A replenishment carrier injection system is provided for adding carrier particles to a developer housing in a two-component developer toner imaging machine. The replenishment system includes (i) a carrier-only hopper for receiving and containing a first quantity of carrier particles; (ii) metering valves connected to a discharge end of the carrier-only hopper; (iii) a pneumatic plenum connected to the metering valves; (v) an air pump connected to the carrier-only hopper and to the pneumatic plenum for pressurizing the carrier-only hopper and for pneumatically conveying a metered quantity of carrier particles in an air stream from the pneumatic plenum; and (vi) carrier injection assemblies each being connected to the pneumatic plenum and including a conduit for carrier flow, a direct injector elbow connecting the conduit to a developer housing for directly injecting fresh carrier from the pneumatic plenum into the developer housing; and a fresh carrier current collector for detecting any fault in fresh carrier flow through said direct injector elbow the system into the developer housing.