An improved arrangement for removably coupling a replaceable cartridge (13) to a housing of a dispenser (10) with the cartridge carrying a piston pump with a movable piston element (57) to be coupled on insertion with an actuator plate(32) of the housing. A ramp mechanism is provided on the actuator plate to engage the piston element and during insertion of the cartridge into the housing move the piston element to a position relative the actuator plate which facilitates proper coupling including a resilient member (67) which prevents radial movement relative a catch member (100) of the housing from a coupled orientation unless the resilient member is deflected from an unbiased inherent configuration.