Below are three iterations of piston pumps, which we have built and used on our windmill.
The first is a 1-1/2" PVC cylinder with a 1" PVC piston. On the bottom of the cylinder there is a 1-way valve (that only let's water into the cylinder). On the bottom of the piston, inside the cylinder, there is another 1-way valve that only allows water to enter the piston pipe. As the piston moves up and down, it alternately creates low and high pressure in the cylinder. Under low pressure, water is sucked into the cylinder through the bottom valve. Under high pressure, water is forced up, into the piston pipe. The piston pipe is connected to the water tank (via a flexible hose that accommodates the up and down movement). Performance: low output due to significant leakages between the piston valve and cylinder wall: 400 l/hr in light-moderate winds.
Next we upgraded to a treadle pump. The treadle pump is modified so that the piston can be attached to the pumping rod. Also, we do away the suction pipe typical of treadle pumps by submerging the pump in the water. We run only one cylinder, while the other cylinder is blocked so not to leak pressure during operation. This pump put out more than 10,000 liters per hour, but required strong winds to get started. Ultimately, it put too much stress on the windmill components, and would need a larger windmill to be a viable pump option.
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Currently we are running the pump pictures below. This pump has some advantages. It has 4 cylinders, and can be configured to run on any combination of 3, 2, or 1 cylinder. We tested it on 4 cylinders and 2 cylinders. Due to light winds on the day of testing, 2 cylinders showed better results. It pumps in the range of 5,000-7,000 liters per hour in moderate winds.
One advantage of this pump is that the cylinders are 1-1/4" PVC and the piston seals are leather bicycle pump seals. This makes for a rather affordable pump. Each piston is made of a bolt, a nut, two metal washers, and two leather seals, the total cost for which is not more than $0.75.
