Reagent dosing system and pump

A reagent dosing system (10) for an internal combustion engine having an exhaust pipe (20) and a pump are disclosed. The reagent dosing system (10) comprises a first pump (26) having input means (30) for receiving reagent from a reagent supply (22) and output means (32) for delivering the reagent to a supply line (28), and a fluid dosing device (12) downstream of the first pump (26), comprising a nozzle (16) and a second pump (14) for receiving the reagent from the supply line (28) and for delivering the reagent to the nozzle (16), the second pump (14) being operable to increase the pressure of the reagent in the nozzle (16) to an injection pressure so as to cause delivery of the reagent through the nozzle (16). The first pump (26) is operable to increase the pressure of reagent in the supply line (28) to a pressure that is less than the injection pressure so as to guard against overheating of the reagent in the supply line (28). A pump (100) according to the invention is arranged such that, when the pump is not operating, an outlet valve means (135) of the pump is held in an open position so as to allow reagent to flow from the inlet means (102) to the outlet means (104) through the pumping arrangement (108, 154).