Single Stage (Venturi) Vacuum Pumps Operation

To generate vacuum, compressed air is supplied to the inlet of a shaped primary nozzle to concentrate the air stream so that it increases in velocity as it passes through the nozzle throat. As velocity increases, pressure decreases until it is below atmospheric pressure (vacuum) and the high-velocity air stream is passed into a second nozzle that is spaced away from the end of the primary nozzle. The gap between the two nozzles occurs within a chamber with a threaded port for connecting to a system requiring a vacuum source. As evacuated air flows into the vacuum port, it is drawn into the second nozzle where it is mixed with the air from the primary nozzle and the combined flow is exhausted to atmosphere after passing through a silencer where expansion continues and noise is absorbed by an acoustic media.

To stop the vacuum, the compressed air supply is removed and vented by a 3-way supply valve. When air flow stops, vacuum is no longer generated and ambient air flows into the exhaust and into the vacuum line to dissipate the residual vacuum, thereby releasing work pieces from the suction cups or other vacuum holders in the system.

Geometry of the primary and secondary nozzles determines the shape of the pump performance curve, depth of vacuum that can be achieved, and air consumption at a particular supply pressure. Nozzles are optimized for operation at specific pressures but can be used at other supply pressures to suit an application. When operating at some non-optimum air pressures, a rapid popping noise may be heard in the exhaust, which is caused when air velocity achieves unstable supersonic/subsonic velocity and can be eliminated by slightly increasing or reducing the air supply pressure.

There are many terms for these devices including “generator”, “ejector” and “venturi”, but they are commonly called vacuum pumps in industry so that is the term we use. No matter what the name, they are very useful for providing a fast, reliable, compact and low cost vacuum source for all manner of applications.