1, pressure
Generally, we only consider the pressure difference between inlet and outlet, but it is very important to know the inlet pressure and outlet pressure separately in order to choose correctly. Because sometimes the inlet of the pump may be negative pressure and sometimes it may be positive pressure. If it is negative pressure, we need to know the specific negative pressure value. When the inlet pressure of the pump is less than atmospheric pressure, the flow rate of the gear pump will be lower than the normal value in the performance curve at the same speed and pressure difference. When the inlet vacuum reaches the limit value, the gear pump will not work normally. In addition, each gear pump has a maximum allowable working pressure, that is, the maximum bearing capacity of the gear pump. When the inlet pressure of gear pump is greater than atmospheric pressure, the outlet pressure
Step 2 be sticky
The viscosity of liquid affects the performance and power of the pump, and the viscosity is also affected by temperature and even shear force. Because of the internal leakage of gear pump, when the pump transports liquid with high viscosity, the internal leakage is small and the actual output flow will be large. Therefore, compared with water with low viscosity, when conveying high viscosity liquid, the actual output flow of the same type of gear pump will be greater at the same speed and pressure difference. However, with the increase of liquid viscosity, the fluidity of liquid itself decreases, and the power consumed by gear rotation in high viscosity liquid will also increase sharply. Therefore, with the increase of liquid viscosity, the working speed of the pump should be reduced appropriately, which can not only reduce unnecessary energy consumption, but also prevent cavitation.
3. Corrosiveness of liquid
The corrosion of liquid will seriously affect the service life of gear pump, so we must ensure that all parts in contact with liquid in gear pump can withstand the corrosion of conveying liquid.
4, particle situation
Due to the tiny clearance inside the micro gear pump, any particles close to the clearance range may block the pump, and even very tiny hard particles may permanently damage the gear or bearing when the gear runs at high speed. Some particles exist in the liquid. In many cases, the liquid may be clean, but there may be particles in system pipes and containers, joints and solder joints, especially in newly installed or modified systems. Therefore, users are advised to install a 300-400 mm mesh filter at the inlet of the pump to protect the safety of the pump.
5. Temperature
When it comes to temperature, we need to consider the temperature of the liquid and the ambient temperature when the pump works:
(1) liquid temperature
The parts of gear pump should be able to work stably in the liquid temperature range for a long time, including the materials of pump body, bearing, gear, shaft, magnetic drive and sealing ring. At the same time, the change of maximum allowable working pressure of gear pump under extreme temperature should also be considered. Especially the bearing capacity of the thinnest magnetic shielding part of the pump body.
(2) Ambient temperature
Ambient temperature has a great influence on the selection of motor. Low or high temperature motors may be required. If a brushless DC motor is configured, the ambient temperature has a considerable influence on the performance of the driver. In addition, some liquids will solidify at normal temperature or low temperature in winter. At this time, it is necessary to consider the way of adding heat pump head to ensure the normal start of the pump. The more common method is to wrap the heat tracing tape around the pump head.
6. Sensitivity of liquid to shear force
When the gear pump works, the meshing between the driving wheel and the driven wheel will produce shear force. Some liquids are very sensitive to shear force, and the properties of liquids will change under high shear force until they cannot be used. For these liquids, it is necessary to reduce the shear force as much as possible by reducing the working speed of the pump and increasing the internal clearance of the pump.
7. Inlet and outlet pipes
Generally speaking, the diameter of the inlet and outlet should not be less than the interface diameter of the pump body. In order to ensure the normal suction of the pump, the inlet pipe diameter should be as short as possible and the elbows should be reduced.
8, the type of motor and power selection
Generally speaking, motors can be divided into AC motors (ordinary AC motors, variable frequency motors, explosion-proof motors, variable frequency explosion-proof motors, single-phase motors, etc.). ), DC brush motor, DC brushless motor (BLDC), stepping motor and servo motor. In the industrial field, various AC motors are widely used. First, whether it is 1x220V or 3X220V or 3X380V, the voltage determines whether it is explosion-proof (explosion-proof grade) or frequency conversion.
9, flow and pressure control mode
The flow control of gear pump is generally realized by controlling the speed of pump. It is a good way to adjust the flow by controlling the speed of gear pump with AC variable frequency motor or DC brushless motor. Servo motors are recommended for occasions with high precision requirements.
Expand small knowledge
Knowledge point 1. What kinds of hydraulic gear pumps are there?
1, external gear pump
External gear pump consists of shell, driving gear, driven gear and end cover. In the process of driving the driven gear to rotate together, in the suction area, the gear teeth are separated from each other, the volume between the gear teeth increases, the pressure decreases, and hydraulic oil can enter. After rotation, the hydraulic oil is transported to the discharge area, where the gear teeth are embedded with each other, forcing the hydraulic oil to flow out.
2. Internal gear pump
The internal gear pump is also composed of two gears, only one internal gear and one external gear, and the rotating shaft is offset. The driving gear is an external gear with smaller diameter, which drives the external and internal gear rings to rotate in the same direction. In the oil absorption area, the space between teeth becomes larger and hydraulic oil can enter. Turning to the oil discharge area, the space between teeth is reduced and the oil is squeezed out.
3. Spiral gear pump
The shell, the driving screw and the driven screw form a sealed cavity. With the rotation, the sealing cavity moves from one end to the other, so that the hydraulic oil flows in the axial direction. The discharged hydraulic oil flow rate is fixed, regardless of the screw position, without drastic pressure change and low noise.
Knowledge point 2. Where is the screw pump mainly used?
1, Screw pump is widely used for conveying water, wet sludge and flocculant liquid medicine in sewage treatment plants because of its large conveying variable, strong self-priming ability, reversibility and the ability to convey liquid containing solid particles.
2. Because of its structure and working characteristics, the screw pump can transport medium with high solid content, with uniform flow and stable pressure, especially at low speed. Because of its good variable adjustability, it can be used for many purposes and conveying media with different viscosities.
3. The installation position of the screw pump can be tilted at will, which is suitable for conveying sensitive items and items easily damaged by centrifugal force.
Knowledge point three. Working characteristics of screw pump
Screw pump mainly has the following characteristics: simple structure, safe and reliable use, convenient use and maintenance, continuous and uniform liquid discharge, stable pressure, low noise and vibration, and self-priming ability, but screw processing is more troublesome.
Knowledge point 4. What is three screw pump?
Screw pump is a rotary positive displacement pump, which can be divided into single screw, twin screw, triple screw and multi-screw pump according to the number of screws. Three screw pump is a screw pump with three screws, which includes a driving screw inserted in the pump barrel, two driven screws engaged with it and three mutually engaged screws. They form a sealed cavity in the pump barrel according to their respective leads, resulting in the seal between the suction port and the discharge port.
Knowledge point 5. What are the uses of peristaltic pump?
Any use scenario of peristaltic pump is to treat fluid (any liquid or solid-liquid mixture with fluidity), and the main function of peristaltic pump is to transport. The conveying accuracy of peristaltic pump can reach up to 0.5%, which can meet the needs of quantitative conveying and quantitative distribution.
From the product function, the main uses of peristaltic pump are: quantitative or metered transportation, quantitative or metered distribution. Therefore, peristaltic pump can be used to meet the application requirements in all application scenarios with quantitative transportation and distribution requirements.
Peristaltic pump has excellent performance and reliability, so it is widely used to meet the application requirements of various processes, including experimental research, analytical instruments and industrial production. Therefore, peristaltic pumps have many uses and uses, mainly in the following fields:
1. Analytical instruments: chromatograph, atomic fluorescence photometer.
2. Medical industry: medical equipment and diagnostic reagents.
3. biopharmaceuticals: coating machine, granulator, fermentor, used for purification, fluid transportation, distribution and filling, and high-precision liquid preparation.
4. Laboratory and research equipment.
5. Food and beverage: beverage machine, yogurt machine, vending machine, intelligent milk tea machine, condiment distribution and addition, beer industry.
6. Environmental industry: water quality analysis instruments, quality control instruments, water quality sampling instruments and flue gas analyzers.
7. Printing and packaging: transport ink and coating solvents, coatings and adhesives.
8. Inkjet ink: Inkjet printers and printers.
9, washing and cleaning: washing machines, dishwashers.
10, ceramic industry: eliminating pores, quantitatively adding defoamer and ceramic slurry.
1 1. Mining: conveying abrasive ore and tailings slurry, supplying liquid by filter, metering and chemometering flocculant, sampling ore and pumping thickener underflow.
12, industrial application: measurement of sand-based colloid, measurement of grinding coating solution, measurement of high viscosity resin, chemical recovery, coatings and paints.
13. Pulp and paper industry: filler, technology in pulp pretreatment, ideal pump for pulp coating, water and sewage treatment in pulp and paper industry, accurate and quantitative transportation of chemicals and additives, and transportation of dyeing additives.
14, household appliances: intelligent toilet, soap dispenser, sterilizer, sweeper, mopping machine.
15, industrial machinery: grinder, glass fiber spinning machine, photovoltaic production.