In the process control system, the control valve accepts the control signal of the control instrument, directly touches with the fluid, adjusts the flow of the fluid, and controls the flow, pressure, temperature, liquid level and other elements in the system, so it understands the fundamental structure and characteristics of the control valve, and selects it correctly according to the process conditions of the system.
There are three main parts of the control valve
1. Valve body assembly
The valve body assembly shall have the following elements: structural type, nominal diameter, nominal pressure, connection type with pipeline, applicable temperature scale, raw materials of valve body and internals, valve seat diameter or rated flow coefficient, flow characteristics, valve seat leakage level, etc.
2. Executive organization
The executive organization is generally divided into two types: pneumatic and electric (sometimes there are also hydraulic types). The pneumatic actuator is divided into two types: membrane tension spring type and cylinder piston type. The cylinder piston type is divided into two types: horizontal type and vertical type, and each type is divided into two types: tension spring type (single acting) and non-tension spring type (double acting) (in special cases, there are also membrane non-tension spring type and cylinder piston with tension spring type)
They need to have the following elements:
The number of a certain type of actuator recognized according to the thrust required to agree to the differential pressure, as well as the size of the tension spring, the supply pressure, the stroke, and the form of action recognized according to the position of the valve at the time of degassing.
3. Control valve accessories
The accessories of the control valve mainly include valve positioner, air filter pressure reducer, azimuth signal generator (valve position transmitter, travel switch), handwheel organization, electromagnetic reversing air valve, accelerator and air source protection device, etc., which are recognized according to the needs of the system.
About the acquisition of control valves:
New items: the selection parameter table provided by the design institute or specific parameters, such as flow rate, medium, inlet and outlet pressure, etc
Spare parts: provide a photo of the nameplate of the original valve, admit whether it is a complete set of valves or just the valve body, and whether there are other accessories
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