An infusion system in which therapeutic substance from a reservoir is pumped by a bolus pump to an infusion port is disclosed. The therapeutic substance delivered by the bolus pump passes first through a passive check valve located downstream from the pump. The passive check valve opens in response to fluid pressure of the therapeutic substance. After passing through the passive check valve, the therapeutic substance passes through an active check valve located downstream from the passive check if the active check valve is actuated such that it is open. When not activated, the active check valve is closed and fluid flow through the active check valve in the downstream direction is prevented.