The best working position for a dual plate check valve is on horizontal pipeline, with the hinge pin installed vertically. The valve can be used on vertical flowlines as well, provided the flow direction is upward. For the vertical downward stream installation, please explicitly ask for a special spring to be installed while ordering, in order to compensate the gravity effect on the plates.
EACH ORION DUAL PLATE CHECK VALVE HAS A FLOW INDICATION ARROW EMBOSSED ON THE BODY. FOR THE CORRECT INSTALLATION OF THIS VALVE, MAKE SURE THAT IT IS MATCHING THE FLOW DIRECTION.