A combination vacuum and pressure pump

English

The next pump is actually simpler to build (but more expensive because it uses two factory made one-way valves, and that was the most expensive part of the first pump).

This pump can draw a vacuum like the first, but it can also inflate beach toys and air mattresses, or pump water. Whether pumping water or air, the stuff goes in one end and out the other, instead of travelling through a hollow piston like the first pump.

To make it a little less expensive, we use ¾ inch valves instead of 1 inch valves.

Finished

 

The parts are shown in the photo above. We need:

  • One four foot length of ¾ inch PVC pipe.
  • Two three inch lengths of ¾ inch PVC pipe.
  • One ¾ inch PVC "T" fitting.
  • Two ¾ inch PVC one-way valves (also called "check valves").
  • One four foot length of wooden dowel that fits inside the pipe.
  • One rubber stopper whose large end fits snugly into the pipe.
  • One three-inch long wood screw.
Detail

We start by drilling a hole in the end of the wooden dowel just a bit smaller than the wood screw. We also drill a hole in the rubber stopper. We then screw the rubber stopper onto the end of the dowel, as shown below.

We can control the thickness of the rubber stopper by tightening the screw to make it fatter if necessary. The stopper must completely block the pipe, yet still be able to slide in and out when lubricated with petroleum jelly.

Stopper

The next step is to glue the PVC pieces together. Make sure that the arrows on both one-way valves are going in the same direction!

Glue

Here is a closeup of the one-way valve before gluing. On this valve, the arrow is molded into the plastic to the left of the label.

Check valve

When the glue has dried, liberally grease the stopper with petroleum jelly, and slide it into the pipe. As you slide the stopper in, you will hear air coming out of the valve whose arrow points away from the pump. As you then pull the stopper back out, you will hear air entering through the other valve.

Complete

This pump is very effective for pumping water. The inside diameter of the pipe is 0.8 inches. With each 36 inch stroke of the piston, the amount of water pumped is 

36 π (0.4)2 = 18 cubic inches. 

That's about 10 fluid ounces, or 0.3 liters.