Abstract: Disclosed is a manifold control system 80 for a completion tree 10 comprising a manifold plate 92 having a plurality of single port or multi-port two position spring biased piston type valve cartridges 82 mounted thereon, which individually route hydraulic control signals to the various valve and connector operators 14,18 and 30. The two position spring biased piston type valve cartridge thus performs the function of a tree cap and eliminating the need for the latter, and thus eliminating running/retrieval operations required for tree closure and control hook up during installation workover and retrieval. These valve cartridges are detachably connected to the plate and may be replaced, whole or in part, subsea; their number and type selectable according to the needs of the tree; in a workover mode cooperate with a running tool and in a production mode automatically close the cartridges and control lines to seawater, debris and the like.