Diaphragm pump classification and selection:

Diaphragm pumps are volumetric pumps. Diaphragm pumps can be divided into pneumatic, electric, and hydraulic three types according to the power used by their actuators. That is, pneumatic diaphragm pumps with compressed air as the power source, electric diaphragm pumps with electric power as the source, and liquid media ( Such as oil, etc.) pressure-driven electro-hydraulic diaphragm pumps, in addition, according to their functions and characteristics, as well as solenoid valves, electronic, intelligent, fieldbus diaphragm pumps. Diaphragm pumps have many types of products and a variety of structures, and they are constantly updated and changed. In general, valves are universal and can be matched with pneumatic actuators or electric actuators or other actuators.

Diaphragm pumps generally come in four materials: plastic, aluminum alloy, cast iron, and stainless steel. Diaphragm pump according to different liquid media using nitrile rubber, chloroprene rubber, fluorine rubber, polyvinylidene fluoride, polytetraethylene to meet the needs. Placed in a variety of special occasions, for pumping media <br> <br> diaphragm type of conventional pump can not select the kind of aspiration:

1. Diaphragm pump body type selection The choice of the body is the most important part of the diaphragm pump selection. Diaphragm pump body type is many, commonly used straight through single seat, straight through two seats, angle, diaphragm, small flow, three links, eccentric rotation, butterfly, sleeve, spherical and other 10 kinds. Before choosing the valve, carefully analyze the media, process conditions and parameters of the control process, collect enough data to understand the requirements of the system on the diaphragm pump, and determine the type of valve to be used based on the collected data. When choosing specific options, consider the following aspects:

(1) Spool shape structure. Mainly based on selected flow characteristics and unbalanced forces and other factors.

(2) Wear resistance. When the fluid medium is a suspension containing a high concentration of abrasive particles, the valve plug and the valve seat interface are severely rubbed each time they close. Therefore, the flow path of the valve should be smooth, and the internal material of the valve should be hard.

(3) corrosion resistance. Due to the corrosive nature of the medium, a valve with a simple structure can be selected as far as possible in the case where the adjustment function can be satisfied.

(4) Temperature and pressure of the medium When the temperature and pressure of the medium are high and the change is large, the valve whose valve core and valve seat materials are affected by the temperature and pressure change should be selected.

(5) Prevent flash evaporation and cavitation. Flashing and cavitation are only produced in liquid media. In the actual production process, flashing and cavitation not only affect the calculation of the flow coefficient, but also create vibration and noise, so that the service life of the valve is shortened. Therefore, the valve should be prevented from flashing and cavitation when selecting the valve.

2. Selection of diaphragm pump actuators (1) Output force considerations Regardless of the type of actuator, its output force is used to overcome the effective load (mainly refers to imbalance force and unbalanced moment plus friction force. , sealing force, gravity and other related forces.) Therefore, in order for the diaphragm pump to work properly, the actuator must be equipped to generate sufficient output force to overcome various resistances and ensure high sealing and valve opening.

For double-acting pneumatic, hydraulic, and electric actuators, there is generally no return spring. The size of the force is independent of its direction of operation. Therefore, the key to selecting the actuator is to find out the maximum output force and the rotational torque of the motor. For a single-acting pneumatic actuator, the output force is related to the opening of the valve, and the occurring force on the diaphragm pump will also affect the motion characteristics. Therefore, it is required to establish the force balance in the opening range of the entire diaphragm pump.

(2) Determination of the type of actuator After determining the output power of the actuator, select the appropriate actuator according to the environmental requirements for the use of the process. For explosion-proof requirements at the site, pneumatic actuators should be used. The junction box is explosion-proof and electric actuators cannot be selected. If there is no explosion-proof requirement, pneumatic and electric actuators can all be used, but in terms of energy conservation, electric actuators should be used as far as possible. For the hydraulic actuator, its use is not as wide as the pneumatic and electric actuators, but it has the characteristics of high adjustment accuracy, fast operation speed and smoothness. Therefore, in some cases, in order to achieve a better regulation effect, the hydraulic actuator must be used. Institutions, such as the speed regulation of power plant transparent machines, temperature regulation control of refinery catalytic device reactors, etc.

Diaphragm pump action mode selection

Diaphragm pump action only when the choice of pneumatic actuators, its mode of action through the implementation of positive and negative action of the valve and the combination of the valve formed. There are four types of combination: positive (air-closed), forward-reverse (air-opened), positively-inverted (air-opened), and reverse-reacted (air-closed). The diaphragm pumps formed by these four types of combinations are gas-free. Open and air off two. For the choice of the diaphragm pump mode of action, it is mainly considered from three aspects: a) process production safety; b) the characteristics of the medium; c) ensure product quality, and minimize economic losses.

Selection of diaphragm pump flow characteristics

The flow characteristics of a diaphragm pump refer to the relationship between the relative flow rate of the medium flowing through the valve and the displacement (the relative opening degree of the valve). The ideal flow characteristics mainly include four types: straight line, equal percentage (logarithm), parabola, and quick opening. The commonly used ideal flow characteristics are only linear, equal percentage (logarithmic), and quick opening. The parabola flow characteristics are between linear and equal percentages and can generally be replaced by equal percentage characteristics. The quick opening characteristics are mainly used for two-position adjustment and program control. Therefore, the diaphragm pump characteristics are actually selected as linear and equal percentage flow characteristics. s Choice.

The choice of diaphragm pump flow characteristics can be calculated theoretically, but the methods and equations used are complex. At present, more experience criteria are used, specifically considering the following aspects: (1) Analysis and selection from the regulation quality of the regulation system; (2) Considerations from the process piping; (3) Analysis from the load change situation.

Selecting the flow characteristics of the diaphragm pump can determine the shape and structure of the valve plug according to its flow characteristics, but for diaphragm valves, butterfly valves, etc., due to their structural characteristics, it is impossible to change the shape of the valve core to achieve The required flow characteristics, in this case, can be achieved by changing the shape of the feedback cam of the assigned valve positioner.

Diaphragm pump diameter selection

Diaphragm pump diameter selection and determination is mainly based on the valve's flow capacity, Cv. In the design and selection of instruments for various projects, Cv calculations must be performed on diaphragm pumps and diaphragm pump design specifications must be provided. From the Cv calculation of the diaphragm pump to the determination of the bore diameter of the valve, the following steps are generally required:

1, determine the calculation of traffic. The current production capacity, equipment load, and media status determine the Qmax and Qmin of the calculated flow.

2, the pressure difference before and after the valve is determined. Select S (resistance coefficient) according to the selected valve flow characteristics and system characteristics, and then determine the pressure difference.

3. Calculate Cv. Select the appropriate calculation formulas and charts based on the adjusted media to obtain Cmax and Cmin.

4, choose Cv. Based on Cmax, select Cmax that is closest to the first C in the selected product standard series.

5. Check the opening of the diaphragm pump. It is generally required that the opening when the maximum calculation flow is ≯ 90%, and the opening when the minimum calculation flow is ≮ 10%.

6. Checking the actual adjustable ratio of the diaphragm pump. General requirements are actually adjustable ratio ≮10.

7. Determination of seat diameter and nominal diameter. After verification is appropriate, it is determined according to C.