A control valve (10, 60, 70) for regulating flow of fluids comprising: (a) a body having an inlet, an outlet and a passageway through which the fluid passes from said inlet to said outlet, said passageway passing through an opening, (b) an actuator located in a control chamber connected to said body and configured to move along an axis through a range of motion from a retracted position to an extended position; (c) a plug associated with said actuator such that movement of said actuator from said retracted position towards said extended position displaces said plug towards said opening; and (d) a guide-and-seat insert including: (i) a valve seat configured to seal against said opening and to provide a closure surface against which said plug closes, (ii) a plurality of plug guides integrally formed with said valve seat and extending from said valve seat towards said control chamber, and (iii) a collar attached to or integrally formed with said plurality of plug guides and configured for clamping against an internal surface of said control valve (10, 60, 70) so as to clamp said valve seat against said opening, such that, when said plug is displaced by said actuator, said plug moves in sliding engagement with at least two of said plug guides, and such that, when said actuator moves to said extended position, said plug closes against said closure surface of said valve seat so as to block the passage of fluid from said inlet to said outlet, characterised in that said body and said control chamber intersect at a neck portion featuring a circumferential groove, and in that said collar is provided with a circumferential locking element circumscribing a majority of said collar and a tightening arrangement, said tightening arrangement being configured for displacing said circumferential locking element outwards into said groove so as to clamp said collar against said internal surface of said neck portion. (a) a body having an inlet, an outlet and a passageway through which the fluid passes from said inlet to said outlet, said passageway passing through an opening, (b) an actuator located in a control chamber connected to said body and configured to move along an axis through a range of motion from a retracted position to an extended position; (c) a plug associated with said actuator such that movement of said actuator from said retracted position towards said extended position displaces said plug towards said opening; and (d) a guide-and-seat insert including: (i) a valve seat configured to seal against said opening and to provide a closure surface against which said plug closes, (ii) a plurality of plug guides integrally formed with said valve seat and extending from said valve seat towards said control chamber, and (iii) a collar attached to or integrally formed with said plurality of plug guides and configured for clamping against an internal surface of said control valve (10, 60, 70) so as to clamp said valve seat against said opening, (i) a valve seat configured to seal against said opening and to provide a closure surface against which said plug closes, (ii) a plurality of plug guides integrally formed with said valve seat and extending from said valve seat towards said control chamber, and (iii) a collar attached to or integrally formed with said plurality of plug guides and configured for clamping against an internal surface of said control valve (10, 60, 70) so as to clamp said valve seat against said opening,