The choice of valve body is the most important part of diaphragm pump selection. There are many types of diaphragm pump valve bodies, commonly used are straight-through single-seat, straight-through double-seat, angle, diaphragm, small flow, tee, eccentric rotation, butterfly, sleeve, spherical, etc. 10 kinds.
Before selecting a valve, it is necessary to carefully analyze the medium, process conditions and parameters of the control process, collect sufficient data, understand the requirements of the system for the diaphragm pump, and determine the type of valve to be used according to the collected data.
In the specific selection, the following aspects can be considered:
1. The shape and structure of the valve core are mainly considered according to the selected flow characteristics and unbalanced force.
2. Wear resistance When the fluid medium is a suspension containing high concentration of abrasive particles, the valve core and valve seat joint surface will be severely rubbed every time they are closed. Therefore, the flow path of the diaphragm pump valve should be smooth, and the internal material of the valve should be hard.
3. Corrosion resistance Because the medium is corrosive, in the case of satisfying the adjustment function, try to choose a valve with a simple structure.
4. The temperature and pressure of the medium When the temperature and pressure of the medium are high and the change is large, the valve core and valve seat material should be selected with small changes in temperature and pressure.
5. Prevent flash evaporation and cavitation Flash evaporation and cavitation only occur in liquid media. In the actual production process, flash evaporation and cavitation not only affect the calculation of the flow coefficient, but also form vibration and noise, which shortens the service life of the diaphragm pump valve. Therefore, the valve should be prevented from flashing and cavitation when selecting the valve. .
1. Consideration of the output force of the diaphragm pump
Regardless of the type of the actuator, its output force is the effective force used to overcome the load (mainly refers to the unbalanced force and unbalanced moment plus friction, sealing force, gravity and other related forces).
Therefore, in order to make the diaphragm pump work normally, the matching actuator must be able to generate enough output force to overcome various resistances, ensure a high degree of sealing and the opening of the valve. For double-acting pneumatic, hydraulic and electric actuators, there is generally no return spring.
The magnitude of the force has nothing to do with its running direction. Therefore, the key to choosing an actuator is to find out the maximum output force and the torque of the motor.
For single-acting pneumatic actuators, the output force is related to the opening of the valve, and the force on the diaphragm pump will also affect the motion characteristics, so it is required to establish a force balance over the entire opening range of the diaphragm pump.
2. Determination of the type of implementing agency
After determining the output force of the actuator, select the corresponding actuator according to the requirements of the process use environment.
For explosion-proof requirements on site, pneumatic actuators should be selected, and the junction box is explosion-proof, and electric actuators cannot be selected. If there is no explosion-proof requirement, both pneumatic and electric actuators can be used, but from the perspective of energy saving, electric actuators should be selected as far as possible.
Hydraulic actuators are not as widely used as pneumatic and electric actuators, but have the characteristics of high adjustment accuracy, fast and stable action. Therefore, in some cases, in order to achieve better adjustment effects, hydraulic actuators must be selected. Mechanisms, such as speed regulation of transparent machines in power plants, temperature regulation and control of catalytic reactors in oil refineries, etc.