Pedal-Power irrigation pump

Right now we are watering the new-planted trees in the orchard by hand with buckets, but discovering that my grandparents old man-made “deer pond” is just a few inches below the top of the orchard got me thinking about how we might irrigate the orchard, if it ever came to that with climate change and all.  The modern way would be to buy a nice little Honda 1″4 stroke pump to push the water, but there’s no romance or challenge in that.   And if you do the math, it turns out that it doesn’t take much power to move a lot of water if the head (vertical lift) is modest and the system is efficient.   With SI units you can pretty much do it in your head:

P = Mdot * g * h / eta

P is shaft power, Mdot is the mass flow rate (kilos per second), g is gravitation (very nearly 10 kg*m/s^2),  h is the total head (meters) , and eta is mechanical-to-fluid efficiency.  So if you had a 3 meter lift and 50% efficiency, you would get over 1.5 liters per second from a 100W source.  That started me thinking about a pedal-power irrigation pump.  The idea would be to pedal for a few minutes and fill a cistern or reservoir on the ledgy hill above the orchard, whereupon a drip system of some kind would slowly feed that water out around the bases of the trees.  I started by thinking about a piston type pump, because the well pump we have seems remarkably powerful given that it is operated by one hand and looks to be about a hundred years old, with leather valves and whatnot.  It can fill a bucket in just a few seconds of vigorous pumping (~1 liter per second?), and the total head must be between 2 and 3 meters, so it must be capable of around 100W with reasonable efficiency.  With pedal power that amount of effort can be sustained for long periods, and higher rates are possible for a limited time.

In poking around a bit on the internet several groups have built pedal pumps, but nothing that strikes me as really compelling.  Low head pumping is often done with an axial flow pump (basically like a boat propeller in a circular housing), but that requires a setup with a slanted shaft to submerge the prop in the water; sounds like a bit of an annoyance for rigging up pedal power.  So I’ve come around again to the idea of a piston pump.  For efficiency the important things will be to keep the ports and ducts large (to avoid pressure drops) and make efficient check valves (to avoid backflow and pressure drops there).

The idea I’m currently excited about goes as follows.  First, the drive would borrow heavily from the cider mill.  I figure to design for about 1Hz operation; that way it goes at about pedaling speed and you can gear it up or down a bit by fiddling with the sprockets if you get the loading wrong.  Front forks of bike bolt to assembly; a loop of chain goes forward to the main shaft of the pump, which has a thread-on 5-8 speed freewheel clamped to a 5/8″ shaft as with the cider mill.  I’d put another, large sprocket on the main shaft and couple it to a much smaller sprocket on a jackshaft, which would carry another cast iron flywheel to smooth out the rotation and for style points.  A simple machined crank cantilevered off the opposite end of the mainshaft would have threaded holes for a shoulder bolt in several radial positions, to allow the stroke to be adjusted.  A crank arm with spherical rod end bushings would connect the crank to the piston rod, which would be supported in the pump assembly by brass bushings reamed to a close clearance to minimize leakage.  O-rings could be fit but I’m worried about the friction that would ensue.

The pump assembly itself would be double acting to minimize cyclical forces, and it would consist of a 3 or 4″ PVC cylinder (gotta figure how to ream out the inside to eliminate the minor cellulite-like texture that seems to result from the extrusion process).  Each end of the cylinder would have a double side entry reduction fitting (topologically like a T shirt, but with a big neck hole) for inlet and outlet ports, and the axial port would be reduced down to the point where the cylinder guide bushings could be directly attached.  The piston would be a disk of hard plastic, bolted to a shaft collar on the piston rod, with a groove turned in it to accept a teflon strip edgewise to form a piston ring.  I haven’t got the details of the check valves figured out but I think they involve conical reduction fittings and rubber “superballs” to form the one-way seal.

The whole thing would be mounted to a chassis of scrap PT timbers, and it would sit up in the woods where it would command a view of both of the orchard and the pond.  I can picture it in my mind’s eye; now if only I had the time to build it…


4 Responses to “Pedal-Power irrigation pump”

  1. Brian Says:

    I was puzzling over a similar application. I was wondering if a simple rope pump would work to get the water from the source to the elevated reservoir. A rope pump is simply a rope pulled through a pipe (ABS) and the rope has balls matching the inside diameter attached to the rope.

  2. Brian Says:

    P.S. The ABS pipe is submersed and is ‘leaky’ under the surface, with filter to prevent mud/fish/frogs etc. being drawn into pipe. Balls would enter pipe above water level and have a ‘funnel’ to guide balls to inside diameter. ABS 45 degree corners or ‘Y’s” could reduce friction and exit balls in one direction while water empties into reservoir.

  3. simon chibuzor Says:

    what about pedal driven irrigation pump, is it on net. please i”m seeking for project assistance, thanks for co-operation.

  4. Ekwealor simon c Says:

    i really need assistance of pedal foot driven irrigation pump(the isometric view and other view), if possible help to send it to my box, thanks

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