Is a butterfly valve only considered a type of flow control valve if it is automated?
Every type of valve can be generally considered to be a flow control
device. Most types of valves, gate, globe, ball, B’fy can be manually
set anywhere from full open to fully closed and can be set to any
partially open position.
The term control valve generally refers to valves, including butterfly
types that are automatically regulated to modulate a rate of flow
according to a control signal to the valve actuating device. Sometimes
the signal is from a remote sensing element such as the temperature
sensor controlling a refrigeration expansion valve. Sometime the signal
is from within the actuating device itself as in a water pressure
regulator in your home city water supply.
The signal itself can be modulating , as above or it can be on/off such
as an emergency shutdown valve on a steam turbine or the on/off valve
on your washing machine.
No. Butterfly vlvs typically come equipped with a manual locking device and a graduated plate with scale showing the degree of closure. As process conditions require the valve can be manually operated to modulate the flow. The fact that it is not automatically actuated has no bearing on the functional nature of a flow control valve.
