how to draw a vacuum
To see how the pump works, look at the drawing below. The pump consists of a small diameter pipe (called the piston) inserted into a larger diameter pipe (called the cylinder). The drawing shows the pump at two points during its operation. The top drawing shows air being drawn into the pipe by pulling out the piston. The bottom drawing shows air exiting the pipe when the piston is pushed back in. At the right end of the pipe is a commercially bought one-way valve.