The efficiency of a valve is determined by the pressure losses and the leakage losses.
In most cases, the pressure losses Δp dr, which are comprised of form-related losses (form drag ratio) and throttle losses, are predominant for valves:

with p A = system pressure.
It is taken from the Δp -Q characteristic curve (pressure loss/flow rate characteristic curve) of the valve in question.

states the overall efficiency of the valve.
