Near the seat a given stroke change adds little flow, and near full open the same change adds a lot, giving an exponential curve. Because pressure drop across a control valve usually falls as flow rises, this shape tends to straighten out into a near-linear installed curve. It is the default for most pressure and temperature control valves, where the valve takes a small share of total system drop.
Spec it equal percentage, the valve's only taking about a quarter of the system drop at design flow.
Also heard as
- equal %
- =%
Related terms
Flow characteristic
The relationship between how far a valve is open and how much flow it passes.
Cv
Flow coefficient: US gallons per minute of 60 degree F water a valve passes with a 1 psi pressure drop.
Control valve
A power-operated valve that modulates flow on a controller signal to hold pressure, level, flow or temperature at setpoint.