V2 4 wheel parcel van1/32 and G3

[michael mott]

Thanks for the drawings Graham. Unfortunately they do not clarify the situation for me. I cannot see how the linkage in these drawings would actually function, the geometry appears to be working against itself. Or I am completely missing some vital piece of the puzzle. The end elevations are missing some very important parts of the linkages. The bent arm is interesting though and gets around the clearance issue regarding the axles.

Michael

 

[simond]

Michael,

my understanding is as follows:



the shoes are supported vertically by means of hangers, which, with the aid of gravity, keep them aligned with a nominal height centre line of the wheel horizontally, and the tread in a plan view.

the inner shoe is also constrained in plan view because the inner end of the lever is fixed. It can only move on a rather curious 3D arc given the fixed centres of the ends of the lever and hanger. (It’s the intersection of two spheres of different radii)

the outer shoe, (right hand one in view above) is not constrained inboard-outboard, as far as I can see, however, the coning of the tyre would produce force that would tend to move it outboard when applied and this appears to be balanced by the diagonal pull of the pull rod, which, when under load, would tend to pull the inner end of the lever inwards as well as towards the brake shaft.

The linkage between the levers is pin-jointed and therefore doesn’t apply any transverse constraint, though given the inner end is fixed when under load, there will be a small resultant transverse restoring force if the outer end moves outboard.

if my breakfast-time musings are correct, the geometry shows a neat economy. I guess Mr Dean was no muppet…

 

[michael mott]

if my breakfast-time musings are correct, the geometry shows a neat economy. I guess Mr Dean was no muppet…

Simon, Thank you for taking the time to explain how you see the system Working.
What is confusing about the side elevation of the drawing is the common problem of different systems stacked without a clear differentiation. My initial set up followed you description. However the outer shoes want to slide off the wheel as they are pulled, hence my adding the extra support post. The shoe wanting to slide off the wheel can be counteracted for by making the shoe hook over the wheel as they are done on the shoes of the Air loco that I studied that is on display at Bankhead.


I have outlined the two systems as I understand them in this overlay of the drawing you posted which looked like one that Graham had shared.


And my understanding of this is that the hand brake on this set up pushes the inside shoes only against the wheel while the outer ones get pushed away because of the clasping link on the outside of the axleboxes. The Activating levers that are working about the central shaft have to be independent of each other. The arm AA moved by the vacuum cylinder and the arm BB moved by the long hand operated lever.

The V2 parcel van does not have the hand system. The possibility of getting some clear photographs of the underside of the supports and possible guides for the connecting rods from the central lever to the outer arms would be extremely helpful.

Michael

 

[SimonT]

Michael,
I think the system is as follows.

I have left the brake blocks and hangers out. There are no fixed pivot points to pull against. The Swindon drawing shows a link running across between the two inner brake actuating levers. Moving the two actuating rods to the left will just tighten all the links and apply the brakes with equal force (providing the levers are the correct length).
Years ago when I was a member of the Great Western Study Group I did a load of work with Richard Spratt on Victorian coaches; I did the drawings and he provided information on Swindon building practice. We never got to the underframes in this detail as life and, for me, Mr Blair's wars got in the way and the project faded away.

I Hope this helps and many thanks to Graham for the drawings.

Simon

 

[simond]

Simon,

I wholly agree with your diagram, save that the ‘link’ joining the inboard ends of the left hand (inner) levers is, I believe, the frame of the vehicle, those points are fixed in all axes. (Your red crosshairs)

Michael,

I believe that the diagonal angle of the pull rods provides enough inward force to counteract the outward forces caused by the coning. There may be some stability provided by the brake hangers too?

atb
Simon

 

[Dog Star]

Gentlemen,

When I posted these drawings I was aware that the drawing content was unusual and I suggest the the Swindon DO has confused each of you. What I find to be strange about the brake arrangement is that there are four brake rods connected to the brake cross-shaft with two rods acting in compression and two rods acting in tension.... without any (obvious) equalisation to accomodate any "slackness" between brake block and tyre.

Of course, if someone is able to run a Mk.1 eyeball over carriage no. 820 at Didcot....

regards, Graham

 

[michael mott]

Simon T, your diagram shows exactly the way I originally set up the linkages, With Simon d's observation regarding the inside ends of the inside levers being fixed. It worked as described by Simon d with the exception that the shoes wanted to slide off the wheels. and some of the photographs in Russell's book do show what appear to be some strapping to help retain the rods to the levers.

Graham, " Of course, if someone is able to run a Mk.1 eyeball over carriage no. 820 at Didcot...."....Ahmen!

I can only attribute this to the hangers and linkages not being snug enough to prevent the sideways slack.

Gentlemen thank you all for taking the time in helping to clarify these areas of the braking system.

Michael

 

[SimonT]

Simon - not for the first time, I totally disagree! I think the link is clear of the inward face of the cross member. The view is from above and the link is shown hidden by the items above it such as underframe, vac pipe and draw gear.


There is a gap between the link and the cross member and there is no structure connecting the link to the cross member. If the link is an anchor to the cross member for the brake linkage why did Swindon go to the bother if a circular end to the anchor?

Ultimately Graham's remark is correct. I'm not as far west as Michael but I'm far enough for it not be me crawling under 820. At which point I shall bow out!

Simon

 

[simond]

Simon,

I don’t know! I understood that there were straps that go diagonally in side view from the pivots, up to the frame. I think it will be a crawl job. There must be a fixed fulcrum point against which to react the brake application force, or there wouldn’t be any…


Graham,

well, I didn’t think so, the outer pull rods are attached above (one end) and below (the other) the brake shaft, and so both pull - but this view appears to show inner push rods, attached to the opposite ends of the brake shaft levers, which are somehow attached to the above pivots.

This suggests my belief in fixed pivots for the inboard ends of the inner levers was wrong, and would, of course, provide a reaction path for any longitudinal forces, the brake shaft providing the fulcrum.



If anyone knows which vehicle(s) at the SVR have the same gear, I’ll crawl in two weeks if the vehicle is accessible.

atb
Simon

 

[michael mott]

With recognition that the copyright is belonging to J H Russell here is the picture that I have been referring to regarding the the support at the inward end of the shoe levers. in this photograph it is clear that the inside ends of the levers are fixed and supported to the frame.


My problem is that I have no information at the outer end there are no clear photographs in Russell's book this is the best picture, and it is of a six wheel carriage and not a four wheeled one.

I hope this clears up the confusion that drawings can sometimes generate. and clarifies my descriptions and the posts on my model.






it is one of the reasons that our modern systems of drawing clearly have an advantage over the sorts of stacked copies that we are often working from. one cans see that the vertical supports are connected to the the underside of the carriage and there angled support straps that stabilize them.



If admins need I shall take the image down.

Regards Michael

 

[michael mott]

One further comment Simon and Graham the side view in my opinion is of two independent levers operating about a single axis. The links at the V support hanger are a stacked view of these. This has to be the case because the hand brake and the vacuum brakes are two independent systems. The operation of the hand brake is a push system and the vacuum one is a pull system if my logic is correct.

Michael

 

[simond]

That picture clarifies the discussion SimonT & I were having, with the happy result that we were both correct, at least in part. It appears that the inner, inboard ends of the horizontal levers are fixed, by the pillars, and linked to one another.

I remain puzzled by the apparent push rods in the drawings that Graham kindly provided. They appear to go from the levers on the brake cross shaft to the inboard end of the inner levers, but they do not appear in the Russell photo.

I believed that the vac brake and handbrake operated on the same cross shaft, by means of lost travel linkages, but that may not be the case.

I do love a good puzzle!

 

[SimonT]

I've been thinking about the push rods as well. My tupence on the whole system is that are we looking at pre and post modification.

As far as I can see there is no evidence on the drawings of the diagonal braces to the fixed uprights, nor of the fixed uprights - I would expect them to be mounted on a structural member and not, effectively, screwed to the floor. I wonder if both the uprights and braces were introduced to improve the efficiency of the system I described (evidence - not on original drawing but on later photo). I also wonder if the push rods were removed at this time. I wonder if they originally went to the linkage and were intended to push the inner brake shoes against the wheels while the pull rods pulled both the inner and outer shoes against the wheels - the fixed uprights would make the push rods superfluous.

We know that the linkage survived as it later mounted the safety straps for the pull rods.

A cracking riddle, thanks everyone.

Simon
PS I still doubt that we have found the solution!

 

[simond]

I think you might be right. You’d expect to see the pillars in side and end views, but there’s no sign.

That said, the end view shows only one lever and that appears to be floating in space.

 

[michael mott]

As far as I can see there is no evidence on the drawings of the diagonal braces to the fixed uprights, nor of the fixed uprights - I would expect them to be mounted on a structural member and not, effectively, screwed to the floor.

Simon The drawing is of an open small wagon not a four wheel coach. The drawing shows a typical hand brake as well as a vacuum brake. In the plan view the links to the arms that push are on the outside as is the lever to push them it has to be an independent system or when the vacuum is released it would want to push them and pull the central rods at the same time, and both sets would be operating in opposition.

I believe the push rods and the pull rods are set up on different crank arms the central crank arms fixed to the cross shaft that is activated by the vacuum cylinder. the hand brake crank pivoting loosely around the central cross shaft and retained on the outside with a washer and pin.

I do not believe we are looking at pre and post modifications.

Michael

 

[SimonT]

Michael,
I fully know that the drawings are for four wheel carriage wagons. Swindon was about standard components - the same window components being used in a bewildering range of coaches, the same doors and the same brakes. Those carriage wagons were rated to run in express trains and required the same braking systems as the coaches. I'll bow out now.

Simon

 

[simond]

Well, we had an enjoyable weekend on the SVR involving a couple of rides and visits to the museums and this morning a brief sojourn at Bewdley, where I was able to find the vehicle which I believed had the famed Dean brakes


Unfortunately, it doesn’t

Some enquiries led to an introduction to Clive who kindly took me round the back of the goods shed where a further three riding vans were hidden away, however, no cigar!

There is reputedly a fourth at Hampton Loade but I suspect Didcot will be the next opportunity

Sorry!

 

[Pete_S]

There is reputedly a fourth at Hampton Loade but I suspect Didcot will be the next opportunity

Sorry!

This one?

GWR 118 Mess/Riding Van built 1904

 

[simond]

Yep. B####r. That one does have the Dean brakes.

oh well…. I guess we now know which vehicle and where it is. I don’t think I’d have been able to get there today even if I had known, but if anyone is able to get under it, could take some useful photos, and post them here, it would be great.

cherrs
Simon

 

[michael mott]

Oh well thanks for all your efforts to resolve the mystery. I did write to Didcot but have not heard back from them.

Michael