Abstract: A system for controlling the stroke of an air-operated double diaphragm pump includes a first control valve and a second control valve disposed in parallel within a drive air outlet conduit. The first flow control valve has a first air flow capacity and the second flow control valve has a second air flow capacity which is less than about 50% of the first air flow capacity.

Abstract: A system is provided for dispensing liquid coloring agent to concrete delivery vehicles. The invention includes (a) a plurality of bulk tanks, (b) a weighing vessel connected in fluid tight communication with each bulk tank, and (c) a fill line connecting each weighing vessel to the loading zone. Preferably, the weighing vessel has a capacity between about 40 and about 80 gallons and comprises one or more load cells which communicate to a PLC.