A flow of a chemical is mixed with a flow of a primary fluid to form a combined fluid, and during mixing a velocity of the combined fluid is maintained at a threshold value so that a resulting mixture of the chemical and primary fluid has a designated homogeneity. The primary fluid is directed to an end of a passage with a venturi like contour that is inside of a mixer, and the chemical is directed to a side passage that extends laterally in the mixer that intersects the passage. A spring loaded valve in the passage maintains the combined flow velocity at the threshold value.