Abstract: The process and apparatus for effecting savings of compressed injection gs such as oxygen or nitrogen when injecting solids such as burnt lime pneumatically into a receiving vessel, such as the blow-line to steel melt has a solids conveying system, a compressed gas supply source and a conduit and valve system functioning in a sequence, by which the compressed gas upon termination of the procedure is collected and thereupon is recycled. The system is equipped with at least one pressure-reservoir to collect the compressed gas from the previous procedure for recycling it.The pressure reservoir is subdivided by a reciprocating divider such as a membrane or a reciprocating piston to subdivide it into two parts of variable volumes, the divider is pushed by the returning compressed saved gas from one wall of the reservoir to the other. Highly compressed gas is blown into the empty part of the reservoir to increase the pressure upon the returned gas.