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Author Power of Beam Engines
spitfire

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Power of Beam Engines
Posted: 16/02/2009 23:01:41
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The hardwood friction straps you mentioned were known as scoggans. The ones I remember were bound in leather about the same thickness as a razor strap and there was always a couple of spares in the engine house.

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spitfire
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Peter Burgess

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Location: Merstham. Or is it Godstone ...... ?

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Power of Beam Engines
Posted: 16/02/2009 23:21:21
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Getting a little off-topic, but have a look round YouTube for recordings of the Kew engines. Search for Kew Bridge engines.

[web link]

Some of them have good footage of the engines being started. Good stuff.




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Hey, who turned out the lights!
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Morlock

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Power of Beam Engines
Posted: 16/02/2009 23:41:56
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Engine details, note that the vacuum force is greater than the steam force on the piston, if I've done the sums right!
I think a lot of the poor starting is down to failure to establish the vacuum, poor valves etc.



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Morlock

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Power of Beam Engines
Posted: 16/02/2009 23:45:04
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Peter Burgess wrote:

Getting a little off-topic, but have a look round YouTube for recordings of the Kew engines. Search for Kew Bridge engines.

[web link]

Some of them have good footage of the engines being started. Good stuff.




Excellent link.
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spitfire

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Posted: 17/02/2009 14:06:36
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I'm sorry to labour a point but I still think a condenser has no bearing as to the power of an engine, only its efficiency.
Let us assume we have a 80" engine standing at rest coupled to 300 fathoms of pitwork, all of this has to be put into motion. Therefore only steam pressure can be taken into account as there will be no vacuum. An engine pumping from this depth will not become solid for about fifteen to twenty minutes. When vacuum is established the engine will work automatic not with increased power but far more economically.

It is the same as two identical steam boilers working at say 100psi one boiler is lagged the other is not. Both boilers will achieve the same end result but the lagged one will accomplish the task with far less coal consumption, and that is the duty of the condenser.

I admit the equation I posted was a simplistic one and that far more other factors have to be taken into consideration before a final figure can be achieved, friction for one.

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Morlock

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Posted: 17/02/2009 15:08:15
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I believe the efficiency gain is due to the lack of cylinder cooling by the earlier jet type condensers, the passage below gives a clear indication that the later engines were still steam assisted atmospheric engines.
I assume (perhaps incorrectly) that the starting issues are caused by the initial difficulty of establishing a vacuum with short steam strokes due to short strokes associated with expansive working?
In short both types had condensers but the the separate surface condenser improved the efficiency.

"A Scottish instrument maker, James Watt, was given the job in 1763 of repairing a model Newcomen engine for the University of Glasgow, and noted how inefficient it was. In 1765, while wandering across Glasgow Green he conceived the idea of a separate condensing chamber for the steam engine. Watt's idea was to separate the condensation system from the cylinder, injecting the cooling water spray in a second cylinder, connected to the main one. When the piston had reached the top of the cylinder, the inlet valve was closed and the valve controlling the passage to the condenser was opened. External atmospheric pressure would then push the piston towards the condenser. Thus the condenser could be kept cold and under less than atmospheric pressure, while the cylinder remained hot.

Watt also realised that the new operating cycle might increase engine speed and the power produced; low pressure steam could now be substituted for atmospheric pressure. If the top of the cylinder was closed off, the steam could act upon the piston during the power stroke; the low steam pressure would not be sufficient to move it in normal circumstances, but it could if acting upon a vacuum."

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spitfire

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Posted: 17/02/2009 16:57:47
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Now we're getting there. A Watt engine used steam at little more than atmospheric pressure, so yes the condenser would help but even so would have to be worked by hand at full stroke until vacuum could be established.
What I was talking about was the Cornish Engine which used steam at a higher pressure i.e. 40psi and the final development which was 150 psi.
When Watt speaks of an increase of power, that is in comparison with an atmospheric engine and of course he is right.
To work out the power of a Cornish Engine as to a Watt Engine the condenser must be ignored

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mappakernwick

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Posted: 17/02/2009 17:37:25
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Thanks for this, coupled with the rest of the information on this thread I should have enoughto have a go at working out some "ball park" figures.

Howeve,r before I get number crunching could you conform what the all units are in?
Thanks
John
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royfellows

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Power of Beam Engines
Posted: 17/02/2009 17:40:27
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I am following this with interest.
Mr Spitfire, I don’t understand what you mean by "the condenser must be ignored" What I am postulating is that the vacuum created below the piston must offer something in the way of additional power.
Obviously, when the equilibrium valve opens, the steam allowed below the piston is 'spent', in the same way that the early atmospheric engines ran at a virtually zero steam pressure, the steam merely being used to expel the air from the cylinder and when abruptly cooled, produce a vacuum. The job of the condenser is what it says on the tin, to condense this spent steam back to water and in so doing create that vacuum.

I would however, readily admit that any additional benefit from this in the way of power being produced must be minimal.

I apologise if I am making this a 3 way argument.


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'There's a lot of activity for a disused mine!' - Bond in 'A view to a kill'
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Morlock

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Posted: 17/02/2009 17:44:06
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I agree that an early Newcomen engine would not produce any power minus a condenser, a later 40 PSI Watt engine would derive 25% of its power from the condenser vacuum (at 26 inches HG) and at 150 PSI a modern engine would gain 8-9% at the same vacuum.
Difficult figures to ignore when rating an engine for power.
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spitfire

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Posted: 17/02/2009 18:02:12
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I'm sorry if I'm not making myself clear.
When a beam engine is starting from cold there is and cannot be a vacuum. That is why it must be worked by hand until vacuum is established, after that has been done it enables the engine to perform the same task but taking less steam, in other words getting more for less.

The both of you are getting duty confused with power, with duty, yes the condenser plays a major role but not with power.
It is no different than saying if a railway loco' were fitted with a condenser it would pull extra coaches

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spitfire
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royfellows

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Posted: 17/02/2009 18:17:40
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Thinking about this a little further, let us for the sake of argument take the equilibrium valve, condenser, and whole shooting match out of the equation, and see what would happen.
There has to be a point at which the steam under high pressure is shut off, before the piston reaches the bottom of its travel. Otherwise, smash!
And logically, the expansive power of the steam must then decline.
This can be reduced by keeping the cylinder hot of course, the reason for the lagging.
However, from the point that the high pressure steam is shut off, there will be an increasing reduction in power.
Basically, a proportion of the stoke piston stroke achieving nothing, and the impossibility of the engine in way becoming self acting.

From this emanates the logical way forward of utilising the spent steam to create a vacuum and cause the completion of the stoke under atmospheric pressure.
14.69 psi (pressure above vacuum) <> 40 psi (pressure above atmosphere)

I bet that it would be possible to produce a graph of this, power against piston stroke, and I would bet that this would answer a lot of people’s questions.


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'There's a lot of activity for a disused mine!' - Bond in 'A view to a kill'
IP: 78.150.35.187 Edited: 17/02/2009 18:19:15 by royfellows
spitfire

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Posted: 17/02/2009 18:59:06
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I can't see what you're driving at there, of course there has to be a point where steam is shut off that applies to any steam engine!
Also Mr Morloc states in a previous post that an engine would not move withgout a vacuum, how do you think a vacuum is created in the first place?

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spitfire
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royfellows

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Posted: 17/02/2009 19:27:57
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spitfire wrote:

I can't see what you're driving at there, of course there has to be a point where steam is shut off that applies to any steam engine!
Also Mr Morloc states in a previous post that an engine would not move withgout a vacuum, how do you think a vacuum is created in the first place?


I cannot speak for someone else but maybe he means become self acting, sorry but rather obvious I think. His poor choice of words maybe, I can do the same.

EDIT
I have to agree with a lot of what has been said by others, I think that the differences of opinion may well stem from different individual perceptions. I am confident that we are all familiar with the mechanics, I have learned something new from the postings.

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'There's a lot of activity for a disused mine!' - Bond in 'A view to a kill'
IP: 78.150.35.187 Edited: 17/02/2009 19:31:36 by royfellows
Morlock

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Posted: 17/02/2009 19:44:20
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OK, on firm ground, a steam loco would gain power with the addition of a condenser as the steam pressure acting on the piston would effecively be increased by up to 14.7 PSI.

Not so sure about the next bit as it was explained to me by a pump engine driver a long time ago.
Anyway I got the impression the manual operation of the valve gear by the engineman was to manipulate steam to a position below the piston through the inlet, equilibrium and exhaust vales to the condenser to provide the initial starting vacuum.
Once this condition had been established the engine could be locked into auto.

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spitfire

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Posted: 17/02/2009 19:46:54
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Lets go back to your theory about taking out the equilibrium valve. This would turn it into a simple steam engine with the exhaust steam going to atmosphere. The return stroke would be still made by the weight of the rods so it would still be self acting as the scoggan would hit the tappet on the way up

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ICLOK

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Posted: 17/02/2009 20:20:09
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As a steam locomotive enthusiast I thought I would just add the following, the likes of Andre Chapeleon, Stanier, De Caso, Ivatt, Gresley etc never found the need for condensing on steam locomotives as any benefits in thermal gains were lost. Hence the only condensing on steam locomotives was for efficious recovery of water and extending range in application were water was limited such as tunnels, deserts. Condensing on steam locomotives within the power cycle was found not to increase power output but actually reduced it significantly due to losses in the piping. Any potential improvement in thermal efficiency from including the condenser in the power cycle cannot be realised given the space constraints of a typical locomotive even on the continent where greater space was available.

It was looked at repeatedly I believe by Chapeleon.

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IP: 78.145.222.119 Edited: 17/02/2009 20:22:40 by ICLOK
royfellows

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Posted: 17/02/2009 20:26:38
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I know nothing about steam locos, so please advise. I understand that there is a cylinder each side of the loco.
Are they acting together or alternately?

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'There's a lot of activity for a disused mine!' - Bond in 'A view to a kill'
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spitfire

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Posted: 17/02/2009 20:34:52
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All I have to say is THANK GOD AND ICLOCK

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spitfire
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Morlock

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Power of Beam Engines
Posted: 17/02/2009 20:45:53
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spitfire wrote:

All I have to say is THANK GOD AND ICLOCK

Yes, he sums it up as regards locomotives, not enough space or a suitable heat sink.
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