Diaphragm pump selection and classification

	Product introduction :
	QBY series pneumatic diaphragm pump is a new type of conveying machine, which is the most novel type of pump in China. Compressed air is used as the power source. For various corrosive liquids, liquids with particles, high viscosity, volatile, flammable and highly toxic liquids can be exhausted. [details...]

Abstract: The composition and classification of the diaphragm pump, as well as the selection principle and method of the type, actuator, mode of action and flow characteristics of the diaphragm are mainly described. The methods and principles for the selection of the diaphragm are analyzed.

The role of the diaphragm pump in process control is to accept the control signal of the regulator or computer, change the flow of the medium to be adjusted, and maintain the adjusted parameters within the required range to achieve automation of the 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. To achieve the control of certain parameters of the process such as temperature, pressure, flow, liquid level, etc., the diaphragm pump is inseparable. Therefore, the correct choice of diaphragm pump is of great significance in process automation.

1 Composition and classification of diaphragm pumps

Diaphragm pumps, also known as control pumps, are the main type of actuators that change the flow of fluids by means of power control by accepting control signals from the output of the control unit. Diaphragm pumps typically consist of actuators and valves. If the power is used according to the actuators it is equipped with, the diaphragm pump can be divided into three types: pneumatic, electric and hydraulic. It is a pneumatic diaphragm pump with compressed air as the power source and an electric diaphragm pump with electric power as the liquid medium. (such as oil) pressure-powered electro-hydraulic diaphragm pump, in addition to its function and characteristics, there are solenoid valves, electronic, intelligent, fieldbus diaphragm pumps. Diaphragm pumps come in many different types and structures, and are constantly being updated and changed. Valves are generally versatile and can be matched to pneumatic actuators or to electric actuators or other actuators.

2 Diaphragm pump type selection

2.1 Valve body type selection The choice of valve body is the most important part of diaphragm pump selection. There are many types of diaphragm pump bodies, such as straight-through single-seat, straight-through two-seat, angular, diaphragm, small flow, three-way, eccentric rotation, butterfly, sleeve, and spherical. Before selecting the valve, carefully analyze the media, process conditions and parameters of the control process, collect sufficient data, understand the system requirements for the diaphragm pump, and determine the type of valve to be used based on the collected data. In the specific choice, you can consider the following aspects:
(1) The shape of the spool is mainly based on factors such as the selected flow characteristics and unbalance forces.
(2) Abrasion resistance When the fluid medium is a suspension containing a high concentration of abrasive particles, the valve core and the valve seat joint face are severely rubbed each time they are closed. Therefore, the flow path of the 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 meeting the adjustment function, try to choose a simple valve.
(4) Temperature and pressure of the medium When the temperature and pressure of the medium are high and the change is large, the valve and the material of the valve seat should be selected to be small in temperature and pressure.
(5) Prevent flash and cavitation flashing and cavitation only 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, so the valve should be prevented from flashing and cavitation when selecting the valve.

2.2 Selection of diaphragm pump actuator 2.2.1 Output force considerations Regardless of the type of actuator, the output force is the effective force for overcoming the load (mainly unbalanced force and unbalanced torque plus friction, Sealing force, gravity and other related forces). Therefore, in order for the diaphragm pump to work properly, the actuator used should generate sufficient output force to overcome various resistances and ensure high sealing and opening of the valve.
For double-acting pneumatic, hydraulic, and electric actuators, there is generally no return spring. The magnitude of the force is independent of its direction of travel. Therefore, the key to selecting an actuator is to clarify the maximum output force and the rotational torque of the motor. For single-acting pneumatic actuators, the output force is related to the opening of the valve, and the forces appearing on the diaphragm pump will also affect the motion characteristics, thus requiring a force balance across the diaphragm pump's opening range.
2.2.2 Determination of the type of actuator After determining the output force of the actuator, select the appropriate actuator according to the requirements of the process environment. For explosion-proof requirements on site, pneumatic actuators should be used, and the junction box is explosion-proof, and electric actuators cannot be selected. If there is no explosion-proof requirement, pneumatic and electric actuators can be used, but in terms of energy saving, electric actuators should be selected as much as possible. For hydraulic actuators, the use is not as extensive as pneumatic and electric actuators, but it has the characteristics of high adjustment precision, fast and stable movement. Therefore, in some cases, in order to achieve better adjustment effect, hydraulic actuation must be selected. Institutions, such as speed regulation of power plant transparent machines, temperature regulation control of catalytic plants in refineries, etc.

3 Mode of operation of the diaphragm pump The mode of action of the diaphragm pump is only available when the pneumatic actuator is selected. The mode of action is formed by the combination of the positive and negative action of the actuator and the positive and negative action of the valve. There are 4 kinds of combinations, namely, positive (gas-closed), positive and negative (air-open), anyway (air-open), and reverse (air-closed). The diaphragm pump formed by these four combinations has a gas function. Open and gas two. The choice of diaphragm pump mode of action is mainly considered from three aspects: a) process production safety; b) medium characteristics; c) product quality and economic loss.

4 diaphragm pump flow, selection of characteristics

The flow characteristic of the diaphragm pump refers to the relationship between the relative flow rate of the medium flowing through the valve and the displacement (relative opening of the valve). The ideal flow characteristics mainly include four types: straight line, equal percentage (logarithm), parabola and quick opening. The curve and spool shape are shown in Figures 1 and 2. The commonly used ideal flow characteristics are only straight lines, equal percentages (logarithmic), and quick opening. The parabolic flow characteristics are between straight and equal percentages. They can generally be replaced by equal percentage characteristics. The fast opening characteristics are mainly used in two-position adjustment and program control. Therefore, the choice of diaphragm pump characteristics is actually 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, the experience criteria are often used, and the following aspects are considered: 1 from the adjustment quality of the adjustment system and selected; 2 from the process piping; 3 from the load change analysis.
By selecting the flow characteristics of the diaphragm pump, the shape and structure of the valve spool 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 shape of the valve core to achieve The required flow characteristics can be achieved by changing the shape of the feedback cam of the valve positioner.

5 Diaphragm pump diameter selection

The choice and determination of the diaphragm pump diameter is mainly based on the valve's flow capacity, Cv. In the design and selection of instruments for various projects, the diaphragm pump must be Cv calculated and the diaphragm pump design specification provided. From the calculation of the Cv of the diaphragm pump to the determination of the diameter of the valve, the following steps are generally required:
1) Calculate the determination of the flow. The existing production capacity, equipment load and the condition of the medium determine the Qmax and Qmin of the calculated flow.
2) Determination of the differential pressure before and after the valve. S (resistance coefficient) is selected according to the selected valve flow characteristics and system characteristics, and then the calculated differential pressure is determined.
3) Calculate Cv. Select the appropriate calculation formula and graph according to the adjusted medium to find Cmax and Cmin.
4) Select Cv. According to Cmax, select >Cmax and the closest level C in the selected product standard series.
5) Diaphragm pump opening degree check. Generally, the opening degree of the maximum calculation flow rate is ≯90%, and the opening degree at the minimum calculation flow rate is ≮10%.
6) Check the actual adjustable ratio of the diaphragm pump. Generally, the actual adjustable ratio ≮10 is required.
7) Determination of seat diameter and nominal diameter. After verification is appropriate, determine according to C.

6 Conclusion

The choice of diaphragm pump is very meticulous work, not only has a solid professional theoretical knowledge, but also has a wealth of practical experience. Choosing well not only helps to adjust the tuning of the PID parameters of the control loop, so that the adjusted parameters get better control effect, and the service life of the diaphragm pump is greatly increased. The choice of diaphragm pump should be adapted to local conditions, not constant, and should be summarized and innovated in the process of practice. Especially with the application of mechatronics technology, computer and digital information technology, the structural function of diaphragm pump becomes better and more comprehensive. Great convenience for choosing a diaphragm pump.
QBY pneumatic diaphragm pump, DBY electric diaphragm pump

QBY series pneumatic diaphragm pump uses compressed air, steam and industrial waste gas as the power source. It can exhaust all kinds of corrosive liquids, liquid with particles, high viscosity, volatile, flammable and highly toxic liquid. With many advantages of self-priming pumps, submersible pumps, shielded pumps, mud pumps and impurity pumps, it is widely used in petroleum, chemical, electronics, ceramics, textile and other industries.
The pumps are placed in a variety of special occasions to pump a variety of media that can not be pumped by conventional pumps, and have achieved satisfactory results.

Suction medium range:
- Diaphragm pump peanut butter, kimchi, mashed potatoes, small red sausage, jam apple pulp, chocolate, etc.
- Diaphragm pump paint, gum, pigment.
- Adhesives and glues, all types can be pumped with a diaphragm.
- Various tiles, porcelain, bricks and pottery glaze.
- After the oil well is drilled, use the diaphragm pump to deposit and grout.
- Diaphragm pumps for various emulsifiers and fillers.
- Diaphragm pumps for all types of sewage.
- Use the pump as the tanker, and the barge clears the tank to absorb the sewage.
- Hops and baking powder slurry, syrup, molasses.
- Separated water from diaphragm pumps in mines, tunnels, tunnels, beneficiation, and slag.
- Diaphragm pump cement grouting and mortar, various rubber slurries.
- Various abrasives, corrosives, oil and mud, cleaning grease and general containers.
- A variety of highly toxic, flammable, volatile liquids.
- A variety of strong acids, strong bases, strong corrosive liquids.