Building a Donkey Boiler
Submitted: Monday, Mar 24, 2008 at 09:00
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Member - Matt M (ACT)
Morning All,
I had it in my mind that there was an article on donkey boilers somewhere on this site, but can't seem to locate it. Does anyone have a design/drawing for constructing a donkey boiler?
We have just spent the weekend camping on a friend's property and he is all set up with shower/
toilet, etc. and the hot water comes next. It is a pressurised system and about a 20 gallon capacity would be heaps.
My thoughts were a 20 gal drum on its side, welded to a frame to lift it above a fire pit, cold water in the bottom, hot out the top and a pressure relief valve fitted. Anything else to consider or is that about it?
Any ideas appreciated.
Cheers,
Matt.
Reply By: Member - Doug T (FNQ) - Monday, Mar 24, 2008 at 09:21
Monday, Mar 24, 2008 at 09:21
Check the link
Ass Boiler
,
AnswerID:
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Follow Up By: Member - Matt M (ACT) - Monday, Mar 24, 2008 at 10:02
Monday, Mar 24, 2008 at 10:02
Thanks Doug, looks like a great setup. I like the concept of an 'Ass Boiler'. Considering my 'Ass' is usually in hot water anyhow.
Do you reckon that is an open system or a pressurised one?
Cheers,
Matt.
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Reply By: Hairy (NT) - Monday, Mar 24, 2008 at 09:25
Monday, Mar 24, 2008 at 09:25
Gday,
You have got the idea about right but you do have to do your sums , or you could seriously hurt some one.
I would use a gas bottle rather than a tin.
If your tin cant hold the amount pressure your relief valve can, or cant release the pressure fast enough when the water flashes off it will explode. Anyone nearby will be scun like a pig.
Also a drum laying on its side wont be very efficient as most the energy from the fire will disapear out in to the atmosphere. You need to direct the heat into the drum.
I used to make heaps and and have a few different ideas but nothing is on paper.
I ll try and do a couple of drawings if no one else comes up with something.
Cheers
AnswerID:
294357
Follow Up By: Hairy (NT) - Monday, Mar 24, 2008 at 09:42
Monday, Mar 24, 2008 at 09:42
Here is a couple of rough ideas to get your brain ticking.
BUT! be sure you have the right relief valve or you could blow it up!
Might be worth talking to a plumber if your not a competent welder as an old hot water service might be a handy tank?
Sorry about the drawings but if I dont do it now IImage Could Not Be Found probably wont get around to it.
Cheers
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Reply By: Hairy (NT) - Monday, Mar 24, 2008 at 09:44
Monday, Mar 24, 2008 at 09:44
Woops!!!
water in and out on the upright one are around the wrong way obviously.
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Follow Up By: Member - Matt M (ACT) - Monday, Mar 24, 2008 at 10:00
Monday, Mar 24, 2008 at 10:00
Thanks Hairy. I had thought about a gas cylinder and you're probably right re the pressure issue. It won't be in use all day, just light a small fire underneath round bath time, then put it out when done.
Cheers,
Matt.
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Reply By: Hairy (NT) - Monday, Mar 24, 2008 at 10:21
Monday, Mar 24, 2008 at 10:21
Gday Matt,
Im not trying to scare you off. They work great and have used them for years but dont build one half heartedly because it is only going to be on a small fire and only used at bath time.
Ill try and dig out my steam book and give you a bit of an idea about the amount of energy released when water flashes off....its quite amazing how efficient it is.
Cheers
AnswerID:
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Follow Up By: Hairy (NT) - Monday, Mar 24, 2008 at 11:20
Monday, Mar 24, 2008 at 11:20
Here are a few things you might want to take into consideration while building it..
One gallon of water could have the same reaction as 1 stick of dynamite.
You are not trying to produce steam, only hot water, but it is quite possibly going to happen anyway.
A given amount of fuel needs a given amount of air to burn—no more and no less. It also needs the right amount of space to burn. Not enough air and you get incomplete combustion. Too much air and you’re heating air.
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Reply By: Member - bungarra (WA) - Monday, Mar 24, 2008 at 11:01
Monday, Mar 24, 2008 at 11:01
We used one for years...in fact it was our only source of hot water for many years....keep it simple.....
and I wouldnt use a pressure relief valve (as such) but rather an open pipe at an extended height...about the only thing that will block it is
spider webs or hornets mud nests (fly wire will stop that)........as I understand it you will use occasionally and so a mechanical device for pressure relief is potentially more prone to malfunction and they are supposed to be tested manually on a regular basis but who does?........open pipe is always open...cant have a big bomb ticking away that way as it heats up
a simple tap at the cold inlet (bottom) and water must flow out the hot (top) when open....just adjust the tap flow in to = required outflow before it comes out the top "pressure relief spout"..........BE CAREFUL where you allow the vent pipe to discharge...but that applies to any discharge device.
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Follow Up By: Member - Matt M (ACT) - Monday, Mar 24, 2008 at 11:33
Monday, Mar 24, 2008 at 11:33
Bungarra,
Yep, there is some appeal in that type of set up from a safety perspective. If it was to be used just to siphon hot water off, it would probably work
well. The difficulty comes (I think) when you try to bring the hot water into the pressurised (cold water) side, say for the shower.
It is only a gravity fed system, but the pressure is significant (as good as or better than most household systems) and, without doing the calculations, the header pipe would need to be very high to overcome the cold water pressure and feed hot water into the system. A non return valve would overcome the cold water back flow, but you would still need significant pressure in the hot water side to overcome the back pressure from the cold. Does that make sense?
He does have an old (electric) hot water heater and (as Hairy suggested) we might be able to use it as a header tank. Just not sure of it's pressure rating, as they are obviously designed (via the thermostat) not to hold boiling water and steam.
Cheers,
Matt.
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Reply By: MEMBER - Darian (SA) - Monday, Mar 24, 2008 at 13:07
Monday, Mar 24, 2008 at 13:07
Does it have to be under pressure ? - couldn't the hot water in the heater module naturally rise to a header tank while the cooler water comes down via another tube ? - then you could take off the hot water as required from above, but via gravity feed - I have in mind the picture of the side of a holiday
shack in SA some years back - had been blown off by a malfunctioning hot water service - the boom is one thing but the scalding water can kill of course - pressured systems need fail-safe design no ?
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Follow Up By: Member - Matt M (ACT) - Monday, Mar 24, 2008 at 13:15
Monday, Mar 24, 2008 at 13:15
Darian,
That would be ideal, but unless you are just taking off the hot water to tip into a bath or sink, then I can't see how you mix it with the cold water which is under pressure. In the same way that the system in your house delivers both hot and cold water to the shower (for example) at the same pressure. If you introduce cold and hot water at differing pressures then all that will happen is that the higher pressure cold water will just flow back into the boiler and out the overflow.
I think.
Matt.
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Follow Up By: Ray - Monday, Mar 24, 2008 at 15:13
Monday, Mar 24, 2008 at 15:13
Don't forget to fit a magublican or it couls blow up
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Follow Up By: Ray - Monday, Mar 24, 2008 at 15:14
Monday, Mar 24, 2008 at 15:14
Don't forget to fit a magublican or it could blow up
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Follow Up By: Member - Matt M (ACT) - Monday, Mar 24, 2008 at 17:18
Monday, Mar 24, 2008 at 17:18
Ray,
What's a magublican?
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Reply By: Member - Phil/S WA.. - Monday, Mar 24, 2008 at 13:34
Monday, Mar 24, 2008 at 13:34
Matt, pity u live on ''the other side'', I have just removed a solid fuel hot water system from our house. It worked really
well, 500gal. header tank to the system,with a ''shepherds crook'' as a relief valve, about 2.5mts. above the hot
water tank. 40 mins. fire lasts 2-3 days[ 2people showers & dishes etc.] The systems are still quite common,Ideal bach or
bush camp, & very safe, which is your prime consideration I reckon...
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Follow Up By: Member - Matt M (ACT) - Monday, Mar 24, 2008 at 17:14
Monday, Mar 24, 2008 at 17:14
Thanks Phil,
It sounds ideal and I might keep an eye out for one closer to
home. Was this one plumbed in to a regular pressure system? I am interested in what sort of pressure you could run through it before overflowing through the shepherds crook.
Cheers,
Matt.
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Follow Up By: Member - Phil/S WA.. - Monday, Mar 24, 2008 at 22:14
Monday, Mar 24, 2008 at 22:14
Matt,No it was all gravity, the tank was about 2m. above the hotwater system, Plenty of pressure in the house.We would guite often have the water boiling out the ''crook''. On rainwater, so no pressure tank [use less water] have since put electric heater in, no more lightin the fire. What was really strange , the house also had a solid fuel oven in the kitchen, but that did'nt have a ''wet back'' which meant 2 fires in the winter!! Hope u get it sorted....
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Follow Up By: Pajman Pete (SA) - Tuesday, Mar 25, 2008 at 20:53
Tuesday, Mar 25, 2008 at 20:53
Second gravity tank for the cold water fed by a ball cock with the same head as the hot might solve the cold water back pressure problem but it is getting a little complex.
FollowupID:
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Reply By: Member - Willie , Sydney. - Monday, Mar 24, 2008 at 14:22
Monday, Mar 24, 2008 at 14:22
If the Old Boiler had seen you call her a donkey you would be in big trouble .
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Reply By: Chriscd - Monday, Mar 24, 2008 at 17:03
Monday, Mar 24, 2008 at 17:03
Hi Matt,
Built one some years ago - somebody liked it and nicked it Two beer kegs - 1 x 18 gal, 1x 10 gal ( as said a couple of years back)
Cut the top out of the 18 to allow 10 gal to sit inside until reachng first roller ridge, had welded together with plate welded over bunghole in 10 gal. Cut top out of 10 gal. Cut fire door in side of 18, rods placed in holes drilled in sides to carry firebox inside and cut a hole and mounted a
chimney opposite fire door and closer to the top
Coiled 12mm copper tubing - 5-6 meters so would fit into 10 gal - had a couple of holes opposite one another for cold in and hot out. Filled the 10 gal up with water an lit the fire. Top of 18 gal as lid on top of boiler.
Not terribly fuel efficient - but continuous hot water and crab cooker in one.
Could have problem locating keg but a bit of citting and welding could used curren 50 l - aquired from where??? - but release pressure prior to cutting.
Seeya
C
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Follow Up By: Member - Matt M (ACT) - Monday, Mar 24, 2008 at 17:21
Monday, Mar 24, 2008 at 17:21
Sounds like a good one Chris, maybe a bit techo for what I am after. Getting hold of kegs can be an issue now as
well. So the copper tube actually ran through the hot water in the 10? I guess that is one way to prevent boiling in the pipes.
Matt.
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Reply By: Richard Kovac - Monday, Mar 24, 2008 at 17:41
Monday, Mar 24, 2008 at 17:41
Matt
Try this down load hot water maker
HWM
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Follow Up By: Richard Kovac - Monday, Mar 24, 2008 at 17:45
Monday, Mar 24, 2008 at 17:45
Site Link
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Follow Up By: Member - Matt M (ACT) - Monday, Mar 24, 2008 at 17:46
Monday, Mar 24, 2008 at 17:46
Thanks Richard.
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Reply By: Neil & Pauline - Monday, Mar 24, 2008 at 18:21
Monday, Mar 24, 2008 at 18:21
Matt
I would place a pressure reducing valve before the tank. A hot
water tank is dangerous if it happens to bust. Use a shepards crook for pressure release. Much safer. Use straps under the tank and built into the brick walls of the fire chamber. I used a bit of old corrugated iron over the top and poured about 4 inches of concrete as a top. The corrugated iron provides enough strength to support the concrete. I used an old 44 gal drum but it hard to get anything very heavy nowdays.
Neil
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Reply By: GerryP - Monday, Mar 24, 2008 at 20:32
Monday, Mar 24, 2008 at 20:32
I agree with using a shepards crook or open pipe for relief. You can work out the maximum pressure in the vessel according to the height of the pipe above the normal water level in the tank. Every meter in height is equivalent to roughly 10 kpa.
For example, a height above the water level of 2.5 meters would give you 25 kpa.
In psi (for us oldies) there are 6.895 kPa per psi, so 25 kpa would be 3.6 psi.
Just make sure the relief pipe is large enough - I'd be looking at 20 to 25 mm internal diameter.
Cheers
Gerry
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Reply By: Dion - Monday, Mar 24, 2008 at 21:42
Monday, Mar 24, 2008 at 21:42
Matt,
build a water "heater", not a boiler. Once you use the word Boiler, it will bee required to be registered, built to standards, inspected etc blah blah blah, you get the picture.
Cheers,
Dion.
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Reply By: Dion - Monday, Mar 24, 2008 at 22:14
Monday, Mar 24, 2008 at 22:14
Under pressure, 1L of water will produce between 1.3-1.6kL of steam, very very rapidly.
Cheers,
Dion.
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