Steam Chest Pressure

[mbrown]

I seem to remember that loco being described briefly in the ME many years ago.

Malcolm

[John Baguley]

Hi Malcolm,

Yes, it was. A friend at the club came across the article and gave me a copy. It was the 15th December 1967 issue and the original builder was B.Hatfield.

That was when it was first built and didn't have any valve gear as such - the valves were driven directly by the return crank and it would only go forwards and had fixed cut off. The outside Stephenson valve gear was added later, possibly by another owner.

Another strange feature is that there are no coupling rods between the driving wheels. They are connected by a chain inside the frames.

It still runs very well and is very leisurely to drive. It's not superheated though and you get a constant shower when driving it!

John

[andrewtoplis]

Mar 3, 2021 14:25:32 GMT delaplume said:

Mar 2, 2021 20:42:06 GMT andrewtoplis said:

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..... 

It is indeed a good watch. I was interested to see he puts the King into full regulator which I've not seen all that often - it is a BIG engine after all - I wonder what the train weighed? Certainly you could open one of our Ivatt 2s up fully but you would be going too fast before long, but that is the benefit of wooden bodies carriages.

I'd echo the footplate experience comment, if you get a chance - grab it!

[pault]

Re footplate experience if you want the ultimate experience try this
thewolsztynexperience.org/
You will need to be quick though as this could well be the last year. 50-60 mph on a 2-8-2 through a snow storm at night is an experience I will never forget.

[delaplume]

Mar 5, 2021 12:28:31 GMT pault said:

Re footplate experience if you want the ultimate experience try this
thewolsztynexperience.org/
You will need to be quick though as this could well be the last year. 50-60 mph on a 2-8-2 through a snow storm at night is an experience I will never forget.

That's a great shame if it does happen.........I've not been but have talked with those that have and they say the same as you...As mentioned in that article we are all getting on in life and to loose any of the founding members is always a blow.......Here's a link to some Chinese 2-8-2 locos hauling coal in bitter cold ..


youtu.be/XCRjBNaknRw  ................   youtu.be/Ampco2JqSc8  .......... I think they may have been on here before but always good to see our fellow steam friends wherever they may be.....

ps}--- getting back on-thread, I wonder if they have an outside temperature  gauge as well as a steam chest gauge on the backhead ??

[JonL]

After talking about this years ago I've actually started to embody this on the Britannia (when I raised this it was on the William). Could be an interesting experiment, I'll let you know how it goes

[mbrown]

Just a comment on steam chest pressures...

On the Talyllyn, Loco No.1 has big, flat slide vales which are not balanced. When the boiler pressure was raised some years ago, it was obvious that they gave considerable resistance when the steam chest pressure was high. This translated into severe rattling of the reverser in its quadrant as the force to drive the valves is transmitted back through the valve gear and reach rod.

It has therefore become normal practice to ease back on the regulator when the reverser starts banging, thus reducing steam chest pressure and preventing the old loco rattling herself to bits. There is no trouble timing normal trains on the easier regulator setting - indeed the speed seems virtually unaffected.

I think this shows that there is an optimum steam chest pressure, above which the gains are minimal and the mechanical losses increase - especially with slide valves. A bit like easing off the throttle of your car while still maintaining speed on the Motorway.

It's about being kind to your loco. On the TR, opening up so that the reverser rattles is a black mark for the driver. With so few 27" gauge locos available, we can't afford to break them!

Good luck with your experiments Jon - look forward to the findings.

Malcolm

[JonL]

Thank you Malcolm. It may come to nothing, but to be honest the experimentation and honing and improving is my favourite part of the hobby.

[JonL]

Well that was interesting. As some people speculated the pressures were usually quite low, until I notched up a bit on the long incline, but even then the needle wasn't lifting very far. The only time I saw significant pressure was when opening the regulator before the locomotive was underway; as soon as the wheels has started to move it settled fairly low. More experimentation and experience required.

[dhamblin]

Perhaps you need more of a load for it to truly show how the locomotive is performing?

Regards,

Dan

[jma1009]

I’ve often linked a pressure gauge up to steam chests if I’ve run the compressor to the boiler. Haven’t done it very often as my practice was to test the chassis on air to test and set the valve gear and performance.

I have linked up a pressure gauge to the loco steam chests when completed and in steam. I did this as far back as 1986. Sort of inconclusive so far as I recall. I ought to point out that the steam chest pressure in some miniature locos and in a miniature gauge of the quality of a Freddie Dinnis pressure gauge was ‘spiking’. You don’t really want to subject a high quality miniature pressure gauge to rapid fluctuations.

So that sort of lead me down the valve gear and valve setting route that I had already been interested in, and the draughting - that would include steamways and passages and steam chest volume. And obviously the exhaust side.

I hope I got it right with Roger’s “Speedy” for the smokebox draughting!

Cheers,

Julian

[johan]

Nov 1, 2024 14:31:30 GMT JonL said:

Well that was interesting. As some people speculated the pressures were usually quite low, until I notched up a bit on the long incline, but even then the needle wasn't lifting very far. The only time I saw significant pressure was when opening the regulator before the locomotive was underway; as soon as the wheels has started to move it settled fairly low. More experimentation and experience required.

When I read something like that I start thinking. To me that make me think the following:

1: we are not measuring what we think we are measuring. And this occurs very often I must say (also to me). I'll come back to it later.

2: From your short description I assume that the boiler gauge is a something very respectable and showing a "good pressure". Something like 4-6 bar on a copper boiler. But when you coast along the gauge on the steam chest isn't "registering much". That tells me that somewhere between your boiler and the steam chest you loose your pressure. (if we are measuring correctly) I take it you run with the regulator wide open and the distribution at short inlet. So you would expect the steam chest to be at a pressure almost equal to boiler pressure. It is isn't, then something is throtling. That can be the regulator or the piping. From the typical designs I see in the more popular plans, the regulators are very often with very small steam passages. And piping is always too narrow when even not very close to scale. Don't forget that resistance of piping is related to surface exposed to the steam and the surface goes by square while passage goes by cube. So smaller pipes have very fast a large resistance.

3: Having a "significant pressure" when starting (with an almost stationary engine) fits this. There is time enough for steam to pass the throtling narrows of the regulator and piping. The engine isn't consuming much at that time.

4: I come back to point 1: where was that gauge on the steam chest positioned and how was it connected? If I look at the traditional steam gauges in models, they are connected with some very small pipes. and if they are then connected to a steam chest on a sizable engine then maybe we are not measuring very well when the engine is running at a good pace. Steam pressure can be changing faster then a gauge at the end of a long thin tube can register. When the pressure is almost stable like when starting it can be a better reading.

So interesting observations. But what exactly are we observing?

[John Baguley]

I doubt if anyone drives with the regulator fully open controlling the speed with the reverser although that is probably the way to maximise efficiency. The pressure in the steamchest is then always close to boiler pressure and maximum pressure is available when the ports open.

Everyone? drives using the regulator so except when starting off the steam flow is severely throttled by the regulator so the steam pressure in the steam chest will be very low.

David Wardale had a right job getting drivers of the Red Devil to drive the loco with fully open regulator as they were just not used to driving on the reverser.

The problem with driving like that on a model is that the valve gears are usually pretty poor and give very poor valve events as the cut off is increased. A lot will only run in full gear or close to and few will notch up properly.

John

[Balljoint]

I owned a simplex for many years and tried driving it with the reverser controlling the speed but was never successful and reverted to driving it on the regulator.

I now own a B1, which has a valve chest pressure gauge. I now only use full gear and the regulator when pulling away and within a very short time, the reverser can be notched up and the regulator opened fully. The speed being controlled by the reverser until stopping again.

While on the go, the cut off is around 25% (according to the scale) and the steam chest pressure gauge reads boiler pressure, and because the reverser has quite a coarse thread it doesn’t take much movement to control the speed of the engine. I have driven similar engines with much finer thread on the reverser, which makes the process much more labour intensive, to much wheel turning, resulting in the regulator being used for the majority of the time.

Colin

[chris vine]

During the summer I made a video for our YouTube channel, how to drive a steam locomotive:
youtu.be/Du4vGIhqARQ?si=b-Ftv0UCtriaf_Pc
Just after 21:50 you can see the steam chest gauge. It shows around 50psi on a part open regulator.
Later at the end I open the regulator wide but you only just get a glimpse of the gauge, showing perhaps 70 ish.
One thing I have noticed, which is the same on full size, is that if you partly open the regulator and then start to link up as speed rises, you can see the sc gauge pressure going up with shorter cut off. Less steam is being used so the pressure drop through the regulator becomes less.
Chris 🚂🚂🚂

[JonL]

I can confirm I drive on the regulator, moving the reverser as required for efficiency. The steam chest pressure doesn't seem to spike on mine, but I suppose with 4 superheaters it has quite a lot of residual pressure. As mentioned, I would probably notice it more with a decent load on.