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Post by chris vine on Feb 27, 2021 23:17:12 GMT
The wheels might slip with a chest pressure of 30 psi when running slowly and in full gear.
However, running faster and with the valve gear linked up, I would think it would not slip even with almost full boiler pressure.
I realise that Bongo is bigger than a 3.5" gauge loco, but at speed and linked up, you can open the regulator fully and the steam chest pressure is not far off boiler pressure. No slipping, but plenty of fireworks!
Incidentally, I made sure that the steam circuit was pretty large with a 13 mm ball valve (opening fully) for a regulator and then pipes no smaller in total cross-section afterwards.
Chris.
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Post by andyhigham on Feb 28, 2021 0:14:42 GMT
I have found that slip is unpredictable. One of our club locos has a Tomos 2 stroke moped engine with a 2 speed automatic gearbox. Leaving the station gently on a level track then the track climbs, the loco will shift into top gear on the climb and instantly light up the wheels. Gun it from the station and it shifts up on the level and all is well.
I would expect more slip in the lower gear
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Post by suctionhose on Feb 28, 2021 10:38:44 GMT
The wheels might slip with a chest pressure of 30 psi when running slowly and in full gear. However, running faster and with the valve gear linked up, I would think it would not slip even with almost full boiler pressure. Hi Chris, Agreed that should be the case with a good set of VG. In fact, I remember a private run once where a regulator actuating linkage broke. The owner ran the whole day on the reverser including stopping and all in between! |
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Post by chris vine on Mar 1, 2021 11:09:00 GMT
That must have given the driver/builder considerable satisfaction!
Chris.
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Post by delaplume on Mar 1, 2021 21:04:29 GMT
On a similar vein I have heard it said that to achieve a non-slip start on a big single ( Stirling, Midland, etc..) you leave the reverser in mid gear...open the regulator fully, then slowly wind the reverser into forwards..
Did any of the GWR locos have a steam chest gauge ??.....I can't recollect seeing any....maybe the double-chimnied Castle, Kings and Counties had them fitted along with the mechanical lubricators and speedometers ??
At B'north our Ex-BR (WR) driver encouraged us to get the regulator opened fully ASAP and then continue on the reverser.......This gives max. possible pressure available to the cylinders which caught me out one time..........I used to have a 5" LMS parallel boiler Scot with 3 cylinders and slide valves rather than the piston types.........It was an open day at Kinver and I had 3 trucks fully loaded.....Nice,big, long track with good straights where expansive working can be used.....We were halted at the station stop signal.. and then cleared to proceed by the calling-on signal....
I cracked the regulator and we went forwards a fraction --- then tried to go in reverse !!.......This happened several more times so I asked to be manually pushed into the station where the passengers alighted........Subsequent tests later on indicated that one of the slide valves had moved....and of the 3 you can guess which one it was !!.........Yep The Middle One !! requiring a boiler off job.....
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mbrown
Elder Statesman
Posts: 1,790
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Post by mbrown on Mar 1, 2021 21:50:41 GMT
When some of the Kings and Castles went from hydrostatic to mechanical lubrication, they were fitted with a big gauge (roughly where the old lubricator had been in the cab) which showed when steam was being fed to the atomisers.
That gauge was, in reality, a steam chest pressure gauge, just not calibrated in lbs per sq in. So yes, some GWR locos did have a steam chest pressure gauge!
The BR standards also had these when first built. On the Standards, it was dropped because drivers on some regions couldn't get used to coasting with the regulator cracked open (so they modified things so that atomiser steam was fed whenever the cylinder cocks were closed, IIRC). The ex-GWR men, of course, had always used the drift position when coasting.
The full open regulator technique is only really viable when you have a really well designed valve gear that can be notched right up. If we were ever to open the regulator fully on the Talyllyn (unless the pressure was down in the 40-50 range) we'd be shot!
Malcolm
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Post by Deleted on Mar 1, 2021 22:02:58 GMT
I do recall posting before about why driving loco's was changed from driving on the regulator to then driving on the reverser...I recall it was a definate change of practice, might be the change from slide valves to piston valves? Anyway, LNER used cylinder pressure gauges and generally drove on the reverser with regulator fully open. I now know how 4472's steam pressure gauge was plumbed and will follow as close as possible...  Pete |
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Post by delaplume on Mar 1, 2021 23:08:52 GMT
Here you go}---------From an auction catalogue, the backhead on full size KGV and on a fine detail professionally made model    and finally I post this just for the sheer delight of it all...........Been there, done that only on Halls and Manors and 3205.....B'north to Kdder and return with 10 on....including token changes, run-rounds, hooks and lamps et al.......Too old now but the memory and the heat, aroma and feel through the footplate as we move off stays with you forever.... Hope you enjoy it !! youtu.be/BN3EKv0kYn8 |
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JonL
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WWSME (Wiltshire)
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Post by JonL on Mar 2, 2021 19:59:13 GMT
I saw that type of gauge (Oil/no oil) in an old MAP book on model engineering, I forget which one. I thought it was an over simplified gauge, never occurred to me they looked like that in 1:1 scale!
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Post by andrewtoplis on Mar 2, 2021 20:42:06 GMT
Splendid video delaplume, thanks
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Post by trimleytramway on Mar 2, 2021 22:12:20 GMT
Just a quick point GWR loco’s have the jockey valve for allowing lubrication during coasting worked off a linkage in the cab off the regulator quadrant. Coasting with the regulator slightly open is called drifting in dead some locomotives such as the WD’s have a drifting position on the regulator. Coasting IE no cylinder chest pressure should not cut of cylinder lubrication.
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pault
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Post by pault on Mar 3, 2021 12:58:52 GMT
To see how the Steam chest pressure looks have a look at modeleng.proboards.com/thread/7812/7-1-4-dyno-car?page=2As far as using steam chest pressure to prevent a slip, I would suggest there are far too many variables to make it a reliable tool. Mid gear, brakes on, regulator wide open, drains shut, steam chest pressure should equal boiler pressure but no slipping. Something else to consider is that the pressure is not stable in the steam chest when running so can only be regarded as an average. There are plenty of engines (many miniature ones) you can happily drive with the regulator wide open and just wind the reverser backwards and forwards to control the speed. When doing this the steam chest pressure will always be fairly high |
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Post by delaplume on Mar 3, 2021 14:13:29 GMT
To see how the Steam chest pressure looks have a look at modeleng.proboards.com/thread/7812/7-1-4-dyno-car?page=2As far as using steam chest pressure to prevent a slip, I would suggest there are far too many variables to make it a reliable tool. Mid gear, brakes on, regulator wide open, drains shut, steam chest pressure should equal boiler pressure but no slipping. Something else to consider is that the pressure is not stable in the steam chest when running so can only be regarded as an average. There are plenty of engines (many miniature ones) you can happily drive with the regulator wide open and just wind the reverser backwards and forwards to control the speed. When doing this the steam chest pressure will always be fairly high Spot-on Paul.........The important thing being that the steam route is fully open with no wire-drawing effects or restrictions en. route...... That method you described is how we were taught at B'North, and the one our more experienced drivers would employ........Also the method used on my Scot when the slide valve moved.. Just a note for those not experienced in this method}---- it's only of use when you have a service train ie a decent load on the drawbar, and you have a distance of sorts to travel..... No good for a light engine or shunting etc.... To answer a point made earlier about having a decent valve gear .... Locos such as the Hall, Manor, 28xx etc have inside Stephenson's gear which in full setting actually has negative lead----this then changes to positive as you link-up.........hence their ability to start away with ease... |
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Post by delaplume on Mar 3, 2021 14:25:32 GMT
Splendid video delaplume, thanks Good, isn't it ??....... Notice the way the driver handles the regulator ...... and the fireman's stance of one foot on the loco and one on thee tender, using just the minimal of effort to place each shovelfull just where he wants it to go.... Although the King is a 4-cyl.loco the exhaust is as per a 2-cyl one and when going slowly you can see the fire being pulled forwards and released with each beat.... Each time the regulator is closed you'll see it then cracked open such that the jockey valve will allow oil to pass to the cylinders ( and regulator ).. In these Covid times I know it's impossible but if you ever have the chance of a Footplate experience day then grab it with both hands !!.......... For most people it's a once-in-a-lifetime experience and worth every penny it might cost you..... |
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JonL
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Post by JonL on Mar 3, 2021 18:50:49 GMT
Has anyone here seen a steam reverser modelled? I understand it was of variable effectiveness in full scale, so I imagine it was seldom done in our sizes.
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mbrown
Elder Statesman
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Post by mbrown on Mar 3, 2021 18:59:01 GMT
There have been quite a few models of US prototypes with steam reversers. I can't remember the name for the type they were often fitted with, but it is like a small slide valve cylinder with a combination lever like in Walschaerts valve gear - moving the top of the combination lever displaces the valve and admits steam until the other end of the combination lever, connected to the reversing mechanism, pushes the valve back into the lap position. LBSC described this sort in model form sometime in the 1930s or 40s as I recall.
Less common is the Stirling style reverser (SE&CR). I have never seen a model one in operation, but many years ago (1970s) the town museum at Erith in Kent had a 5"G SE&CR D Class model with what was clearly a working steam reverser to the Stirling design. Although in a glass case, it had clearly been intended to be a fully working model. The Library/Museum was completely re-ordered years ago and I have no idea what happened to the model.
Malcolm
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Post by andyhigham on Mar 3, 2021 20:35:03 GMT
The video that Alan posted reminded me of an interesting fact about the Paignton and Dartmouth railway.
The railway station at Dartmouth has never had a train stop at it, in fact there have never been any rails. The railway is on the other side of the river
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Post by Deleted on Mar 3, 2021 20:50:30 GMT
The video that Alan posted reminded me of an interesting fact about the Paignton and Dartmouth railway. The railway station at Dartmouth has never had a train stop at it, in fact there have never been any rails. The railway is on the other side of the river I watched a program with that station in it Andy, IIRC Brunel built it thinking he would get permission to lay track to it, he didn't. Pete |
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Post by mugbuilder on Mar 3, 2021 23:00:49 GMT
I have fitted steam chest pressure gauges to several of my engines and have noted that if the engine is lightly loaded and on a fairly flat track the needle will bearly move off the pin even if well notched up. It takes a very heavy load on a good hill of at least 1-60 to 1-80 and well notched up to achieve a high steam chest pressure reading. On a level track as soon as cylinder pressure overcomes rolling resistance the piston moves and the pressure drops. The average elevated track with maximum 1-100 grade will not,in my experience,give much of a reading unless a very heave load is being pulled.
I agree with the comment that a steam chest pressure gauge fitted to a full size engine can have an hypnotic effect as I watched one on a Victorian narrow gauge 'NA' some time ago and found it facinating. I suspect that with the continued rapid fluctuation of the needle the gauges quickly wore out.
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Post by John Baguley on Mar 4, 2021 1:23:01 GMT
Has anyone here seen a steam reverser modelled? I understand it was of variable effectiveness in full scale, so I imagine it was seldom done in our sizes. My Brother's 5" gauge Forney has got one. I can't remember offhand how it works as it's a long time since I've driven it. It's got two cylinders, a steam cylinder to move the weighshaft into forward and reverse and an oil filled cylinder to hold it in position. The oil filled bit doesn't work as it leaks so you can only put the loco into full forward or full reverse and nothing inbetween.
You can just about see it in this photo:
It also has steam chest pressure gauges. They hardly get off the stop in normal running but do move when the locos working hard.
It's a very unusual loco that we salvaged from a garage where it had sat for years. It's got a steel boiler.
John
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