Flow separation and cavitation effects in a simple homogenizing valve have been studied visually and recorded photographically. The degree of separation depended upon the profile of the seating inlet boundary, the pressure loading and several other interdependent factors. Cavitation did not occur independently of separation; conditions would be suitable for microscale cavitation to occur within the separated flow itself, but this was not discerned with certainty. The suppression of separation and any cavitation, assessed visually, did not influence the homogenizing characteristics of the valve. It was concluded that hydrodynamic forces of cavitation are not responsible for fat globule disintegration in drop-and-lift or poppet types of high-pressure homogenizing valve.