There was a steady stream of locomotives picking up water.

Even at 03:00 on a Sunday morning in January?

[sirbrian]

This posting is in reply to the two comments from Bullhead regarding my posting on the subject of water troughs and their operation.

The first comment asked how the scoop did not knock out the end of the trough if the scoop was still down at the end of the trough. The trough had to be installed on a length of level track, and where there was a suitable source of water. The track leading in to the trough section at each end was slightly higher than the track in the majority of the trough section. So if the scoop had been lowered to pick up water before entering the trough section, the scoop would enter the water gradually during the slight descent. Similarly, at the end of the trough section, the scoop would be raised out of the water gradually as the train moved forwards through the slight ascent. With the scoop now out of the water, the control handle could then be turned to lift the scoop to the raised position.

The second comment concerned the operation of water troughs in sub-freezing weather. I am not sure about this one. To the best of my memory, I can not remember a time when the troughs were de-activated due to cold weather. This does not mean that it did not happen. The troughs were made of wood, which would be a good thermal insulator.

The New York Central Railroad in the USA used water troughs. The weather conditions on the Central lines in the American North-East are much more severe than in the UK. I have seen a photograph of a 'Niagara' picking up water from a trough when there was snow on the adjacent ground. It takes appreciable time for water to freeze, otherwise our rivers and lakes would freeze over more quickly than they actually do. I think the same reasoning applied to water troughs, especially in the UK, where temperatures rarely go significantly below the freezing point.

Essentially, if water is kept moving, it does not freeze, even when the ambient temperature is well below 32 F or 0 C. This may have been the technique used on the water troughs - fill at one end and allow a drain-off at the other end so that the water was kept moving along the trough.

Sir Brian

[Bullhead]

If water is kept moving, it does not freeze, even when the ambient temperature is well below 32 F or 0 C.

The Thames Ice Fair of 1683:

[x568wcn]

The River Ouse in York has frozen a couple of times before!

[Bullhead]

Can someone recommend a good book that actually explains precisely how a steam train works?

The former British Transport Commission published a "Handbook for Railway Steam Locomotive Enginemen", explaining pretty much every facet of the operation of steam locomotives including the different varieties of valve gear, etc., etc.

It's almost 200 pages long, well illustrated with coloured diagrams, and well worth looking in 2nd-hand bookshops/eBay for. The inside cover of my copy is stamped "Shed Master's Office - Eastfield - 15 Nov 1957".

[sirbrian]

'Sassanid' asks about a good book describing steam locomotives and their operation. My recommendation is:
"Steam Locomotives And Their Working", by Simpson and Roberts, 2 volumes, published 1952 by Virtue & Company, London, E.C.1.
This book contains 562 pages of excellent material. I have a copy myself, given as a twentyfirst birthday present. If you can find a copy today somewhere, it will answer most of your questions.
I believe there is a copy in the Institution of Mechanical Engineers Library. Whether the Institution would allow you to borrow their copy, assuming it is still there, is another matter. You can always try. Sometimes libraries will lend through other libraries, so you might try that route.

Sir Brian

[x568wcn]

The former British Transport Commission published a "Handbook for Railway Steam Locomotive Enginemen", explaining pretty much every facet of the operation of steam locomotives including the different varieties of valve gear, etc., etc.

It's almost 200 pages long, well illustrated with coloured diagrams, and well worth looking in 2nd-hand bookshops/eBay for. The inside cover of my copy is stamped "Shed Master's Office - Eastfield - 15 Nov 1957".

15th November? 22 years to the day before I was born!

anyway

there's several
http://search-desc.ebay.co.uk/search/se ... age=search

Looks a good book, but 1957 1st edition? 9 years before the end? They only had since 1948!

[Bullhead]

I hate to go on about this question of the difficulty of raising the water scoop, but I still reckon that the fireman would be expected to raise it before reaching the end of the trough . I have, in no particular order, three reasons for this:

I've re-watched the BTF "Elizabethan" film, with particular reference to what the fireman does when the A4 is taking water from a trough. As the tank fills (which seems to be indicated by the crude but effective means of a pipe with holes drilled in it at different points, which spout a fine jet of water when the tank reaches whatever level is indicated), the fireman - who doesn't look like Sylvester Stallone - spins what I presume to be the water scoop control handle round to raise it. The fact that he's being sprayed with water may have been an additional motivating factor, but I reckon that the gearing is also low enough to enable him to overcome whatever resistance the scoop is generating against the bow-wave in the trough.

I've also spoken to a colleague, a Track Maintenance Engineer by profession. He observes that if the water trough was mounted on the sleepers (as I believe was normal practice) raising the rail level would necessitate a deviation from this - such as longitudinal timbers, or packing underneath the baseplates - because if you raise the sleepers, the water trough will be raised with them. The effect of raising rail level relative to the sleepers on ride quality and stability, especially on a section of track with a moderate linespeed, would be questionable.

The LNWR Society at http://www.lnwrs.org.uk/Glossary/glossarywa.php says on the subject of water scoops, "It was essential that the crew raised the scoop before the end of the trough".