Throttles as an independent element in the context of flow resistances are used to change a flow rate. A differentiation is made between constant throttles with the two forms of nozzle and orifice that each have a pre-defined bore.
There are also adjustable throttles with a changing cross-section that can have different forms and therefore different pressure flow characteristics. In addition, the throttle form affects the sensitivity to viscosity and the clogging behaviour.
The most common form of variable throttles are needle throttles, the longitudinal notch with orifice and with triangle, the peripheral notch and the slotted throttle.