In the past, oil-sealed vacuum pumps were widely used in various semiconductor processes, with rotary vane and piston vacuum pumps being the most common. However, their performance in many applications was not ideal. As a result, dry vacuum pumps were developed.

I. Introduction: From Oil-Sealed to Dry Vacuum Pumps

1. Limitations of Traditional Oil-Sealed Pumps

Historically, oil-sealed vacuum pumps (e.g., rotary vane and piston types) dominated semiconductor and industrial processes. Yet, their performance fell short in many scenarios—often due to oil contamination, maintenance demands, or inefficiency in specific applications.

2. Emergence of Dry Vacuum Pumps

To address these drawbacks, dry vacuum pumps were developed. Unlike oil-sealed models, they operate without oil lubrication, making them suitable for clean, high-performance requirements in modern industries.

II. Classification of Dry Vacuum Pumps by Mechanical Structure

Over the years, several types of dry vacuum pumps have been designed, differing significantly in mechanical structure. The main categories include:

• Circular lobe pumps

• Claw pumps

• Hybrid (roots-claw) pumps

• Screw-type pumps

These designs are now widely adopted by manufacturers across industries.

III. Working Principles: Multi-Stage vs. Single-Stage Pumps

1. Multi-Stage Dry Vacuum Pumps

Circular lobe, claw, and hybrid (roots-claw) pumps are classified as multi-stage pumps. Their working principles are similar:

Vacuum is created by repeatedly compressing gas through multiple vacuum chambers in sequence.

During compression, the gas undergoes significant changes in temperature and pressure, which can alter its physical properties (a key consideration for process compatibility).

2. Single-Stage Dry Vacuum Pumps

Screw-type pumps are single-stage pumps, generating vacuum using only one vacuum chamber. They are further divided based on gas compression methods:

• Internally compressed screw pumps

• Externally compressed screw pumps

IV. Key Lobe Designs: Twin-Lobe and Three-Lobe

1. Twin-Lobe Design (Most Popular)

The twin-lobe design, similar to the Roots pump, is currently the most widely used dry pump design. Key features:

Based on combining Roots pump technology, it uses a multi-stage approach to create a large gas path.

Requires a high nitrogen flow rate at each stage for dilution and sealing.

Demands strict sealing at all stages to achieve good vacuum performance.

Advantages: Relatively low power consumption; Disadvantage: Higher internal compression ratio.

2. Three-Lobe Circular Design

The three-lobe design operates on the same principle as the twin-lobe version but divides gas into three parts instead of two. Key notes:

Shares similar advantages (e.g., process compatibility) and disadvantages (e.g., nitrogen demand) with the twin-lobe design.

To reduce power consumption, some manufacturers use two DC motors in the drive section—but this may lower torque and restart capability.

Like the twin-lobe design, it requires a high nitrogen flow rate for effective gas dilution.

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