Selection principle and classification function of

2022-08-02
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Selection principle and classification function of diaphragm pump

the function of diaphragm pump in process control is to receive the control signal of regulator or computer, change the flow of regulated medium, and maintain the regulated parameters within the required range, so as to achieve the automation of production process. If the automatic adjustment system is compared with the manual adjustment process, the detection unit is the human eye, and the adjustment control unit is the human brain, then the execution unit diaphragm pump is the human hand and foot. In order to realize the adjustment and control of a certain parameter in the process, such as temperature, pressure, flow, liquid level, etc., the diaphragm pump is indispensable. Therefore, the correct selection of diaphragm pump is of great significance in process automation

1. Composition and classification of diaphragm pump

diaphragm pump, also known as control pump, is the main type of actuator. It changes the fluid flow by receiving the control signal output from the control unit and by means of power operation. Diaphragm pump is generally composed of actuator and valve. According to the power used by the actuator, the diaphragm pump can be divided into pneumatic, electric and hydraulic, that is, the pneumatic diaphragm pump with compressed air as the power source, the electric diaphragm pump with electricity as the power source, and the electro-hydraulic diaphragm pump with the pressure of liquid medium (such as oil) as the power. In addition, according to its functions and characteristics, there are solenoid valves, electronic, intelligent and Fieldbus diaphragm pumps. Diaphragm pumps have many types of products and structures, which are constantly updated and changed. Generally speaking, the valve is universal, which can be matched with pneumatic actuator, electric actuator or other actuators

2. Selection of diaphragm pump type

2.1 selection of valve body type for diaphragm pump 14 Main motor source: ~ 380V ± 10% 50Hz reliable grounding measures must be taken, which is the most important link in the selection of diaphragm pump. There are many types of diaphragm pump valve bodies, including 10 commonly used types, such as straight through single seat, straight through double seat, angle, diaphragm, small flow, tee, eccentric rotation, butterfly, sleeve and spherical. Before selecting the valve, 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 is mainly considered according to the selected flow characteristics, unbalanced force and other factors

(2) wear resistance when the fluid medium is a suspension containing high concentration of abrasive particles, the valve core and valve seat interface will be seriously rubbed every time they are closed. Therefore, the flow path of the valve shall be smooth and the internal material of the valve shall be hard

(3) corrosion resistance as the medium is corrosive, the valve with simple structure shall be selected as far as possible under the condition that the regulating function can be met

(4) temperature and pressure of the medium when the temperature and pressure of the medium are high and change greatly, the valve whose material of the valve core and valve seat is less affected by the change of temperature and pressure shall be selected

(5) prevent flash and cavitation flash and cavitation are only produced in liquid medium. In the actual production process, flash and cavitation not only affect the calculation of flow coefficient, but also form vibration and noise, which shortens the service life of the valve. Therefore, when selecting the valve, the valve should be prevented from flash and cavitation

2.2 selection of diaphragm pump actuator

2.2.1 consideration of output force

regardless of the type of actuator, its output force is used to overcome the effective load (mainly refers to the effect of unbalanced force and unbalanced torque plus friction, sealing force, gravity and other related forces). Therefore, in order to make the diaphragm pump work normally, the matched actuator should be able to generate enough output force to overcome various resistances and ensure high sealing and valve opening

generally, there is no return spring for double acting pneumatic, hydraulic and electric actuators

the magnitude of the force is independent of its running direction. Therefore, the key to selecting the actuator is to find out the maximum output force and the rotating torque of the motor. For the single acting pneumatic actuator, the output force is related to the opening of the two types of valves, and the force on the diaphragm pump will also affect the motion characteristics. Therefore, it is required to establish a force balance in the entire opening range of the diaphragm pump

2.2.2 determination of actuator type

after determining the output force of the actuator, select the corresponding actuator according to the requirements of the process use environment. When there are explosion-proof requirements on site, pneumatic actuator shall be selected, and hr15n junction box is explosion-proof, so electric actuator cannot be selected. If there is no explosion-proof requirement, pneumatic and electric actuators can be selected. However, in terms of energy saving, electric actuators should be selected as far as possible. As for the hydraulic actuator, it is not as widely used as the pneumatic and electric actuator, but it has the characteristics of high adjustment accuracy, fast action speed and stability. Therefore, in some cases, in order to achieve better adjustment effect, the hydraulic actuator must be selected, such as the speed adjustment of the transparent machine in the power plant and the temperature adjustment control of the catalytic device reactor in the refinery

3. Selection of action mode of diaphragm pump

the action mode of diaphragm pump is only available when pneumatic actuator is selected, and its action mode is formed through the combination of positive and negative action of actuator and positive and negative action of valve. There are four types of combinations, namely positive (air off type), positive and negative (air on type), negative (air on type) and negative (air off type). The diaphragm pump formed by these four combinations has two types of action modes: air on and air off. For the selection of diaphragm pump action mode, three aspects are mainly considered: a) process production safety; b) Characteristics of media; c) Ensure product quality and minimize economic losses

4. Selection of flow characteristics of diaphragm pump

the flow characteristics of diaphragm pump refer to the relationship between the relative flow of medium through the valve and the displacement (relative opening of the valve). The ideal flow characteristics mainly include straight line, equal percentage (logarithm), parabola and. The characteristic curve and valve core shape are shown in Figure 1 and Figure 2. There are only three commonly used ideal flow characteristics: straight line, equal percentage (logarithm) and. The parabolic flow characteristic is between the straight line and the equal percentage, which can generally be replaced by the equal percentage characteristic, and the characteristic is mainly used in two-position regulation and program control. Therefore, the selection of diaphragm pump characteristics is actually the selection of straight line and equal percentage flow characteristics

the flow characteristics of diaphragm pump can be selected by theoretical calculation, but the methods and equations used are very complex. At present, empirical criteria are mostly adopted, specifically considering the following aspects: ① analyzing and selecting the regulation quality of the regulation system; ② Considering the process piping; ③ Analyze from the load change

after selecting the flow characteristics of the diaphragm pump, the shape and structure of the valve core can be determined according to its flow characteristics. However, for diaphragm valves, butterfly valves, etc., due to their structural characteristics, it is impossible to change the surface shape of the valve core to achieve the required flow characteristics. At this time, it can be achieved by changing the shape of the feedback cam of the valve

5. Selection of diaphragm pump caliber

the selection and determination of diaphragm pump caliber is mainly based on the flow capacity of the valve, namely cv. During instrument design and model selection of various projects, CV calculation shall be carried out for the diaphragm pump, and the design specification of the diaphragm pump shall be provided. From the accurate CV calculation of the pressure control of the diaphragm pump to the determination of the valve diameter, the following steps are generally required:

1) determination of the calculated flow. The existing production capacity, equipment load and medium conditions determine the Qmax and qmin of the calculated flow

2) determination of pressure difference before and after valve. Select s (resistance coefficient) according to the selected valve flow characteristics and system characteristics, and then determine the calculated differential pressure

3) calculate cv

select the appropriate calculation formula and chart according to the adjusted medium to obtain Cmax and cmin

4) select cv. According to Cmax, select the first level c.

5) diaphragm pump opening that is>cmax and closest to Cmax in the selected product standard series. Generally, it is required that the opening at the maximum calculated flow shall be ≯ 90%, and that at the minimum calculated flow shall be ≮ 10%

6) checking calculation of actual adjustable ratio of diaphragm pump. Generally, the actual adjustable ratio is ≮ 10

7) determination of valve seat diameter and nominal diameter. After verification, determine according to C

6. Conclusion

the selection of diaphragm pump is a very meticulous work, which requires not only solid professional theoretical knowledge, but also rich practical experience. A good selection is not only conducive to the adjustment of PID parameters of the control loop, so that the adjusted parameters have a better control effect, but also greatly increase the service life of the diaphragm pump. The selection of diaphragm pump should be based on local conditions, not unchanging. It should be summarized and innovated in the process of practice. Especially with the application of electromechanical integration technology, computer and digital information technology, the structure and function of diaphragm pump become better and more comprehensive, which provides great convenience for the selection of diaphragm pump

QBY pneumatic diaphragm pump and DBY electric diaphragm pump

Product Overview:

qby series pneumatic diaphragm pumps use compressed air, steam and industrial waste gas as power sources. They can pump and absorb all kinds of corrosive liquids, liquids with particles, high viscosity, volatile, flammable and highly toxic liquids. They have many advantages of self-priming pumps, submersible pumps, canned pumps, mud pumps and impurity pumps, It is widely used in petroleum, chemical, electronic, ceramic, textile and other industries

this series of pumps are installed in various special occasions to pump various media that cannot be pumped by conventional pumps, and satisfactory results have been achieved

suction medium range:

- diaphragm pump peanut butter, pickles, mashed potatoes, small red sausage, jam apple juice, chocolate, etc

- diaphragm pump paint, gum and pigment

- all kinds of adhesives and glues can be taken by diaphragm pump

- all kinds of tile, porcelain, brick and pottery glaze

- after the well is drilled, use diaphragm pump to deposit and grout

- various emulsifiers and fillers for diaphragm pumps

- various sewage of diaphragm pump

- the oil tanker is pumped, and the barge is used to clear the warehouse to absorb the sewage in the warehouse

- hops and fermented powder slurry, syrup and molasses

- accumulated water in mines, tunnels, mineral processing and slag of diaphragm pump

- diaphragm pump cement grouting and mortar, various rubber grout

- all kinds of abrasives, corrosive agents, oil and mud, cleaning oil dirt and general containers

- various highly toxic, flammable and volatile liquids

- various strong acid, alkali and corrosive liquids

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