A delivery apparatus for pressurized medical liquids has a primary reservoir that pressurizes a medical liquid therein to a driving pressure, a second reservoir having an inlet connected to receive pressurized liquid from the primary reservoir via a controllable intermediate valve, and an outlet for discharge of the received medical liquid via a controllable dosing valve. A pressure measuring unit measures the pressure in the secondary reservoir and a control unit controls the intermediate valve and the dosing valve by monitoring the operation of the intermediate valve and the dosing valve dependent on the measured pressure value from the pressure measuring unit. The control unit generates a status signal dependent on predetermined rules for measured pressure changes compared with calculated pressure changes.