Abstract: A fluid dosing cartridge (110) comprising a fluid reservoir (112), a delivery conduit (114) with an output nozzle (22), a nozzle socket (24), a pump chamber (42) and plunger (44), and a check valve assembly (118). The check valve assembly (118) comprises a valve housing (26), defining a valve chamber (32), and first (34), second (36) and third (38) valve ports, and first and second check valves (28, 30). Each check valve (28, 30) comprises a stainless steel ball (46) resiliently biased under the action of a spring (50) and a valve seat (48). The valve seat (48) comprises a body member (52) and a circular wall member (56) defining a valve aperture (54).