A simple rotary pump is constructed on the principle of creating a vacuum in a rubber tube and so causing water to rise to fill the vacuum. Figs. 3, 4 and 5 show all the parts needed, excepting the crank and tubing. The dimensions and description given are for a minimum pump, but a larger one could be built in proportion.

Details of Rotary Pump

Through the center of a block of wood 4 in. square and 7/8 in. thick (A, Figs. 1, 2 and 3) saw a circular opening 2-7/8 in. in diameter. On each side of this block cut a larger circle 3-1/4 in. in diameter, having the same center as the first circle (Fig. 3). Cut the last circles only 1/4 in. deep, leaving the first circle in the form of a ridge or track 3/8 in. wide, against which the rubber tubing, E, is compressed by wheels. Bore two 1/4 in. holes (HH, Fig. 1) from the outside of the block to the edge of the inner circle. Put the rubber tube, E, through one of these holes, pass it around the track and out through the other hole. Notice the break (S) in the track; this is necessary in order to place in position the piece holding the wheels.

Fig. 4 shows the wheel-holder, B. Make it of hard wood 3-1/8 in. long, 1 in. wide and a little less than 7/8 in. thick, so that it will run freely between the sides (Fig. 5) when they are placed. Cut two grooves, one in each end, 1 in. deep and 1/2 in. wide. In these grooves place wheels, CC, to turn on pins of stout wire. These wheels should be 3/4 in. in diameter. When placed in the holder their centers must be exactly 2 in. apart, or so arranged that the distance between the edge of the wheels and the track (K, Fig. 1) is equal to the thickness of the tubing when pressed flat. If the wheels fit too tightly, they will bind; it too loose, they will let the air through. Bore a hole through the middle of the wheel-holder and insert the crankpin, D, which should be about 1/2 in. in diameter. The crankpin should fit tightly; if necessary drive a brad through to keep it from slipping.

In the sides (Fig. 5) bore a hole in the center of the crankpin to run in loosely. Now put all these parts together, as shown in the illustration. Do not fasten the sides too securely until you have tried the device and are sure it will run smoothly. For the crank a bent piece of stout wire or a nail will serve, though a small iron wheel is better, as it gives steadiness to the motion. In this case a handle must be attached to the rim of the wheel to serve as a crank. The drive wheel from a broken-down eggbeater will do nicely. For ease in handling the pump, a platform should be added.

To use the pump, fill the tube with water and place the lower end of the tube in a reservoir of water. Make a nozzle of the end of a clay pipe stem for the other end of the tube. Then turn the crank from left to right. The first wheel presses the air out of the tube, creating a vacuum which is immediately filled with water. Before the first wheel releases the tube at the top, the other wheel has reached the bottom, this time pressing along the water that was brought up by the first wheel. If the motion of the wheels is regular, the pump will give a steady stream. Two feet of 1/4-in. tubing, costing 10 cents, is all the expense necessary. --Contributed by Dan H. Hubbard, Idana, Kan.