The water windmill, more accurately termed a wind pump, is a mechanical device that harnesses the kinetic energy of wind to perform the work of lifting water from underground sources. This apparatus is distinct from large wind turbines, which generate electricity, and from water wheels, which use the flow of water itself to create power. The classic design features a large, multi-bladed wheel atop a tall tower, a configuration specifically engineered to produce the high torque necessary for pumping action even in moderate winds.
Core Components of the Wind Pump
The structure begins with the tower, typically a lattice framework of steel or wood, which elevates the working components high above the ground to capture stronger, more consistent winds. At the very top of this support structure is the wind-catching mechanism, which centers on the rotor, also known as the wheel or sail assembly.
The rotor is characterized by its large diameter and numerous, closely spaced blades, which gives it a high solidity ratio. This design maximizes the starting torque, which is the twisting force needed to initiate the heavy pumping stroke, rather than prioritizing high speed. The tail vane, a large flat surface positioned opposite the rotor, acts like a weathercock. This vane constantly pivots the entire head of the mill on the mast pipe so the rotor always faces directly into the wind for optimal performance.
Converting Rotary Motion to Pumping Action
The rotary power generated by the wind-driven wheel must be fundamentally altered before it can be used to move water. This transformation occurs within the gearbox, which is mounted directly behind the rotor at the top of the tower. The primary function of the gearbox is to convert the relatively fast, low-torque rotation of the wheel into a much slower, high-torque reciprocating motion.
Inside the gearbox, a series of meshed gears achieves a significant reduction in rotational speed while simultaneously multiplying the twisting force. The initial high-speed shaft from the rotor drives a smaller gear, which in turn rotates a much larger gear connected to an eccentric crank or a pitman arm assembly. This mechanical arrangement transforms continuous circular motion into the up-and-down movement required for pumping.
The eccentric crank, acting like a bicycle pedal, is the component that translates the final rotational output of the gearbox into a linear stroke. This crank is directly connected to the pump rod, often called the sucker rod, which is a long, slender rod that extends all the way down the well into the water. The pump rod transmits the necessary mechanical energy deep underground.
The Mechanism of Water Extraction
The linear motion transmitted by the pump rod drives the final stage of the water lifting process, which takes place in the pump cylinder submerged below the water level in the well. This cylinder houses a sealed plunger, which acts as a piston, and the entire pumping action relies on the precise function of two check valves. One valve is a foot valve, fixed at the bottom of the cylinder, and the second is the plunger valve, which is built directly into the piston itself.
During the upstroke, the plunger rises, creating a vacuum in the cylinder below it. Atmospheric pressure pushing down on the water in the well forces the water up past the foot valve to fill this low-pressure area. The foot valve then closes, holding the column of water in place as the pump rod begins its descent.
On the subsequent downstroke, the plunger travels back toward the bottom of the cylinder, and the water trapped below it forces the plunger valve open. The water passes through the plunger to sit on top of it, while the foot valve remains closed to prevent water from falling back into the well.
With the next upstroke, the water sitting on top of the plunger is lifted and forced up the drop pipe toward the surface to be discharged into a storage tank.