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Machine Design

Linear actuator uses bellows as a seal and to generate force

Linear actuators that move back and forth across a pressure boundary, such as those located outside a vacuum chamber or furnace but extending inside them, should not leak or be prone to contamination.

In this example, the actuator is operating across the pressure boundary separating a vacuum chamber from the out lab's atmosphere. Solid welds connecting the bellows to the cylinder prevent pressure or contaminants from crossing into or out of the chamber.

The Prime Mover, a linear actuator from Senior Aerospace Metal Bellows in Sharon, Mass. (, can handle such applications because it uses a metal bellows to generate force. The bellows is welded inside a cylinder. The bellows acts as a spring to keep itself extended when operating pressure is removed. When enough pressure is applied, the bellows collapses, extending the actuating pin welded to the bottom up and out of the cylinder. The bellows serves as a hermetic seal, keeping the inside and outside pressures separate and preventing contaminants from getting in or out. There are no dynamic elastomeric seals, letting it operate from cryogenic temperatures to 450°C, and in pressures to 120 psid. The all-metal actuator is compatible with the harshest of chemicals, plasmas, and fluids, so it will work in corrosive environments. It meets ISO-14644 Class-1 cleanliness requirements, and there are no wearing components, so there are no variations due to friction. The unit can exert up to 1,000 lb in force and use optical or magnetic position sensors. The durable devices last up to 10 million cycles.

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