The surface wetting behaviour of spray ball jets was investigated by considering the simple case of a single horizontal, coherent jet of liquid impinging normally on a vertical surface. The liquid flows radially outwards from the point of impingement until a feature resembling a hydraulic jump is formed. The liquid subsequently drains downwards to give a uniform falling film, here labelled gravity flow, or a thin strand labelled rivulet flow. A simple model of the radial flow region based on momentum balances gave excellent agreement with measurements of flow region radius and falling film width data reported previously by Morison and Thorpe (2002) for various aqueous solutions and surfaces under typical industrial flow rates. The model also gave good predictions of flow region dimensions in new, unreported bench scale tests performed with water on glass and Perspex at lower flow rates. The latter studies involved wetting rates lower than the stability criterion reported by Hartley and Murgatroyd (1964). A transition between gravity and rivulet flow was observed with water on glass between 40 degrees C and 60 degrees C: only rivulet flow was observed with water on Perspex, indicating the importance of contact angle in this region. The model is reported in dimensionless form, which allows the wetted width to be predicted directly from the mass flow rate. (C) 2011 Elsevier Ltd. All rights reserved.