How to size a Venturi vacuum ejector correctly
A Venturi vacuum ejector turns compressed air into vacuum - with no moving parts and no separate pump. This guide shows how to balance suction rate, ultimate vacuum and air consumption, and how to pick the right nozzle for your handling task.
View vacuum ejectorsHow does a Venturi ejector create vacuum?
A Venturi vacuum ejector forces compressed air through a converging nozzle. At the narrowest cross-section the air accelerates to supersonic speed, the static pressure drops and air is entrained from the suction port. This creates a vacuum with no moving mechanical parts.
Three figures drive the selection: suction rate in l/min describes how fast air is evacuated and therefore the evacuation time. The ultimate vacuum (maximum vacuum) of single-stage ejectors is typically -85 kPa, about 85 % vacuum. The air consumption is the price you pay - it sets the running compressed-air cost.
How do I calculate suction rate and nozzle size?
Sizing starts with the workpiece. Sealed, smooth parts (sheet metal, glass) need only a small suction rate because little leak air flows in. Porous or rough parts (cardboard, wood, foam) demand a much larger suction rate to compensate for leakage.
The holding force follows F = p × A: vacuum level times effective suction area. At -70 kPa over 20 cm² of effective area you get about 140 N of holding force. Add a safety factor of 2 for static loads and up to 4 for dynamic, fast-moving loads.
- Sealed workpieces: small suction rate, focus on high ultimate vacuum.
- Porous workpieces: large suction rate, a multi-stage ejector helps.
- Short cycle time: larger nozzle or reservoir volume for fast evacuation.
- Keep supply pressure steady at 4‑6 bar - higher gains almost nothing.
How do I cut air consumption?
Compressed air is expensive, and a continuously running ejector keeps consuming air even after the vacuum has settled. Modern ejectors with an air-saving function monitor the vacuum level and shut off the compressed air once the setpoint is reached. A check valve holds the vacuum until leakage drops it below the switching threshold.
On sealed workpieces this can cut air consumption by up to 90 %. Multi-stage ejectors, with several nozzles in series, deliver a higher suction rate for the same air consumption and suit porous parts or large cups.
- Air-saving function for sealed parts - payback often under one year.
- Integrated blow-off pulse releases the part quickly and cleanly.
- Vacuum switch for process monitoring and safe part-present release.
- Silencer cuts noise and guards against dust clogging the exhaust.
Frequently asked questions
What ultimate vacuum does a Venturi ejector reach?
Single-stage ejectors typically reach -85 kPa, about 85 % vacuum. Multi-stage or high-vacuum versions get to around -93 kPa. An absolute vacuum is not possible with the Venturi principle.
How much supply pressure does an ejector need?
The optimum is 4 to 6 bar at the nozzle inlet. The nozzle is designed for that point; higher pressure raises air consumption sharply without meaningfully increasing the vacuum.
When is a multi-stage ejector worth it?
For porous workpieces or large suction areas. Several stages deliver a much higher suction rate for the same air consumption and handle leak air better than a single nozzle.
Vacuum ejector or vacuum pump?
Ejectors excel at cyclic, decentralised handling with short cycles and low maintenance. A pump pays off for continuous, large vacuum demand with many cups running at once.
Looking for the right vacuum ejector?
We supply single- and multi-stage Venturi ejectors with air-saving function, vacuum switch and blow-off - matched to your workpiece and cycle time.
Energy efficient
Air-saving function cuts compressed-air use by up to 90 %.
Correctly sized
Suction rate and ultimate vacuum matched to your workpiece.
Process safe
Integrated vacuum switches for reliable part detection.
Expert advice
Specialists support selection and calculation.