(1) Reciprocating vacuum pumps, rotary vane vacuum pumps, slide valve vacuum pumps, and Roots vacuum pumps rely on the reciprocating motion or rotation of pistons to suck in, compress, and discharge gases. Their advantage is that the newly put into use pump has a relatively high vacuum degree, but the piston is a moving component, so the wear of the piston is inevitable. With the increase of maintenance times, the working vacuum degree will continue to decrease until it cannot meet the production requirements. This type of pump has fatal disadvantages such as high working noise, high fuel consumption, and high failure rate. Generally, one backup pump needs to be used, which invisibly increases equipment investment and operating costs. In addition, if this type of pump is used to pump condensable gases such as water vapor, it will emulsify the lubricating oil, so it can only be used to pump non condensable (air) gases and cannot pump media with particles, which limits its applicability.

(2) The water ring vacuum pump relies on an eccentric rotor with multiple blades installed inside the pump casing to rotate, throwing water towards the pump casing to form a water ring concentric with the pump casing. The water ring and rotor blades form a periodic change in volume to suck in, compress, and discharge gas. Its advantages are that it can extract large amounts of air during low vacuum and can directly extract condensable gases such as water vapor. Its disadvantage is that it has a low vacuum degree and cannot suction media with particles.