ماشین حساب ضریب جریان شیر

Kv is the volumetric flow of water at 15°C in m³/h that passes through a valve with a pressure drop of 1 bar. It is a measure of the valve's flow capacity — higher Kv means the valve can pass more flow for the same pressure drop.

Example: A valve with Kv = 10 passes 10 m³/h of water at 1 bar ΔP.

Kv — European/ISO standard. Flow in m³/h of water at ΔP = 1 bar.

Cv — US standard. Flow in US GPM of water at ΔP = 1 psi at 60°F.

Conversion: Cv = 1.156 × Kv (or Kv = 0.865 × Cv).

Steps for valve sizing:

• Calculate required Kv for your worst-case operating conditions
• Select a valve with Kv ≥ 1.3× calculated Kv (safety margin)
• Ensure the valve operates between 20–80% open at normal flow
• Check cavitation: ΔP should not exceed the valve's FL² × (P1 – Pv)
• Verify noise level is acceptable

No. Gas flow is compressible, so the liquid formula underestimates the required Kv. Use the gas-specific formula that includes upstream and downstream absolute pressures, temperature, and compressibility factor Z.

For critical flow (P2 < 0.53 × P1), the flow becomes choked and the formula changes further.

Cavitation occurs when the local pressure drops below the liquid's vapor pressure, forming bubbles that collapse violently — causing noise, vibration, and valve damage.

Flashing occurs when downstream pressure stays below vapor pressure — the liquid partially vaporizes permanently.

Check the valve's FL factor (pressure recovery factor). The allowable ΔP for no cavitation is: ΔP_max = FL² × (P1 – Pv), where Pv is vapor pressure.