Comprehensive Analysis of Application, Selection, and Performance of Threaded Full Brass Safety Valves in Refrigeration

Comprehensive Analysis of Application, Selection, and Performance of Threaded Full Brass Safety Valves in Refrigeration Equipment

Introduction

In refrigeration systems such as chillers, cold storage units, and commercial refrigerating equipment, safety valves serve as the final mechanical safeguard against abnormal pressure rise. When system pressure exceeds the allowable threshold, a safety valve must open rapidly and discharge excess pressure to prevent catastrophic failures such as compressor damage, pipeline rupture, or refrigerant leakage.

Among various safety valve types, threaded full brass safety valves are widely adopted in refrigeration applications due to their excellent compatibility with common refrigerants, stable thermal conductivity, reliable sealing performance, and ease of installation. They are extensively used across industrial refrigeration systems, commercial refrigeration equipment, and compact household refrigeration units.

According to ASME BPVC Section VIII, the deviation between the safety valve set pressure and the system Maximum Allowable Working Pressure (MAWP) must be controlled within ±3%, while the relieving capacity must satisfy at least 1.2 times the system’s maximum pressure generation capability. ISO 4126-1 further specifies that leakage rates for safety valves used in refrigeration systems shall not exceed 10⁻⁶ mbar·L/s. Under standard operating conditions, threaded full brass safety valves can reliably meet or exceed these requirements.

In-Depth Product Analysis: Structural and Material Advantages

Structural Composition and Material Characteristics

Threaded full brass safety valves typically adopt an integrated brass valve body design, with H59-1 brass or H62 brass selected based on application requirements.

H59-1 brass offers excellent machinability and high thread precision, making it suitable for commercial refrigeration systems requiring frequent installation and maintenance. Its tensile strength and hardness allow it to withstand repeated pressure fluctuations.

H62 brass provides superior corrosion resistance and mechanical stability. It is chemically compatible with ammonia and mainstream HFC refrigerants and offers high thermal conductivity, which reduces the risk of stress cracking caused by rapid temperature changes.

Working Principle and Key Performance Data

Operating Mechanism

Threaded full brass safety valves operate based on the spring-loaded direct-acting principle. Under normal conditions, the spring force presses the valve disc against the valve seat to maintain a sealed state. When system pressure reaches the preset value, fluid pressure overcomes the spring force, lifting the disc and allowing excess pressure to be discharged. Once the pressure falls to the reseating level, the spring resets the disc and restores sealing.

Performance Verification

Relieving capacity tests conducted according to API 526 demonstrate discharge coefficients between 0.9 and 0.95, significantly higher than those of cast iron safety valves. For example, a DN20 valve operating with R404A refrigerant can achieve a relieving capacity of approximately 180 kg/h, sufficient for 5-ton commercial refrigeration systems.

Response time ranges from 0.1 to 0.3 seconds across operating temperatures from −40°C to 120°C. Durability testing shows sealing degradation below 3% after 10,000 cycles, with service life typically reaching 8–12 years under proper maintenance.

Applicable and Restricted Scenarios

Advantageous Applications

Threaded full brass safety valves are compatible with HFC refrigerants such as R134a, R404A, and R410A, as well as ammonia systems. Corrosion rates remain significantly lower than those observed in carbon steel valves. Threaded connections allow fast installation without welding, making them ideal for confined spaces.

At low temperatures, H62 brass retains high impact toughness, providing reliable operation in low-temperature refrigeration environments.

Restricted Applications

Brass safety valves are not suitable for chlorine-containing refrigerants such as R22 or R123 due to chemical reactions that may cause corrosion. In systems where MAWP exceeds 3.5 MPa, alloy steel safety valves should be selected instead.

Selection Guide: A Data-Driven Approach

Pressure Parameter Determination

Set pressure should be defined as 1.05–1.10 times MAWP while remaining below the valve’s rated pressure. Reseating pressure typically ranges from 90% to 95% of the set pressure, with higher values recommended for systems sensitive to pressure fluctuations.

Relieving Capacity and Size Selection

Relieving capacity must be calculated according to API 520 methodology, considering refrigerant properties and system cooling capacity. Nominal diameter selection should be based on calculated flow area rather than pipe size alone.

Environmental Adaptability

Thread type, corrosion protection, and low-temperature material selection must be verified. Nickel-plated valve bodies and SUS316L springs are recommended for corrosive or low-temperature environments.

Common Selection Mistakes and Avoidance Methods

Typical selection errors include choosing valves solely based on pipe diameter, setting pressure equal to MAWP, ignoring refrigerant compatibility, or using standard springs in low-temperature conditions. These issues can be avoided through proper calculation, material verification, and compliance with applicable standards.

Installation Precautions

Installation Position and Piping

Safety valves should be installed vertically at the highest pressure point of the refrigeration system. Inlet piping must not restrict flow, and discharge piping resistance must remain within allowable back pressure limits.

Commissioning and Maintenance

After installation, airtightness and set pressure calibration must be verified using inert gas testing. Regular inspection and recalibration every one to two years are essential to maintain long-term reliability.

Application Scenarios and Practical Examples

Industrial Ammonia Refrigeration Systems

In ammonia cold storage facilities, properly selected brass safety valves demonstrate stable operation and lower maintenance costs compared with cast iron alternatives.

Commercial Refrigeration Equipment

Supermarket refrigeration systems benefit from consistent sealing performance under frequent start–stop conditions, improving temperature stability and reducing operational complaints.

Household Refrigeration Units

Compact brass safety valves provide reliable pressure protection while meeting strict space and noise constraints in household refrigeration equipment.

Conclusion

Threaded full brass safety valves play a critical role in safeguarding refrigeration systems through reliable pressure relief, fast response, and excellent material compatibility. Proper selection and installation based on calculation and environmental conditions ensure long-term safety, reduced maintenance costs, and stable system performance.