Restrictor
Flow restrictor is a key component frequently found in air, gas and fluid flow control applications. At its simplest, it is a precision hole drilled through an otherwise solid surface that would block a flow stream. Here are some generalized uses for orifices:
Reduce flow
Increase air or fluid velocity
Precisely meter flow
Flow restrictors are found in critical applications, including fluid metering, controlling the speed of actuators, or snubbing pressure pulses.