Which components in an air compressor, air receiver tank, refrigerated dryer, and filters qualify as pressure vessels?

Statutory Definition Standards for Pressure Vessels

Before examining the specific attributes of equipment, it is necessary to clarify the statutory criteria for defining a “pressure vessel.” According to the relevant safety technical regulations for special equipment, an item is generally considered a pressure vessel only if it simultaneously meets the following three basic conditions:

• Work stress: Maximum working pressure is greater than or equal to 0.1 MPa (Gauge pressure).
• Volume and Dimensions: A volume greater than or equal to 30 L and the inner diameter (for non-circular cross sections, this refers to the largest geometric dimension of the inner boundary of the cross section) is greater than or equal to 150 mm.
• Working mediumThe service medium is a gas, a liquefied gas, or a liquid whose maximum operating temperature is equal to or higher than its standard boiling point.

Gas storage tank: a typical pressure vessel

In the air compressor aftertreatment system,Gas storage tanks are explicitly classified as pressure vessels.Its primary functions are to store compressed air, stabilize the pipeline pressure, and perform preliminary moisture separation.

The working pressure of conventional industrial gas storage tanks is typically in the range of 0.7 MPa To 1.0 MPa Even higher, far exceeding 0.1 MPa the threshold; its volume ranges from several tens of liters to several cubic meters, with the vast majority exceeding 30 L Moreover, the inner diameter is greater than 150 mm It meets the dimensional requirements; its internal medium is compressed air. Consequently, the air receiver fully satisfies the definition of a pressure vessel. In practice, air receivers are typically classified as either “simple pressure vessels” or “fixed pressure vessels” and must be registered, undergo periodic inspections, and have their safety accessories (such as safety valves and pressure gauges) calibrated in accordance with the relevant regulations for special equipment.

Refrigerant dryer: The entire unit is not a pressure vessel; internal components depend on the specific circumstances.

Refrigerated air dryers are primarily used to lower the dew point temperature of compressed air. From the perspective of overall equipment classification,The air dryer unit as a whole is not classified as a pressure vessel under the law.rather, it falls under heat exchange equipment or general-purpose machinery.

However, the refrigerant dryer internally comprises both a refrigeration system and an air system. Certain components within the refrigeration system—such as the receiver‑drier, condenser, and liquid‑gas separator—will, if their design pressure, volume, and working fluid satisfy the three criteria for pressure vessels outlined above, be considered pressure vessels; these…Specific internal pressure-bearing componentsIn such cases, the equipment must be designed and manufactured in accordance with pressure vessel standards. However, for end users, refrigerated air dryers are typically procured and managed as complete units, and there is no need to register the entire machine as special equipment under pressure vessel regulations.

Filter: Generally not classified as a statutory pressure vessel.

Precision filters are used to capture solid particles, oil mist, and moisture from compressed air. Although the filter housing must withstand the same compressed-air pressure as the piping network (typically greater than 0.1 MPa), and the internal medium is a gas, butIts volume is usually small..

The volume of the vast majority of industrial pipeline filters is far smaller than 30 L, it is impossible to simultaneously satisfy both the volume and dimensional requirements of a pressure vessel. Therefore, filters are generally not classified as statutory pressure vessels but are instead regarded asPressure piping componentsIt may also be managed and inspected as a conventional pressure‑bearing device. During maintenance, users should primarily monitor the filter element’s replacement schedule and conduct shell‑pressure tests; there is no need to follow the periodic inspection procedures for pressure vessels.

Device Compliance Management and Security Recommendations

Accurately distinguishing between pressure vessels and non-pressure vessels in compressed air systems is critical for ensuring workplace safety and compliance. It is recommended to implement the following measures during routine operations and maintenance:

• Establish an equipment ledgerClearly distinguish between gas storage tanks (special-purpose equipment) and refrigerant dryers and filters (general-purpose equipment), and establish management records by category.
• Periodic Inspection and Safety-Related Component VerificationFor gas storage tanks, it is imperative to conduct periodic body inspections in strict accordance with the requirements of the local special equipment regulatory authority, and to calibrate safety valves and pressure gauges on schedule.
• Standardize daily inspectionsFor refrigerant dryers and filters, although they are not complete pressure vessels, they still qualify as pressurized equipment. The shell must be inspected regularly for deformation, corrosion, or leaks to ensure the equipment operates safely within its design pressure range.