Drag ball valve

An impedance assembly for retrofit attachment to a rotary closure element defining an axis of rotation and selectively movable between a fully open position and a fully closed position, the impedance assembly comprising:

• a plurality of impedance plate assemblies secured to each other in a stacked arrangement such that the impedance plate assemblies collectively define an inflow end and an outflow end of the impedance assembly;
• each of the impedance plate assemblies including a plurality of openings formed therein which collectively define a plurality of tortuous passageways extending from the inflow end to the outflow end when the impedance plate assemblies are stacked upon each other.

A method of retrofitting a rotary valve including a rotary closure element which defines an outer surface, a bore and an axis of rotation, and is selectively movable between a fully open position and a fully closed position with an impedance assembly, the method comprising the steps of:

• (a) securing a plurality of impedance plate assemblies to each other in a stacked arrangement along a plate assembly axis to form the impedance assembly, each of the impedance plate assemblies including a plurality of openings formed therein which collectively define a plurality of tortuous passageways extending from an inflow end to an outflow end of the impedance assembly when the impedance plate assemblies are stacked upon each other;
• and
• (b) mounting the impedance assembly within the bore of the closure element.