Vacuum Pumps: Types, Applications, and How They Work

A vacuum pump is a device that removes gas molecules from a sealed chamber or container, creating a partial or complete vacuum. Vacuum pumps are widely used in various industries and research fields, such as aerospace, electronics, metallurgy, chemistry, medicine, and biotechnology. Vacuum pumps can also be used for applications such as vacuum packaging, vacuum forming, vacuum coating, vacuum drying, and vacuum filtration.

In this article, we will explain what vacuum pumps are, how they work, what are their main features and types, and what are some of their common applications.

What is a Vacuum Pump?

A vacuum pump is defined as a device that reduces the pressure inside a chamber or container by removing gas molecules from it. The degree of vacuum achieved by a vacuum pump depends on several factors, such as the design of the pump, the type of gas being pumped, the volume of the chamber, the temperature of the gas, and the leakage rate of the system.

The first vacuum pump was invented by Otto von Guericke in 1650. He demonstrated his device by using two hemispheres that were evacuated by his pump and then attached together. He showed that even teams of horses could not separate them due to the atmospheric pressure acting on them. Later, Robert Boyle and Robert Hooke improved Guericke’s design and conducted experiments on the properties of the vacuum.

What are the Main Features of a Vacuum Pump?

There are three main features that characterize a vacuum pump:

• Exhaust pressure

• Degree of vacuum

• Pumping speed

Exhaust Pressure

Exhaust pressure is the pressure measured at the outlet of the pump. It can be equal to or lower than the atmospheric pressure. Different vacuum pumps are rated for different exhaust pressures. Normally, pumps for creating high vacuum have low exhaust pressure. For example, for creating a very high vacuum of 10-4 or 10-7 Torr (a unit of pressure), a very low exhaust pressure of the pump is required.

Some high-vacuum pumps require a backing pump to maintain a low exhaust pressure before they can operate. The backing pump can be another type of vacuum pump or a compressor. The pressure created by the backing pump is called backing pressure or forepressure.

Degree of Vacuum

The degree of vacuum is the minimum pressure that can be created by a vacuum pump inside a chamber or container. It is also known as ultimate pressure or base pressure. Theoretically, it is impossible to create an absolute vacuum (zero pressure) inside a chamber, but practically it is possible to create a very low pressure of about 10-13 Torr or lower.

The degree of vacuum achieved by a vacuum pump depends on several factors, such as the design of the pump, the type of gas being pumped, the volume of the chamber, the temperature of the gas, and the leakage rate of the system.

Pumping Speed

Pumping speed is defined as the rate at which a pump can remove gas molecules from a chamber or container at a given pressure. It is measured in units of volume per time, such as liters per second (L/s), cubic feet per minute (CFM), or cubic meters per hour (m3/h). Pumping speed is also known as suction capacity or throughput.

Pumping speed depends on several factors, such as the design of the pump, the type of gas being pumped, the pressure difference between the inlet and outlet of the pump, and the conductance of the system.

What are the Types of Vacuum Pumps?

There are many types of vacuum pumps available in the market. They can be classified into two main categories: positive displacement pumps and kinetic pumps.

Positive Displacement Pumps

Positive displacement pumps work by trapping a fixed volume of gas at the inlet and then compressing it to a higher pressure at the outlet. They can create low to medium vacuums (up to 10-3 Torr). Some examples of positive displacement pumps are:

• Rotary vane pumps

• Piston pumps

• Diaphragm pumps

• Screw pumps

• Scroll pumps

• Roots blowers

Rotary Vane Pumps

Rotary vane pumps are one of the most common types of positive displacement pumps.

They consist of a cylindrical rotor with radial vanes that slide in and out as the rotor rotates inside a stator. The vanes divide the space between the rotor and stator into chambers that change in volume as they move from inlet to outlet. As a chamber moves from inlet to outlet, it traps gas at low pressure and then compresses it to high pressure before releasing it to the outlet.

Rotary vane pumps can be either oil-sealed or dry.

Oil-sealed rotary vane pumps use oil as a lubricant and sealant between the vanes and stator. The oil also helps to cool down and remove some gas molecules from the system. Dry rotary vane pumps do not use oil but rely on other materials or coatings to reduce friction and wear between the vanes and the stator.

Rotary vane pumps can create vacuums up to 10-3 Torr with pumping speeds ranging from 0.5 to 1000 L/s.

Piston Pumps

Piston pumps are another type of positive displacement pump that use one or more pistons to compress gas inside cylinders. The pistons move back and forth inside cylinders that have valves at both ends to control gas flow. As a piston moves forward, it pushes gas out of one end of its cylinder while drawing gas in from another end through an inlet valve. As it moves backward, it closes its inlet valve while opening its outlet valve to release compressed gas.

Piston pumps can be either single-stage or multi-stage. Single-stage piston pumps have only one cylinder per piston, while multi-stage piston pumps have two or more cylinders connected in series per piston. Multi-stage piston pumps can create higher vacuums than single-stage piston pumps by compressing gas multiple times before releasing it.

Piston pumps can create vacuums up to 10-3 Torr with pumping speeds ranging from 1 to 1000 L/s.

Diaphragm Pumps

Diaphragm pumps are another type of positive displacement pump that use flexible diaphragms to compress gas inside chambers. The diaphragms are attached to rods that move back and forth by an electric motor or an eccentric cam. As a diaphragm moves forward, it pushes gas out of its chamber through an outlet valve while drawing gas in from another chamber through an inlet valve. As it moves backward, it closes its outlet valve while opening its inlet valve to allow gas flow.

Diaphragm pumps are dry pumps that do not use oil or other fluids as lubricants or sealants. They are suitable for pumping corrosive, flammable, or sensitive gases that cannot be contaminated by oil. They can also operate in any orientation without affecting their performance.

Diaphragm pumps can create vacuums up to 10-3 Torr with pumping speeds ranging from 0.1 to 100 L/s.

Screw Pumps

Screw pumps are another type of positive displacement pump that use two intermeshing screws to compress gas inside chambers. The screws rotate in opposite directions inside cylindrical housings that have inlet and outlet ports at both ends. As the screws rotate, they move gas along their threads from the inlet to the outlet while reducing its volume and increasing its pressure.

Screw pumps can be either oil-sealed or dry. Oil-sealed screw pumps use oil as a lubricant and sealant between the screws and housings. The oil also helps to cool down and remove some gas molecules from the system. Dry screw pumps do not use oil but rely on other materials or coatings to reduce friction and wear between the screws and housings.

Screw pumps can create vacuums up to 10-3 Torr with pumping speeds ranging from 10 to 1000 L/s.

Scroll Pumps

Scroll pumps are another type of positive displacement pump that use two spiral-shaped scrolls to compress gas inside chambers. One scroll is fixed while the other scroll orbits around it, creating crescent-shaped chambers that change in volume as they move from inlet to outlet. As a chamber moves from inlet to outlet, it traps gas at low pressure and then compresses it to high pressure before releasing it to the outlet.

Scroll pumps are dry pumps that do not use oil or other fluids as lubricants or sealants. They are suitable for pumping corrosive, flammable, or sensitive gases that cannot be contaminated by oil. They can also operate in any orientation without affecting their performance.

Scroll pumps can create vacuums up to 10-3 Torr with pumping speeds ranging from 1 to 100 L/s.

Roots Blowers

Roots blowers are another type of positive displacement pump that use two-lobed rotors that rotate in opposite directions inside cylindrical housings that have inlet and outlet ports at both ends. As the rotors rotate, they move gas along their lobes from the inlet to the outlet without compressing it. The compression occurs when the gas exits the housing into a downstream stage, such as another roots blower, a rotary vane pump, or a piston pump.

Root blowers are often used as backing pumps for high-vacuum pumps, such as turbomolecular pumps, diffusion pumps, or cryogenic pumps. They can increase the pumping speed and reduce the backing pressure of the system.

Roots blowers are often used as backing pumps for high-vacuum pumps, such as turbomolecular pumps, diffusion pumps, or cryogenic pumps. They can increase the pumping speed and reduce the backing pressure of the system. Roots blowers can create vacuums up to 10-3 Torr with pumping speeds ranging from 10 to 10000 L/s.

Kinetic Pumps

Kinetic pumps work by transferring momentum to gas molecules by means of high-speed blades, jets, or magnets. They can create medium to high vacuums (up to 10-11 Torr). Some examples of kinetic pumps are:

• Turbomolecular pumps

• Diffusion pumps

• Molecular drag pumps

• Ejector pumps

Turbomolecular Pumps

Turbomolecular pumps are one of the most common types of kinetic pumps. They consist of a series of rotating blades and stationary stators that accelerate gas molecules from the inlet to the outlet of the pump. The rotating blades impart momentum to the gas molecules in the direction of the outlet, while the stators redirect the gas molecules to the next stage of blades. The gas molecules are thus compressed and transferred to a backing pump that exhausts them into the atmosphere.

Turbomolecular pumps require a backing pump to operate, as they cannot start at atmospheric pressure. They also require cooling systems to prevent overheating due to friction and compression. Turbomolecular pumps can create vacuums up to 10-11 Torr with pumping speeds ranging from 10 to 4000 L/s.

Diffusion Pumps

Diffusion pumps are another type of kinetic pump that uses a jet of vapor to transfer momentum to gas molecules.

The vapor is usually oil or mercury that is heated by an electric heater at the bottom of the pump. The vapor rises up and expands through a series of nozzles that direct it toward the walls of the pump. The gas molecules inside the pump are entrained by the vapor jet and diffuse towards the outlet of the pump, where they are captured by a backing pump.

Diffusion pumps also require a backing pump to operate, as they cannot start at atmospheric pressure. They also require cooling systems to condense the vapor and recycle it back to the heater. Diffusion pumps can create vacuums up to 10-10 Torr with pumping speeds ranging from 100 to 20000 L/s.

Molecular Drag Pumps

Molecular drag pumps are another type of kinetic pump that use a combination of rotating blades and vapor jets to transfer momentum to gas molecules.

They consist of two stages: a turbomolecular stage and a diffusion stage. The turbomolecular stage works similarly to a turbomolecular pump, while the diffusion stage works similarly to a diffusion pump. The gas molecules are thus compressed and transferred to a backing pump that exhausts them into the atmosphere.

Molecular drag pumps also require a backing pump to operate, as they cannot start at atmospheric pressure. They also require cooling systems to prevent overheating and condense the vapor. Molecular drag pumps can create vacuums up to 10-11 Torr with pumping speeds ranging from 1000 to 100000 L/s.

Ejector Pumps

Ejector pumps are another type of kinetic pump that use a jet of fluid (liquid or gas) to create a vacuum by entraining gas molecules from a chamber or container. The fluid is supplied by a compressor or a pump at high pressure and flows through a nozzle that converts its pressure into velocity. The fluid jet then passes through a venturi tube that creates a low-pressure zone at its throat, where it entrains gas molecules from the chamber or container connected to it. The fluid-gas mixture then exits through a diffuser that converts its velocity back into pressure.

Ejector pumps do not require any moving parts or oil, making them simple, reliable, and low maintenance. They can also handle corrosive, flammable, or dirty gases without damage. However, they consume a lot of energy and produce noise and heat during operation. Ejector pumps can create vacuums up to 10-2 Torr with pumping speeds ranging from 1 to 10000 L/s.

What are some Applications of Vacuum Pumps?

Vacuum pumps have many applications in various industries and research fields, such as:

• Aerospace: Vacuum pumps are used for altitude simulation, space simulation, leak detection, vacuum brazing, vacuum sintering, vacuum casting, vacuum coating, and vacuum impregnation.

• Electronics: Vacuum pumps are used for semiconductor fabrication, thin film deposition, plasma etching, ion implantation, photolithography, electron microscopy, and laser processing.

• Metallurgy: Vacuum pumps are used for vacuum melting, vacuum annealing, vacuum degassing, vacuum carburizing, vacuum nitriding, vacuum hardening, and vacuum quenching.

• Chemistry: Vacuum pumps are used for distillation, evaporation, crystallization, filtration, drying, sublimation, and extraction.

• Medicine: Vacuum pumps are used for sterilization, surgery, dental procedures, wound healing, blood transfusion, and drug delivery.

• Biotechnology: Vacuum pumps are used for freeze-drying, lyophilization, cell culture, DNA sequencing, and protein purification.

Conclusion

Vacuum pumps are devices that remove gas molecules from a sealed chamber or container, creating a partial or complete vacuum. Vacuum pumps have three main features: exhaust pressure, degree of vacuum, and pumping speed. Vacuum pumps can be classified into two main categories: positive displacement pumps and kinetic pumps. Positive displacement pumps work by trapping and compressing gas inside chambers, while kinetic pumps work by transferring momentum to gas molecules by means of high-speed blades, jets, or magnets. Vacuum pumps have many applications in various industries and research fields, such as aerospace, electronics, metallurgy, chemistry, medicine, and biotechnology.

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