Many users focus on set pressure and connection size but ignore the orifice area – the actual flow path when the safety valve opens. Undersize it, and the valve cannot relieve enough; oversize it, and the valve chatters.The main safety valve product names of China Safety Valve Network include:Gas Specific Fall Lift Safety Valve,GA49H-DN20 Pulse Safety Valve,High Temperature and Pressure Fall Lift Safety Valve,Hydraulic Safety Valve,Impulse Safety Valve,Impulse Spring Safety Valve,JIS Safety Valve,Main Safety Valve,Overflow ValveOil Refining Specific Safety Valve,Pulse Safety Valve

Orifice area is not the connection size

The effective discharge area depends on lift and nozzle throat diameter. A conventional‑lift valve has area ≈ seat bore × lift; a full‑lift valve gives full throat area. The same DN50 connection may have very different orifice areas.

Why calculations go wrong

API 520 or GB/T 12241 require three key inputs: required relief load, set pressure, and discharge coefficient. The most common mistake is using normal flow instead of maximum credible relief load – forgetting fire case vaporisation or control valve failure.

Discharge coefficient is not fixed

Catalog coefficients are measured with clean air at full lift. For steam, liquids, or two‑phase flow, derate the coefficient. Polymerising or fouling services may need a coefficient only 60% of the lab value. Always add 20–30% margin.

Two‑phase flow is tricky

Boiling liquids or flashing mixtures need special handling. Using gas‑area undersizes the valve; using liquid‑area grossly oversizes it. Follow ISO 4126‑10 or select a pilot‑operated valve certified for two‑phase service.

Quick check

Calculate required area = mass flow ÷ (discharge coefficient × fluid factor). Compare with the valve’s actual effective area. If actual is less than 90% of required, go to a larger throat size.

Bottom line: Orifice area determines relief capacity. Ignore connection size – calculate throat area, account for fluid phase, and add margin. Correct area means the valve will open, relieve, and close when needed.

Do you still need to know or purchase the following safety valve products:

• Safety Check Valve
• Static Weight Type Safety Valve
• Safety Decompression Valve
• sanitary Safety Valve
• SFV Danfoss Refrigeration Safety Valve