When selecting a valve, factors such as nominal diameter, nominal pressure, applicable fluid temperature, leakage standard, flow characteristics, allowable differential pressure, and medium characteristics should be considered. The nominal diameter range is usually DN20~200mm, and the nominal pressure ratings are PN10, PN16, PN40, PN64, etc. The applicable fluid temperature range is wide, from -200℃ to +560℃. The leakage standard is Class IV or Class VI, and the flow characteristics are linear or equal percentage. The allowable differential pressure needs to be determined according to the specific working conditions [7]. For special media such as strong corrosion and easy crystallization, the appropriate valve body material and sealing structure should be selected. Before installation, check whether the whole machine parts are missing or loose.
The valve must be tested for strength, sealing, leakage, and accuracy. The pipeline should be cleaned, and there should be a sufficient straight pipe section at the valve inlet, and a filter should be provided. The flange connection between the valve body and the pipeline should be kept coaxial. The valve should be installed upright. If it is unavoidable, it can be installed at an angle. Horizontal installation should be avoided as much as possible. In cases where the valve has a large self-weight or is subject to vibration, a support frame should be used. The direction of medium flow should be consistent with the arrow on the valve body, and the air source should be dry and oil-free. To ensure continuous production in case of automatic control system failure or valve maintenance, a bypass valve should be installed. The flow characteristics and stroke of the bypass valve must be consistent with the original valve.
The packing seal of a bellows control valve is the first protective seal. Once the bellows is damaged, it must never be used as a packing-sealed valve. The bellows should be repaired or replaced immediately, and a strict airtightness leak test must be performed after replacement. During maintenance, the appropriate cleaning method should be selected according to the properties of the medium. When disassembling the valve, the machined surfaces of precision parts such as the valve seat, valve core, valve stem, and push rod must be protected. Minor wear on the valve core and valve seat sealing surfaces can be repaired by machining; severe damage requires replacement with new parts. Damaged valve stem surfaces also require replacement.