What is the maximum negative pressure that a vacuum pump can achieve?

Vacuum levels are generally classified into rough vacuum, medium vacuum, high vacuum, and ultra-high vacuum. Generally, if the vacuum level can reach 0.1 mbar, or if it is around 10 mbar to 1 mbar, it can be considered a high vacuum. There is no clear definition for the highest possible vacuum level; it depends mainly on the actual application, as a higher vacuum level is not necessarily better

The maximum negative pressure that can be achieved by the vacuum pump is dependent on the atmospheric pressure at the site, and does not exceed -1 atmosphere.

Vacuum levels are divided into ultimate vacuum and operating vacuum. The ultimate vacuum is an indicator used to measure the performance of a vacuum pump, while the operating vacuum refers to the vacuum level in the vacuum system once the vacuum pump is connected to it. It should be noted that this vacuum level depends on the location where it is measured; a higher vacuum level is obtained at locations close to the vacuum pump, whereas a lower vacuum level is measured at locations farther away from it. Considering the actual operating conditions, the vacuum level is related to the physical properties of the material, such as boiling point, saturated vapor pressure, molecular weight, and so on. The current vacuum levels used as pre-pumps in the chemical industry are as follows: screw vacuum pumps > vertical reciprocating pumps > water ring pumps ~ water jet pumps. By the same logic, it can be concluded that the vacuum level of rotary screw vacuum units is higher than that of rotary reciprocating vacuum units, and higher still than that of rotary water ring vacuum units. I hope this can be of help to you.