While we’re constantly on the lookout here for simple ways to do chores without electricity, sometimes slick solutions surface quite by accident. Using a hand water pump as an air compressor to pump up a flat tire was one of those serendipitous discoveries.
After using our hand pump to fill the pressure tank for watering our vegetable gardens, my husband commented about the amount of compressed air in the tank.
Pointing to the condensation line on the outside of the tank, he said, “You know, I bet I could fill a tire with this.”
The next thing I knew, he was digging through miscellaneous parts in the shop. In no time, he came out with an air chuck, hose and fittings. To test his theory, he used the compressed air in our 40-gallon pressure tank to fill an inner tube.
The 14-inch inner tube filled in just a few seconds, without using all the air in the tank. Even if the task required filling a tire to 35 PSI, it could be done. We would simply drain the water from the tank (preferably by watering some plants), and then pump it up again. After repeating the process, pressurized air is transferred from the tank to the tire – all without energy of any sort except human power.
Most homes with private wells have cold water pressure tanks. When the water is forced into the tank (by hand pumping or electric pump) the air above the water is compressed. As we found out, this compressed air can be utilized.
In any transfer of air from one vessel to another, the air will equalize in the containers. For example, if there is 50 pounds of air in Tank A and 0 pounds in Tank B (or a tire), the air will equalize in each tank. So, to fill Tank B to 35 pounds, Tank A must be pressurized again to 50 pounds and repeated until Tank B reaches 35 PSI.
Of course, the small amount of compressed air at the top of a pressure tank would not be practical for operating pneumatic grinders and such. But, in an emergency, this would be a quick, reliable way to pump up a flat tire. Compressed air could also be transported to the field with a portable air tank.
How to Use a Hand Pump as an Air Compressor
Any hand water pump capable of pressurizing a tank for indoor plumbing will work, along with a pressure tank that has connections for air fittings. (A larger tank will hold more air than a smaller one.)
Remove the top plug or cap from the top of the pressure tank and install fittings for a quick-connect air coupling. Connect the air hose to the coupling. The end of the hose should have an air chuck to fit your tire or tube valve stem.
Pressurize the tank by filling it with your hand pump as usual. Do not exceed the manufacturer’s recommended safe limit. We fill ours to 50 pounds of pressure. Now connect the air chuck to whatever needs to be inflated. That’s all there is to it.
The concept of pressurizing air with water is not new, but has been virtually forgotten since fossil fuels enabled humans to compress air mechanically, as John R. Hunt points out in a 1977 Mother Earth News story, Harness Hydro Power with a Trompe. Long before electricity, humans compressed air with the help of falling water from rivers.
“For the homesteader or farmer with a small waterfall or a good-sized stream on his property, the trompe is a natural,” writes Hunt. “It offers a virtually inexhaustible supply of free compressed air ... cool, dry air that can be used to operate a forge, drive machinery, or air-condition a house or barn in hot weather.”
A 1978 Mother Earth News article, Mother’s Homemade Air Compressor, explains how to build an air compressor.
To see a video demonstration and more photos of our setup, please see our blog, Compress Air with a Hand Water Pump (includes video).
Linda Holliday lives in the Missouri Ozarks where she and her husband formed Well WaterBoy Products, a company devoted to helping people live more self-sufficiently off grid with human power, and invented the WaterBuck Pump.