The invention relates to a dosing pump assembly which is used to mix a liquid reducing agent to an exhaust gas flow, which comprises a dosing pump (2) which is used to transport the reducing agent anda pre-mixing device (39) wherein the reducing agent transported by the dosing pump (2) is mixed with the compressed gas in a mixing area (18). The dosing pump assembly comprises a pumping head provided with a central plate (40), wherein at least the dosing pump (2) and the pre-mixing device (39) are arranged.