Compressed air, recognized as the fourth most widely used energy source after electricity, plays a critical role in various industries. Air receivers, commonly known as air tanks, are essential components in compressed air systems, providing stable air supply and improved efficiency. These pressure vessels are generally classified into two categories based on their safety ratings: simple pressure vessels and fixed pressure vessels.
In this article, we’ll explore how simple pressure vessels are defined and distinguished from fixed pressure vessels, covering their applications, structure, materials, manufacturing standards, and testing requirements.
What Is a Simple Pressure Vessel?
A simple pressure vessel is defined by specific design and operational criteria:
- Design Pressure: ≤ 1.6 MPa
- Volume: ≤ 1000 liters
- Pressure × Volume (PV): Between 2.5 MPa and 1000 MPa
- Working Medium: Air, nitrogen, or steam from distilled water
- Design Temperature: ≥ -20°C
- Maximum Working Temperature: ≤ 150°C
These vessels are typically used in applications where pressure demands are moderate, such as in standard industrial compressed air systems.
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Comparison: Simple vs. Fixed Pressure Vessels
| Category | Simple Pressure Vessel | Fixed Pressure Vessel |
|---|---|---|
| Working Pressure | ≤ 1.6 MPa | ≥ 0.1 MPa |
| Volume Range | ≤ 1000L | ≥ 30L and internal diameter ≥ 150mm |
| PV Range | 2.5 MPa ≤ PV ≤ 1000 MPa | PV ≥ 2.5 MPa |
| Working Medium | Air, nitrogen, distilled steam | Gas, liquefied gas, or liquids with boiling points below operating temperature |
| Temperature Range | -20°C to 150°C | Varies with medium and application |
Structural Definition
Simple Pressure Vessels Include:
- First threaded joint or flange connected to external piping
- Pressure-bearing cover parts and fasteners
- Welded joints connecting non-pressurized components to the vessel body
- Safety accessories such as safety valves, rupture discs, pressure gauges, level indicators, and thermometers
Fixed Pressure Vessels Include:
- First circular weld seam connected to external pipes
- Flange faces, threaded joint ends, or dedicated sealed connectors
- Pressure covers and welds at openings
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Material Requirements
Simple Pressure Vessels:
- Made from calm steel in hot-rolled or normalized condition
- Carbon content ≤ 0.25%, phosphorus and sulfur ≤ 0.045%
- Ultimate tensile strength < 540 MPa
Fixed Pressure Vessels:
- Often made from low-alloy steel plates
- Must also meet tensile strength requirements under 540 MPa
These strict material requirements ensure long-lasting durability and safety under pressure conditions. Baldor offers energy-efficient compressed air systems that integrate high-quality materials for optimal performance.
Manufacturing Conditions
Simple Pressure Vessels:
- Manufactured by certified units with A1, A2, C, D1, or D2 qualifications
- Batch production allowed (≤1000 units for ID ≤ 400mm; ≤500 for ID ≥ 400mm)
- Shared manufacturing and welding process documents permitted within the same batch
Fixed Pressure Vessels:
- Require a Special Equipment Manufacturing License
- Each vessel must have a unique manufacturing and welding record
Proper manufacturing is critical to safety. Learn about compressor room management best practices to ensure your entire air system is built to the highest standards.
Inspection and Testing
Simple Pressure Vessels:
- At least one vessel per batch must undergo radiographic inspection
- Hydraulic testing recommended; small tanks may use air pressure testing
- Air testing must only be conducted under strict safety protocols
Fixed Pressure Vessels:
- Every unit must undergo radiographic inspection
- Testing methods include hydraulic, air, or combined pressure testing
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Conclusion
Understanding the classification and characteristics of simple pressure vessels is essential for selecting the right air storage solution for your application. Whether you need a compact, cost-effective option or a robust, high-pressure vessel, Baldor offers industry-leading equipment and technical support to ensure your compressed air system operates safely and efficiently.
For more expert guidance and product solutions, visit https://baldor-air.com.