A small boiler

[firebird]

Hi

Well today was the big day. Steam test on the boiler. I mounted the boiler on an upturned baking tray to keep the heat off the bench. Mounted using the 3 studs formed on the ends of the stays and resting on a saddle at the near end. Julian (Barneydog) came round to assist/observe/advise and play cameraman. I took quite a lot of video which I have had to cut down and split up in order to upload (which may take a while) and photos as well. Heres how I got on.

The boiler mounted on its test stand.

The first piece of video showing the initial set up.



More to follow

Cheers

Rich

 

[firebird]

Hi

Heres the second part of the video.



Cheers

Rich

 

[firebird]

Hi

You can see from the video that the safety valve didn't work properly. The 'O' ring design worked perfectly on the hydraulic pump with cold water and worked OK with a cold hydraulic test but seemed to be sticking in the relief valve under hot steam pressure. I have made a modification to the relief valve. Do away with the 'O' ring and use a stainless steel ball instead. This is the original design.

This is the modified design.

The only new part is the 5/32 stainless steel ball. The stainless steel valve stem was put back in the lathe had the triangular part turned off. The end was then lightly centred and then touched with a 5/32 drill. A 5/32 stainless steel ball dropped into the brass valve body and with a small punch and hammer the ball was tapped to seat it.

Heres the modified valve.

Under test this worked a lot better.

Heres the last part of the video.



You can see that works a lot better. I expected it to blow off and hold the pressure at a constant 30psi but it drops the pressure to 20psi before it closes off then builds up to 30psi then blows off and drops to 20psi again???????? Any Ideas.

Cheers

Rich

 

[ksouers]

Um, hook a whistle to it?

 

[GailInNM]

Rich,
You have accidentally constructed a "pop" safety valve where the closing pressure is lower than the opening pressure. I like a little bit of pop action as the valve does not leak when you are close to the pop off pressure, and generally set them up for about a 2 or 3 pound differential between open and close.

What is happening is when the valve starts to open, the 1/8 x 1/4 section of the valve stem is acting like a loose fitting piston and since it has a lot larger area than the section closed off by the ball it has more lifting force. Reduce the diameter of the 1/8 x 1/4 section and that will reduce the differential between the opening and closing of the valve. I does not take a lot of reduction to have a large effect as you are both reducing the area of the section acting like a piston and increasing the clearance so the steam can flow past the stem easier.

Gail in NM,USA

 

[steamer]

Ahhh Gail beat me to it! ;D

He is absolutely correct and I would take it down .005" at a time and graph the results.

A few points on the graph and you will probably be able to predict where you need to be.

I believe the function is annular diameter to the 4th power, so a slight change will make a big difference.

Mklotz if your reading this, Let me know if I am right about the 4th power

Plot it in EXCEL and use a trend curve and you'll have it....if you know how to ask, it will give you the equation of the line

Its NOT linear thats for sure!....OK I've over engineered it...its a fatal disease and there is no known cure! ;D

Dave

 

[steamer]

Oh and more importantly....update the print with the right dimension for the rest of us! ;D

Isn't engineering great! ;D

Dave

 

[firebird]

Hi

That makes sense. I'll Strip it and take a few thou off and try again.

I intend to house the boiler in a frame and plate work with wood cladding over the top. I have a sheet of aluminium 2mm thick Would that be suitable for the plate work.

Cheers

Rich

 

[firebird]

Hi

Heres the construction of the burner. I drew and printed the design for the tank. I printed it out on sticky paper, stuck the paper to the brass sheet theen cut it out.

Drill the hole for the feed tube

Using a sheet metal folder to form the box.

Then silver solder together

Cut a square top, make and silver solder in a threaded bush for the filler bung.

Press 2 copper cups and make 2 discs. The method of pressing was described earlier.

This time I didn't bother to dish the discs as it didn't make any difference to the flame and I silver soldered them into the cups before drilling all the jets.

Now drill the jets

The feed tube mounted in a rotary atble on the mill having the bush holes drilled.

Solder in the bushes, solder the feed tube into the tank and solder the lid onto the tank

Solder in the wick tubes.

I had to make some 3/16 copper washers.

Assembled

Cheers

Rich

 

[CrewCab]

:bow: you just make it look so dam easy Rich 8)

Great write up

CC

 

[Bernd]

You can see that works a lot better. I expected it to blow off and hold the pressure at a constant 30psi but it drops the pressure to 20psi before it closes off then builds up to 30psi then blows off and drops to 20psi again???????? Any Ideas.

Cheers

Rich

Ya, you need to hook it to a steam engine. The pressure is raising to the pop off and going to the lower setting then popping off again because no steam is being used. This is what should happen if the steam line gets plugged or the engine stops and doesn't use any steam. I'd say your pop valve is working just fine. Once hooked to an engine and the use of constant steam to the engine this shouldn't happen.

Bernd

 

[firebird]

Hi

I took the valve to bits and shaved .005 off the spindle, it now measures .245. A definite improvement, it now drops from 30psi to 22psi so 5 thou has made a difference of 2 psi approx. I'll take another 5 thou off tomorrow and see if that raises it another 2psi.



Cheers

Rich

 

[firebird]

Hi

Shaved the stem down a few thou at a time. At .235 it works perfectly, maintaining 30psi.



Heres the modified drawing.

Seeing as I have a nice little pump I am going to use it to inject water into the boiler. Sandy suggested at the build stage to fit a bush as it would be easier then than later. I'm glad I did now. Can I make an injector based on the safety valve idea, ie ball and spring or is there something else I should know. I asked earlier if 2mm ally plate would be OK to make the boiler housing from but now replies to that question yet so I'll ask again.

Cheers

Rich

 

[SandyC]

Well done Rich,

I think you now know a bit more about safety valves.... fun ain't they.

The most important thing about them is that they lift reliably at the set pressure and that the throughput (rate of steam release) is such that the pressure cannot excede 10% above the max operating pressure even with maximum firing rate (burner running flat out).

The device you need for the water pump inlet is a NON-RETURN valve.... it need no springs.
I attach a very rough sketch of the type I use... It does not show dimensions directly, however, it is drawn at 2 x full size so you should be able to measure the main dimensions.

I use a Nitrile rubber ball in mine, since I find these seal more reliably than stainless steel or bronze ones, however, if you wish to try a metal ball then make sure you seat it down with a suitable punch (as you did with the safety valve).

Hope this gives you enough to go on.

Ali will be ok for your outer casing but I suggest that you line the inside with 1/4" thick 'Kaowool' ceramic insulation
obtainable from 'Blackgates'
Make sure you leave some air holes along the lower outer edges for the burner to breath.


Lastly, when you come to fit the steam outlets for your engines etc, I suggest that you move the safety valve to the centre bush on your boiler.... well away from the steam outlets...and fit the filler plug to the top of the dome. you may get a localised pressure drop in the dome when running the engines whilst the main boiler pressure could be somewhat higher..... GOOD BOILER OPERATING PRACTICE.

Keep up the great work.

Best regards.

Sandy  ;D


View attachment Non-Return Valve.pdf

 

[steamer]

Rick,

Great Job....as I suspected it "taint linea"

Glad you could creep up on it!

Nice job! :bow:



Dave

 

[firebird]

Hi Sandy

Thanks again for all your help. I have the non return valve printed out and understand it Ok. Am I right in saying that it is screwed in till vertical then locked in position with the nut. Do I just seal the threads with PTF tape. The safety valve will go in the centre bush as per your drawing, it was easier to fit it there (the highest point) and use it as the filler while I was hydraulic testing and adjusting the pressure valve.

Thanks Dave, I'm afraid your level of maths is a bit beyond me, interesting stuff though.

Cheers

Rich

 

[SandyC]

Hi Rich,

Yes you mount it as you have said.

I, personally, don't care much for using PTFE tape on boiler fittings, it often breaks up into small bits inside the boiler (gets cut by the threads) these then float about in the water and can get (and have been found) caught up in steam valves or , worse still, safety valves with the obvious results.

I tend to screw fitting in, with a copper washer fitted, until they are a couple of turns from their final position. I then use a small amount of Loctite 254 (Loc - n - seal) on the last couple of turns of thread and the washer faces, then nip up the fitting (or the fitting lock nut) into it's final position.
Doing it this way eliminates the possibility of the whole threaded length getting jammed in the boiler bush through too much sealant being used.
I find this works every time.

Ok on the revised location for the safety valve...... I had it in mind that you originally planned for the mid-location.... but just thought it of no harm to mention it, just in case you had overlooked it.

Dave,
I think you will find very few things in this model engines lark follow a linear path, especially when it comes to steam...Ha Ha.

Keep happy.

Best regards.

SandyC  ;D ;D

 

[steamer]

Hi Rick,

NOt intended to confuse or bedazzle....just an observation.

Point 1 is where you started diameter wise and the vertical scale shows 10 psi differential

Point 2 is your first reduction in diameter and the resultant 8 psi differential

Point 3 is the last reduction in diameter and the resultant 0 psi differential.

You diameter changed in a straight line ( in blue), but the differential changed in a very non-straight line ( in red)

SandyC.....few things in steam big or small are linear! :big: Still tons of fun though!


Dave

 

[firebird]

Hi Sandy

When I was hydraulic testing the boiler I had copper washers on all the bungs but a couple of them I could not get to seal completely so I used a bit of PTFE tape rolled into a string and that cured the problem. I take your point though that small bits could get inside the boiler. I'll give it a good was out before I use it on an engine. Maybe I should have annealed the copper washers first. If you use lock and seal do the fittings come out OK if they need to be removed for any reason. I have some boiler insulation material, is it fireproof? do you stick it to the inside of the ali case with something?

Hey Dave

Everythings much clearer now ??? ??? ???

Cheers

Rich

 

[SandyC]

Hi Rich,

Using loc-n-seal is just fine as long as you don't go mad with it.

Whatever you do, don't just put it all over the threads..... you just need a small amount on the last turn or two nearest the nut/head/washer...and a little on the washer faces.

I have used it for years and have never had any difficulty removing or replacing fittings.

PTFE tape rolled up and wound round the same location/area of the threads should present no problems with internal break off.... where a lot of users get this wrong is...they wind the tape over the whole thread and then screw the fitting in....the result is the tape gets chewed up and the bits get inside.

Copper washers are supplied ready annealed so shouldn't be a problem.
It may, however, be of some benefit to re-anneal any that are being re-used, since they will have been somewhat compressed and therefore work-hardened.

I always try and use a single washer of at least 0.010" or thicker unless I am adjusting for orientation of say a water gauge fitting, in which case several washers of varying thickness may be required.

'Kaowool' insulation is fireproof and can withstand in excess of 1200deg C.
It is, I believe, a spin off from the space shuttle program...it being a more refined form of one of the ceramic materials tested /developed for the heat shield tiles, however, I believe it did not meet with the mechanical strength requirements it being physically too soft for the intended application...... great heat shielding characteristics though.

I have used the 1/4" thick stuff as a flame shield when silver soldering pipework close to a painted surface with perfect results and not a sign of heat damage to the paintwork. Naturally, I cannot speak of any other brand, since I have not tried any.

It can be held in place using a few small dabs of silicone sealant (this is what I use), or even contact adhesive,,,, if the latter is used, be sure it is fully cured though, before going near a flame source, as this type of adhesive gives of flamable vapours in it's drying stages..... it won't hurt the ceramic, but it don't do the glue much good ;D ;D ;D :'( :'(

Keep happy, keep safe.

Best regards.

Sandy.