Years ago, I had a friend who was interested in steam cars. If you google "monotube boiler", you will get lots of hits:
A monotube boiler is a coil of tubing that has water injected in one end and steam coming out the other end. The key is that it has a low internal volume, so it doesn't store a lot of energy that can explode.
The link, above, has articles on converting lawnmower engines to steam using a monotube boiler.
My guess is that would be an excellent fit for your application.
55 Main Street
Newtown, CT 06470
The drawing is not to scale (done with MSPaint - still need to get my head around 3dmax)
As to the sizes etc - all it must do is irrigate the same area (about 1/4 hectare or 50 x 50 yards) that 10 people are currently doing using buckets with 1 guy on the machine and 1 on a hose. Not high pressure, just a small flow maybe 5 to 10 liters/min (1 to 3 gallons), just enough water directly around the base of the plant to sustain the plant. No high pressure spray irrigation.
Currently 10 people each carrying about 15 liter in a bucket at about 5 minutes per bucket do the job in about 6 hours and it is back breaking work - especially in the tropical heat. The aim is to have 2 guys do the work which will release the rest so that they can go to school.
Nyrenere Mike (my Malawian partner in my transport business) came up with the idea of building a 10ft tower at each plot next to the well point (at 8 ft you get enough water) and having 6 or 8 44 gallon drums on the top with a simple interlinking manifold. One pump on a trailer could then move around the community filling the drums and then moving on to the next point.
The operators could get the necessary training and be paid by the community and the family could then do the actual watering of thier crop.
I hope this doesn't detract form the spirit of the thread but its something to consider...
Why do you need steam at all?....It would probably be easier and just as effective to just make a hand operated pump with a BIG wheel to be turned by one or two people. This would remove the need to gather firewood for one, and still dramatically reduce the amount of hours spent using buckets for irrigation. Im sure with a good gearing mechanism the operation would not be tiring at all, and you could pump the same amount of water as a steam system, except it would be a simpler operation. If someone is going to adopt the unit anyway he might as well operate it manually. They could also switch around for 5min turns if they want, or if not then thats fine too, as I said with the correct gearing it wouldnt be very tiring.
I know it wont look as good bringing it to your friend, but it would work and probably be more robust and durable in the long run being out in the elements with minimal maintenance. The 'technology' has been used long before steam ever made an appearance. Also it could be made almost entirely from wood, so that if it breaks they could even make replacement parts themselves locally using primative hand tools.
Hi THK, have you ever had to work in the tropical heat?
In australia we are currently in a drought situation and the summer temps frequently reach 35 deg C.
Too damm hot to work that hard, even if your life depended on it, which means using the brain instead of the brawn.
The steam project is definately viable provided it can be brought together.
AUBREY, the problem with piston and cylinder technology is lubrication of the piston and cylinder, and making sure when you have reciprocating masses that bits don't fly off.
In 1910 the British admiralty under Lord Fischer changed over from triple expansion reciprocating engines to steam turbines to drive the Dreadnought type battleships.
If you are going down this path, of steam production, then be aware that you will be producing steam at superheat temperatures and in rapid quantities that without carefull controls just becomes lethal.
I think possibly a low pressure steam turbine would suit your needs and with only one working part becomes a simple mechanical device that could handle a fluctuating steam supply without blowing a gasket or seizing up due to lack of lube.
Have you considered the other end of the energy spectrum, and that is to exploit the vast amounts of dung that african society generates with cattle, animals and humans being the main producers?
Dung can be used to produce methane gas that would drive a conventional engine without modification and also be used for cooking etc.
The women and children could collect the dung from around the living areas, so reducing the fly population etc, and minimising the need to cut wood.
But it seems to me that these people are working for 6 hours in that heat carrying buckets of water anyway. Maybe its just me, but I'd prefer to stand in the shade of a tree or umbrella or whatever and slowly turn a handle instead of plonking back and forth carrying heavy buckets.....Maybe Im alone in this view?
Its not exactly 'work'. If geared up and attached to a 4ft diameter wheel the handle could turn really slow. You could even ditch the handle and use a set of bicycle pedals and chains instead so everyone could sit down and enjoy the nice weather.
...or gear a smaller handle to the bigger wheel so you dont have to stretch turning a big 4' thing! Just sit in a seat and turn an 8" handle which turns the big wheel which is geared to the pumping mechanism. All solid gears for durability, but they could be old fashioned wooden ones like on the old water mills.
Hi THK, when it's 35 deg C+ in the shade, you don't want to be turning no 'ol handle.
I suppose you could always pump at night when it's cooler, but then the bl##dy lions would get you.