Abstract: A pump comprises a housing (141) having a cavity (142) with an inlet valve (143), an apparatus (144) for raising fluid pressure in the cavity (142) and a discharge valve (145), the discharge valve (145) comprises a valve head (160) movable between an open and closed position and a valve seat (167), wherein the pump further comprises a booster piston (182) arranged in a booster cylinder (183), the booster piston (182) has a first face (191) exposed to a low pressure zone (189) and a second face (194) exposed to fluid pressure in the cavity (142), and at least one of the booster piston (182) and the booster cylinder (183) is movable relative to the other to add an opening force to the discharge valve. The pump is preferably a mud pump for circulating drilling mud through a drill string in a wellbore or a cement pump which may be of the type for pumping cement into a wellbore.

Abstract: A pump comprises a housing (141) having a cavity (142) with an inlet valve (143), an apparatus (144) for raising fluid pressure in the cavity (142) and a discharge valve (145), the discharge valve (145) comprises a valve head (160) movable between an open and closed position and a valve seat (167), wherein the pump further comprises a booster piston (182) arranged in a booster cylinder (183), the booster piston (182) has a first face (191) exposed to a low pressure zone (189) and a second face (194) exposed to fluid pressure in the cavity (142), and at least one of the booster piston (182) and the booster cylinder (183) is movable relative to the other to add an opening force to the discharge valve. The pump is preferably a mud pump for circulating drilling mud through a drill string in a wellbore or a cement pump which may be of the type for pumping cement into a wellbore.

Abstract: A variable throttle device comprises at least two fixed throttle orifices and one switch device. The at least two fixed throttle orifices are connected in series; and the switch device is connected in parallel with at least one of the at least two fixed throttle orifices. In another implementation, a variable throttle device comprises at least two throttle passages and one switch device, each of the at least two throttle passages has at least one fixed throttle orifice or a plurality of fixed throttle orifices connected in series, the at least two throttle passages are connected in parallel, and the switch device is connected in series with at least one of the at least two throttle passages to selectively open or close the at least one throttle passage. The variable throttle device can increase or decrease the throttling resistance to meet the requirements of the valve seating velocity under different operating conditions.