Author Topic: Just been to collect my new toy - a Tubal Cain 5" vertical boiler  (Read 4390 times)

Offline Jasonb

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #15 on: November 09, 2017, 07:16:17 PM »
The only disadvantage of a steam pump is that it will use up steam so you will need to add back more water. Maybe think about a mechanical pump driven from the engine which would give it something to do rather than just go round and round.

Offline Gas_mantle

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #16 on: November 09, 2017, 07:29:21 PM »
Thanks Jason, I have contemplated using my Stuart 10H as a permanently attached feed pump engine. The boiler is intended as a general purpose item that I can use for different engines but I'd consider using the Stuart just as a feed engine if I can buy or make as suitable pump.

Offline Stuart

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #17 on: November 09, 2017, 08:42:43 PM »
Those pumps are tiny more like watch making , I have built on it does work but very tricky to get going , as it has a slide valve controlling a shuttle valve in the same chamber itís very congested in there .

I found sealing the valve plate a bit troublesome

Get ready for 10ba fixings  :Jester:

Stuart
My aim is for a accurate part with a good finish

Offline Gas_mantle

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #18 on: November 09, 2017, 08:46:29 PM »
Thanks Stuart, I've seen on youtube that a few people have had trouble getting them to work well and that kinda puts me off.

Do you think your 3" pump would supply enough water to feed a 5" boiler ?

Offline Jasonb

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #19 on: November 09, 2017, 08:50:27 PM »
You need a proper sized steam pump :mischief:


Offline Gas_mantle

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #20 on: November 09, 2017, 08:54:58 PM »
Wow that's a stunner Jason, is it one of your barstock creations ?

Online MJM460

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #21 on: November 10, 2017, 05:12:11 AM »
Hi Gas Mantle, when you evaluate those feed pumps, the boiler pressure is not really an issue.  The steam piston has boiler pressure, and the rod force is differential pressure on the piston times area.  With and free flowing atmospheric exhaust, gauge pressure is essentially the same as piston differential pressure.  On the other hand the water ram is working against the boiler pressure with a little allowance for the check valves.  So the ram needs a force boiler pressure times ram area.  The steam piston is always enough larger than the water ram to have an adequate force margin so the pump will operate.  Normally I expect the steam would be regulated down to get the right speed for the required water flow, but that piston rod force is always just enough above the ram resistance to overcome friction as the pump operates.  In principal it is quite efficient on steam consumption and has the advantage that the steam consumption is reduced at low flow.  Thermodynamically, the power required by the water ram is a very small fraction of the power available from the same mass of steam, so it should not add greatly to the steam load.  However, in a model pump, it is difficult to keep the friction forces in proportion, so more important than the theory is the experience of others in using these pumps.  And Stuart's comment on the one with the shuttle plus slide valve being tricky may be the deciding factor.  The smaller one with the simpler valve gear may be easier to make, but I don't know if it is any easier to adjust for reliable working.

An engine driven pump has the advantage that the water flow is always proportional to the engine speed.  Just what you need for any transport operation like a locomotive or a boat, but for driving several models on a display, the relationship is not quite so direct.  I believe a bypass is normally used to balance the water flow, wasteful of power if you are needing the max, but not so important if you are looking for a load for your engine anyway.  Most designs I have seen are gear or worm driven, as the volume of water required to make the steam for each engine revolution is very small.  Some have a few stroke adjustment steps to get it nearly right.  A simple boiler steaming test will give you an idea of the amount of water you need.  Practical considerations, which I will leave others to advise on, will determine how much you need to allow for real pump volumetric efficiency, and which is actually easier to make work really well.  Like you, I am still a beginner machinist, and have not built either.

Both would make great additions to a display, and in the spirit of the principal of having two separate water make up devices, perhaps both could eventually be incorporated into your display.

MJM460
The more I learn, the more I find that I still have to learn!

Offline Jasonb

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #22 on: November 10, 2017, 07:40:35 AM »
Wow that's a stunner Jason, is it one of your barstock creations ?

Indeed it is http://www.modelenginemaker.com/index.php/topic,4438.0.html

Offline sbwhart

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #23 on: November 10, 2017, 07:54:52 AM »
Hi Would a southworth pump do the trick I think you can still buy the castings but to be honest casting aren't really needed it can easily be made from bar, all you need is the drawings.



Stew

PS this is the link to the build log http://madmodder.net/index.php/topic,4763.0.html

Stew
« Last Edit: November 10, 2017, 08:27:27 AM by sbwhart »
A little bit of clearance never got in the way

Offline Gas_mantle

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #24 on: November 10, 2017, 02:36:12 PM »
Jason, is your pump capable of pumping against boiler pressure? it looks a great model  :)

Stew, yes the Southworth pumps are still available here :-

http://www.southworthengines.com/steam-feed-pumps/vertical-steam-pumps/

I had your Potty Grasshopper design engine running on coal yesterday, it runs great. I'll make a video of the boiler powering it in the next few days.

Offline Jasonb

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #25 on: November 11, 2017, 08:12:18 AM »
When I made it I had no intension of using it to feed a boiler so some of the construction used would probably not be upto working at 100psi, I'm thinking mainly of the JB Welded joints mostly as the soldered ones would not be a problem.  The Original cast version would not have had these problems and if scratch built to that size could probably be silver soldered together. I have also got the packing quite loose so it runs slow and smooth with no load so that would need attending to if working at higher pressure.

It will inflate a latex/vinyl glove held over the pump outlet when running on a few pounds of pressure.

Offline Gas_mantle

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Re: Just been to collect my new toy - a Tubal Cain 5" vertical boiler
« Reply #26 on: November 11, 2017, 02:39:37 PM »
Thanks Jason, I'd be interested to know how it performs.

I had another go on coal today and it's full time job keeping it fed with coal and water, no doubt a better pump will help but there's certainly a knack to firing these things properly that I haven't yet mastered   :facepalm:

Offline NickG

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I know itís been a while since the last post on this thread but it looks like a lovely boiler. Would a small injector work with this sort of setup?


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