Vacuum generator

A vacuum generator is described by two values: the vacuum level it can reach and its suction capacity, that is the flow rate it removes from the system. The vacuum level determines holding force per area; the suction capacity determines how fast the vacuum builds up and how much leakage the generator can make up for.

Both at maximum are not available together. Designs with a high vacuum level move little air; designs with a high flow rate reach only a moderate vacuum. The choice therefore follows from the workpiece.

In an ejector, compressed air flows through a nozzle and entrains the air from the suction port – the Venturi principle. An ejector has no moving parts, is small and light and can sit directly on the gripper; the vacuum is there without any start-up time.

The price is air consumption for as long as suction is applied. On tight workpieces an air-saving function reduces it by switching the ejector off once the set point is reached and topping up when the level drops. On porous workpieces it has no effect, because air leaks in continuously.

Electric vacuum pumps – often rotary vane pumps – reach a high vacuum level at medium suction capacity and are economical in continuous duty. They need maintenance, such as changing filters and vanes, and are heavier than an ejector.

Vacuum blowers, for example side channel blowers, move very large volumes of air at a low vacuum level. They are the answer to highly porous workpieces such as cardboard boxes, sacks or raw wood-based panels, where leakage is the normal state.

Whatever the type, the generator alone does not make a safe lifting attachment. A check valve stops air flowing back on failure, a reservoir keeps a reserve, and monitoring signals falling vacuum visually and audibly. With ejectors it must also be clear what happens when compressed air fails; with pumps, what happens when power fails.

Mistakes mostly arise from looking at the vacuum level alone.