The main difference between a vacuum pump and a pressure pump is the part of the system in which they are intended to control pressure.

A vacuum pump is primarily used to reduce pressure at its inlet side, often below atmospheric pressure. A pressure pump, compressor or blower is used to raise the pressure of a fluid or gas for another part of the process.

For the basic vacuum side of the subject, see how a vacuum pump works.

What does a vacuum pump do?

A vacuum pump removes gas from a chamber or transfers gas away from a process volume so that the pressure falls below atmospheric pressure.

Typical purposes include:

+ Evacuating a vacuum chamber
+ Creating suction for gripping and handling
+ Supporting vacuum packaging
+ Drying and degassing
+ Creating controlled low-pressure process conditions

Vacuum pumps do not all work in the same way. Rotary vane, dry screw, liquid-ring, turbomolecular, diffusion and capture pumps use very different operating principles.

These technologies are compared under different types of vacuum pumps.

What does a pressure pump do?

“Pressure pump” is a broad term rather than one specific machine type.

In liquid systems, a pump transfers mechanical energy to the fluid so that flow can be produced against system resistance.

Examples include:

+ Water booster pumps
+ Hydraulic pumps
+ Process pumps
+ Dosing pumps

For gases, the terms compressor or blower are often more technically appropriate when the objective is to increase discharge pressure.

For the wider machine-pump structure, see the Pumps main category.

Are vacuum and positive pressure complete opposites?

They are different operating regions of the same physical quantity: pressure.

For example, with atmospheric pressure close to 1 bar:

Gauge pressure = 0 bar → approximately atmospheric pressure

Gauge pressure = -0.8 bar → vacuum region

Gauge pressure = +6 bar → positive gauge pressure

Absolute pressure is referenced to perfect vacuum and does not become negative.

For the wider pressure terminology, see pressure fundamentals.

Does a vacuum pump really “suck”?

In everyday language we say that a vacuum pump “sucks”, but technically the pump lowers pressure on one side of the system.

Gas then moves from the higher-pressure region toward the lower-pressure region because of the pressure difference.

The same principle explains why a vacuum cup can hold a workpiece: the holding force comes from the pressure difference across the cup.

Can the same machine create vacuum and positive pressure?

Some machine designs can be configured for either suction or positive-pressure service.

Examples may include selected:

+ Side-channel blowers
+ Rotary vane machines
+ Special-purpose gas pumps

However, a vacuum pump should not automatically be used as a compressor, and a compressor should not automatically be used as a vacuum pump.

The manufacturer's permitted:

+ Inlet pressure
+ Discharge pressure
+ Pressure ratio
+ Temperature limits

must be respected.

Why is vacuum pump selection different?

Vacuum pump selection usually focuses on:

+ Required absolute pressure
+ Pumping speed
+ Chamber volume
+ Gas and vapour load
+ Pump-down time
+ Ultimate pressure

For a positive-pressure liquid pump, the important parameters are more likely to include:

+ Flow rate
+ Head
+ Required discharge pressure
+ Fluid properties

For practical vacuum selection, see vacuum pump selection criteria.

How are vacuum and positive pressure measured?

Vacuum measurement may use diaphragm, capacitance, Pirani or ionization technologies depending on the pressure range.

Positive-pressure systems can use piezoresistive, strain-gauge, ceramic or other pressure-sensing technologies.

This means that the difference between a vacuum sensor and a pressure sensor is not simply “negative pressure versus positive pressure”.

The distinction is explained under vacuum sensor vs pressure sensor.

Why does atmospheric pressure matter?

Atmospheric pressure is particularly important in gauge-vacuum measurements because it forms the reference point.

Changes in altitude and weather can alter local atmospheric pressure, so the absolute-pressure equivalent of the same gauge reading is not always identical.

The wider distinction is discussed under vacuum technology and atmospheric-pressure operation.

Is there an energy difference?

Energy use in either system depends on more than motor power.

In a vacuum installation, consumption can increase because of:

+ Air leakage
+ Producing deeper vacuum than the process needs
+ Oversized pumps
+ Continuous operation

For the vacuum side, see vacuum pump energy consumption.

Vacuum pump vs pressure pump: short answer

Vacuum pump:
Reduces pressure at the inlet or process side to create a below-atmospheric-pressure condition.

Pressure pump:
Transfers energy to a fluid so that flow and higher pressure can be produced in the system.

Compressor:
Compresses gas to increase gas pressure at the discharge side.

Common point:
All of them transfer energy to a fluid or gas; the difference is the pressure region and process objective for which the machine is designed.

For examples of where vacuum pumps are actually used, see vacuum pump applications.

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Related topics

How a vacuum pump works | Vacuum pump types | Vacuum pump applications | Choosing a vacuum pump

Energy consumption | Vacuum sensor vs pressure sensor | Pumps

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

Vacuum and positive pressure are different operating regions of the same physical quantity. Pump or compressor selection depends on which pressure condition the process needs to create and control.

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