Types of Vacuum Pump

In recent years, a new type of vacuum pump that can be achieved from atmospheric pressure to high vacuum with only one pump has been developed, but generally speaking, for obtaining high vacuum, ultra-high vacuum and extremely high vacuum, multiple vacuum pumps are connected in series to complete the pumping task. Thus, knowing the type of pumps properly is important for user to choose affordable and suitable vacuum pump. The following passage is brief description of vacuum pump type. (The chart behind the passage is for users to understand the passage eaiser and better.)

Gas transfer pump
The gas transfer pump is a vacuum pump that can continuously suck and discharge gas to achieve the pumping purpose. There are basically two types of this type of pump: Variable volume vacuum pump and Momentum transfer pump.

Variable volume vacuum pump
A vacuum pump that uses the periodic change of the pump chamber volume to complete the suction and exhaust process, and the gas is compressed before being discharged. This pump also has been divided into two types: Duplex and Rotary vane.

1. Duplex vacuum pump: It is an equipment that sucking, compressing and discharging gas by using the piston in the pump cavity to do reciprocating motion. Thus, it is also called piston vacuum pump.
2. Rotary vane vacuum pump: It is an equipment that sucking, compressing and discharge gas by using the piston in the pump to do cavity to do rotational movement. It also has been divided into several forms as following:

•  Oil-sealed vacuum pump: It usually has got gas ballast, so it is also called gas ballast vacuum pump.
•  Dry screw vacuum pump: It is sealed variable volume vacuum pump without oil or any other liquid substances.
•  Liquid ring vacuum pump: There is a motor with multiple blades is eccentrically mounted in the pump casing. When it rotates, it will throw the liquid (normally oil or water) into pump casing to form a concentric annular liquid in pump casing. The annular are formed into several small volumes with periodic changes with rotor blades.
• Sliding Vane Rotary Vacuum Pump: Which advantages are compact structure, small volume, light weight, low noise and vibration and so on. Therefore, it is widely used as the frontline of diffusion pump. In addition, it is more suitable for precision instrument matching and laboratory use.
• Roots Vacuum Pump: It is a rotary variable volume vacuum pump which can be used in a wide pressure range with the cooperation of the fore-stage pump, has a larger pumping speed, and is not sensitive to dust and water vapor contained in the pumped gas. It is widely used in metallurgy, chemical, food, electronics and electronic coating fields and so on.

Momentum transfer pump
This pump relies on high-speed rotating blades or high-speed jets to transfer momentum to the gas or gas molecules, so that the gas is continuously transmitted from the pump inlet to the outlet. It can be divided into the following types:

1. Molecular vacuum pump: It is a vacuum pump that relies on high-speed rotor to bring energy to gas molecules to compress, discharge it.
2. Jet vacuum pump: It is a momentum transfer pump that transfers the gas to outlet by using the high-speed jet produced pressure from VENTURI effect. And this is suitable for working in viscous retention and transitional flow conditions.
3. Diffusion pump: A vacuum pump that uses low pressure and high-speed steam flow (vapor such as oil or mercury) as working medium.
4. Diffusion jet pump: It is a momentum pump which has single-stage or multi-stage nozzles that has diffusion pump characteristics. Oil booster pump belongs to this form.
5. Ion transfer pump: It is a kind of vacuum pump that transfer the ionized gas to the outlet under the action of electromagnetic field or electric field.

Gas trap pump
It is a kind of vacuum pump which gas molecules are adsorbed or condensed on the inner surface of the pump so that reducing the number of gas molecules in the container to achieve the purpose of pumping vacuum. There are some forms as following:

• Adsorption pump: It is a trapping vacuum pump that mainly relies on the physical adsorption of adsorbents with large surface (such as porous substances) to pump air.
• Getter pump: It is a kind of vacuum pump that uses getters to chemically combine to capture gas. Normally, getter is like metals or alloys in the form of lumps or deposited fresh films. Sublimation pump belongs to this form.
• Getter ion pump: It makes the ionized gas is adsorbed on the surface of the gettering material by the action of electromagnetic field or electric field to achieve the pumping purpose.
• Cryopump: It is a vacuum pump that uses low temperature surface to trap gas.