Cv is the flow coefficient of a control valve, a standard number that shows how much fluid a valve can pass through under given conditions.

  Simply defined,Cv is the number of US gallons of water per minute that a fully open valve can flow with a pressure drop of 1 psi at 60°F.

  Structurally, it describes the valve’s effective flow‑passing capacity. It depends on the valve size, internal design, opening percentage, and fluid properties.When fully open: The Cv reaches its maximum value, representing the largest possible flow rate the valve can handle.When partially open: The Cv decreases, limiting flow to achieve regulation.

  Because different fluids (oil, gas, steam) have different viscosity and density, their actual flow needs correction from the basic water‑based Cv value, but Cv remains the core reference for selecting and sizing control valves in petroleum and industrial systems.