Fail-close hydraulically actuated control choke

Abstract

A fail-close hydraulically actuated control choke includes a choke with inlet and outlet flow passages intersecting in a cylindrical flow chamber. A reverse acting trim configuration which utilizes downstream pressure to assist in closing includes a flow cage with a wear sleeve of tungsten carbide shrink fitted therein is reciprocable within the flow chamber to control flow between the inlet and outlet flow passages. The flow cage is closed at one end with a stem extending therefrom which is reciprocated by a fail-close hydraulic actuator. The hydraulic actuator includes a pressure responsive piston in combination with a torque operated driving mechanism. The driving mechanism is positioned within the piston and includes a traveling nut assembly to allow manual positioning of the stem and flow cage independently of the position of the piston. The pressure responsive piston is double acting with a boost pressure supplied to the closing side of the piston and a signal pressure supplied to the opening side of the piston. A loss of signal pressure causes the boost pressure to shift the piston, stem and cage to a closed position. Restoration of the signal pressure moves the cage to its original flow controlling position without requiring a resetting of the flow cage position. Additionally, should the hydraulic circuits or pressure responsive piston become inoperable, the torque operated driving mechanism can still reposition the cage as needed.