Vacuum Brake arrangements for a 4-wheel coach

[Edwardian]

The aim is not to attain nth degree detail, but I would like the arrangement to look reasonably prototypical.

 

Any drawings, photographs or information would be helpful.

 

Would someone with knowledge of prototype arrangements mind considering how credible the arrangement drawn below is or have we misunderstood anything?

 

Thank you. 

 

 

 

[45125]

Not a lot wrong with the brake linkage.

 

[Miss Prism]

1 hour ago, Edwardian said:

we

 

Who's we?

 

[Guy Rixon]

Perfectly functional as drawn. Two points might bear further consideration.

 

In the top drawing, there's a V-hanger for the brake shaft against the nearer solebar, but the vacuum cylinder is closer to the further solebar. I'd expect to see a V-hanger against the solebar nearest to the cylinder and the other as near the centreline as it can get without fouling the centre crank.

 

In the bottom drawing, the pull rod to the right-hand axle  goes up at a sharp angle to engage the lever above the axle. This is sometimes used --- LNWR fitted wagons were like that --- but other railways might bring the rod out near horizontal and engage the lever below the axle. Like this:

...which is how the SER did it for coaches with handbrakes. Note that on both axles here there is rigging running under the axle, trapping the wheelset. This is awkward to model, unless one makes the brake assemblies as separate parts to be added after the wheels.

Edited March 31, 2021 by Guy Rixon
Add diagram.

[Miss Prism]

Not dissimilar to a Toad clasp brake - extract from Brian Morgan's brake gear article (figure 26):

 

[brossard]

On 4 wheeled stock with clasp brakes that I have built, the link that you show on the right, should be on top:

 

 

This is a LNER 32 ft General Purpose Van.  Also fitted with Westinghouse gear which should be ignored.

 

John

[Edwardian]

18 minutes ago, Miss Prism said:

 

Who's we?

 

 

Me and the bloke who's doing the CAD work.

 

It's to design and print 1870s Metropolitan & Carriage Works 4-wheel coaches as supplied to the West Norfolk Railway, and as running circa 1905, long after inter alia vacuum automatic brakes have been fitted. So, a purely private passion.  

 

I am given to understand that the yoke linkage at the end of the push rods should not be mounted on fixed points, as currently drawn, rather it should be supported on a link that is pivoted off a bracket attached to the end longitudinal. 

 

14 minutes ago, Guy Rixon said:

Perfectly functional as drawn. Two points might bear further consideration.

 

In the top drawing, there's a V-hanger for the brake shaft against the nearer solebar, but the vacuum cylinder is closer to the further solebar. I'd expect to see a V-hanger against the solebar nearest to the cylinder and the other as near the centreline as it can get without fouling the centre crank.

 

Thanks Guy. So, if I understand you, the V hanger nearest the cylinder should be moved out against the adjacent solebar.  The further V hanger moved in closer to the centre line. 

 

Quote

In the bottom drawing, the pull rod to the right-hand axle  goes up at a sharp angle to engage the lever above the axle. This is sometimes used --- LNWR fitted wagons were like that --- but other railways might bring the rod out near horizontal and engage the lever below the axle. 

 

Yes, it seems it is too steep. It has been suggested that the V hangers may be too large/low and that the central crank is too big. A question of the proportions of the elements rather than a mechanical solecism I think. 

[Guy Rixon]

3 minutes ago, Edwardian said:

I am given to understand that the yoke linkage at the end of the push rods should not be mounted on fixed points, as currently drawn, rather it should be supported on a link that is pivoted off a bracket attached to the end longitudinal. 

Correct, but the only aspect of this bearing on the visible bits is that the vertical supports --- which I think might be called pendulum links --- would typically be parallel-sided plates, not tapering brackets as drawn. 2" x 0.5" section is typical. They'd also be cranked outward at their top ends to meet the brackets on the longitudinals, but that detail is above the solebars and hidden.

 

V hangers varied greatly in size. The SER used massive parts here, with a relatively small opening-angle, similar to the ones on your drawing. More typical coaches had lighter sections in the hangers and a wider angle in the V.

 

BTW, if you want something prototypical but a little quirky, you could have push-pull brakes as on the SER. But then you'd have the brake shaft offset towards one axle.

 

The tips of the trunnions supporting the vacuum cylinder often showed below the solebars. You might care to add these.

 

Also, where are your safety loops? Are you to add these from wire, for strength?

[Compound2632]

30 minutes ago, Edwardian said:

it should be supported on a link that is pivoted off a bracket attached to the end longitudinal. 

 

The pendants to the bosses are typical.

[Edwardian]

40 minutes ago, Guy Rixon said:

 

Also, where are your safety loops? Are you to add these from wire, for strength?

 

No, simply omitted from ignorance

[Wickham Green too]

10 hours ago, Edwardian said:

... the V hanger nearest the cylinder should be moved out against the adjacent solebar.  The further V hanger moved in closer to the centre line. ...

Yes, the outer Vee would have been bolted to the solebar and the inner one to one of the longitudinals - obviously beyond the centreline .......... if you can find photos of a Southern PMV or CCT - or, better still, a chassis being fitted with a 'recovered' body in preservation - you'll get a typical 4wh coach vac setup.

[Edwardian]

1 minute ago, Wickham Green too said:

Yes, the outer Vee would have been bolted to the solebar and the inner one to one of the longitudinals - obviously beyond the centreline .......... if you can find photos of a Southern PMV or CCT - or, better still, a chassis being fitted with a 'recovered' body in preservation - you'll get a typical 4wh coach vac setup.

 

That makes perfect sense, thank you

[Compound2632]

5 hours ago, Wickham Green too said:

Yes, the outer Vee would have been bolted to the solebar and the inner one to one of the longitudinals - obviously beyond the centreline .......... if you can find photos of a Southern PMV or CCT - or, better still, a chassis being fitted with a 'recovered' body in preservation - you'll get a typical 4wh coach vac setup.

 

Except with the note of caution that those Southern underframes are steel not wood and of much later date - James' carriages have underframes of 1870s vintage fitted with clasp brakes and vacuum gear in the late 1880s, I suppose.

Edited April 1, 2021 by Compound2632
sp.

[brossard]

If it helps there are SR PMV underframe pictures here:

 

https://www.rmweb.co.uk/community/index.php?/topic/123148-sr-4-wheeled-cct/

 

John

[Edwardian]

Sketched proposed amendments for comment please

 

 

 

 

 

 

[Compound2632]

Looks good amidships though I think the vee would still be a vee. 

 

The swinging link supporting the crank* connecting the yokes to the pull rod is quite slender but is pretty well hidden between the wheels.

 

Safety loops for the pull rods, as @Guy Rixon said.

 

*I don't know what this piece is called. The crank connecting the pull rods to the cross-shaft is the tumbler.

[Guy Rixon]

Two sets of safety loops are needed: for the brake yokes and for the pull rods. The loops around the pull rods would be narrow U-shapes splaying out at the top where they're  bolted to the longitudinals. For the safety of the yokes, two arrangements are possible. First, two trapezoidal straps can enclose both yokes, on strap on each side. Second, each yoke can be guarded by a pair of forged rods, shaped like inverted question-marks, one next to each wheel.

 

I'm not sure that the cross shaft should be moved up as much as indicated. The drawings I have on hand (which are for SER perversions, but still) show the shaft set about a shaft diameter (i.e. 3") above the axle centre-line. If you do move it up, the cylinder should also be moved up, as the crank to the vacuum piston-rod is already at about the right angle.

 

One of your brake yokes looks weird. They should have the same, triangular shape, but you have one short triangle and one long triangle. This is because both yokes have been extended to meet the we-don't-know-what-it's-called lever in the middle. You should have rods coming from the centre of each yoke to attach to this lever, and those rods will be very different lengths. If you look at the graphic I posted above you'll see how it's done.

 

If the coaches follow LSWR design-patterns, then the brake yokes are mutant. Rather than being simple triangles, they have an extra member along the centreline: i.e. the rod attached to the point of the triangle passes through the triangle and attaches halfway along its back member. Presumably this was to add strength, but I've not seen any other railway bother with it.

 

The tumbler can also be called the centre crank.

 

PS: please fix the brake blocks. As drawn, they look worn many inches beyond scrapping size and the nice chap from the BoT will be terribly upset. If you added an annular sector, perhaps 2" thick radially, on the wheel side of what is currently there, then they would look better. But I think the blocks for brake-fitted stock were very uniform between railways, so perhaps we can sort you out with some better geometry. I have some drawn for my SER coaches that I can send you, if we can agree on file formats; also similar for LNWR fitted wagons.

Edited April 1, 2021 by Guy Rixon

[Edwardian]

4 hours ago, Compound2632 said:

Looks good amidships though I think the vee would still be a vee. 

 

Do not understand that comment

 

4 hours ago, Compound2632 said:

The swinging link supporting the crank* connecting the yokes to the pull rod is quite slender but is pretty well hidden between the wheels.

 

Safety loops for the pull rods, as @Guy Rixon said.

 

*I don't know what this piece is called. The crank connecting the pull rods to the cross-shaft is the tumbler.

 

Thanks

 

3 hours ago, Guy Rixon said:

Two sets of safety loops are needed: for the brake yokes and for the pull rods. The loops around the pull rods would be narrow U-shapes splaying out at the top where they're  bolted to the longitudinals. For the safety of the yokes, two arrangements are possible. First, two trapezoidal straps can enclose both yokes, on strap on each side. Second, each yoke can be guarded by a pair of forged rods, shaped like inverted question-marks, one next to each wheel.

 

I don't think my guy can do anything without a visual reference

 

3 hours ago, Guy Rixon said:

I'm not sure that the cross shaft should be moved up as much as indicated. The drawings I have on hand (which are for SER perversions, but still) show the shaft set about a shaft diameter (i.e. 3") above the axle centre-line. If you do move it up, the cylinder should also be moved up, as the crank to the vacuum piston-rod is already at about the right angle.

 

Noted, thanks

 

3 hours ago, Guy Rixon said:

One of your brake yokes looks weird. They should have the same, triangular shape, but you have one short triangle and one long triangle. This is because both yokes have been extended to meet the we-don't-know-what-it's-called lever in the middle. You should have rods coming from the centre of each yoke to attach to this lever, and those rods will be very different lengths. If you look at the graphic I posted above you'll see how it's done.

 

Thanks

 

3 hours ago, Guy Rixon said:

If the coaches follow LSWR design-patterns, then the brake yokes are mutant. Rather than being simple triangles, they have an extra member along the centreline: i.e. the rod attached to the point of the triangle passes through the triangle and attaches halfway along its back member. Presumably this was to add strength, but I've not seen any other railway bother with it.

 

The tumbler can also be called the centre crank.

 

PS: please fix the brake blocks. As drawn, they look worn many inches beyond scrapping size and the nice chap from the BoT will be terribly upset. If you added an annular sector, perhaps 2" thick radially, on the wheel side of what is currently there, then they would look better. But I think the blocks for brake-fitted stock were very uniform between railways, so perhaps we can sort you out with some better geometry. I have some drawn for my SER coaches that I can send you, if we can agree on file formats; also similar for LNWR fitted wagons.

 

Yes, now I look at them ...!

 

Any drawings welcome.

[Compound2632]

27 minutes ago, Edwardian said:

Do not understand that comment

 

On your side view, you had sketched what looked like a triangular plate in place of the V. I was trying to say that I though it would most likely be a V even if shallower, rather than solid.

Edited April 1, 2021 by Compound2632

[Guy Rixon]

11 hours ago, Compound2632 said:

 

On your side view, you had sketched what looked like a triangular plate in place of the V. I was trying to say that I though it would most likely be a V even if shallower, rather than solid.

The only place where I've ever seen a V-hanger made of solid plate was under a goods brake. It must have been extremely heavy and I think they were using it as part of the ballast.

[Edwardian]

30 minutes ago, Guy Rixon said:

The only place where I've ever seen a V-hanger made of solid plate was under a goods brake. It must have been extremely heavy and I think they were using it as part of the ballast.

 

I don't think that's intended as such; just the designer sketching the change in position

[Edwardian]

 huge thanks to everyone.

 

I hope I have understood the advice adequately enough.

 

These are the revised drawings.  Please do comment.  Thanks.

 

 

 

[Miss Prism]

Which position are those brakes in - on or off?

 

[Compound2632]

Pulling the pull rods pulls the brakes on, which is done by rotating the tumbler clockwise from the side we're looking at, which must mean that if the connecting link to the vac cylinder piston is "up" as in the sketch, then the brakes are on. 

 

Brakes off - vacuum on both sides of the piston:

 

Breakes on - air pressure from the train pipe forces the piston up:

[By Archibald Williams - en:Project Gutenberg, Public Domain, https://commons.wikimedia.org]

[Edwardian]

So the cylinder needs to come lower?