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Post by joanlluch on Feb 1, 2015 23:03:18 GMT
The aim of the exercise was to measure the loss between the regulator and the cylinders. It appears that only about 40 psi gets to the cylinders, which is not really enough when climbing our bank with a half load So this means that in the case of this loco the regulator does not open fully, or it is too small, or that there are too much flow restrictions on the piping. Is this right?
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Feb 1, 2015 23:17:39 GMT
hi joan,
i presume simon had the regulator wide open but produced only approximately half the boiler pressure in the steam chests. some pressure drop is to be expected, and 'Wren's' cylinders are quite big and so forgiving of a drop in boiler pressure to still provide full power at the cylinders, but simon specifically states boiler pressure is at working pressure (or just below).
there is something wrong somewhere though measuring accurately steam chest pressure is somewhat problematic in miniature and a very accurate sensitive precision gauge is required (which those used by simon definitely are not - see my recent thread on FSD miniature pressure gauges).
a degree of 'wire drawing' at the regulator can be permitted, but the whole of the steam and exhaust circuit ought to be generous. it is clear from the pics that the external steam pipes are far too small - but what else isnt to the design? you are quite correct that other parts could also be inadequate in size.
i think with this loco things are a bit more complicated! if i had opened out the regulator wide open on the 'Wren' i used to drive at full boiler pressure the power in the cylinders would have been more than the adhesive weight could cope with and the wheels would have slipped madly with a decent load!
cheers, julian
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Post by ejparrott on Feb 2, 2015 11:02:10 GMT
I drive 2 Romulus fairly regularly, one coil sprung one leaf as original design - ditch the coils!! The leaf sprung one is a very steady engine, the coil however is a bucking bronco and can't be used at any kind of speed if you want it to stay on the rails. It's firebox failed last year, so while we're waiting for a new boiler we're now making leaf springs and modifying the chassis to take them!
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foote
Active Member
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Post by foote on Feb 2, 2015 12:06:50 GMT
I fully agree with Ed, my Wren had leaf springs and was absolutely fine. I think the steam pipes shown in the pics are the same size as mine were. Sold my Wren back in 2007, but my current loco has leaf springs and is fine too. The leaf springs provide damping that coil springs don't! Current project (7 1/4" Fiji Hudswell Clarke) will have leaf springs too!
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Post by joanlluch on Feb 2, 2015 17:21:26 GMT
No coil springs will provide any damping effect by themselves, but the stronger they are the shorter the oscillating period and the smaller the oscillating length, so if they are strong enough the "bouncing" effect is significantly reduced. I particularly disagree with the spring settings that I found on the Britannia plans, they are quite soft springs with a significant initial compression. I would change that by stronger springs with just the minimal initial compression to allow for half the required suspension movement.
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Post by simon822 on Oct 20, 2015 18:13:31 GMT
Ok, thought I would just update the thread a little.
1. After a season running I have now managed to pull 2 tons round the club track, which did make it sound quite good, but it is still not quite right. 2. The loco is now stripped, and new steam pipes are being made to the correct 3/8 od pipe. 3. New leaf springs are being made, this is where today's question starts.
The springs:
9 leaves of .048 thou by 1/2 inch spring steel as per the drawings. That is ok, my question is Ken Swan provides the profile for the top leaf, and a picture of the leaves under load of 60lbs. The spring seems quite firm, but not been heat treated yet and I am concerned that it will be too firm if all the leaves are made the profile of the top leaf.
Can anyone with experience of making these springs assist, the intention is to make firmer springs, but these seem very firm!
Thanks in advance,
Simon.
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Post by ejparrott on Oct 21, 2015 11:32:46 GMT
I'm afraid all I can do is point you in the direction of a calculator and the workshop practice series, not a lot of help I'm afraid. Given time I could sit down and work it out for you.
Don't whatever you do try the spring between hardening and tempering...it tends to result in a shower of leaves...just like Autumn!
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Post by simon822 on Jan 10, 2016 18:21:24 GMT
Thought it was time for an update regarding this winters work so far:
1. New steam pipes fitted, correct diameter, but new design, no corners only smooth curves. 2. Snifting valve refitted. 3. Boiler refitted, with better fixings and support. 4. New spring hangers made and fitted. 5. New leaf springs made and fitted. 6. New cladding made and fitted. 7. Fitted longer injector overflow pipe.
The first steaming was very interesting, the previous oscillation under power and load has almost disappeared, she runs much better at lower pressures, no longer stalls on the grade waiting for pressure to raise. The valve setting is not bad, sounding a bit like a machine gun with a full load on the grade. All in all all the changes seem to have been worth while. Just a few irritating things to iron out:
1. The feed pump no longer works, which did before I stripped the loco. 2. The snifting valve leaks with light steam, stealing with more steam. 3. The injector seems very slow.
All in all a good day. Just need reduce the snagging list now.
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Post by simon822 on Jan 10, 2016 18:37:49 GMT
Photo's of the new springs and hangers: The he springs have been made to the ken Swan design, but the hangers are my own as the modifications to the frames would have been too much work.
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Post by simon822 on Jan 10, 2016 18:40:51 GMT
Photo's of the new steam pipes:
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Post by simon822 on Jan 10, 2016 18:53:24 GMT
Suppose a photo of the test train would also be useful, most of the time it was run empty, but towards the end of the day I did take passengers, totalling about 12. This is really more that she is designed for, but she did sound good!
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Post by simon822 on Jan 10, 2016 20:51:44 GMT
And to entertain you a couple of videos showing the Wren tackling the 2 difficult corners at wakefield. The load was 4 coaches, which is about 1 ton. youtu.be/CvP5EJgBlw4youtu.be/TNiyw_NNxEABoth curves are sharp and on a grade, which is a bad combination for a small engine, even worse in the wet! Enjoy.
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foote
Active Member
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Post by foote on Jan 10, 2016 21:07:52 GMT
Looks and sounds good in the video, especially the wobbling hand brake column. Had it loosened or does it just need a strap to the cab rail?
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Post by ejparrott on Jan 10, 2016 21:15:06 GMT
I like it, nice work
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Post by simon822 on Jan 10, 2016 21:15:54 GMT
To move the engine I have to remove the chimney and the cab, most inconvenient, as I intended to bring it home again, I only bolted the cab on with half the bolts and left as much off as possible to save effort, the hand brake strap was one. The coaches have an electric air brake, so the hand brake was not needed, but worked fine when applied. You might also notice the vacuum gauge is also not attached.
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