Abstract: This invention concerns a multi-liquid flow proportioning device comprising a vessel adapted to contain a first liquid, a container within said vessel adapted to hold a second liquid separate from said first liquid, separate inlet and outlet means respectively for the portion of said vessel adapted to contain said first liquid and for said container, said container including a wall portion adapted to move in use in resopnse to changes in pressure of its liquid contents, and means operable by the movement of said wall portion to control the liquid flow into the inlet of said container whereby tending to maintain the volumetric contents thereof generally constant. The invention has particular application to combining water and fire retardant.