Micro gear pump usually refers to the small size, low flow pump products. According to different technical principles can be divided into micro centrifugal pump, micro gear pump, micro diaphragm pump, micro piston pump, micro peristaltic pump, micro rotary vane pump, vortex pump, etc., according to the drive mode can be divided into direct connection, magnetic drive type, according to the movement mode can be divided into reciprocating and rotary, according to the material can be divided into metal pump, plastic pump, composite pump, etc., according to the temperature of the transported liquid can be divided into Low temperature pumps, high temperature pumps and room temperature pumps, according to different power sources can be divided into pneumatic pumps, DC pumps (12V, 24v, 48v, etc.), servo pumps, AC pumps, inverter pumps, etc.. Users are often accustomed to use their actual needs to name the pump, such as circulation pump, pressurization pump, sampling pump, cooling pump, urea pump, chromatography pump, flushing pump, atomization pump, etc..

No matter what type of pump, everything changes, their role is to make the liquid to be transported by doing work, so that the liquid to be transported to produce the required flow. Here comes the most basic parameters of pump selection: flow rate and pressure. Generally speaking, it is difficult for centrifugal pumps to achieve high head (high pressure) at low flow rates, so volumetric pumps appear very frequently in situations where small flow rates and high pressures are required. One of them is micro gear pump.

The characteristics of micro (magnetic) gear pump are

1. the active and driven wheels need to mesh with each other during operation

2. small clearance inside the pump, the clearance between the gear and pump body, shaft and bearing are in the range of several tens of microns

3. the bearings and gears are generally made of polymer materials, and the torque of the motor is transmitted to the shaft through a magnetic coupling.

So when choosing this type of pump, you need to consider the flow rate of the liquid, inlet and outlet pressure, viscosity, corrosiveness of the liquid, particle condition, temperature, sensitivity of the liquid to shear, inlet and outlet piping, type of motor, flow and pressure control methods (precision, batch, backstop), etc.

1. flow rate: well-manufactured miniature magnetic gear pump's can generally work in the speed range of 50~4000rpm. By finding the flow-pressure-rpm curve of each model, it is easy to make the selection (lpm is l/min, slash represents differential pressure)

Due to the existence of gaps inside the pump, there is always a part of high pressure liquid at the pump outlet end will flow back from the pump inside to the pump inlet end along the gaps inside the pump, causing the actual output flow of the pump to be less than the theoretical value. And with the increase of the difference between the import and export pressure, the internal flow back also increased accordingly. The actual flow rate of the pump = theoretical flow rate of the pump - the internal leakage of the pump. From the above graph, it can be seen that the higher the pressure, the lower the actual flow rate at the same speed. It can also be seen that in the case of stable outlet pressure, the flow rate of the pump and the rotational speed are linearly related, which is the theoretical basis for the gear pump to be used as a metering pump. But if the pressure fluctuation, then the linear relationship will be broken, this phenomenon is more obvious in the system of transporting low viscosity liquids.

2. pressure: generally we only consider the differential pressure between import and export, but it is vital to understand the inlet pressure and outlet pressure respectively for the correct selection. Because sometimes the pump inlet may be negative pressure, sometimes may be positive pressure. If it is the case of negative pressure, you 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 pump will be lower than the normal value in the performance curve under the same speed and differential pressure. When the inlet vacuum reaches an extreme value, the pump will not work properly (NPSHa<NPSHr). In addition, each pump has a maximum allowable working pressure, that is, the maximum pump pressure, when the pump inlet pressure > atmospheric pressure, must ensure that the outlet pressure < the maximum pump pressure, that is, "inlet pressure + differential pressure < the maximum pump pressure", so as to ensure the long-term safety of the pump work!

In addition, we also need to correctly understand the pump outlet pressure. Gear pump is a kind of volume pump, we usually say that NP series miniature magnetic pump can reach 20 bar differential pressure, where 20 bar refers to the capacity of the pump. But after the pump is installed in a system, the actual working pressure that can be achieved is determined by the resistance of the system. Resistance of the system = resistance of the liquid flow in the pipeline + possible vessel pressure

3. viscosity: the viscosity of the liquid has an impact on the performance and power of the pump, viscosity is also affected by temperature and even shear force. Because of the existence of internal leakage of gear pumps, the greater the viscosity of the pump in conveying the liquid, the smaller the internal leakage, the actual output flow will be large. So compared to low viscosity water, when conveying high viscosity liquid, the same type of pump in the same speed and differential pressure, the actual output flow rate of the pump will be larger. (Add comparison curve). However, as the viscosity of the liquid rises, the liquid itself decreases in fluidity, while the power consumed by the gears rotating in the high viscosity liquid also rises sharply, so as the viscosity of the conveyed liquid rises, the working speed of the pump should also be reduced appropriately, which not only reduces unnecessary energy consumption, but also prevents cavitation. Gear pump work, due to the meshing between the gears, friction between the bearings and shaft and the loss of magnetic coupling will produce a temperature rise, which in turn will have an impact on the viscosity of the liquid, if the liquid properties or process requirements are very sensitive to temperature changes, then the selection needs to consider pump speed, internal clearance, tooth design and other factors to limit the impact of pump work on the temperature of the liquid. If the liquid is very sensitive to the shear force, then the need to respond by reducing the speed.

4. The corrosiveness of the liquid: the corrosiveness of the liquid will seriously affect the service life of the pump. We must ensure that all the parts in the pump that are in contact with the liquid are able to withstand the corrosion of the liquid conveyed. Generally speaking, the NP series gear pump body using 316L stainless steel material for a variety of liquid corrosion resistance is relatively easy to find, our ceramic shaft corrosion resistance is also very good, mainly PEEK / PPS gears and bearings for different chemical media need to be further considered.PEEK and PPS itself is very good corrosion resistance, a wide range of applications, but there are some liquids will make They swell, especially they are only very slight swelling in some liquids, may be judged in other applications as "usable", but due to the very small internal clearance of the micro pump itself, these very slight swelling may cause the pump to seize. 5.

5. Particle condition: Due to the micro gear pump internal clearance, any particles close to the clearance range may seize the pump, in addition to even very small hard particles, may be in the case of high-speed gear operation will be permanently damaged gear or bearing. Some particles are present in the liquid, and in many cases the liquid may be clean, but there may be particles in the system piping and vessels, joints, welding joints, especially in new installations or retrofit systems such cases are very common. Therefore, it is recommended that the user install a 300-400 mesh filter at the pump inlet to protect the pump. In addition to the choice of filter to ensure that the material is not corroded by the liquid, but also consider the temperature, pressure and overflow area of the filter. If the overflow area is too small will lead to excessive inlet resistance and may also cause frequent clogging of the filter.

6. Temperature: When it comes to temperature, we need to consider the temperature of the liquid and the ambient temperature of the pump work two aspects.

(1) liquid temperature: pump parts should be able to ensure that they can work stably in the liquid temperature range for a long time, including the pump body, bearings, gears, shafts, magnetic drive and seal materials. At the same time we also need to consider the maximum allowable working pressure changes in the pump at extreme temperatures. In particular, the pressure-bearing capacity of the thinnest part of the pump body, the magnetic cover. For magnetic couplings, we have to consider not only the temperature resistance level of the magnetic powder used, but also the aging temperature of the magnet after molding. The magnetic drive of NP series magnetic pump of Shanghai Suofu Pump Industry are aged at 150 degree Celsius, and the whole pump body can work stably in the range of -40~150 degree Celsius for a long time. Liquid temperature also affects the clearance inside the pump. Because of the different materials and sizes of different parts, the amount of dimensional change of different parts at the same temperature rise is different, resulting in changes in clearance. In general, it is possible to cause the flow rate to be too small at low temperature, and the pump may seize at high temperature. Therefore, the temperature range of the liquid under actual working conditions should be considered during the preliminary consultation in order to set the proper clearance in the pump at the factory. In other words, even if our pumps can work at -40~150 degrees Celsius. But if the liquid temperature provided in the inquiry is too different from the actual range, there is a possibility that the pump will not have enough flow or jam during operation. As the pump and motor are connected by connecting frame, the temperature of the pump head will also be transferred to the motor, which will also have some influence on the temperature resistance level of the motor

(2) ambient temperature: the ambient temperature will have a great impact on the motor selection. May have to configure low or high temperature motors, if the configuration of brushless DC motors, then the ambient temperature on the performance of the drive is also quite large. In addition, some liquids will solidify at room temperature or low temperature in winter, when it is necessary to consider the use of pump head heating to ensure normal pump start, the more common way is to wrap the tropical band around the pump head.

7. the liquid is sensitive to shear: gear pump in the work, the active wheel and the engagement between the driven wheel will produce shear force. Some liquids are sensitive to shear, and the properties of the liquid will change under large shear until it cannot be used. For these liquids, the pump must be used to reduce the working speed, increase the clearance in the pump to minimize shear. More often it may be necessary to choose diaphragm pumps, peristaltic pumps and other pump types with less shear to complete the delivery. We can provide you with consulting services in this regard.

8. Inlet and outlet pipeline situation: in general, the inlet and outlet pipe diameter to be not less than the interface diameter of the pump body. In order to ensure the normal suction of the pump, the inlet pipe diameter is expected to be as short as possible, and to reduce the elbow. All factors of inlet line length or pump and liquid level difference can be attributed to the concept of NPSHa range, the only difference is that NPSHa is the case corresponding to the pump inlet filled with liquid. If the inlet line is empty before the pump works, then the maximum allowable operating time of the pump in a liquid-free state and the pump's pumping capacity in this case must be considered. For occasions where self-priming is required, the dry running capability of the pump and the pumping capacity during dry running are very important, otherwise the pump will simply burn out. Shanghai Suofu NP series miniature magnetic gear pumps can achieve a maximum dry running time of 100 hours and a vertical suction capacity of about 1 meter in full dry condition. The outlet pipe diameter will affect the system pressure at the outlet, especially when conveying high viscosity liquid, sometimes the outlet pipe diameter is one level larger, the outlet pipe pressure can have 30% or even higher drop, which will play a very big role in energy saving for daily operation.

Dry running: There are several typical cases of dry running: 1.) Before the pump starts, the inlet pipe is empty and the pump needs to suck the liquid from far away into the pump by itself. 2) When the delivery is over, the system does not have a self-stop function or there is a delay in the self-stop function, the pump needs to run dry again for a while. 3) The liquid conveyed by the pump is very easy to vaporize or is itself a medium that conveys gas and liquid in two phases, and there is often the presence of gas in the pump.

9. motor type and power selection: Generally speaking, motors can be divided into AC motors (ordinary AC motors, inverter motors, explosion-proof motors, inverter explosion-proof motors, single-phase motors, etc.), DC brush motors, DC brushless motors (BLDC), stepper motors and servo motors. In the industrial field of various AC motors are used more, the first look is 1x220V or 3X220V or 3X380V, the voltage is determined and then see whether to explosion-proof (explosion-proof level) or frequency. Choose inverter is usually because to adapt to a certain range of flow, but a high cost of inverter motor, but also to install additional inverter, so customers can also adjust the flow by way of export bypass. Because of the relatively large size of AC motors, speed regulation accuracy is not high, in many commercial equipment is not easy to install, at this time a variety of DC motors, stepper motors or servo motors can show their talents. Ordinary brush DC motor can be directly through the supply voltage for speed regulation, but due to the short life of the carbon brush, brush wear after the tiny carbon powder may cause harm to the system, so the use of various types of professional equipment less and less. Brushless DC motor is compact, leaving behind the traditional carbon brushes, the service life is prolonged, and it can be manually regulated locally, remotely by analog signal or remotely by digital signal, which is more and more accepted by the market. When customers need tiny flow and high precision control, you can consider using stepper motor or servo motor, stepper motor cost is relatively low, the speed is generally <800rpm, so if you need a large span of flow and high precision, then it is recommended to consider using servo motor.

10. Flow and pressure control method: The flow control of micro gear pump is generally achieved by controlling the speed of the pump. For example, NP039, its nominal displacement is 0.39ml/rev, which means that for every revolution of the pump, it should theoretically output 0.39ml of flow. So if the pump speed is 1000 rpm, then the theoretical flow rate that the pump should output is 390 ml/min. So by adjusting the pump speed, the desired flow rate can be easily achieved. Therefore, if the system does not require high accuracy of flow rate (+-2% or so), it is a good way to achieve the adjustment of flow rate by using AC inverter motor or DC brushless motor to control the speed of gear pump. In the case of high precision requirements (~0.5%), servo motors are recommended.

The flow accuracy of micro gear pump is also affected by the pressure fluctuation of the outlet line. Many people may have questions: the pressure is not generated by the pump? How can it be said that the pressure fluctuation of the outlet pipe is affected? Because the pressure after the displacement pump is actually determined by the resistance and load of the pipe network, if the outlet of the displacement pump is directly connected to the atmosphere, then the actual working pressure is 0 (gauge pressure). It is typical of "strong when it meets strong, weak when it meets weak". Pipe network resistance is the resistance of the liquid flowing through the pipeline products, straight pipes, bends, reducers, valves, etc. will bring pressure drop; load can include height difference, container pressure, actuator power, etc.. The fluctuation of pump outlet pressure will not only directly cause the fluctuation of pump output flow, but also the fluctuation of torque caused by the pressure fluctuation and then cause the fluctuation of motor speed. Therefore, in a precise metering system, it is necessary to install a pressure stabilizing valve after the pump and to use a motor whose speed is not affected by torque variations.

The structure of micro gear pump is different from piston and diaphragm pumps, which have inlet and outlet check valves in the pump, so the liquid cannot flow when the pump is stopped. The gear pump does not have a built-in check valve, so the liquid in the piping can flow when the pump is stopped, which may cause the phenomenon of "dripping" or the possibility of finding air entering the piping after a period of stopping. If you do not want to have this phenomenon, you can install a check valve in the pump outlet to open the pressure as small as possible. In addition, gear pumps without a check valve feature also has many benefits, such as shutdown before the motor can simply be reversed to discharge the liquid in the pipeline into the tank, will not occur in the diaphragm pump "air lock" and other phenomena.