According to ISO3529/1 definition, vacuum refers to a diluted gas or related state gas whose gas pressure or concentration is lower than the surrounding atmospheric pressure. In the SI International System of Units, the pressure unit is Pascal (Pa). In vacuum technology pressure is usually referred to as absolute pressure.
1Pa =1N/m2

A pressure of 1Pa is equal to a force of 1 Newton applied to a flat surface of 1 square meter.

Standard atmospheric pressure: the temperature is 0 ℃, the atmospheric pressure at sea level is called the standard atmospheric pressure, and the value is 101325Pa.

Obviously, the value of Pa is relatively small, so there are many practical units in practical engineering applications. See conversion below.

In some application fields, such as medical vacuum suction, vacuum suction cups, etc., when the absolute pressure is higher than 100Pa, there is still the concept of using negative pressure and vacuum degree (relative vacuum).

The concept of negative pressure is to take the standard atmospheric pressure of sea level as "zero", and the absolute vacuum is minus 1 atmosphere of pressure.

Relative vacuum, expressed by vacuum degree: (Pn-P) / P *100%.

When the pressure is Pn, the standard atmospheric pressure, the vacuum degree is 0%, and when the absolute vacuum is P=0, the vacuum degree is 100%.

In the field of practical vacuum application and vacuum technology research, the currently available and applied pressure range is: 105-10-10 Pa.

Spans 15 orders of magnitude. In order to facilitate technical communication and according to the characteristics in different pressure ranges, it is usually divided into four vacuum regions.
 

Before leaving the factory, vacuum pumps, vacuum pump sets, vacuum systems and various vacuum equipment need to measure the ultimate vacuum, working pressure and other vacuum degrees that they can achieve, and check according to relevant standards to see whether they meet the factory standards and work requirements.

In addition, after the vacuum equipment has been running for a period of time, due to various factors, certain failures and failures of the vacuum equipment will occur. Often the vacuum degree and pumping efficiency cannot meet the required requirements, and the related equipment needs to be maintained. This measures vacuum.

According to different application requirements and different vacuum pumps, there are corresponding vacuum measuring instruments (vacuum gauges).

When the vacuum degree does not meet the factory standard or working requirements, there is often a certain leak in the vacuum equipment, so it is necessary to check the relevant equipment and parts for leaks. In addition, in many important vacuum application fields, it is not only necessary to measure the degree of vacuum, but also to perform necessary leak detection on the vacuum pump, vacuum system, vacuum chamber and various components. The main leak detection methods are as follows: