The pressure at the top of the Coke Drums affects the type of coke produced and the yield distribution of the gas oil and lighter products. Increasing the drum pressure increases coke yield and gives a better coke product, in terms of pore structure, density and VCM content, while decreasing the end point of heavy gas oil product and increasing the amount of C4 and lighter vapors produced. Pentane and heavier liquid product yields are decreased at higher pressure. Since coke is only by-product of the process, the Coke Drum pressure should be operated at the lowest pressure possible within equipment limitations in order to maximize the overall yield of liquid products from the coker. if you decrease the pressure is the opposite to the explained