How to Quickly Identify Full Lift vs. Low Lift Safety Valves: 3 Proven Methods

Identification for Unmarked API 526 Safety Valves

For overseas engineers handling unmarked or mixed-standard valves, our lab at Shanghai Xiazhao Valve recommends three verification steps.

Method 1: Decoding the Model (GB/T 32808)

In the Chinese GB coding system, the structure digit is a definitive marker:

• Code 1: Indicates a Low Lift structure.
• Code 0, 2, or 4: Indicates a Full Lift structure (Code 0 for cooling fins, Code 4 for test wrenches).

Method 2: Brand & Series Screening (API Focus)

While API 526 doesn't have a unified code, major series are type-verified:

• Verified Full-Lift: Crosby JOS/JBS series, Shanghai Xiazhao High-Pressure series.
• Caution: Always cross-reference with the manufacturer's specific datasheet before installation.

Method 3: Lab Measurement (Data-Driven Verification)

We conducted a comparison test on DN50 valves with the same seat diameter:

• Full Lift Results: Measured lift = 8mm (1/4 of throat). Result: 1,280 kg/h steam flow.
• Low Lift Results: Measured lift = 1.2mm (1/27 of throat). Result: 162 kg/h steam flow.
• Conclusion: The 7.9x capacity gap proves why low-lift valves are dangerous for gas relief.

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