Development of an Oil-Free Vacuum Pump using a Unique Bellows

A new oil-free vacuum pump has been developing to substitute for the conventional oil-sealed rotary vacuum pumps. The pump is a four-stage positive displacement pump whose pumping unit consists of a special bellows, an inlet valve and an outlet valve. The shape of the bellows is based on a unique polyhedron consisting of twelve faces. Some valve plates are driven simultaneously from the outside using magnetic couplings. The use of the new bellows and the driven valves enables the pump to increase pumping speed and to lower ultimate pressure. The target values of the pumping speed, ultimate pressure and operational lifetime of the pump are determined to be 3 L/s, 1 Pa and 2 years, while the highest pumping speed and the lowest pressure achieved by an experimental pump are about 2.2 L/s and 20 Pa, respectively. The high ultimate pressure of the pump is mainly due to a relatively large “dead volume” when the bellows is folded. The experimental pump has been used for about 500 hours in total under various operating conditions so far.