The most fundamental difference between vacuum pumps and other types of pumps (such as water or oil pumps) lies in their operational purpose and working medium.
In simple terms, ordinary pumps (like centrifugal or gear pumps) are designed to "transport" fluids (moving water or oil from point A to point B), whereas vacuum pumps are intended to "create an environment" (removing air from a sealed container to establish a vacuum state).
To give you a more intuitive understanding, here is a detailed comparative analysis:
1. Differences in Core Purpose and Working Medium
| Dimension | Vacuum Pump | Ordinary Pump (Water/Oil Pumps, etc.) |
|---|---|---|
| Core Purpose | Evacuation / Creating Vacuum: Reducing gas pressure within a sealed space. | Transport / Pressurization: Increasing the elevation, pressure, or flow rate of liquids. |
| Working Medium | Primarily gases (air, water vapor, corrosive gases). | Primarily liquids (water, oil, chemical solutions, slurries). |
| Suction Side State | Suction pressure is below atmospheric pressure (negative pressure). | The suction side typically has liquid head pressure or positive inlet pressure. |
| Discharge Side State | Discharges into the atmosphere or to a subsequent pump stage. | Discharges into pipelines, elevated tanks, or high-pressure systems. |
2. Internal "Family Variations" of Vacuum Pumps
Vacuum pumps themselves form a diverse family, with vastly different operating principles and application scenarios depending on the type. Based on whether they use oil lubrication, they are primarily categorized into two major groups: Dry and Wet (Oil-sealed / Liquid-ring).
A. Dry Vacuum Pumps (e.g., Screw Pumps, Scroll Pumps, Diaphragm Pumps)Characteristics: No oil inside the pump chamber; the gas does not come into contact with lubricating oil during pumping.Advantages:
Clean and pollution-free: Exhausted gas remains pure without risk of oil backstreaming contaminating experiments or products (essential for semiconductor and food industries).
Simple maintenance: No waste oil disposal required; certain designs (like screw pumps) feature non-contact operation, resulting in longer service life.Disadvantages: Complex manufacturing processes, generally making them more expensive than oil-lubricated pumps of comparable performance.
B. Wet / Oil-Sealed Vacuum Pumps (e.g., Rotary Vane Pumps, Water Ring Pumps)Characteristics: Utilize oil or water as sealing and lubricating media.Advantages:
Simple structure and low cost: For instance, rotary vane pumps are the most common "economical" equipment in laboratories.
High temperature resistance / Explosion-proof: Water ring pumps utilize water sealing and operate via isothermal compression, making them highly suitable for extracting flammable and explosive gases (commonly used in chemical plants).Disadvantages:
Contamination risk: Oil pumps may emit oil mist requiring filters; water ring pumps generate wastewater that needs treatment.
Limited vacuum degree: Restricted by the saturated vapor pressure of the working fluid, making it difficult to achieve extremely high vacuum levels.
3. Comparison of Performance Limits
Different types of pumps can achieve vastly different "degrees of vacuum" (ultimate pressure), which is a critical metric during equipment selection:
Rough Vacuum (1000 Pa - Atmospheric Pressure):
Representative Pumps: Water ring pumps, piston pumps.
Applications: Vacuum packaging, material lifting/handling, wastewater treatment.
Medium to Low Vacuum (1 Pa - 1000 Pa):
Representative Pumps: Rotary vane pumps (oil-sealed), dry screw pumps, scroll pumps.
Applications: Vacuum drying, freeze-drying, electronic encapsulation.
High / Ultra-High Vacuum (< 0.1 Pa):
Representative Pumps: Molecular pumps, Roots pumps (typically require a backing pump in series).
Applications: Semiconductor coating, mass spectrometry, particle accelerators.