 It had a larger grate, enabling grate sections to be compatible with those of the N class and permitting an increase in firebox volume sufficient to allow two arch tubes to be installed.Another innovation was the use of a regulator valve incorporating a centrifugal steam separator (to draw away any water and thus provide the driest steam), rather than the simpler (though extremely reliable) D regulator valve used in the K class.The J class also featured substantially redesigned cylinder porting to improve steam flow and efficiency.