In a blood pressure cuff air is pumped in first, before any measurements are taken. Then a needle valve is slightly opened and air is allowed to escape while the pressure is read from a sphygmomanometer (or sphygmometer).

Here, the air intake is on the right side of the drawing and the tube connects to the blood pressure cuff which is strapped to the patient's arm (not shown.)

In this squeeze bulb the valves are just rubber flapper valves like those used in many fish tank diaphragm air pumps. Other valve configurations are possible.

(This is a still representation and possibly also a low-resolution image of a pump which is fully animated in the CD-ROM version of this glossary.)