Variable resistance type throttling trim

Claim 1

A variable resistance type valve throttling element comprising: a. a seatring having a cylindrical bore of constant diameter throughtout its entire length, therein providing inner wall surfaces, and having an upper and a lower terminating portion; the upper terminating portion of said seatring providing sealing means; b. a cylindrical valve plug slidingly engaged within the cylindrical bore of said seatring and having an upper terminating portion, the upper terminating portion of the cylindrical plug having a slightly enlarged rim portion to provide sealing means able to cooperatively engage with the sealing means of said seatring and to provide at that point a stop shoulder to limit the depth of engagement of the plug within the seatring bore; said plug further having a lower generally plane terminating surface; c. a number of throttling flow channels penetrating radially inward from the outer cylindrical surface towards the central, longitudinal axis of said plug, commencing the penetration of at least one channel slightly below said rim portion and terminating all channels within the lower terminating surface of said plug thereby providing a number of openings within said lower terminating surface of said plug disposed to provide access for fluid in a direction along the longitudinal plug axis, and wherein the major portion of the length of one or more of said flow channels are covered by the confining inner wall surface of said cylindrical seatring bore while the plug is fully engaged within said seatring bore, and wherein said channels are comprised of one or more penetrating grooves extending circularly at least partway around the interface between the reciprocating plug and said cylindrical seatring bore; each groove provided with one or more communicating vertical passage ways to the next groove.