What equipment can achieve a pressure of −7 to −9 atmospheres?

Clarification of a Physical Concept: The True Meaning of “−7 to −9 Atmospheres”

In physics, the lower limit of absolute atmospheric pressure is 0 (absolute vacuum); there is no such thing as an absolute pressure of “−7” or “−9” atmospheres. In engineering and scientific contexts, this notation typically refers to one of two scenarios:

• Industrial gauge pressure (relative pressure): refers to -0.7 MPa To -0.9 MPa The negative pressure (commonly referred to as −7 to −9 kgf/cm²) corresponds to an absolute pressure of approximately 0.3 to 0.1 standard atmospheres, placing it within the range of rough vacuum or low vacuum.
• Absolute pressure in scientific notation: Refers to pressures ranging from 10⁻⁷ to 10⁻⁹ standard atmospheres (approximately 10⁻² to 10⁻⁴) Pa), which falls within the high-vacuum to ultra-high-vacuum range.

Achieving industrial negative pressure (-0.7 ~ -0.9 MPa) vacuum equipment

For the common rough-vacuum and low-vacuum requirements in industrial applications, the following equipment can reliably deliver negative pressure within this range:

• Oil-sealed rotary vane vacuum pump: It uses sliding vanes within the pump chamber to vary the volume and achieve pumping. Single-stage or two-stage rotary vane pumps can easily attain -0.09 MPa The aforementioned vacuum levels are widely used in packaging, degassing, and basic laboratory applications.
• Liquid ring vacuum pump: Using water or other liquids as the working fluid, it is well suited for extracting gases containing substantial water vapor or trace amounts of dust, and excels in the chemical and paper‑making industries.
• Roots vacuum pump unitRoots pumps cannot directly evacuate to atmospheric pressure; they are typically used in series with rotary vane pumps or liquid-ring pumps as backing pumps, which significantly increases the pumping speed and reduces the time required to reach the target vacuum.

Vacuum equipment capable of achieving high vacuum (10⁻⁷ to 10⁻⁹ atm)

If the required vacuum level is extremely high—on the order of one ten-millionth to one billionth of atmospheric pressure—conventional mechanical pumps are insufficient; high‑vacuum or ultra‑high‑vacuum pumps must be employed.

• Turbomolecular pump: By means of rapidly rotating blades, gas molecules are directed toward the exhaust port. It typically requires a backing pump and serves as a core component for achieving high and ultra-high vacuums, commonly used in semiconductor manufacturing and surface analysis.
• Cryogenic condensation pump: It utilizes cryogenic surfaces to condense or adsorb gas molecules. Characterized by high pumping speed and oil-free operation, it is well suited for vacuum coating and space environment simulation.
• Sputter ion pump: Gas molecules are ionized via a Penning discharge, and the resulting ions are accelerated by an electric field to implant into a titanium cathode, forming a buried layer. This is a motion‑free ultra-high vacuum pump designed to maintain extremely low vacuum conditions.

Recommendations for Vacuum Equipment Selection and System Configuration

When selecting the appropriate vacuum equipment, it is essential not only to consider the ultimate pressure but also to take into account the following factors:

• Gas compositionIf the gas contains corrosive components or a large amount of condensable vapor, corrosion-resistant materials must be selected, or a cold trap and filter should be installed.
• Pumping speedThe time required to reach the target pressure depends on the pump’s effective pumping speed and the system volume; large-volume chambers should be equipped with high‑pumping‑speed pump units.
• Cleanliness requirementsFor applications sensitive to oil contamination, oil-sealed mechanical pumps should be avoided; instead, dry screw pumps or oil-free pump units should be used as backing pumps to ensure a clean vacuum environment.