LBSC Ivy Hall 3 1/2″ steam engine

[Philip SlaterParticipant @philipslater86297]

A few years ago I purchased a part finished 3 1/2″ gauge Ivy Hall steam engine, the design for which was featured in the model engineer magazine in 1955 / 1956. The original builder who has now deceased appears to have modified the design slightly and fitted an air brake system complete with air cylinder and small air pump to the loco. I’m now working through the loco trying to understand it and give it a clean up and renovation. It was started back in 1956 so it’s got a few years of grime on it.

My question is has anybody seen such a design for brakes on a 3 1/2″ gauge model steam loco before? I’m concerned the brakes will not be strong enough in service. The air pump is like a miniature version of a bicycle pump driven from the engines main cylinder linkage. The seals of the pump have perished so doesn’t do a great deal of compressing of air at the moment. What sort of seals are normally used?

This is my first visit into the world of model steam trains so I’m pretty clueless at the moment.

Thanks

[Bruce VoelkerdingParticipant @brucevoelkerding91659]

something you may want to check – is the Brake system designed to work as a VACUUM or a COMPRESSED AIR System ?

I may be totally wrong on this (I live over the Pond), but I was under the Impression that some Great Western Locomotives used such a Pump to generate a Vacuum. I believe I read this in ME in one of the Locomotive Constuction Series (LBSC, Martin Evans or Don Young). The Point was raised as the Designer converted it to a Water Feed Pump.

[Clive Brown 1Participant @clivebrown1]

Can’t help with the design of the air-pump, but I’d doubt if the system as a whole would be effective. The weight of a 3.5″ G. loco is quite small compared with the driving truck, driver and possible passengers, the wheels will probably just skid. Braking of a moving train is best done with truck brakes. A wind-on “parking brake” on the loco is useful however.

[Nigel Graham 2Participant @nigelgraham2]

Bruce –

You are almost certainly right: a braking system of that vintage in British practice would be vacuum not compressed-air type. Although some miniature locomotives do indeed disguise the boiler feed-pump as a vacuum-pump, where the full-size versions had those prominently fitted (a rare practice), the existence of a receiver does suggest that indeed, this model is fitted with an air or vacuum brake pump.

The far more common practice, culminating in being so on all British Railways’ “Standard” class locos, was that the vacuum is drawn by steam-jet ejector, not a mechanical pump. Two in fact: a large-capacity ejector for releasing dropping the pressure in the entire train system rapidly, and a small one for maintaining the vacuum during the run.

Many miniature locomotives now are fitted with ejectors etc. for vacuum-braked rolling-stock.

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Clive –

Indeed. The vacuum system is not for stopping the train and locomotive, but the train, although whether this 3.5″ g. instance would produce enough “nothingness” to be very effective is another matter. It’s still an interesting development though, so I hope this one does work, with suitably-fitted rolling-stock!

Even in full-size the locomotive’s steam-brake is separate from the vacuum system, albeit in some the two systems are linked in one unit whose single handle operates a complicated relay-valve arrangement putting the train-brakes on slightly before the loco brakes, and vice-versa.

The old adage is that the locomotive starts the train, the train stops the locomotive.

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Philip –

It would be great to see the locomotive back in service!

So we know the vacuum or air-brake dose not stop the engine. It stops the train. So….

The big clue is the nature of the brake pressure-gauge if fitted as one should be: a Vacuum or a Positive-pressure type? NB – pressure-gauges are delicate, and small vacuum-gauges especially so.

Otherwise, to verify what its pump actually does, and understand how its system works, when overhauling it examine which way the valves “point” in relation to the receiver and other fittings.

There should also be a connection on the drag-beam, for connecting the rolling-stock brake plumbing.

Such examination will show which way the air flows through the system when the brakes are applied:

– from the train-pipe, to atmosphere for Vacuum;

– from atmosphere through the system to the train-pipe for Air-brakes.

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Normally, brake-application admits the vacuum-destroying air through a hole or holes on the valve itself, located among the other controls on the driver’s side of the footplate. The full-size types have not one air-inlet hole but lots, like a sieve, and quite prominently so.

A simplified, miniature version of the Brake Valve typically has just two positions: Off, and On (admits air to the train pipe, but may give little or no gradual or partial application effect). The receiver’s task is to help regain rapidly, and hold, the vacuum that holds the brakes Off.

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Where to locate the brake valve – if not yet installed?

Though LBSC’s designs err on the side of simplicity and “ergonomics”, it’s good to represent the cab reasonably accurately, if the Brake Application Valve has not yet been fitted. It’s a smallish but fairly distinctive beast, and you need reach it easily from the driving-truck.

I don’t know GWR cab layouts in detail other than being right-hand drive, but full-size steam-locomotive brake controls were generally either on a stand bolted to the footplate, or apparently on to a bracket on the back-head at about the seated driver’s shoulder-height.

Obviously for the latter case we can’t screw things to the model’s boiler unless suitable mountings for it have been fitted during that unit’s construction, which I doubt here. So we mount a robust but discreet bracket on the cab structure to hold the valve about where it ought be – find some photos of full-size examples to guide you.

(I am assuming by the name this is a GWR loco but the model’s drawings lack such luxuries as train-brake systems. In fact I think putting proper vacuum or brake systems on smaller miniature railway equipment generally, is quite a recent development.)

 

 

[duncan webster 1Participant @duncanwebster1]

Gwr locos had a vacuum pump driven direct off the crosshead. In models this is often used as a pump to put water in the boiler. There was a fad back in the 70s to have an air bottle on the outlet from the water pump to even out pulsations. I’m not sure this was either effective or necessary, seems to have fallen out of favour. Is this perhaps what you have? As others have said, model loco brakes are useless for stopping the train

[Nick Clarke 3Participant @nickclarke3]

Personally I shouldn’t bother as a crosshead air pump, as against the water pump LBSC designed because it will need some form of lubrication otherwise the seals, if not the ram and cylinder will wear. The effectiveness of the system even if working has been mentioned but there is also the question of safety.

Having driven trains fitted with continuous vacuum brakes but with ejectors you either have a simple brake where the vacuum applies the brake and if the loco is not moving you will not have any vacuum and if automatic you cannot pull the brakes off until you have a vacuum and you don’t have a vacuum until you move with a crosshead pump.

Full size locos had ejectors in addition to the pump which was only to make up a vacuum lost to leaks (or a second small ejector was fitted)

[Nigel Graham 2Participant @nigelgraham2]

In full-size, vacuum-pumps on steam-locomotives were indeed GWR practice but unusual elsewhere. Most, including the BR Standard Classes, relied entirely on ejectors, with a large one for creating the vacuum rapidly.

However, the entire train system was quite complicated and included large vacuum reservoirs – if that’s not a somewhat self-contradictory term!

I think certain railways were fitted with air-brakes, using an independent pump.

Miniature steam-locomotives can be, and many are, fitted with simplified versions of ejector and reservoir systems; but as on full-size the vacuum-brake does not act on the locomotive and the primary braking effort is distributed among the rolling-stock.

 

It would seem Philip’s locomotive has a pump but so far we are not certain of its purpose, and it might be a boiler feed-pump disguised as the prototype’s vacuum-pump. The puzzle is the purpose of the reservoir. It needs the system and fittings installed so far to be examined carefully to determine exactly what’s what on this particular “Ivy Hall”.

 

 

 

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