In harsh working conditions in fields such as chemical engineering, mining, and water treatment, media often have corrosiveness, high viscosity, contain solid particles, or require aseptic properties. Ordinary valves are difficult to handle, and pneumatic diaphragm proportional valves, with their unique isolation structure, have become the ideal choice to solve these problems. Proper selection is the key to ensuring long-term stability and precise control of the system.
1. Clarify traffic characteristics: lay the foundation for control
The flow characteristics determine the relationship between valve opening and flow rate, directly affecting the stability and accuracy of the control system.
Equal percentage characteristic: recommended for most harsh working conditions. It has a gentle flow rate change when the opening is small, providing fine control to prevent overshoot; When the opening is large, the flow rate changes dramatically to ensure the passing capacity. It is very suitable for situations where the system pressure fluctuates greatly or requires wide range adjustment (such as pH precise dosing).
Linear characteristics: When the pressure drop of the valve is relatively stable and the opening is required to have a linear relationship with the flow rate. More suitable for quantitative load distribution or traffic matching.
2. Core consideration: Selection of membrane material
The diaphragm is a key component that isolates the process medium from the actuator, and its material directly determines the lifespan and applicability of the valve.
PTFE (polytetrafluoroethylene): It can be called the "king of corrosion resistance" and can withstand almost all strong acids, alkalis, and organic solvents. At the same time, the surface is smooth and non adhesive, making it a high-purity or highly corrosive medium.
EPDM (Ethylene Propylene Diene Monomer Rubber): It has good resistance to weak acids, alkalis, and high temperature water vapor, good elasticity, and low cost. Commonly used in water treatment, hot water, and certain chemical solutions.
FKM (Fluororubber): Excellent in high temperature and oil resistance, able to withstand most mineral acids, hydrocarbons, and fuels. It is an ideal choice for oil or high-temperature media.
Food grade film (such as white EPDM or PTFE): meets hygiene standards such as FDA and is designed specifically for the food, pharmaceutical, and biotechnology industries.
Selection Summary
To select a pneumatic diaphragm proportional valve for harsh operating conditions, the following steps should be followed:
Firstly, analyze the characteristics of the medium: clarify the corrosiveness, temperature, concentration, solid particle content, and hardness of the medium.
Secondly, determine the control objective: whether fine tuning or wide range adjustment is needed, in order to choose between equal percentage or linear flow characteristics.
Finally, match the membrane material: Based on the analysis of the medium, select the membrane that is most resistant to chemical corrosion and meets the temperature and pressure requirements.
Through these three steps, you can select the "capable workers" who are suitable for your demanding working conditions, achieving both precise and reliable process control.