The frictional interaction between the glass stream and the channel surface results in a
reduction in glass level at the spout entrance called head loss. The degree of head loss
increases with tonnage but is also influenced by the temperature profile in the forehearth, the forehearth dimensions, the spout width and, to a lesser extent, the glass colour. Check that the tonnage required is within the design specified operational range. If the forehearth is not sloped consider introducing a slope of not more than 20mm.