Steam Locomotive braking and vacuum brakes

[NickM]

Gentlemen,

Some questions about vacuum braking and slowing down in general, specifically applicable to steam engines.

I am the proud owner of 7 ¼ Milner Hunslet, completed six months ago. It is fitted with a vacuum ejector and generally pulls myself and up to 5 passengers, myself on an un-braked 4 wheel driving car, the passengers on a twin bogie riding car with vacuum brakes on one bogie.

A combination of a very free running engine and a seriously long gradient means that on the down grade the train definitely starts pushing the engine and some gentle braking is required. Having seen other drivers do it, I have found that ‘feathering’ the pole reverser into reverse provides gentle and controllable braking but I wonder is this an acceptable practice and can it do any harm to the engine? My vacuum brake lever is a combined vacuum and steam brake lever from PNP and does not have a lap position so using the riding car brakes tend to be a bit all or nothing.

Also, in order to maintain the vacuum and keep the brakes off, I have to keep the ejector running all the time. This isn’t a problem as the ejector exhaust, although piped up the chimney, does not appear to affect the drafting in any way but I do find the constant hiss from the ejector most annoying as the rest of the loco is exceedingly quiet. Is there such a thing as a vacuum one way valve? Surely once the vacuum is created in the system and the system is pretty much leak free with such a valve the ejector would only be needed to re-establish vacuum in the system after a brake application?

You thoughts, as always, would be most appreciated.

Regards

NickM

[ejparrott]

The ejector should have a non return ball built into it, but yes they do run continuously.

You should not use the reverse to slow the train, especially if you don't have a snifting valve.

Having brakes on only one bogie is pretty pointless IMO.

Lap position is not required. I can hold a 3-carriage train (2 braked 1 piped) on our 1:80 downhill with the brake valve on our Scot at a constant speed by only opening the drivers rake valve the required amount to 'leak' the system just enough for the brakes to retard the train but not decelerate it.

Fit brakes to your driving truck.

[NickM]

Thanks for the rapid reply EJP, my immediate response to yours would be:

1. Why?

2. Why?

3. Why?

4. As I said, with my PNP brake valve on our 1:43 it's all or nothing.

5. Why?

My dad always said 'why?' was my favorite word when I was a kid; please don't use his favorite reply of 'because I say so!'

[nonort]

Hi I have to agree with EJP why would you not have brakes on all the axles of the train. You wouldn't expect to by a car with brakes on one axle. I suspect that your engine plus the driving trolley is considerably heavier than the the passenger wagons when empty you should not be expecting the passenger wagons to be stopping you and your engine. The brake valve could be modified to give a smooth operation by elongating the ports with a triangular file so as to give smaller pilot port so to speak. I also suspect that you have over done the ejector size none of my engines makes a hissing sound one has the ejector exhaust fed to the ashpan. A large ejector only reduces the time it takes to replenish the vacuum used in the brake application. Does the Hunslet have a handbrake as this would be more effective as a brake due to the weight of the loco. I hope this helps in some way

[jma1009]

hi nick,

you dont state whether your loco has a steam brake and if this operates when the vacuum is released for the train.

if the PNP valve is the one im thinking of you need a more refined brake valve. i do not like steam brake valves where the front of the valve is exposed and held on by a spring. it should be fully enclosed. it is quite easy to operate the vacuum brake if reservoirs are fitted as all you do is watch the vacuum gauge and allow the vacuum to fall a certain amount depending on the brake application. it is quite easy to make a combined brake valve of simple type but with a partial application position as well as full release of the vacuum.

suggest you look at and study the excellent articles by Brian Hughes in ME late 1980s.

cheers,
julian

[ejparrott]

Not a problem, much prefer people challenge my suggestions, so here we go...fuller explanation now as I'm not at work either

May 26, 2015 21:27:57 GMT NickM said:

Thanks for the rapid reply EJP, my immediate response to yours would be:

1. Why? Ok, so if I'm honest, on this one I can't give you a technical answer, but all the ones I've had in bits have one

2. Why? If you don't have a snifter, then you will suck all the smokebox char down the blast pipe as the cylinders reverse their cycle and become compressors. This char will then find it's way through the cylinders and damage all the working faces. Also, you place strain on valve gear components that were not designed to take it. IT's a well known road loco trick, but locomotives are not built to take it.

3. Why? You have two bogies, which should be identical, so use them! You have to be careful with loading and weight distribution if you're only using one bogie. Our club coaches brake much better when loaded...shouldn't make a difference but it does. Also, why build bogies that are not identical? If you're running on 1:43, you need all the braking you can get....Remember, BR had to build brake tenders to run with some diesels to get the braking power up. Stopping the train is more important than starting it.

4. As I said, with my PNP brake valve on our 1:43 it's all or nothing.

5. Why? As above, you need all the braking power you can get, not just when you're running full trains, but when you're on your own as well.

My dad always said 'why?' was my favorite word when I was a kid; please don't use his favorite reply of 'because I say so!'

From your description it sounds like you have one of these brake valves :

www.pnp-railways.co.uk/products/7-10-combined-vacuum-steam-brake-valve/

If you have then you have something wrong. I was driving a Tinkerbell the other week which has one of these but without the steam brake connected. The brake control on that was very fine, exactly as I described with running our Scot - hold the train by just admitting enough air into the system to retard the train but not decelerate it. That was with 4 of our braked coaches which are damned heavy, and an engine that normally runs at Weston Park near Wolves which has a pretty severe gradient too. Have you got a steam brake connected to it? The description says the train brakes should be applied before the steam.

[pault]

If you put the loco into reverse when going forward, snifting valves won’t make any difference as you will actually pressurise the main steam pipes/superheaters, even if the the regulator is shut. This will hold the snifting valves shut negating the value of them. The cylinders acting as compressors will create significant heat which may cause lubrication problems. The air/combustion gasses/grit possibly being sucked down into the valve chest can cause obvious problems. Since the main steam pipes and superheaters have relatively small volumes and no pressure relief valves the pressure in them may reach a point where damage could occur. Opening the regulator would mitigate against a number of these problems.
Personally I would sort the brakes out, brake all axles you can with a controllable system. Hand brakes are useful for controlling speed on gentle descents.

[Deleted]

Fit a vacuum maintaining pump .

 

[steam4ian]

La Chatelier braking is still used on the West Coast Wilderness railway in Tasmania.

On the loco there are separate exhaust stack for the braking steam, as seen by the two brass pipes behind the Funnel.

Other than having that equipment fitted braking by reversing the engine can do significant damage to valve gear. This has been demonstrated in full size practice when somebody forgot to couple the air brakes to the train and then omitted a brake test; the only way they stopped the runaway was by reversing the engine.

[penybontshed]

So its hands off that reverser Mr Moody!!

[ejparrott]

Mountaineer on the FR has her ejector exhausting up a separate pipe behind the chimney. Personally I've never had any issues with ejectors up the chimney, my 3.5" Hunslet has hers in the ashpan.

[GeorgeRay]

Early locomotives had no brakes and the train was brought to a halt by putting the locomotive in reverse. The Rocket replica which was built was exactly the same it required skill and considerable dexterity with the feet to get the slip eccentric valve gear into reverse to be able to stop the train. There was a one shot airbrake fitted for emergency use if all else failed, but it was considered bad form to use it, because an air compressor had to be attached to the reservoir to recharge it. So obviously early engineers allowed for putting it into reverse to stop but presumable this knowledge was lost with more modern designs if damage has occurred when putting into reverse while running forward. :-)

[ejparrott]

Lion (1838) has four little wooden brake blocks on her tender, nothing on the engine.

[gwr14xx]

Throwing a steam engine into reverse to stop it is not unusual in some other forms of steam traction. As a schoolboy, I was fascinated by the 2 cylinder compound beam engines that powered the old Southampton floating bridges - being marine engines, they were fitted with condensers, so that no steam was wasted - an added bonus was the vacuum that was generated on the exhaust side of the engine. Having crossed the river, when the 'skipper' rang down for half speed, the steam would be shut off and the engine thrown into reverse - to carry on coasting towards the shore on the vacuum. The next ring would be for 'slow speed' - in which case, a quick puff of steam would kill the vacuum. The final ring would be 'stop' - and a final puff of steam would bring the vessel to a standstill. These floating bridges were hauled across the river by a large hawser with one turn around a drum about 8 feet in diameter, and relied completely on the beam engine to keep the vessel in place (or even inch it away from the shore as the tide dropped).
Eddie.

[Deleted]

Almost all steam locomotives had good brakes in later years .

Real problem though was that the engine brakes alone are often inadequate for stopping a heavy train  . Through braking on passenger trains came in early so that was ok but unfitted goods trains were still in use up to and even past the end of steam working .

On the steeply graded lines which abound around here it was sometimes nescessary to use two or even three engines on heavy goods trains - not only to drag them up the hills but also to provide adequate braking power when descending .

There were strict rules about amount of braking power needed for specific trains and routes though drivers did have some discretion and some no doubt ignored the rules now and then .

Common practice when running unfitted goods trains on the worst graded lines was to stop at scheduled locations to apply or release a specific number of handbrakes on the wagons before proceeding . This was often done several times in one journey .

If you look at old railway pictures you will sometimes see cast signs saying things like ' All Goods Trains to Stop Dead Here and Pin Down Brakes '

Further braking was supplied by the guard and brake van but the amount available was usually woefully inadequate .

Sometimes multiple brake vans were used .

(By the way an important auxilliary purpose of a brake van was to keep the train couplings taut)

Right up until just a few years ago all braking when shunting of full and empty coal wagons at Powells Dyffryn yard just up the road was still done by means of shunters running alongside wagons and applying brakes by hand - sometimes with a pole and sometimes by just jumping up and applying their full weight to the brake lever while riding precariously along .

[Deleted]

May 28, 2015 10:45:40 GMT gwr14xx said:

Throwing a steam engine into reverse to stop it is not unusual in some other forms of steam traction. As a schoolboy, I was fascinated by the 2 cylinder compound beam engines that powered the old Southampton floating bridges - being marine engines, they were fitted with condensers, so that no steam was wasted - an added bonus was the vacuum that was generated on the exhaust side of the engine. Having crossed the river, when the 'skipper' rang down for half speed, the steam would be shut off and the engine thrown into reverse - to carry on coasting towards the shore on the vacuum. The next ring would be for 'slow speed' - in which case, a quick puff of steam would kill the vacuum. The final ring would be 'stop' - and a final puff of steam would bring the vessel to a standstill. These floating bridges were hauled across the river by a large hawser with one turn around a drum about 8 feet in diameter, and relied completely on the beam engine to keep the vessel in place (or even inch it away from the shore as the tide dropped).
Eddie.

That's interesting .

Steam engines in steel hot rolling mills were always fitted with instant reverse valve gear - the mill rollers could not be allowed to be stopped on the plates or rails being rolled both because an indentation would form and because the plate would be chilled locally to below acceptable rolling temperature .

Some steam rollers were also fitted with instant reverse for essentially the same reasons when laying Tarmac . 

[ejparrott]

Which is why Brake Vans weigh in at 20T, and aren't just a shed on wheels housing a bench and a brake wheel...hard work explaining it to some people though...

[penybontshed]

That's also why the work of a guard on an unfitted freight was so skilled. Knowing the road and being able to judiciously utilise the braking force of the van to assist controlling the train.

[Deleted]

The old railway companies seem never to have had much interest in improving brake vans . On most railways it was very late in the day before heavier and longer wheelbase vans with more braking power were provided .

LNER brake vans saw rapid improvement - legend has it - after Gresley
got a lift back to the works on the brake van of a night goods train and
was shocked by the appalling riding of the vehicle and it's poor
braking .

GWR hardly developed the brake van at all - the essential design of theirs was the same for nearly eighty years .

It is hard to imagine now the life of an unfitted goods train guard - completely alone and isolated trying to control a train with no communication with the driver except whistled instructions from engine and swung lamps at night time .

[pault]

Being a bit thick can anyone explain to me how the valve gear becomes damaged if the transition from forward to reverse is made relativity slowly when related to the rotational speed of the engine. As you move from full forward towards reverse the valve travel and velocity decrease to the point where there is little movement of the valve and the velocity is fairly low. A change from forward to reverse at this point should cause little distress.

There is of course the documented damage to one of the leader power bogies when it when from forward to reverse however that was a sleeve valve set up with sleeve rotation as well and could be described as a troublesome design at the best of times. For that reason I don't think it counts in this situation.

I would venture to suggest that people do not do it on railway locos for one of two reasons. A) mechanical sympathy with the loco, I agree with that.B) most loco wheels are braked adding additional braking force on the wheels is likely to result in them locking or rotating the wrong way which will have the effect of reducing brake force. A traction engine unlike a railway engine has more grip than power so significantly more brake effect can be put to good use.