Building a Boiler for a 3 1/2" Gauge Locomotive

[sbwhart]

StewThanks

David/Tim/Graham/Jack

Jack

I will be doing a hydrostatic test myself before I submit the boiler to the inspector, the reason I havn't done the test is the gauges I have are of unknown quality (they followed me home) and I don't know if they are working correctly, so I could end up testing at far too high a pressure and cause damage to the boiler, the club inspector is going to test them against his calibrated gauge which I'm waiting for him to do this before I do the test.

If you are going to source your own material for a boiler jmake shure its of the correct thickness with the correct fastor of safety for the working pressure of the boiler and that any tube is of seamless type.

Cheers

[Bernd]

Stew,

 Very nice build and write up.

I'd like to add something of interest here at this point since it's time to check the boiler for leaks. I don't mean to hi-jack the thread, so I'll make it short.

A net search,some past reading, and having been a memember of a live steam club, has got me to understand what goes into testing a pressure vessel. There are acutally two tests. The so called "hydrostactic" test can't be preformed at home, or maybe it can. Reason I say this is because a hdrostaic test has the pressure vessel in a tank of water. The pressure vessel is then brought up to whatever the pressure it needs to be and the displacement of the water is shown on a gauge. For more info on this go and do a wikipedia search on hydrostact test.

The other test is, I believe just called, a static test where the pressure vessel is filled with a fluid and checked for leaks. I couldn't find anything in Wiki for that.

If this subject is going to get carried on beyound Stews build here, please start another thread to disscuss the merits of this subject.

Now I return you to Stew's boiler build.

Carry on Stew.

Bernd

[Brass_Machine]

Nice job Stew. Great write up too!

 

Eric

[NickG]

Excellent Stew   
Bernd,

I believe the only tests required or our Boilers are hydraulic test - (correct me if I'm wrong Stew) water pumped into boiler to 1.5 times working pressure (probably around 120psi for Stew's) it's got to hold that for a set amount of time which a certain permissible drop in pressure. Then there's the steam test, really to check all fittings and mainly that the safety valves can release sufficient steam such that the pressure won't rise a certain amount over working pressure with the blower fully on.

I think these are done every year, the boiler has to come out of the frames every 4 years (not 100% sure on that, think it's changed recently.)

Cheers,

Nick

[madjackghengis]

Hi Stew, thanks for clearing that up for me, I've read about such testing of boilers for decades, but never had to deal with such a thing myself, in my own line.  I think your boiler looks like it should hold up very well to all the tests, I can't say I've ever seen a better job on structural soldering, and your log shows all the work you've done along the way to make sure everything is in its proper place.  I'm really looking forward to the day you show the video of it steaming, and driving an engine.  You have truly done a "definitive build, particularly having had the problem with door/fitting interferance, and the remaking of the parts that caused problems.  The refit and moving of the mounts and such clearing the door yet keeping a decent looking set up, not too crowded with clutter.  Fingers are crossed for this test mad jack

[Bernd]

Nick,

Yes, that's it, just a plain hydraulc test. The other is a Hydro test.

The one you do is to make sure there are no leaks and that the saftey valves work. Got it straight now.

Bernd

[sjb]

Hi Stew,

Having built several boilers and made some mistakes I can offer this:

The secret to a successful boiler is cleanliness and having enough heat. The seivert 2943 should give you enough therms.

Do not clean your flanged plates with emery cloth.

Mix plenty of flux with clean water.

Use citric acid, Wilkinsons sell it but you need to ask for it.

If you can get hold of an old storage heater they have lots of refractory blocks to make a hearth with. Less gas that way 

Add bushes for the firebox door hinges.

Do not skimp on the chamfering when making the foundation ring.

Use 1/8 rivets for side stays and fit them before fitting the firebox door plate as it's easier to braze them that way.

If you can get hold ALEC FARMERS book on boiler making it's worth the read.

If you know all this already please ignore, the work looks good so far.

kind regards

Steve

[sjb]

All,

Ignore my last post, Just realized there are lots and lots more pages, doh. 

Steve

[madjackghengis]

Well Steve, with all that boiler advise, and just noticing all the posts, we expect to see some fine work out of you now!  I've been watching this build since it started with intense scrutiny, as I intend to build one for a steam engine I'm working on, and Stew has done a bang up job in both the build, with great material, and good working practice, and in the write up, showing all the details, and truly providing a "definitive build log" for any newbie who has never built a boiler, like myself, but who plans on doing one, and wants to do it right.  I'm looking forward to the posts you will be putting up for us to see, consider, and poke fun at, or demonstrate our awe, which ever is the right thing at the time.  Welcome, if I may, to a great bunch of guys building engines and things. mad jack

[sbwhart]

Thanks for your input Chaps.

I've had this on hold for a few weeks, as I've been waiting to have some pressure gages checked out I'd acquired them over the years and was not sure if they were working OK and I didn't want to test the boiler with them not being sure if they worked. The guy who was going to check them let me down somewhat so last weekend I retrieved them.

After giving it some thought I thought the best thing to do was to make a manifold so that I could compare the gauges one with the others (I've four to choose from) that way a faulty gage would be eliminated by the other three.

I connected them to the boiler feed pump I made, like this looks a bit heath but it worked.



I couldn't get the gauges to tighten so that you could see both faces.

But this is what I got.





They were all different scales but I was able to detect that one gauge was reading 20 PSI light so that was dumped the other three were Ok and gave similar readings with each other.

Tomorrow will know be the big day:-I'll fix a couple of leeks i've got with the screw coupling on the regulator and one of the screwed longitudinal stays, then it will be fingers crossed.


This will be own test if all goes well I'll cut the end off the stays off and submit the boiler for official inspection.

Stew






 

[shoey51]

Good luck Stew but im sure all will be fine. I will be in London on sunday so probably wont find out your results for a month.
If i get a chance to log in ill leave a comment

cheers Graham

[Stilldrillin]

Good luck Stew!  



Oooohhhh...... Graham! Not long now......  

I tried to get you two to meet up....... Hmmmmm...... 


David D

[sbwhart]

Thanks Graham/Dave

We'll have to see what we can do about a meet up.

Stew

[Dean W]

Good luck, Stew!! 
As you may know, your build here is a popular one.  Good to see what you're up to with it.
I like your idea of testing the gauges against each other to check calibration.  The "rotten
egg elimination process". 
 

Dean

[sbwhart]

Well I sort of tested the boiler yesterday, I took it up to 40psi there was a leek from the inside of the hollow blower stay, so I gave the nut a tweak, when ping the bloody thing broke.



 

So did a bit of investigating the drawing calls for 5/32*22g copper pipe I was supplied 3/16*22g pipe as part of the boiler kit which I turned the end down and threaded 5/32 * 40 which had the effect of thinning the wall of the tube down that and being one turn short to tighten the nuts down resulted in overloading and the break. So I've got to order some 5/32 pipe next week before I can conduct the test again. On the positive side as 40 psi there was no signs of any other leeks.

Stew

[NickG]

Stew, that's unlucky  , at least you found the culprit though. I think I said before, my club wanted to see both hollow and solid stays soldered in - maybe they've seen this sort of thing before. I can't see why not to solder it really or did lbsc have a specific reason for this? All the other ones i've seen are soldered.

Either way, it looks like 1 job and it's an official tested boiler   

Nick

[sbwhart]

I'm coming round to the idea of soldering the longitudinal stays Nick. I showed the inspector the threaded stays last week and he didn't say anything about them, but I know some of the guys at the club solder them.  They screw into the front tube plate which is about 2.5mm thick so they are not holding onto much. I'm particularly concerned with the wet header Its 3/8 * 32 thread and it doesn't feel positive at all, I've screwed it into the tube plate with stud lock but I'm considering bushing it.

Stew

[madjackghengis]

Hi Stew, again, you show the weak point of design, demonstrate it admirably, (hard to get a better picture of tube failure than the one you show), and give us on the sidelines, a lesson for our own build, when it comes time.  Your comment on the "wet stay" and it's 3/8ths 32 thread touches a nerve of my own, having had failures which were just because I took a flat too many on a very fine thread.  Perhaps I'm speaking out of ignorance, correct me if you think so, but have you considered simply firing up a torch and soldering the threaded wet stay in place, as it stands now?  I have long used a "back nut" on long studs threaded into a plate I consider barely within the limits, and have had second thoughts and added solder after the nut, just for security.  Much of the work I used to do was on miniature electronics as goes in military aircraft, and finding hardware that was just barely within its capacity was not unusual, particularly with the equipment that we still had that came from the war era, some of it pre-war, from the early thirties.  With radar and high frequency radio, one is working with boxes and tubes very much like boilers, as "resonant chambers", and the fastening hardware has to hold up to the extremes of flight and the vibration of enormous engines and sheer inertia was a common culprit in the breaking of fasteners.  In any case, I hope your time with the inspector proves out the boiler, and gets you certified, so you can move forward closing it up and all. :nrocks:mostly because of the mechanics who work it. mad jack

[NickG]

Yeah, that's what they said to me, if they aren't being soldered they should be bushed. It's all together a slightly strange design I think. Anyway, you've made a few good mods to yours, it'll be sorted soon, bet you can't wait to crack on with it now!

Nick

[shoey51]

thats bad luck Stew but im sure you will sort it

Graham In sunny midlands lol

[sbwhart]

An update:-

I've now tried two more blower tubes using tube from different suppliers, John and maccmodels, Johns tube was 5/32" I don't know what the wall thickness was, the macc tube was 5/32 * 22g (0.028 wall thickness) they both went ping when I tried tightening them down, now you're probably thinking I over tightened, but this is far from the truth, as a rule I'm what you would call a gentle engineer, some times I would admit I'm too gentle, and having one tube break I was extremely careful. The drawing calls for 5/32" tube it doesn't say what gauge. To put some numbers around the problem in the UK the standard gauge for 5/32 pipe seems to be 22g  (0.028" or 0.71mm) this has to be threaded 5/32*40 ME that will leave a wall thickness less than 0.015" or 0.38mm no wonder it's breaking.

I'm left with a number of options:-

Find some 3/32 tube with a thicker gauge, I've located a supplier who has some 20g (0.036" or 0.92mm) tube but I think he will only be interested in supplying a couple of tons which is out of the question I'm going to call him on Monday and see if he will supply me a small sample (don't ask don't get)

I can get 3/16 * 18g (0.048" or 1.2mm) tube, I would have to increase the thread in the fitting to 3/16 * 40 ME this would leave me a wall thickness of 0.032" or 0.81mm or more than twice what I've got know.

Fit a solid stay and rout the blower around the outside of the boiler.

I think I'm going to go for the 3/16 tube unless any of you Guys can suggest anything else.

Stew

[lordedmond]

Save yourself the bother   run the blower feed out side the boiler and fit solid stays



Stuart

[madjackghengis]

This idea might be more bother than it's worth Stew, but you could carefully peen the end of the 3/16ths tube down to 5/32nds the length of the thread and thus upset and thicken the tube right where you are threading, and actually have it stronger right there, making up for the cutting of the threads weakening the tube.  That keeps you with the original threads in the fitting, no loss of strength in it opening it up for the 3/16ths, and still using the larger and thicker tubing.  It's not too hard to keep a soft tube like copper, round, while reducing its diameter thirty thousandths, but I'd anneal the peened end of it before threading, just to be sure a crack doesn't show up from work hardening.  I've had to do it to get a piece of straight tube into a tapered hole so it could be well soldered in, and had success.  I like to buy studs rather than make them because threaded studs as bought are roll threaded and much stronger than cutting threads for your own studs and I'd recommend rolling the thread instead of cutting it, but I don't know anyone with thread rolling equipment other than for bicycle spokes, and I think they are for fixed sizes and not merely adjustable for different spoke thicknesses.  There's always the possibility of motorcycle spokes happening to be the right gauge and a shop having a rolling machine.  For what it's worth,  mad jack

[NickG]

Stew,

I will whip mine out of the boiler tonight and see how it's been done just for info. Suppose you could route it outside the boiler but where? It could look messy unless you went through cab floor underneath running board. You'd have to go in through the side of the smoke box though as the cylinders are underneath it.

Nick

[lordedmond]

NickG

most of the British standard class loco's have the blower feed outside not though the boiler. my class 4 tank has it outside and fits just under the ejector elbow, just a part of the smoke box furniture so to speak with the ejector itself bolted on there it look fine


I am not evan sure if any 12 inch to the foot loco's had the blower feed integral with the boiler

if the sight of the pipe offends then disguise it as a hand rail


then normal model why was to fit a concentric bush 40 tpi outside and 40 tpi internal and screw that in to the boiler shell and pipe together therefor no stress on the pipe but a good seal if you use copper slip it will seal
 
Stuart