Method of introduction of liquid additives utilizing an improved dosing assembly

This invention relates to an improved dosing assembly (valve/feed line/liquid collecting vessel) which permits nearly immediate response time to an actuator signal. Such an assembly is used for the controlled introduction of any liquid through a valve into a collecting vessel. In particular, the inventive assembly exhibits substantially no leakage from the feed line into the liquid collecting vessel when the valve is closed and an instantaneous introduction of the feed line liquid into the liquid collecting vessel upon opening of the valve, both when a liquid possessing a surface tension of about 50 dynes/cm 2 is used as the measurement standard. This assembly is particularly and preferably suited for injecting colorants into reactants for the production of polyurethane slabstock foam and permits a substantial reduction in foam waste due to low colorations during an on/off cycle. Preferably, this inventive assembly comprises a ball valve, a manifold, and a connector pipe which may contain at most 30 mL of liquid at any single moment and which is measured in diameter of at most 0.42 inches (about 1.07 cm). Such a connecting pipe permits substantially instantaneous shut-off and -on without appreciable leakage or pressure drop and without the need to utilize a high throughput flow rate. Also, such a specific connecting pipe is wide enough to permit high through-put rates should the need arise. The valve/pipe/manifold configuration is contemplated within this invention.