Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[xrad]

Hi George, I will be using the burner I designed shown above in post 30. Here is a larger pic of the plan. The three front views on bottom are different methods for inserting the pigtails. You want some flow so that the hot steam drives the cooler water at bottom of tank down into the pigtails. This is obtained with one end of the tail reaching higher into the tank.   Final pigtail design not chosen yet. Alternating 'high' next to 'low' tail length may be better for mixing?? Or all 'high' on one side...don't know yet.
Some surface are calculations, so don't pay attention to that mess.  All I can tell you is that when the burner hits a 6in coil, the water steams nearly instantly, and then some general calculations on how many pigtails, and how much volume in tank and the the time to steam the tank----just guessing really, but somewhere around 10-12min or less. How long to pressure of 60lbs...don't know???
Endcaps .0625...I may go thicker
Copper tank is .090 thick (L) x 8 in long.  Seemless, very nice, bought 18in off ebay for 45$ delivered a few months back.
Waiting on some 3/16 22 g copper tube for the pigtails.
Electronic water level sensor in middle below steam dome. One stay down the middle, probably brass or stainless...

[ooyah/2]

Hi George, I will be using the burner I designed shown above in post 30. Here is a larger pic of the plan. The three front views on bottom are different methods for inserting the pigtails. You want some flow so that the hot steam drives the cooler water at bottom of tank down into the pigtails. This is obtained with one end of the tail reaching higher into the tank.   Final pigtail design not chosen yet. Alternating 'high' next to 'low' tail length may be better for mixing?? Or all 'high' on one side...don't know yet.
Some surface are calculations, so don't pay attention to that mess.  All I can tell you is that when the burner hits a 6in coil, the water steams nearly instantly, and then some general calculations on how many pigtails, and how much volume in tank and the the time to steam the tank----just guessing really, but somewhere around 10-12min or less. How long to pressure of 60lbs...don't know???
Endcaps .0625...I may go thicker
Copper tank is .090 thick (L) x 8 in long.  Seemless, very nice, bought 18in off ebay for 45$ delivered a few months back.
Waiting on some 3/16 22 g copper tube for the pigtails.
Electronic water level sensor in middle below steam dome. One stay down the middle, probably brass or stainless...

Hi xrad,
Thanks for the pics


Your boiler idea is more or less the same as the one that I made,my boiler had a 2" dia shell with 9 x 1/4" dia coils coming from the underside as shown in pic No 1.


The burner had a 1.25" dia flame tube with a vaporizer coil around the tube , jet in burner was .025" and burned paraffin ( kerozene ) from a copper tank pressurised to 60 p.s.i. as shown in pic No 2.


I fitted a sight glass as shown in pic No3 and to get a decent column of water made banjo fittings top and bottom of the tube.
This proved useless as the turbulence inside the boiler under steam was so violent that a water level reading was impossible.


Pic No 4 shows 3ft of 1/4" dia copper super heater tube coiled down the inside of the casing in direct line of the burner,
150 p.s.i. was raised in about 30 secs and it was necessary to have  a constant water feed.


I never had this rig in a boat as I went on to develop a flashsteam plant with a Uniflow Poppet valve engine which I installed in a deep "V" hull boat.


I look forward t seeing your further development of the boiler.


George.

[KBIO]

Hello!
It will be intesting to open a post jut for this type of boiler/burner.
I do not want to spoil the Xrad's one, but i have a question!
I made a Scott boiler same type of yours.
Mine is 15cm long and fitted with 8 coils of 6x1x 25cm long, underneath.
I have a 20mm diam burner with 0.35  (from the corner shop)
I feed with gaz @ +/- 2 bar , tank pressure.
I usually get +/-6 bar pressure in 4 min.
My question is: what do I have to improve to increase my steam production.
I need to feed a fast 4cc engine à 7 bar steady and +/- 1500rPM with a 60mm propeller high pitch.
I wonder if the parafin burner shown by George is not the solution.
Sorry to interfere , thanks fot your answer. Eventually in MP.
Regards.

[xrad]

Nice George.  The blow lamps are nice for heat and good for 1/4 in coils.
KBIO: Check to see if your coils are touching.  You may try to space the coils by 1/2 the coil diameter, AND then add a cap at end of coils so that the heat must escape out between the coils. Of course, you also have to build deflector inside boiler housing close to the outside of coils.   Look closely at my design (bottom right of picture is a 'Y' shape deflector that runs the length of the coils to the flue exit).
 I would need to see pics of your boiler.
Otherwise, bigger boiler and more heat....

[KBIO]

Hello!
Thanks for those informations. Yes, my coils are touching and isolation is around/touching the coils.
I'll do pic tomorrow with more details. maybe I open another topic to avoid to spoil yours, as we have pleasure to follow it. What you think???
Cheers.

[xrad]

Spread the coils apart a little bit and open the insulation so heat can circulate .  The rear of the insulation/shield should be open to the rear flue and the last pigtail should be blocked on the backside forcing the heat through the gaps in the pigatils.  I made this change on my last boiler and it made all the difference.  The direct heating surface will increase to almost 50-60% on the coils.

[KBIO]

Hello!
I have to resize my pics, i am not too clever with this!
Cheers!

[ooyah/2]

Hello!
It will be intesting to open a post jut for this type of boiler/burner.
I do not want to spoil the Xrad's one, but i have a question!
I made a Scott boiler same type of yours.
Mine is 15cm long and fitted with 8 coils of 6x1x 25cm long, underneath.
I have a 20mm diam burner with 0.35  (from the corner shop)
I feed with gaz @ +/- 2 bar , tank pressure.
I usually get +/-6 bar pressure in 4 min.
My question is: what do I have to improve to increase my steam production.
I need to feed a fast 4cc engine à 7 bar steady and +/- 1500rPM with a 60mm propeller high pitch.
I wonder if the parafin burner shown by George is not the solution.
Sorry to interfere , thanks fot your answer. Eventually in MP.
Regards.

Yves.
I think that your problem is that you want a boiler to feed your engine that is going to produce a fast boat.
I am of the opinion that it cannot  be done using L.P.G. and your small 20 mm dia burner.
During my early experiments with this boiler and a burner I wanted to fire it with L.P.G. the burner would start off very good but with the large .025" jet it started to perform like all other L.p.G. burners by the large volume of gas being used it dropped the temperature in the tank which dropped the pressure until there was virtually no power in the burner.


I then changed to paraffin burner with a vaporizing coil and the fuel tank pressurized to 60p.s.i. which solved the burner problem
As the burner was fired from the 60p.s.i. tankit had to be pumped up when the pressure in the boiler started to drop.
When I developed my flashsteam plant I again used paraffin as a fuel with 3- burners each with a .025" jet and the fuel pump and the water pump were engine driven, this meant that if the engine stopped on the water the burners were extinguished immediately.
One of the problems with a pressurized fuel tank is that if the boat stops the burners keep going which can cause problems.


XRAD is spot on regarding having spaces between the coils but if as you say your boiler is to the same design as mine you need to have a clear passage to allow the gases free passage to exhaust, it has been known with this design to put the exhaust pipe just below the casing opening to act like a blast pipe as the loco boys do.
Also the super heater coil going down into the casing acts as a breaker to hold the heat and spread it around the coils.


If you want to go fast and produce steady high pressure steam as high as 7bar you will need to go to paraffin as a fuel and a large burner to burn it.


What engine are you proposing to use ?


Here is a pic of the boiler that I built, hope that the pic is large enough to see the coil spacing.
Also the link to my flashsteam thread, have a look on page 2 where there are some pics of the engine with the engine driven water and fuel pumps, just click on the image for larger pics. ( page No 2  post No 26)

http://www.modelboatmayhem.co.uk/forum/index.php/topic,24568.25.html


George

[KBIO]

Hello.
Thanks for the drawing George.
This is exactly the one I did: A.Rayman.
I open a new post in R&D steam , to leave the Xrad's clean and easy to follow up.
I'll have plenty questions, anyway.
thanks and see you there.
Regards

[xrad]

Thanks KBIO.

Here are a few pics of the pig tails brazed into place. There are 13 3/16 pigtails on 0.5 in centers, with opposite side offset by 0.25 in. which leaves just the right amount for air space between coils......
Pigtail diameter determined by the burner, which was built first and runs well.

[KBIO]

Hello Xrad.
Thanks for this clear explanation. I guess that I have to rebuild the boiler, as per Rayman's drawing, and listen to what you say with Ooyah.
I'll follow your interesting post and I opened one in R&D to avoid spoiling yours with my comments.
Cheers.

[xrad]

Boiler end plates: First, determine the diameter which is the inside shell diameter minus x2 the thickness of the endplates, plus a hair more.  I made a former out of hard oak floor remnant formed on lathe.   

Cut out the endplates. I used .065 copper. Too thick for shears, and would not fit into my small plate shear. so had to use the lathe. This required a center bolt hole which will be used for the brass stay threaded lug.  Cut copper out a bit bigger than the boiler diameter because you have to form the edge. If you do a nice job cutting it out, you will not have to trim anything after forming. Copper is a PITA to machine so go medium slow rpms with sharp cutting tool. I found that a few drops of tap magic worked fairly well.

Once the copper is cut out, heat it until light cherry red.  I focused the heat on the edges that will be formed.  Easy to form over hard oak a bit at a time. Took four heat cycles to get the piece perfect. Many little hammer dings which will fill with silver solder.  SAnd and egt rid of any rough or sharp edges.

Then I gently pressed into boiler end after fluxing the boiler and the end plate. Silver soldered up well. Need to get near red hot for solder to flow. don't overdo the flux so less runs into boiler.
 
My torch is a small tip for fine work , but I have it hooked to a bottle of MAPP and a big O2 tank so it just works for the endplates.

[xrad]

Here is a brazed end plate. I wanted a nice solder bead so I recessed the endplate. I have to do some work on the steam dome and a few fittings before I braze in the other endplate.
 
The end hole went a little wonky during drilling. The other holes are drilled just undersized and then reamed to correct diameter.
 
I need a pickle solution...

[xrad]

Note: above post states "light cherry red."  By this I mean just lightly turning red....

[xrad]

Had to get some more silver solder....finished most of the brazing except for sight glass mounts.  Tested citric acid(purchased at local health food store). About 2 tablespoons into 1 liter H2O and soaked for 10 hours leaves nice finish. easy to polish if i wanted to.
My H2O pressure set-up tested to 200+ psi multiple cycles without issue. I guess that with any pressure vessel, One test to test pressure (ie one cycle) is not enough. I performed about 15 cycles to 200+ psi and held pressure there after each cycle.  My operating pressure is about 60-70 psi.  So looking good so far.  After final bungs brazed, another pressure test will be performed.
 
cost so far:
~100$ silver solder
~60$ for copper
sight glass set-up 6mm ~ 50$
time in machining bungs, steam dome, and building tank = ~10 hours
 
Still have to make steel housing and smoke stack.....

[xrad]

First steam up:  My calculations were close. It took 10 minutes to reach 25 psi and 13 minutes to reach 50 psi. This is with several small fitting leaks and a leaky safety valve. Also found a pin hole leak #4 coil solder joint(hence the orange flame). Last coil has copper baffle soldered to it.
 
Also, no side baffles or casing which will improve heat conservation.
 
Otherwise...lookin good...
Vid:
https://www.youtube.com/watch?v=tP6ES3Kt7bY&feature=youtu.be
 

[KBIO]

Hello!
It looks nice and performing good.
I have a better idea of the copper end plate which will definitly force the heat around the coils toward the bafle.
It will be interesting to see the performances and the behavior with in the final assy.
Cheers.

[xrad]

Thanks KBIO
On one of my other Scott type boilers, I tried a brass tube with a solid brass cone on the end. It was about 1/3 to 1/2 the internal diameter of the coils. This ran up the middle of  the coils to try to disperse heat to the coils. Concept looked good on paper, but did not work well in real life.  In one experiment, the brass tube melted (no cooling water), so then I tried a solid brass rod with cone tip pointed at flame. I varried the length of the cone in the coils in 3 positions(towards the front at the tip of the heat cone, in the middle of the coils, and 1/3 from rear; but it made no real difference in time to steam pop off.
 
The 3 biggest improvements to design were

1) flame heat
2) rear most coil baffle.
3) spreading the coils
4) helpful but not necessary: wood lagging on top half of boiler.

The detriments were

1) narrow chimney bad..need the largest chimney reasonable in the model design (and depends on height as well) There is a time required for heat to be absorbed into the water, and to get this correct is a balance between the maintaining at a 'set' value heat entering the system and then heat absorbtion, and then the heat leaving the system. 
2) heat flow from out of the coils needs no significant restriction as it enters the smoke box towards the chimney (so about 1/2 inch gap to internal baffle all the way around the coils)
3) Flame heat must be kept up. I used a partly heated fuel cannister kept at near room temp. If the gas cools, less heat and worse boiler perfomance.
4) impingement of airflow to burner is as much an issue as backpressure from poor exhaust, so need to watch this as well
 
The boiler steam test in my above post was with cold water out of a basement tap. Probably in the 40 degree range.  Room temp water would have shortened the boil time. Also the boiler was nearly full (I suspect 80% full) so that is about 720cc, which is a good amount to heat off a number 8 jet.
 
 

[xrad]

Boiler box almost complete...

[xrad]

9 minutes to 50psi with the above setup.....

[xrad]

Boiler nearly done. If you add ten tablespoons of citric acid to hot water, your boiler will be clean enough in one hour. Rinse inside and out very well.

Components of the boiler base:  Outside shell, inside cone baffle, bottom shelf(stainless).  The internal cone baffle opens slightly towards the smokebox. This is to allow the heat to expand and flow out towards the smokebox because of the last coil blocking baffle. So there is about 1/4 in air gap at the front progressing to about 1/2 in at rear(smokebox) end.  If you hold your hand over the smoke stack, the heat does not come shooting out. it has a more gentle but relatively hot flow pattern. Much heat is contained and therefore transferred to the water by my baffle design.
 
using harbor freight blow torch. I bought the 29$ version because it had a piezo start. Yep, crap. that lasted until just after the first heatup. Buy the 19$ one. Hooks right up to propane tank. It makes a VERY hot flame. I had it set on med low via handle valve. Too huch heat and all your fittings will fall off. It has a ~2.5 inch dia torch head so not good for small jobs...
 
Hardwood lagging almost done...
 
Painted with VHT 900 degree brake caliper paint. It will not take direct flame, which is why the baffle is not painted.
 
Remade the water side of my pump, now it works great(only one side used now). 3/4 steam piston, 1/2 water piston. There was something  wrong with the original internal channels. Even with new balls and seats, it never had any pressure.....If you look really closely, you can just see the edge of  a bright spot in the front top of the water pump cylinder. this is a small drill hole for air relief from topside of piston.

[xrad]

For any beginner boilermaker like myself, this has been a great project, and not too complicated. I think this boiler is much more efficient than the Stuart and runs better with gas (stuart would be better with the blow torch on parrafin/kerosene).

I think this is now a great match for the Stuart marine twin going into the Tramp Steamer. I have a good duplex waterpump, hand pump, electronics for water level control.

Now to design the water tanks and general layout.....

[xrad]

finished the lagging. Overall looks OK. Not the best , but surely functional. Will be hidden by boat structure anyway...
 
I don;t like philips head screws, but that is all my local hardware store had. Need to find some tiny lag bolts....
 
I cut the stainless straps on a harbor freight 8 in shear/brake. I tried to cut the boiler box plate with it (.05/18 gauge steel) and I damaged part of the shear. Still works fine for thinner sheet...
 
There is a 25 cent coin in the last pic for size reference..
 
Last pic is the harbor freight sander. Ok for hobby use but nothing more. On sale for 60$. Belt top acts like a drum sander which is perfect for the lagging inner curve, and the disc for the bevels. Also sanded the trimmed floor board to the required thickness before ripping each plank off on my micromark hobby saw.  Using 120 grit. This floor wood was VERY dense and very hard. Even the dremel had some problems sanding out the holes for the steam fittings.  Free wood sample from local flooring store....don't know the species....
No, I don't work for harbor freight, they just happen to carry the tools I need....

[Jerry C]

Well, you learn something new every day. I've got one of those sanding stations. I didn't know it tilts up though!?
Jerry.

[xrad]

loosen the big two nuts a turn or two , just behind the sanding disc. They form a clamp on the belt positioning base.
 
By the way Jerry, nice models on your blog.
 
Total cost: about 225$ parts, silver solder costs more than anything. About 20 hours total build time.  Nice cost for the overall effort considering that a boiler of this type does not exist, and  the closest unit is Maccsteam's(The boiler company I would buy from if I had to choose one) 4.5 in boiler at ~900$. And they don't offer the mounting box.