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From Plans / Re: Senft "Poppin" engine
« Last post by crueby on Today at 02:43:24 PM »
Good ideas on the redesign. Still curious as to why that 2-56 die did not work - maybe they just botched the edges on it. I've gotten a few drill bits that were ground wrong, with the area of the flute behind the tip projecting higher that the tip, so all it did was rub on the metal. Was the shaft you were threading brass or steel? If brass, it should have cut fine at that diameter, if steel it would need to be a bit smaller. I'm amazed that you have done this many models without making threads that small, I use the 2-56 and 3-48 all the time. Though, George would call those sizes the huge ones, for the tiny work he does!
From Plans / Re: Senft "Poppin" engine
« Last post by Brian Rupnow on Today at 02:28:15 PM »
This morning I have decided to put on my design engineers hat. Mr. Senft did a marvelous job on this engine, But---there are a couple of spots that I see as potential problems. The 1/8" diameter cross shaft which operates the valve was originally designed as having the ends turned down to .085" and threaded #2-56 and the flat arm with the roller on it was sandwiched between the nut and the shoulder on the shaft. There was no key of any kind to make that arm hold it's position, and as expected, it slips. I have been warned of this by my own experience on similar mechanisms and by Nick, a gentleman who has successfully built and ran one of these engines. Yesterday when I tried threading the ends of the rod I had made with a new #2-56 die I had just purchased, it screwed up the end of the shaft and didn't leave any thread??? So--this morning, a redesign. The cross shaft now has plain ends with no turn down. The plate "arm" how has a hub with two #5-40 set screws holding it in position on the shaft. The far end of the shaft which originally held a spring clamped between two hex nuts will receive a similar treatment with a hub and set-screws holding the spring.

Engines / Re: Building a new Upshur Farm Engine
« Last post by cheepo45 on Today at 02:24:12 PM »
I think this will be a great engine. My first model engine was an Upshur Farm Engine built in 1996. It has many hours of running on it, and it still runs well. I have displayed it at every Cabin Fever show except the first one. Thanks for posting, Dave!
From Kits/Castings / Re: Tug's Corliss Tandem Compound Project
« Last post by Gas_mantle on Today at 12:36:18 PM »
Looking fantastic, the base itself is a work of art  :)
Thanks Brian,
It's nice to hear from a fellow Canuk.
Chatterbox / Re: Talking Thermodynamics
« Last post by MJM460 on Today at 10:53:33 AM »
Hi Gas Mantle, I am starting to feel that you are right, and much smaller pipes could be used. 

Certainly energy losses due to change in velocity at size changes directionally lose pressure, but when the calculations are completed with realistic model engine data, the losses, even though they occur over and over, do not add up to much.  The same energy losses occur at changes of direction, and in driving the steam around the valve outline but in total for a the typical length of tube used on a model again is not much.

My initial thoughts on velocity are certainly over conservative, and much higher velocities are definitely acceptable. 

All the discussion so far has been about energy considerations and the effect of velocity changes.  In addition, we need to take friction into account as a source of loss, which is especially significant on long pipelines.  I have looked to the old fluid mechanics book, and carefully checked the calculations.  For drawn tube, which has a very smoothe wall, the friction factor results in about 0.3 kPa for a 300 mm length, and still only about 2 kPa for Willy's 28 inch long tube, so this again does not explain much.

I do keep thinking I am missing something, as there are some inconsistencies.  I am sure that I have read recommendations based on a proportion of piston diameter.  And most models seem to have at least 5/32 tubes.  Also, if you look at scale sizing, I am not sure what a typical full size engine of the type Willy is constructing would be.  Perhaps 4" bore, so 3/4 inch bore is about 1/5 full size.  I don't know what size steam line would have been used, but perhaps around 1 1/2", so proportional diameter around 7.5 mm, say 5/16" tube. 

Certainly exhaust has additional considerations.  First a much higher degree of pulsation means acceleration losses at every exhaust stroke.  And as I mentioned earlier, a little back pressure reduces flow from the exhaust, meaning higher back pressure on the piston and reduced work output.  I suspect this effect increases the importance of those small pressures enormously, but I am rapidly running out of ideas for calculations that would prove it.  I might just have to accept that much smaller pipes would be satisfactory unless more information turns up.  A bit of a surprise after working for forty years with full size piping, which is sized to reduce pressure drop, though the pipes are much longer.

Of course the obvious answer is to try it.  The steam pipe on a simple test setup, (not after the full diorama treatment) is not a very big task. I would be very interested to hear the result if anyone just tries a very small tube, and I think I now have to add to my project list a few experiments on pressure drop.  I think that measuring the pressure drop would require better instruments than I can afford, however if I do something simple, like say setting up my boiler and engine about  a metre apart, and make up two or three steam pipes say 3/16 that I currently use, 5/32 and 1/8 if I can get a suitable length.  I think it is used in refrigeration so it should be available, but the lengths I have at the moment are only about a foot long.  If I get sensible results with a very free exhaust, it would be interesting to continue by trying a smaller exhaust with some length as well.

The advantage of this approach is that the engine will make the flow pulsations realistic, and I can calculate the flow based on water consumption.  I am thinking some plastic tube will either melt or provide suitable insulation.  Don't hold your breath, but I will get there eventually.

Hi Willy, what do you think would be a suitable scale steam line size for your engine?  I have probably exhausted that topic in discussing Gas Mantles comment.  While in principal increasing the size earlier is best, in practice I think I finally have to agree that in practice you are unlikely to see a difference, especially with the governor in operation, so let availability of the tube and appearance dictate.

When there is air in the boiler, and steam is introduced by evaporation over the whole liquid surface area, the system is well mixed and we have liquid and vapour and a phase change and the air affects the boiling temperature.

In your steam pipe, it is very different, you are just mixing two gases, the air does not affect the liquid boiling temperature.  When you first open the boiler valve and steam enters the end of the pipe and the small cross sectional area does not allow good mixing.  There is a tendency for the steam to act a bit like a piston, and compress the air to the same pressure as in the boiler.  However, without a solid piston to clearly separate the two, there is some mixing and the interface will involve a more or less gradual change in concentration from steam at the inlet end of the pipe to air at the other, with most of the change occurring over a short length.  If the pipe is still blocked at the engine end, that random molecular motion we have talked about before will result in mixing over a longer length, but I am not sure how long it would take to be completely mixed.  More likely you open the valve to the jacket and engine, and the flow is initially air but quite soon the entire mass of air has gone and you then have steam from the boiler.  Of course, if the boiler already had air in it from when it was filled, the process will involve the air in the pipe being pressurised by that steam/air mixture.  There will still only be slower mixing with the extra air initially in the pipe, so the engine end will still be mostly air until it is purged out.  As there should be no air being admitted unless there is a lot of air dissolved in the feedwater, the mass of air initially in the boiler is soon purged out and the engine is run on steam.  The initial air in the steam jacket will affect the condensing temperature, which will not be 100 degrees until the air is purged out.  Makes that initial heating a bit gentler I suspect, ideally an air vent as well as the condensate drain valve, but a bit to theoretical to worry about unless you find a problem.

Yes, the steam leaking from the locomotive safety valve wastes energy, as the heat in the steam cannot be recovered and used in the engine, but as you say, the coal fire is not as easy to turn down as your electric element so they don't have much choice.  Another advantage of your electric boiler, the heat input is fully controllable between zero and 100%.

In the talk about pressure drops, I have glossed over the heat transfer issue.  There is the same flow through the pipe, what ever its size.  Clearly, a larger tube has a larger surface area and a longer residence time for heat loss so probably looses more heat.  On the other hand, a smaller tube has higher velocity so higher convection film coefficient on the inside thus increasing the heat transfer.  So pluses and minuses.  I think the main thing is that both require insulation, and if the outside temperature burns if you accidentally touch it, try more insulation thickness.

I thought I was aiming for a shorter post tonight, just as well I was not expecting a long one.

Thanks for looking in,

From Plans / Re: 1/3 Scale IHC Famous
« Last post by TobyTetzy on Today at 08:49:48 AM »

a little update of our IHC.

My father soldered and rounded off the tank and crankcase.
And has built the water pumps holder.

Next, some levers were built. For that I could do the blanks on my CNC milling machine.
My father then finished the rest of the levers.

Some parts of the tank fittings are already finished.


From Kits/Castings / Re: Lane and Bodley 400hp Corliss
« Last post by sco on Today at 08:42:17 AM »
Interesting that the key does not look like it has a keyway in the shaft. Possibly a step turned on the shaft which would make it a larger dia than we can see but still a very flat key.

Maybe there is some weight reduction going on in the web and the plate is simply to give a neater look by covering the void

Back to the oilers, the photo would suggest that they screw to the darker "plate" which sits ontop of the cap and may not be screwed directly into the cap which could be covering a trough with several oil holes down to the bearing to spread the oil across it's width. Hope you have been to specsavers so you can see to make those oilers!

I have a better picture of the key - will post when I get home, it has a very shallow register (at least what is visible) in the crank but also a surprising amount of side clearance.

From Kits/Castings / Re: Lane and Bodley 400hp Corliss
« Last post by Ramon on Today at 08:26:25 AM »
That's a good point about the key thickness Jason - wonder if anyone from over the pond can shed any light on it's function and make up. Can't see why they would want 'weight reduction' in such a high stress area - surely they would do that in the web body itself if weight was a concern?

Oilers shouldn't be too much of a problem Simon - I have a easier way than using glass tubing should you want. You'll just need to buy yourself a good paint brush :D

From Kits/Castings / Re: Tug's Corliss Tandem Compound Project
« Last post by Ramon on Today at 08:15:19 AM »
Morning guys, thanks for looking in.

Willy - maybe you could bring that catalogue to Forncett if you wouldn't mind - I'd love to have a look at it. I too have only recently seen how to hold hex in a SC 4 jaw - I think it was a post on here somewhere. Works a treat as I used the idea several times on the brass bits just done.
'Ten shillings a ton' - Ha! I went to post a letter the other day - second class. Gave the woman a pound and didn't even get 'ten shillings worth' of change  :o - Inflation eh ::)

Jason - Finally managed to get some paint on the cast parts yesterday - no pics as I want to get the masking off first. I'm still not too sure about the shade of green but it is growing on me  :)

Thanks for your comments John - the feeling is entirely mutual as I'm really enjoying what you are doing too  :ThumbsUp:

Will try to get some pics later but I'm off out this morning with probably garden later.

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