Overview of vacuum system and the core role of valves
1. Definition and classification of vacuum system Vacuum system is to reduce the air pressure in a confined space to an environment below atmospheric pressure through vacuum pumps and other equipment. It is widely used in semiconductor manufacturing, aerospace, scientific research experiments, vacuum smelting, food packaging and other fields.
According to the vacuum level, it can be divided into:
Low vacuum (1000~100 Pa): Commonly used in vacuum packaging and vacuum cleaning equipment.
Medium vacuum (100~0.1 Pa): Applied to vacuum coating and vacuum drying furnace.
High vacuum (0.1~10⁻⁵ Pa): Applicable to semiconductor wafer manufacturing and electron beam welding.
Ultra-high vacuum (<10⁻⁵ Pa): Used in cutting-edge fields such as space simulation cabins and particle accelerators.
2. The core function of valves in vacuum systems Vacuum valves are the "control hub" of vacuum systems.
The main functions include:
Isolation and cutoff: Block the airflow during system maintenance or process switching to prevent atmospheric intrusion.
Flow regulation: Accurately control the gas flow to meet the process's requirements for vacuum gradient.
Safety protection: prevent vacuum pump oil backwash, pressure relief during overload, and avoid equipment damage.
Pressure balance: slowly ventilate between the vacuum chamber and the atmosphere to prevent boiling or impact.
Main types and characteristics of vacuum valves
1. Classification by structure and working principle
1.1 Butterfly Valve
Principle: opening and closing by rotating the baffle (disc), simple structure, strong flow capacity.
Features
Applicable pressure range: 10⁵~10⁻³ Pa (medium and low vacuum).
Sealing method: rubber or metal sealing ring, metal sealing type can be used for high vacuum.
Advantages: small size, light weight, fast response speed. Disadvantages: rubber seals are prone to aging and are not suitable for corrosive gases. Typical applications: pre-exhaust pipelines of vacuum coating machines (such as DAM series baffle valves of LEYBOLD, Germany). Exhaust circuits of food vacuum packaging machines.
1.2 Gate Valve
Principle: The gate slides perpendicular to the direction of the fluid, and the flow resistance is extremely small when fully open.
Features
Applicable pressure range: 10⁵~10⁻⁹ Pa (from atmospheric pressure to ultra-high vacuum).
Sealing method: metal bellows + fluororubber, which can achieve zero leakage.
Advantages: excellent sealing, suitable for cutting off high vacuum pipelines.
Disadvantages: complex structure, long opening and closing stroke, and high cost. Typical applications are vacuum chamber isolation of semiconductor lithography machines (such as the 2000 series gate valve of VAT in the United States). The main exhaust pipeline of the vacuum melting furnace (such as the GU series gate valve of ULVAC).
1.3 Ball Valve
Principle: There are flow holes on the sphere, which can be opened and closed by rotating 90°, and the flow path is straight.
Features
Applicable pressure range: 10⁵~10⁻⁴ Pa (low to medium vacuum).
Sealing method: polytetrafluoroethylene (PTFE) or metal hard seal.
Advantages: small flow resistance, strong corrosion resistance, suitable for granular media.
Disadvantages: high processing precision requirements and high cost for metal hard seal.
Typical applications: air intake regulation of vacuum drying equipment (such as GV series ball valves from Edwards, UK). Discharge pipeline of vacuum reactor in chemical industry.
1.4 Angle Valve
Principle: The valve body is a right-angle structure, and the valve core moves along the axial direction, with both cutting and diversion functions.
Features
Applicable pressure range: 10⁵~10⁻⁸ Pa (high vacuum to ultra-high vacuum).
Sealing method: metal bellows + fluororubber, which can withstand high temperature baking.
Advantages: smooth flow channel, suitable for fast gas flow scenarios.
Disadvantages: high installation space requirements, vertical or horizontal installation is required.
Typical application: gas injection pipeline of vacuum ion implanter (such as Pneumatic Angle Valve of Kurt J. Lesker, USA). Main exhaust valve of space simulation cabin (such as the ultra-high vacuum angle valve independently developed by the Chinese Academy of Sciences).
1.5 Diaphragm Valve
Principle: Blocking the airflow through the deformation of the elastic diaphragm (rubber or metal), no stuffing box design.
Features
Applicable pressure range: 10⁵~10⁻² Pa (low vacuum).
Sealing method: The diaphragm material directly contacts the medium and is corrosion-resistant.
Advantages: Zero leakage, easy to clean, suitable for corrosive or high-purity gases.
Disadvantages: The diaphragm has a limited life and needs to be replaced regularly. Typical applications Material control of vacuum distillation equipment in the pharmaceutical industry (such as the diaphragm valve of Swiss GF Piping Systems). Vacuum cavity air intake valve in lithium battery production workshop.
Key technical indicators and selection points of vacuum valves
1 Core technical indicators
Leak rate
Definition: The gas flow rate passing through the valve seal per unit time, in Pa・m³/s.
Standard: High vacuum valves need to be ≤10⁻⁹ Pa・m³/s, and ultra-high vacuum valves need to be ≤10⁻¹² Pa・m³/s.
Applicable temperature range
Stainless steel + metal seals are required for low temperature scenarios (such as liquid helium cooling), and baking-resistant designs (200~450℃) are required for high temperature scenarios (such as vacuum annealing furnaces).
Conductance
Definition: The gas flow rate when the valve is fully open, which is related to the caliber and structure (such as the gate valve conductance is higher than the ball valve).
Corrosion resistance
When handling corrosive gases (such as Cl₂, SF₆), Hastelloy valve body + PTFE seal is required.
2 Selection process and precautions
Clear vacuum level
For low vacuum, select a flapper valve or ball valve, and for high vacuum/ultra-high vacuum, a gate valve or angle valve must be used.
Analysis of media characteristics
For medium containing particles, select a ball valve (straight-through flow channel), and for corrosive gases, select a diaphragm valve or a coated valve body.
Matching control requirements
For quick cut-off, select a pneumatic gate valve (response time < 0.5 seconds), and for precise adjustment, select an electric needle valve (such as the SS-4NV series of Swagelok in the United States).
Installation space and compatibility
For compact equipment, select a right-angle valve (space-saving), and the flange interface must match the pipeline standard (such as ISO, CF).
Application cases of vacuum valves in typical industries
1. Semiconductor manufacturing: Precision control of ultra-high vacuum environment
Case: Vacuum valve group in photolithography process
Process requirements
The vacuum chamber of the photolithography machine needs to maintain an ultra-high vacuum of 10⁻⁶ Pa to prevent gas molecules from interfering with the beam path. Frequent wafer loading/unloading requires fast valve switching speed (<1 second) and zero leakage.
Solution
Main isolation valve: pneumatic gate valve (such as VAT 2000 series), metal bellows seal, leakage rate ≤10⁻¹² Pa・m³/s.
Gas injection valve: electric needle valve (accuracy ±0.1 sccm), control the flow of purge gas (N₂).
Safety protection: electromagnetic vent valve (response time < 50ms), quickly balance the pressure in the event of vacuum pump failure.
Key advantages
The inner wall of the valve is electrolytically polished (Ra≤0.2μm) to reduce particle adsorption and meet the semiconductor cleanliness requirements.
Support remote digital control (such as RS-485 interface), seamless linkage with the lithography machine control system.
2. Aerospace: Vacuum simulation and extreme environment testing
Case: Spacecraft thermal vacuum test chamber
Process requirements
Simulate space vacuum (10⁻³ Pa) and extreme temperature (-120~+120℃) to test the reliability of spacecraft components.
The passage between the vacuum chamber and the vacuum pump and calibration gas source needs to be frequently switched.
Solution
Main exhaust valve: large-diameter angle valve (DN200), flow conductance ≥5000 L/s, water-cooled jacket is used to cope with baking temperature rise.
Pressure balance valve: pneumatic flapper valve with buffer device, adjustable flow rate (0~1000 Pa/s) during ventilation to prevent impact on equipment in the cabin.
Calibration gas valve group: multi-channel ball valve array to achieve rapid switching of multiple gases such as O₂ and CO₂.
Key challenges and responses
Temperature cycles cause thermal expansion and contraction of seals, and Invar bellows are used to compensate for deformation.
Control of material outgassing rate under high vacuum, the valve body is made of 316L stainless steel + electrolytic polishing, and the surface outgassing rate is ≤10⁻¹⁰ Pa・m³/(s・cm²).
3. Vacuum smelting: complex environment of high temperature, high pressure and metal vapor
Case: Melting control of vacuum arc furnace
Process requirements
During the smelting process, the vacuum degree needs to be maintained at 10⁻² Pa to prevent metal oxidation; at the same time, inert gas (Ar) needs to be introduced to adjust the pressure in the furnace.
Metal vapor (such as Ti, Zr) is highly corrosive, and the valve needs to be resistant to erosion and adhesion.
Solution
Vacuum valve: water-cooled gate valve, the valve body is sprayed with tungsten carbide (WC) coating, which is resistant to metal vapor erosion.
Inflatable valve: pneumatic ball valve, the valve core surface is plated with nickel-phosphorus alloy (Ni-P) to prevent metal droplets from sticking.
Safety valve: spring-loaded pressure relief valve, set pressure 0.15 MPa, automatic exhaust when the furnace is overpressured.
Operation effect
The valve life is extended from 3 months of ordinary stainless steel to more than 1 year, reducing downtime maintenance costs.
The inflation accuracy is ±5%, ensuring that the oxygen content is controlled below 20 ppm during the melting process.
4. Food and medicine: special requirements for sanitary vacuum systems
Case: Aseptic control of pharmaceutical freeze dryers
Process requirements
Drug freeze drying needs to be carried out in a low vacuum environment of 10~1 Pa to prevent the denaturation of drug components.
The system must comply with GMP standards, the inner wall of the valve is smooth and has no dead corners, which is convenient for online cleaning (CIP).
Solution
Main valve: sanitary diaphragm valve (such as the 600 series of GEMÜ in Germany), the valve body is made of 316L stainless steel, and the inner surface is polished Ra≤0.8μm.
Steam sterilization valve: pneumatic angle valve, supports 134℃ wet heat sterilization (SIP), the sealing ring is perfluororubber (FFKM), chemical corrosion resistant.
Air-breaking valve: flapper valve with bacterial filter, filtration efficiency ≥99.99% (0.22μm particles) when air is passed.
Compliance
Advantage valve design complies with ASME BPE standards, and material certificates and surface roughness test reports can be provided.
Spring-free and gap-free structure to avoid microbial growth caused by residual liquid.
Maintenance and troubleshooting of vacuum valves
Daily maintenance points
Sealing test
Scan the valve connection regularly with a helium mass spectrometer leak detector, and replace the sealing ring or repair the bellows when the leakage rate exceeds the standard.
Surface cleaning
High vacuum valves need to be wiped with anhydrous ethanol or acetone, and grease-based cleaners are strictly prohibited (to prevent contamination of the vacuum system).
Drive mechanism maintenance
Regularly check the air source pressure (0.4~0.6 MPa) for pneumatic valves and test the motor insulation resistance (≥5 MΩ) for electric valves.
