Equipment: Dry-Mix Gun, Hose, Nozzle, and Air/Water Controls
A dry-mix system includes the gun (rotor or pressure vessel), delivery hose, nozzle assembly, and air and water controls. The gun meters dry material into the air stream; the hose conveys it; the nozzle introduces water through a water ring and mixes it before exit. Understand each component's function and failure modes.
Air pressure and volume must be sufficient to keep material moving and to mix water thoroughly. Too little air causes slugs, surging, and poor mixing; too much increases rebound and wear. Water pressure at the nozzle should generally exceed air pressure so water injects into the stream rather than being blown back; a common rule is water pressure at least about 15-25 psi above air pressure at the nozzle. Water rings with multiple small holes produce finer, more uniform mixing than a single large port. Hose diameter, length, and bends affect pressure drop and slugging; long runs and sharp bends require attention. Nozzle size and tip wear change spray pattern and output.
Traps: assuming higher air always improves placement; ignoring water-to-air pressure relationship; neglecting hose inspection for wear, kinks, and moisture; forgetting that worn water rings or nozzle tips degrade mixing.
Worked example / rule of thumb: if nozzle air pressure reads 100 psi, set water pressure at the nozzle to roughly 115-125 psi so water penetrates the stream. Inspect hoses and water rings routinely; replace worn components before they cause dry pockets or uneven wetting.