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Post by greenbat on Apr 22, 2012 22:37:34 GMT
Does anyone know of any decent drawings/diagrams/pictures of how caprotti gear works? Purely out of curiosity, I've looked on the duke website and googled but can't see anything that explains it all. I found an old thread where someone mentioned having a 7 1/4" duke with working caprotti, do they have any pictures perhaps?
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Post by peterseager on Apr 23, 2012 10:25:08 GMT
I have two references for Caprotti valve gear. 1) Handbook for Railway Steam Locomotive Enginemen; Ian Allan; ISBN 0 7110 0628 0 2) The Journal of the Institution of Locomotive Engineers Vol XV, No 68, Jan-Feb 1925, Pages 86-119 Ref 1 gives is more about how it is fitted to a loco and the method of working such locos. Ref 2 has a lot of detail and pictures of the open cam box etc. The attachment is from Ref 2 and shows one of a pair of gearboxes fitted to a 4 cylinder loco. Peter Attachments:
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Post by donashton on Apr 23, 2012 10:26:02 GMT
There is a chapter with illustrations on various poppet valve arrangements in Martin Evans' "Model Locomotive Valve Gears" reprinted in 2010 by TEE Publishing Ltd. Pictures will not show much, but these are clear diagrams of the cam boxes, etc.
Don
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Post by peterseager on Apr 23, 2012 10:37:13 GMT
This diagram shows how the reverser, under the control of the driver, moves the cams along the scrolls, which alters their timing, and the effect of the two cams is summed by the rollers and operates the valves. Fig 1 is inlet and Fig 2 exhaust. Peter Attachments:
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hudson
Involved Member
Posts: 92
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Post by hudson on Apr 23, 2012 11:02:18 GMT
Hi,
For patented items I always search in Google patents and very often
the desired information is found.
In this case there are 3 entries for patents granted to A. Caprotti and
a few others which related contents.
Best regards,
hudson
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nonort
Part of the e-furniture
If all the worlds a Stage someone's nicked the Horses
Posts: 279 
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Post by nonort on Apr 23, 2012 11:28:47 GMT
I Think you will find a simplified version on Charlie Dockstaders valve gear program. You can set it in motion and move the gear through foward to reverse and see all the bits moving.
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Post by Nigel Bennett on Apr 23, 2012 11:51:47 GMT
The miniature version of the Duke of Gloucester was built by the late Denis Evans. He built at least two versions - in 7.1/4"G and 3.1/2"G. He may have built one in 5"G as well, but I do know he built a BR Standard Caprotti 5 in that gauge.
It's my intention to build a 3.1/2"G 9F with Caprotti gear - but it won't be any time soon!
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jma1009
Elder Statesman
Posts: 5,917
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Post by jma1009 on Apr 23, 2012 17:57:52 GMT
it is a great shame that dennis evans isnt still with us. what a supurb craftsman and model enginner! he achieved the impossible!
cheers,
julian
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Post by Deleted on Apr 23, 2012 19:57:49 GMT
The interesting thing about Caprotti gear is that the valves are held shut by steam pressure. The cam rockers force the valves down against steam pressure, to admit steam to the cylinder, or to exhaust it to atmosphere. This means that when the engine is coasting with the regulator shut, the valves drop away and compression is avoided.
The downside to this is that while a conventional engine will move on a breath of steam, a Caprotti engine has to have enough boiler pressure to lift the valves, otherwise all you get is a roar up the chimney!
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Andrew C
Part of the e-furniture
Posts: 447
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Post by Andrew C on Apr 24, 2012 21:49:17 GMT
There are a couple of bits of info I have found that might be of interest. The caprotti gear fitted to the LMS black 5's the exhaust cam was fixed. So it always opens fully no matter what cut-off changes, and there was a plate in the cabs telling the driver to fully close the regulator when coasting so the valves would drop away from the seats I read some where it only took a few psi to snap the valves shut as there were passage ways and a piston like extension on the bottom of the valve stems The 5" BR class 5 is owned by a member of this forum who's details I had but via a pc crash have now lost  Andrew |
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Post by greenbat on Apr 25, 2012 9:38:05 GMT
Thanks for all that, I've ordered Martin Evans book. Starting to get a clearer idea now (didn't know the camshaft ran across the clyinder instead of parallel to it), just can't grasp the variable cam bit.
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Post by Laurie_B on Apr 25, 2012 10:07:32 GMT
The 5" BR class 5 is owned by a member of this forum who's details I had but via a pc crash have now lost Andrew There is a video of an excellent 5" gauge Caprotti (or is that 'British-Caprotti'  ) fitted BR Standard 5 on youtube here. Is the loco built by the late D.Evans?Perhaps someone could confirm this. |
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Post by RGR 60130 on Apr 25, 2012 10:16:55 GMT
Yes, the Class 5 is alive and well. I gave it a run at the Tyneside track a couple of months ago. I'm now in the process of building a new brass tender body to replace the rusted out zintec one. I had hoped to have it at Harrogate show this year for all to see rather than keeping it hidden away but my work rota is such that it is not going to be possible. It was possibly in 2009 that Dennis's Duke of Gloucester models were displayed at Harrogate. Beside one of the locos were some spare cam assemblies. Did anyone get some good pictures of them by any chance? If so, please would it be possible for me to get copies? If I have the story right, I think the original Caprotti valve gear only had 1 exhaust cam, whereas the British Caprotti valve gear had 2 exhaust cams. Reg Attachments:
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Post by RGR 60130 on Apr 25, 2012 10:33:09 GMT
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Post by jordanleeds on Apr 25, 2012 12:55:45 GMT
I have a Number of photos of the 5" gauge Std five sat on the runningboards of 73129 do you want me to post them?
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Post by Laurie_B on Apr 25, 2012 13:53:10 GMT
It was possibly in 2009 that Dennis's Duke of Gloucester models were displayed at Harrogate. Beside one of the locos were some spare cam assemblies. Did anyone get some good pictures of them by any chance? If so, please would it be possible for me to get copies? Reg Hello Reg, Dennis Evan's 'Duke of Gloucester' models were at the 2009 Harrogate show,and I managed to take a few photos of .Bear in mind my photograhy is worse than my model engineering!Here's the first: Attachments:
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Post by Laurie_B on Apr 25, 2012 13:54:56 GMT
And the second,which I think was the 5"gauge model,though I might be wrong: Attachments:
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Post by Laurie_B on Apr 25, 2012 13:56:33 GMT
And one more Attachments:
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Post by RGR 60130 on Apr 25, 2012 18:03:20 GMT
I have a Number of photos of the 5" gauge Std five sat on the runningboards of 73129 do you want me to post them? Hi, I would be very interested to see the pictures if you would be so good as to post them. I'm sure others would find them interesting too. Many thanks, Reg |
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Post by RGR 60130 on Apr 25, 2012 18:21:59 GMT
[/quote].Bear in mind my photograhy is worse than my model engineering![/quote]
Hi Laurie,
Thankyou for taking the time to post the pictures which are very good!
I can see a spare / prototype cam in the second picture but can't quite make out the detail. I have a feeling that the cams in the Dukes were different from the Class 5. One day I'll perhaps find time and courage to open up the Class 5 boxes for a look. At the moment I'm hoping to run it regularly over the summer if the rain ever stops.
Reg
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) fitted BR Standard 5 on youtube 
