Single-stage units use one nozzle and reach a deeper ultimate vacuum, which suits smooth, sealed surfaces such as glass and finished sheet. Multi-stage units chain nozzles so each adds evacuation capacity, giving a much higher suction rate at a lower ultimate vacuum. Porous or leaky workpieces - corrugated board, sawn timber, moulded parts - need the flow rather than the depth.

Because the cycle is set by how long the pads take to reach the release threshold, not by the vacuum the unit could eventually reach. On a leaky part the two are unrelated: the system may never approach ultimate vacuum and simply settle where leakage equals suction rate. Sizing therefore starts from pad volume and expected leakage.

The supply air consumed while the part is simply being held. A vacuum switch inside the ejector cuts the compressed air once the set level is reached and re-admits it only if the vacuum decays, so a sealed part is held on trapped vacuum with the supply off. On long holds the saving is most of the air the unit would otherwise use.

Because switching the supply off leaves residual vacuum in the pad and the line, and the part clings until it bleeds away. A short pulse of positive pressure into the suction line clears it immediately, which is what allows fast place cycles. The pulse duration is adjustable, and too long a pulse blows the part out of position.

The exhaust cannot clear, back pressure builds against the nozzle and the achievable vacuum falls. It is the most common cause of an ejector that has slowly got weaker, and it presents as parts dropping on the heaviest picks first. Silencer elements are consumables, and units in dusty air need them changed on a schedule rather than on failure.

It depends on the duty. For short, intermittent picks an ejector wins because it only consumes air while it runs and needs no motor, no cooling and almost no maintenance. For continuous vacuum over hours, a pump usually costs less to run, because generating compressed air and then throwing it through a nozzle is an inefficient way to move a lot of air.

As close to the pads as the layout allows. The volume between the ejector and the pad has to be evacuated on every cycle, so a long hose adds directly to the evacuation time and to the air consumed. Decentralised mounting on the end effector is the reason compact ejectors exist.