How Pumps Work

To see the basic principle of a tubing pump in action, lay a soft rubber or plastic tube across a hard, flat surface. (See Diagram Below) With a rolling pin, pinch the tube closed at the line A-A, then roll the rolling pin toward the line B-B. As the rolling pin is pushed forward, any fluid (liquid or gas) is pushed along in front of it. Behind the rolling pin, the tube springs back into its original shape, which creates a vacuum; atmospheric pressure pushes the fluid in to fill the vacuum. As the rolling pin approaches line B-B, start a second rolling pin at A-A. This will allow the pump to stay in operation when the first rolling pin is removed.

By placing the tubing in a "U" shape slightly larger than 180°, you can use two rollers to seal the tube against a rigid, concentric housing of slightly more than 180°. As the first roller goes around, the fluid in front of it gets pushed out. As the tube springs back, atmospheric pressure pushes more fluid into the tube. Before the first roller leaves the sealed condition, the second roller starts to squeeze the tubing tight. Now you have a rotary pump.