The significance of choosing the correct valve
In the fluid pipeline system, the valve is the control element, its main function is to isolate the equipment and the pipeline system, regulate the flow, prevent backflow, regulate and discharge the pressure. The correct selection of valves is essential to ensure the safe production of the device, increase the service life of the valve, and meet the long-term operation of the device. Because it is very important to choose the most suitable valve for the piping system, it is also important to understand the characteristics of the valve and the steps and basis for selecting the valve.
Principles for selecting valves
Valves for chemical production equipment should meet the following basic principles:
Chemical production requires continuous, stable and long-term operation. Therefore, the required valve should have high reliability and a large safety factor. It cannot cause major production safety and personal injury or death accidents due to valve failure; to meet the requirements of long-term operation of the device, long-term continuous production is the benefit.
2. Meet the requirements of process production
The valve should meet the needs of operating medium, pressure, temperature and application, which is also the most basic requirement for valve selection. For example, if the valve is required to protect against overpressure and discharge excess medium, safety valves and overflow valves should be used; if the medium needs to be prevented from flowing back during operation, check valves should be used
3. Convenient operation, installation and maintenance
After the valve is installed, it should enable the operator to correctly identify the valve direction, opening sign, indication signal, and facilitate the timely and decisive handling of various emergency faults. At the same time, the structure of the selected valve type should be as simple as possible and convenient for installation and maintenance.
Choose a valve with a reasonable price and a simple structure, and the general material can meet the requirements of use. There is no need to choose a higher grade material.
Valve selection steps
The following steps are generally adopted for valve selection:
1. Clarify the use of the valve in the device or process pipeline, and determine the working conditions of the valve, such as operating medium, operating pressure, and operating temperature.
2. Determine the type of valve according to the purpose of the valve: such as regulating valve, safety valve, open and closed circuit valve, etc.
3. Determine the form of the valve: According to the use and operating conditions, determine the valve type: globe valve, ball valve, butterfly valve, diaphragm valve, check valve, bottom valve, etc.
4. Determine the valve Determine the way to operate the valve: manual, electric, pneumatic or hydraulic, electric linkage or electro-hydraulic linkage, etc.
5. Determine the nominal parameters of the valve: the nominal pressure and nominal diameter of the valve should be matched with the installed process pipeline. In general, the standard system applied in the design of process piping is the basis for determining the application standards for other components of pressure piping. Valves are generally installed in process piping. Therefore, the operating conditions should be consistent with the design selection of the process pipeline. After the pressure level of the pipeline is determined, the nominal pressure, nominal diameter, and valve standard of the valve can be determined.
6. Determine the material of the valve: determine the material of the shell and internal parts of the selected valve according to the medium, working pressure and working temperature of the process pipeline.
7. Determine the connection method between the valve and the pipeline: determine the connection between the valve cross section and the pipeline by operating conditions and conditions such as flange connection, socket welding, glue welding, hot-melt butt welding, etc.
8. After the valve model is determined, the geometric parameters of the selected valve can be found: structural length, connection type and size, valve height when opening and closing, the size of the bolt hole connected, the overall size and weight of the valve, which lays down for on-site installation basis.
Basis for selecting valve
While understanding the steps to select a valve, you should further understand the basis for selecting a valve.
1. The purpose, operating conditions and operation control method of the selected valve.
2. The nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is a flammable or explosive medium, the viscosity of the medium, etc.
3. Requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing level, etc.
4. Installation size and external size requirements: nominal diameter, connection method and connection size with pipeline, external size or weight limitation, etc.
5. Additional requirements for the reliability, service life and explosion-proof performance of electric devices.