For the purpose of increasing yields ratio of diesel and gasoline，the most refinery and petrochemicals often take measures of decreasing ASTM D86 end point of gasoline product of main fractionators in RFCC unit in China

in which serious problems of poor stability and pressure drop rising were encountered in operation of main fractionators equipped with the jet tray. Based on the observations of operation phenomena and test on perform contact tray tested by FRI

a reliable analogy for that on jet trays in industrial tower was made. The results demonstrate that the serious inlet weeping and inlet jetting phenomena take place on the jet tray of main fractionators

showing the significant scale-up effect in largedistillation tower. The key to solve this problem is to control the distribution of liquid layer on the tray. In this paper

the program installing the inlet and outlet weirs on the tray was proposed to regulate the liquid layer and eliminate the scale-up effect

thus lowering the tray pressure drop and improving the operating effects. The results showed that under the conditions of processing capacity of 140 million tons per year

the tower pressure drop from original 28—34 kPa (design experiential values in China) reduced to a stable 16 kPa that is agree with design predicted value 18 kPa

reducing 50%; the total yield of gasoline and diesel increased from 68.13% to 68.48%

the yield of light oil increased 0.35%

the diesel-gasoline ratio increased from 0.82 to 0.88

the gasoline and diesel products from the overlaping 28℃ before the technological revamping reduce to overlaping 6℃

which demonstrated that the separation efficiency was improved. Under the condition of processing capacity of 160 million tons per year

the tower pressure drop rose only to 26 kPa

still lower than that before revamping

and achieved to the smooth operation and qualified product.