A printhead cartridge for releasable mounting in a printer. The printhead cartridge includes a pagewidth printhead and an ink manifold defining multiple fluid flow paths in fluid communication with respective ink channels in the printhead. The ink manifold includes a plurality of openings for detachable connection with conduits in an interface of the printer; a plurality of shut off valves at each of the openings respectively, each shut off valve having a biasing member configured for biasing each shut off valve into an open position; an actuator biased towards a closed position by a resilient element such that the actuator holds all the shut off valves closed when in the closed position. The actuator is configured for engagement with the interface such that movement of the openings into connection with the interface simultaneously moves the actuator to an open position wherein the shut off valves are held open.