Vacuum Ejector

Overview

A vacuum ejector (or pneumatic vacuum generator) creates suction by converting high-pressure compressed air into low pressure using the Coanda effect. Unlike mechanical vacuum pumps, ejectors have no moving parts, are maintenance-free, and generate vacuum instantly. The Vacuum Switch and Blow-Off Valve enable rapid pick-and-place cycles on automatic assembly machines: the ejector builds vacuum to grab a part, the switch signals completion, and the blow-off exhausts vacuum to drop the load.

How it works

Regulated compressed air (typically 6–8 bar) enters the Inlet Silencer and accelerates through the first Primary Nozzle Stage. Here, a Coanda profile, a precision-shaped throat, accelerates the air to near sonic speed. At this high velocity, the air's static pressure drops dramatically (Bernoulli principle), creating a region of suction. The Suction Port 1 taps into this low-pressure region; atmospheric pressure on the load forces air into this port, carrying the load into contact with the picker.

The suction from stage 1 is relatively modest (might achieve −0.3 bar). To improve vacuum, the ejector incorporates a second Secondary Nozzle Stage that takes the suction from stage 1 as an input and amplifies it through another Coanda nozzle. This secondary air jet reduces pressure further. A third Tertiary Nozzle Stage continues the cascade, achieving a final vacuum of −0.4 to −0.7 bar gauge (0.3–0.6 bar absolute).

All three stages exhaust into the Outlet Silencer, which muffles the noise. The pressure ratio efficiency is typically 60–75%: for every 10 L/min of useful vacuum output, the ejector consumes 8–15 L/min of supply air.

Control system

The Vacuum Switch is a diaphragm-operated pressure relay. When the vacuum port reaches the setpoint pressure (adjustable 0.3–0.8 bar), the Diaphragm deflects, closing an electrical contact that signals "vacuum ready" to the robot controller. This prevents part motion until vacuum is secure.

The Blow-Off Valve is a solenoid-piloted poppet valve connected in parallel to the vacuum outlet. When de-energized (normal state), it blocks the outlet, allowing vacuum to build. When the controller sends a 24 VDC signal (part release command), the Solenoid Coil opens the poppet, venting the vacuum line to atmosphere. The load drops in < 50 ms. Re-energizing the solenoid re-seats the poppet and allows a fresh vacuum build cycle.

Sizing and deployment

Ejectors are sized by vacuum capacity (L/min) and supply pressure. A small 10 L/min ejector might hold a 200 g plastic part; a 100 L/min unit handles heavy stamped steel components. Supply air must be clean (0.5 μm or finer) and regulated to prevent pressure spikes that damage nozzles. Many OEMs integrate ejectors directly into the gripper head, eliminating long suction lines that would reduce vacuum due to air leakage.

Because ejectors are passive (no electrical control except the solenoid blow-off), they are inherently reliable and used in food, automotive, electronics assembly, and printing industries where thousands of pick cycles per shift are routine.