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Pansy Valve Gear

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Peter Maloney06/01/2014 21:31:50
33 forum posts
12 photos

Hi All.

Can someone help with dimensions of Pansy valve gear?

ME Mag states :- Expansion link length 1.75in

Eccentric strap length 4.625in

MAP Drawing states :- Expansion link length 1.75in

Eccentric strap length 4.8125in

Nexus Drawing states :- Expansion link length 1.875in

Eccentric strap length 4.8125in

As a raw beginner I am totally confused. I am hoping that there is a Pansy

builder out there who can set me straight.

Thanks in anticipation

Pete

julian atkins06/01/2014 22:43:43
avatar
1235 forum posts
353 photos

hi pete ,

if you pm me with your email address i'll send you the modifications i made to the PANSY valvegear on my own 57XX example, worked out in accordance with don ashton's book and subsequently double checked by don ashton on his simulator.

there are far more errors than as stated by you above.

cheers,

julian

Jim York22/04/2014 20:27:58
1 forum posts

Hi Pete or Julian,

I have recently purchased a Pansy and I have been trying to locate the details of the valve gear modifications. Please could you email a copy of the improvements if possible.

Thanks in anticipation,

Jim

julian atkins22/04/2014 21:23:09
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1235 forum posts
353 photos

hi jim,

ive sent you a PM.

cheers,

julian

fizzy22/04/2014 21:30:12
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1755 forum posts
120 photos

Thats just great...I put off building SPEEDY as I was totally confused with all the valve gear mods by different people and opted instead for PANSY....and now you tell me! Very confusing! (thats my way of saying thanks Julian, no linkages made yet so no damage done).

Peter Maloney23/04/2014 14:18:36
33 forum posts
12 photos

Hi Jim ,fizzy

Yes, it was totally confusing wasn't it. I see Julian has already replied.

Julian was the only one to reply to my original posting and as he seems to know what he is talking about I have put my faith totally in him.

I have had to remake a few pieces but worthwhile for a better result. It's all slow progress though.

Julian lives only 18 miles from me so I hope to pop across when Merthyr MES has an open day.

Good luck all

Pete

Weary23/04/2014 16:33:48
319 forum posts

Perhaps someone could post the 'improved valve gear' specifications here for the benefit of future Pansy builders, or maybe an article for Model Engineer?

Regards,

Phil

Ompa Ompa23/04/2014 19:12:11
43 forum posts
1 photos

I am always amazed when several mod's come up for discussion. I built my 'Pansy' over 30 years ago, using the set of drawings supplied at that time (LBSC's I believe). This was my very first locomotive and obviously I took care to follow the dimensions to the letter. Amazingly the thing worked from day one and never has let me down regarding any valve event problems. Now of course fair wear and tear are taking their own toll on events, but more importantly the locomotive still runs and will still pull a good number of passengers, in fact it sounds more like the real thing with all the clanking etc it makes when working.

julian atkins23/04/2014 21:59:51
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1235 forum posts
353 photos

Ompa Ompa,

that rather begs the question whether your Pansy can be notched up and whether you have experienced driving a loco with excellent valve gear events. superficial setting of the valve gear for fullgear for PANSY in forward gear gives passable results but the cut offs and exhaust points are still way off and uneven. as the loco is notched up this discrepancy gets much worse. checking for equal leads isnt enough. a check of the cut offs shows them to be very bad on the as designed gear.

one day i will get round to doing an article on same for ME!

cheers,

julian

John Baguley23/04/2014 23:24:10
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478 forum posts
51 photos

What really screws up the Pansy valve gear is the rocker drive to the valves which puts the valve motion 180° out of phase to the piston motion. The fact that the expansion link is suspended from the top rather than the middle doesn't help either. A fairly simple mod to the existing gear which makes a vast improvement to the valve events in forward gear is to extend the lifting arm on the weighshaft to 2.33". I did this on a friends 94XX which was basically a Pansy chassis. I had to put a crank in the new lifting arm to clear something (can't remember what now).

weighshaft.jpg

This won't be as good as a complete redesign but might be useful if you already have the gear built and don't want to start again.

John

julian atkins24/04/2014 08:44:30
avatar
1235 forum posts
353 photos

john's excellent modification deals with one of the problems but there remain others.

there are 2 types of problems; geometric, and practical/mechanical.

of the practical/mechanical, parts of the valve gear are far too flimsy and wear badly and cause lost motion. the single rocker arm bearing and top lifting link pin for the expansion link are culprits. valve setting is compromised by the difficulty of adjusting the valves by altering the position of the rocker arm. some easy modifications and improvements can solve these problems.

geometrically LBSC (and Don Young) drew all their loco link stephensons gear out incorrectly. i wont go into the details here other than to say that the radius of the expansion links is wrong, and the position of the rocker arm pivot and weighshaft are critical to provide acceptable valve events and need altering. the position of the weighshaft isnt even dimensioned on the drawings (though is stated in the ME construction notes, not that LBSC got it it quite right). other minor improvements can be incorporated by providing Don Ashton's 'corrected lengths' for the eccentric rod centres to give equal leads, and modifying the usual valve setting proceedure and removing the exhaust clearance on the valves.

instead of a PANSY that will only run in forward gear (still with lumpy cut offs and exhaust events) you should be able to have a loco that can be notched up to 25-30% in forward and reverse. anyway mine does!

there are lots of errors and bad design features in the original drawings that catch out the unwary on the rest of the loco. of these the boiler barrel being too short and the wet header interfering with the petticoat pipe are perhaps the best known, as is the need to turn the front axle down to 5/8" dia between the axleboxes to avoid it hitting the bottom slidebars.

if anyone wants a full list and details i will happily send them.

cheers,

julian

Bruno Taylor03/08/2019 15:55:06
avatar
48 forum posts
14 photos

Hi Julian

I know that this is an old thread, but l would be very interested in the modifications to Pansy valve gear as l am in the process of drawing up the valve gear prior to commencing a build.

Many thanks

Fowlers Fury03/08/2019 16:34:25
avatar
355 forum posts
80 photos

Yet another plea, as Bruno's above !
I have a Pansy (original builder unknown) and she runs well enough. Notching-up is effective to a degree but the big problem now is wear in the valve gear (e.g. elongated holes in stretchers!).

Anticipating a major rebuild of the valve gear, can we see these mods of Julian Atkins please?

julian atkins04/08/2019 10:31:10
avatar
1235 forum posts
353 photos

If you would both like to send me a PM I will email you my 'blurb'.

Cheers,

Julian

Bruno Taylor04/10/2019 08:17:42
avatar
48 forum posts
14 photos

Hi All

Many thanks to Julian who sent me the dimensions for his modified valve gear. I have created a physical model with the assistance of Model Engineers Laser who cut the parts. I have made provision to adjust the lateral position of the rocker pivot.

2019-10-02 14.55.05.jpg

First trials are promising and l will see what cut-off l get. It also demonstrates where the "slop" is so extra special care in machining. If you look closely you can see the cylinder bore is notched at each 10% of travel.

Regards

Bruno

Neil Wyatt04/10/2019 10:57:53
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Moderator
18409 forum posts
718 photos
78 articles
Posted by Bruno Taylor on 04/10/2019 08:17:42:

Hi All

Many thanks to Julian who sent me the dimensions for his modified valve gear. I have created a physical model with the assistance of Model Engineers Laser who cut the parts. I have made provision to adjust the lateral position of the rocker pivot.

2019-10-02 14.55.05.jpg

First trials are promising and l will see what cut-off l get. It also demonstrates where the "slop" is so extra special care in machining. If you look closely you can see the cylinder bore is notched at each 10% of travel.

Regards

Bruno

That's a good idea Bruno, I would happily run an article on that in MEW, but ME might be the right place for it, I suggest you send a note about it to Martin or Diane.

Neil

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