Introduction

Valves are crucial for controlling flow, pressure, and purity in high-purity gas systems. Selecting the appropriate valve type depends on gas purity, toxicity, and flammability.

Ball Valves

 • Suitable for systems ≤99.999% purity.

 • Stainless steel 304 construction is standard.

 • Soft-metal or PTFE gaskets are acceptable for moderate purity systems.

 • Advantages: Simple design, low cost, and easy operation.

Diaphragm Valves

 • Ideal for systems ≤10 ppm or when contamination must be minimized.

 • Features: Minimal internal dead space, easy purging, reduced contamination.

 • Commonly paired with EP-treated stainless steel pipelines for ultra-high-purity applications.

Bellows Valves

 • Required for toxic, corrosive, or flammable gases.

 • Provides leak-free operation with metal bellows sealing.

 • Ensures safety while maintaining high purity.

Valve Selection Guidelines

Connection Considerations

 • Threaded connections: Limited to low-purity or ppm-level systems.

 • Welded connections: Preferred for high-purity applications to avoid dead spaces.

 • VCR fittings: Standard for ultra-high-purity systems with soft-metal gaskets.

Practical advice

 • For POU and critical paths, prefer diaphragm valves (metal diaphragm) or bellows valves.

 • Where ball valves are used, choose versions with metal seats or specialty low-dead-volume designs, and limit their use away from critical POU.

 • Match valve body and internal materials with the chosen pipe finish (EP recommended for most UHP applications) and use metal gaskets at all flanges.

Conclusion:

Choosing the correct valve type and connection ensures control, safety, and purity throughout the system. Diaphragm and bellows valves are particularly recommended for ppb/ppt-level systems or hazardous gases.