Request For Comment

[lerman]

Years ago, I had a friend who was interested in steam cars. If you google "monotube boiler", you will get lots of hits:

http://www.lynxsteamengines.com/

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.

Ken

[aubrey]

Is there a total lack of wind there?

Hi Russel.
There is wind - every other month - just enough to make you think that "cool" may exist.
Seriously, the normal farm windmill borehole pump only manages a couple of liters and then the wind is gone.
Aubrey

[aubrey]

Hi aubrey,
Best of luck with this project, its very interesting.

Im just wondering how your calculating the piston diameter in relation to the size of your steam chest, and the size of the steam storage, and generation rate, in relation to the expected piston movements (rpm) ?

I dont know anything about engineering one of these but in your pic above the piston looks very large compared to the steam box. I'd think that maybe the steam box should be larger....

Hi and Thanks.
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.

[aubrey]

Hi Ian

First off it would severely limit the weight and size that you can make it to.

Valid point. However, the unit only needs to pump about 2 to 3 gallons a minute to a head of maybe 10 to 13 feet to make it successfull.

Secondly it would have to be fired up and cooled down which would make it awkward to use.

Nice point: mount it on its own trailer which could then be dragged to the next "irrigation point". (see below)

....fixed in position with the infrastructure around it to keep it happy, also someone will "adopt" it and keep it lovingly tended to make it reliable. Some people just get "broody" that way with machinery.

Each familys plot is at least 500 yards away from the next (to allow for firebreaks and cattle grazing etc) so a fixed central position would require excessive piping etc.
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.

Looking back on the designs of the model railway engine builders, the injection pump should take the form of a displacement plunger pump where the piston doesn't actually touch the cylinder bore but displaces the water by it's intrusion into the pumping space.
This will prevent lack of lubrication on the pump piston from failing it prematurely, or causing the "boiler" to coke up due to oil being burnt there.
These pumps are usually driven by the axle of the loco and have to pump against boiler pressures of about 80 - 100 psi.
They are a bronze casting with a stainless steel ram and have a long wear life, very reliable. Gland sealing is effected by either Viton "o" rings (high tech, not recommended due to hard to get etc) or just greased braided yarn,cotton fibre etc.
The design is very simple and can be cast in the backyard type foundry and machined in very primitive simple machinery, even a drill press.
I would recommend that the firebox be made from cast iron so that it can be fired up and hold the heat while the water is just injected at a controlled rate to give the flash steam volume.
If the firebox/boiler is cast as one piece, it can be made to a simple pattern, by the dozen, with minimum machining, to enable it to be bolted on and off for simple replacement when it scales up or corrodes out.
The piston cylinder bit may be tricky, due to lubrication requirements.
Here I would use a large two-stroke engine (vespa scooter 150CC ?) with the transfer ports blanked off so that piston lube can be added to the steam supply and totally exhausted to prevent boiler contamination, and crankshaft lube contained in the sump off side.
Using a car type engine has too much mass and lubrication of the bores and big ends and main bearings would be a serious problem, where hot steam and water in quantity were present.
In this endeavour I would strongly advise contacting someone in the live steam model railway fraternity, and pose the scenario that you intend to pursue.

Ian, this is what I am looking for - - dont know of any steam clubs up here but I'll ask my brother-in-law. He's into old farm tractors and maybe he knows of a steam club up here in Joburg

[aubrey]

http://www.lynxsteamengines.com/
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.
Ken

Ken - you are a star
OK - seems like the concept will work

[thkoutsidthebox]

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.

[handlewanker]

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.
Ian.

[thkoutsidthebox]

Hi THK, have you ever had to work in the tropical heat?......Too damm hot to work that hard....you will be producing steam at superheat temperatures and in rapid quantities that without carefull controls just becomes lethal.

I have to admit that I never had the pleasure.

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.

[thkoutsidthebox]

...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.

[handlewanker]

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.
Ian.

[thkoutsidthebox]

I suppose you could always pump at night when it's cooler, but then the bl##dy lions would get you. Ian.

LOL......lions?....Fair a'nuf! I have succumbed to those more knowing. Was just an idea.

[thkoutsidthebox]

Aubrey have you seen this link, undoubtedly some knowledgeable people in it who may not have come across your own thread yet.

Show us your steam engine