Selecting an appropriate breakaway valve is critical to ensuring the safety and efficiency of LNG dispenser operations, as it directly addresses emergency disconnection scenarios (e.g., accidental hose pulling by vehicles) and prevents LNG leakage. The selection process should focus on the following core criteria, aligned with the unique operating conditions of LNG dispensers (ultra-low temperature, frequent loading/unloading, and mobile vehicle interaction):
1. Match the Operating Pressure and Temperature Ratings
LNG dispensers typically operate at a specific pressure range (e.g., 1.6MPa–2.5MPa for on-road vehicle refueling) and an ultra-low temperature of -162°C (LNG’s boiling point at atmospheric pressure). When selecting a breakaway valve:
Ensure the valve’s maximum working pressure (MWP) is not lower than the dispenser’s system pressure, and its minimum design temperature is compatible with -162°C (or lower, to account for potential temperature fluctuations).
Avoid using valves rated for higher-than-necessary pressure/temperature (which increases costs) or lower ratings (which pose safety risks like valve body rupture or seal failure).
2. Confirm the Breaking Tension/Force Setting
The breakaway valve’s triggering threshold (breaking tension for hose-connected dispensers) must match the LNG dispenser’s hose specifications and on-site operation needs:
Not too low: Overly sensitive valves may trigger false disconnection during normal hose handling (e.g., slight tugging during refueling), disrupting operations.
Not too high: Excessively high breaking tension may fail to trigger when the hose is pulled by a moving vehicle, leading to hose tearing or dispenser damage.
Typically, select a valve with adjustable breaking tension (within a range like 1.5kN–5kN) or a fixed tension pre-calibrated to the dispenser’s standard hose (e.g., 2.5kN for 1-inch LNG refueling hoses).
3. Evaluate Sealing Performance and Material Compatibility
LNG’s volatility and ultra-low temperature demand strict sealing and material durability:
Sealing: Prioritize valves with multi-layer sealing structures (e.g., metal-to-metal primary seals + cryogenic-resistant polymer secondary seals, such as PTFE or perfluoroelastomers). Verify that the valve meets "zero leakage" standards (e.g., ISO 10497) for both normal operation and post-disconnection states.
Materials: The valve body and internal components (e.g., springs, check valves) must be made of cryogenic-resistant materials to avoid brittle fracture. Common options include:
Valve body: Austenitic stainless steel (e.g., 316L)
Seals: Perfluoroelastomers (FKM) or modified PTFE
Trigger components: High-strength alloy steel (to withstand tension without premature wear).
4. Consider Flow Rate Compatibility
The breakaway valve’s internal flow channel diameter and design must match the LNG dispenser’s rated flow rate (e.g., 50L/min–200L/min for heavy-duty vehicle refueling):
A valve with an undersized flow channel will cause excessive pressure drop, slowing down refueling efficiency.
An oversized channel may increase the risk of turbulent flow, which can damage internal seals over time.
Select a valve with a flow coefficient (Cv) corresponding to the dispenser’s flow requirements (e.g., Cv ≥ 5 for a 100L/min dispenser).
5. Verify Safety Certifications and Industry Standards
To ensure compliance with LNG industry safety norms, select valves that hold recognized certifications:
International standards: ISO 13628-6 (for LNG transfer systems), API 6A (for pressure equipment), or CE (for European markets).
Regional standards: For example, DOT (U.S. Department of Transportation) certification for North American applications, or GB standards (e.g., GB/T 37247) for China.
Avoid uncertified valves, as they may lack rigorous testing for cryogenic performance and emergency reliability.
6. Assess Installation and Maintenance Convenience
Practicality in on-site use is another key factor:
Installation: Choose valves with standardized connection interfaces (e.g., flange, thread, or quick-connect) that match the dispenser’s hose and pipeline specifications, reducing installation time and modification needs.
Maintenance: Prioritize valves with modular designs (e.g., replaceable seals, easy-to-access trigger components) to simplify routine inspection (e.g., tension calibration) and repair. Avoid valves requiring specialized tools or lengthy disassembly for maintenance.
In summary, the selection of an LNG dispenser breakaway valve is a balance of safety, performance, and practicality. It requires aligning the valve’s technical parameters with the dispenser’s system requirements, while ensuring compliance with industry standards—ultimately minimizing emergency risks and ensuring smooth refueling operations.