Abstract: In hydroprocessing unit, high pressure pump outlet is connected to high pressure recycle hydrogen system, so facilities must be installed to prevent back flow and pressure breakthrough in case of emergency shutdown, thus avoiding the over-pressure leakage of low-pressure system and the consequent fire and explosion accidents. This paper introduces three types of valves commonly used in China to prevent back flow and pressure breakthrough including check valve, control valve and emergency cut-off valve, analyzes the advantages and disadvantages of each design, and puts forward some suggestions for preventing back flow and pressure breakthrough at high pressure pump outlet. According to the actual operation experience, some optimal suggestions are given for the type selection of emergency cut-off valve and the interlocking transmission sequence in interlocking design.

Key words: hydroprocessing unit, high pressure pump, check valve, emergency cut-off valve