A vacuum pump removes gas from a chamber, pipe or process volume so that the pressure falls below atmospheric pressure. It does not create an empty space in the literal sense; it reduces the number of gas molecules remaining inside the system.

Vacuum pumps are used in packaging, robotic handling, CNC workholding, drying, vacuum furnaces, laboratory equipment, coating systems and many other industrial processes.

For the main product and application section, see our Vacuum Pumps homepage.

What does a vacuum pump actually do?

When gas is removed from a fixed volume:

• Fewer gas molecules remain inside the system
• Gas density falls
• Absolute pressure decreases

and the system moves into a vacuum region.

A vacuum pump therefore does not “suck vacuum”. It removes or transfers gas so that pressure becomes lower.

How does a simple vacuum system work?

A basic arrangement can be represented as:

Process chamber → vacuum line → vacuum pump → exhaust or backing stage

Once the pump starts, gas is transported away from the process volume.

Depending on the pump technology, the gas may be:

• Trapped in a changing mechanical volume and compressed
• Driven toward the outlet by momentum transfer
• Captured on or within a pumping surface

This is why not every vacuum pump can be described simply as “air enters, is compressed and is blown out”.

How do positive-displacement vacuum pumps work?

Positive-displacement pumps trap a quantity of gas, mechanically change the volume around it and move it toward the exhaust.

Common examples include:

• Rotary vane pumps
• Dry screw pumps
• Scroll pumps
• Diaphragm pumps

In a rotary vane pump, for example, vanes mounted in an eccentric rotor create changing internal volumes. Gas enters through the inlet, is transported and compressed, then leaves through the exhaust.

How do momentum-transfer pumps work?

Some high-vacuum pumps do not rely on sealed compression chambers.

Turbomolecular pumps use rapidly rotating blades to transfer directed momentum to gas molecules and drive them toward the foreline.

Diffusion pumps use high-speed vapour jets to entrain gas molecules and move them toward a higher-pressure region.

These pumps normally cannot exhaust directly to atmospheric pressure and therefore require a backing or forevacuum pump.

The main pump families are compared under different types of vacuum pumps.

Are there vacuum pumps that capture gas instead of exhausting it?

Yes.

Some high and ultra-high-vacuum technologies remove gas by capturing it on surfaces rather than continuously exhausting it outside the system.

Examples include certain:

• Cryogenic pumps
• Sorption pumps
• Ion pumps

This is another reason why “all vacuum pumps compress and discharge air” is not technically correct.

How do a vacuum pump and vacuum sensor work together?

They perform two different jobs:

Pump → reduces the pressure.
Sensor → measures the pressure that was actually achieved.

A running pump does not guarantee that the required vacuum has been reached.

Actual pressure can be affected by:

• Leakage
• Long or restrictive pipework
• Dirty filters
• High process gas load
• Pump wear

For this reason, automated systems often use a vacuum sensor to verify the actual process pressure.

Is the pump's ultimate pressure the same as system pressure?

No.

The ultimate pressure shown in a pump specification is the lowest pressure the pump can reach under specified test conditions.

The pressure in a real machine also depends on:

• Pumping speed
• Pipe and valve conductance
• System volume
• Leakage
• Outgassing from internal surfaces
• Process gas load

A pump capable of a very low ultimate pressure does not automatically guarantee that the complete system will operate at that pressure.

What is pumping speed?

Two pump specifications are often confused:

Ultimate pressure: the lowest pressure region the pump can reach under defined conditions.

Pumping speed: how effectively gas is removed from the system at a given pressure.

A pump may achieve a low ultimate pressure but still take a long time to evacuate a large chamber.

This is why choosing a pump by asking only “how many mbar can it reach?” is not enough.

How should a vacuum pump be selected?

At minimum, the following should be known:

• Required operating pressure
• Chamber or system volume
• Required pump-down time
• Process gas or vapour
• Gas load
• Dry or oil-sealed pump requirement
• Continuous or intermittent duty

For a practical selection guide, see what to consider when choosing a vacuum pump.

How does a pump maintain vacuum?

A real vacuum system normally has some continuous gas load.

Gas may enter or be released through:

• Small leaks
• Seals and fittings
• The process itself
• Outgassing from material surfaces

The pump removes this incoming or released gas so that the system can remain near the required operating pressure.

In well-sealed systems, pump operation may also be controlled to reduce unnecessary energy use.

See vacuum pump energy consumption for the energy side of the system.

How does a vacuum pump work in simple terms?

A useful summary is:

1. Gas is transported away from the process volume.
2. The pump compresses, transfers or captures the gas depending on its technology.
3. Fewer gas molecules remain in the chamber.
4. Absolute pressure falls.
5. A vacuum sensor measures the actual pressure reached.

A working vacuum installation should therefore be treated as a complete system:

pump + pipework + valves + chamber + seals + process gas + vacuum sensor

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Related vacuum pump topics

Types of vacuum pumps | Vacuum pump applications | Vacuum pump maintenance | Advantages and disadvantages | Choosing a vacuum pump

Vacuum pump oils | Vacuum pump vs pressure pump | Vacuum pump energy consumption

Sensor side:
How a vacuum sensor works | Choosing a vacuum sensor

Main sections:
Vacuum Pumps homepage | Vacuum Sensors | Vacuum FAQ

Vacuum pump selection should be based on operating pressure, pumping speed, system conductance, gas load and process compatibility rather than ultimate pressure alone.

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