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Author Topic: Mark 2 monotube boiler, with single valve throttle control  (Read 5839 times)

Synthpunk

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Mark 2 monotube boiler, with single valve throttle control
« on: August 23, 2014, 02:11:31 pm »

Mornin chaps-
Ive been working on another, smaller monotube boiler.
This time with the aim of being able to drive a decent sized engine (d10 or similar) with a minimum of fuss, controls and hassle. And be easily convertable to radio control.


This is the prototype-






Its a double layer, counterflow version of the previous design. Still got 23 feet of pipe, but in half the space. Cold water feed to the top double loop layer, steam from the bottom triple loop layer, and another camping gas stove as the heater.


Heres the test rig-



Boiler, 100:1 mfa como pump motor, 1/4 inch ram pump, and a twin cylinder single acting piston valve engine.


It worked, but was a trifle wet, and still had 3 valves to control it during startup and run and shutdown, which was a bit complicated. Ok for a straightrunner but rubbish for RC as none of them really acted as a throttle.


So i designed a steam separator/ water trap/ throttle / bypass unit that does everything with just one valve.





And it seems to work, hurrah. Totally throttleable, single valve control of a monotube boiler that doesnt send slugs of water to the engine, just steam. Still needs a load of work cos i threw it together in a bit of a rush out of more bits from the spares box.
Vids-
First test, before making the separator-
https://www.youtube.com/watch?v=_rFd2lG_PIk


Test of the separator and throttle valve.-
http://youtu.be/h4ErAfMiQMg


Heres the basic plan for the separator, but i think i neglected to draw attention to the hole in the bottom that goes to the outlet valve. It needs to be really small. I used a 0.5 mm drill and it seems to work. You can set it up so it automatically purges the tank of water at the same rate it fills up, without losing steam pressure. I made mine from an old spirit lamp from a junk shop. Its made of chunky turned brass, and i silver soldered all the connections, as it runs at boiler pressure, but obviously not in a flame. Good idea to hydrostatically test it first....





And heres the system flow diagram. Mine actually includes a safety valve as well, its on the steam separator, and blows at 80psi.





Cheers!


Rich.
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Jerry C

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Re: Mark 2 monotube boiler, with single valve throttle control
« Reply #1 on: August 23, 2014, 03:19:56 pm »

I've heard of the Half Pretzel, and the Full Pretzel, but I've never seen a Mega Pretzel!!
Jerry.

Synthpunk

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Re: Mark 2 monotube boiler, with single valve throttle control
« Reply #2 on: August 23, 2014, 03:20:14 pm »

The planned next areas of research and development are;

Insulation of the steam separator and main steam line to the engine, using ceramic kiln insulation,

Making a better boiler enclosure. The one shown above is actually borrowed from a two drum yarrow style boiler in in the process of restoring.

Construction of a separate superheater coil after the separator,
This may get its own separate gas tank and burner, at least during the test phase. One of the members of my local club recently very kindly gave me a five foot length of 3/16 stainless steel tubing that seems like the ideal thing to make it out of.

And modification of the gas burner in the main boiler to a 'poker' type, using k&s brass tubing and some fine stainless steel gauze.
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Synthpunk

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Re: Mark 2 monotube boiler, with single valve throttle control
« Reply #3 on: August 23, 2014, 03:26:48 pm »

Heheh- good name! I'm going to steal that if that's ok.. ;c) The idea behind the pretzel coil is to get maximum amount of tubing into the flame space without occluding anything else.

The top figure 8 is wound first, then the winding jig adjusted, another former inserted and then the triple loop is wound at 90 degrees to the first. Then I squished the two together, interleaving the loops and passing the ends through and round to form economiser and superheater ends.

Looking at it end ways, the top layer has 12 inches of tubing per figure eight loop, and the bottom, triple loop has 18 inches. So two and a half feet per pretzel. They are 4 inches across and 2 high.

But yeah- the Pretzel coil. I like it.. :D
Rich
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Jerry C

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Re: Mark 2 monotube boiler, with single valve throttle control
« Reply #4 on: August 23, 2014, 06:17:34 pm »

You're bent!!! :-)
Jerry.

Synthpunk

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Re: Mark 2 monotube boiler, with single valve throttle control
« Reply #5 on: August 29, 2014, 01:00:56 am »

new video -


http://youtu.be/E9XPgUXAtHw


its now regularly running at 60psi sustained with a minimum of surging, priming, or other nasties. the steam separator/throttle is working a treat, as is the lagging on the separator.
i made a new 'poker' style burner like Rfurzer's , except mines shorter and i put a wrapped up tube of 20 gauze stainless mesh inside it. also i wrapped the coil in more mesh, and have started making a smaller outer housing, which you can see some of in the above video. its wrapped in ceramic kiln wool in the video to try and keep the flames and heat in..


to be honest I'm really pretty chuffed with how its working so far.... next step - finishing the housing, tidying up all the lagging and insulation and trying it with my Big 3 cylinder valveless engine that sounds like a merlin spitfire engine. oh yes... 8)


cheers!
rich.
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derekwarner

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Re: Mark 2 monotube boiler, with single valve throttle control
« Reply #6 on: August 29, 2014, 02:10:10 am »

Guys........I reckon we should all chip in few BOB & get you a pair of safety glasses for Rich....:o......[Jerry C ...you are closer ...do you have a spare pair?]

As best as I could count  ;D.......the boiler feed pump geared motor is approx. 100 RPM.......what is the bore & stroke?.....[4x6?].......too difficult to guestimate from 22,000 km away  {-)

Keep us posted with progress  :-)) ..... Derek
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Derek Warner

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Illawarra Live Steamers Co-op
Australia
www.ils.org.au

Synthpunk

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Re: Mark 2 monotube boiler, with single valve throttle control
« Reply #7 on: August 29, 2014, 02:17:56 am »

hehe... yeah, i stood on my safety spex the other day, whoops.... %)


its 1/4 inch bore and 1.1 inch stroke. the transfer passages inside the pump have been embiggened for maximum throughput.
i figure its better to have to turn the pump down than not quite have enough grunt for the job...


cheers!
rich
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silverbrewer

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Re: Mark 2 monotube boiler, with single valve throttle control
« Reply #8 on: February 26, 2015, 11:12:05 pm »

Does the steam separator container constitute a pressure vessel big enought to require a boiler certificate? In boiler styles using the Lamont system they certainly seem big enough to start attracting attention as they often have water sight glasses as part of the control system
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