I would like to ask again about the three-valve assembly at the inlet and outlet of the hydrogen compressor.
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Dear teachers: According to Article 12.3 of the \"Code for Design of Process Piping in Refining Units\" (SH∕T 3122-2013), double isolation valves should be installed on the inlet and outlet pipes of hydrogen compressors. An exhaust pipeline equipped with a three-valve assembly is to be installed between these two valves. Is the three-valve assembly composed of three valves connected in series? Is it a shut-off valve or a one-way valve? If the two cut-off valves are very close to each other, is it still necessary to install a three-valve assembly?
A three-valve assembly usually refers to a combination of two stop valves and one bypass valve. This design is intended to allow the two main valves to be closed during maintenance, and then the medium in the pipeline can be discharged through bypass valves to ensure safety. The valves in a three-valve assembly are usually globe valves. If the distance between the two isolation valves is short, a three-valve assembly is still required to meet the requirements for safe discharge. .
In this configuration, two stop valves are connected in series, with a tee placed in between as a bypass, and an exhaust valve is also included. The principle behind its operation is that when the equipment stops running, it is necessary to close two shut-off valves. To prevent leakage from these valves, after closing them, the bypass valve is opened fully to discharge the load and remains in this open state, thereby preventing leakage from the shut-off valves into the equipment. Typically, the diameter of the tee bypass valve is very small, and a globe valve is suitable for use as well. For reference.