High viscosity pump when conveying liquid, the viscosity is high

The high viscosity pump must ensure that the conveying medium can flow smoothly when the viscosity of the conveying liquid is high or when the system works in a cold environment. Many oils contain waxy components, which are easy to crystallize at low temperature, and the freezing point of the conveying medium should be lower than the expected minimum operating temperature. In addition, the medium to be transported must be compatible with rubber materials such as seals, gaskets and hoses in the system. If they are incompatible, the transmission medium must be determined again. The transmission medium is not only the medium of energy transmission, but also the medium of lubrication, sealing and heat transfer. Too high liquid viscosity will increase internal friction resistance, reduce output power, waste energy and produce too high system temperature. The outlet pipeline of high viscosity pump shall also be equipped with safety valve and other protective devices, so that once the outlet channel of the pump is blocked, the safety valve can be opened for pressure relief. For high viscosity pumps requiring forward and reverse rotation, safety valves shall be set on the inlet and outlet pipelines.

1. Installation and commissioning of high viscosity pump

The support or flange of the high viscosity pump and its driving motor shall adopt a common installation foundation, and the foundation, flange or support shall have sufficient stiffness to reduce the vibration and noise generated during the operation of the high viscosity pump. The motor and high viscosity pump must be connected with elastic coupling, the coaxiality shall be less than 0.1mm, and the inclination angle shall not be greater than 1 degree. When installing the coupling, do not knock with a hammer to avoid damaging the gear and other parts of the high viscosity pump. If driven by pulley, sprocket, etc., bracket support shall be set to prevent radial force on driving gear bearing. When fastening the anchor screws of high viscosity pump and motor, the screws shall be stressed evenly and connected reliably. When rotating the coupling by hand, you should feel that the high viscosity pump can rotate easily without clamping and other abnormalities, and then you can pipe. The inner diameter of the oil suction pipe of the high viscosity pump shall be large enough, narrow channels or sharp bends shall be avoided, elbows shall be reduced, unnecessary valves and accessories shall be removed, the installation height of the pump shall be reduced as much as possible, and the length of the oil suction pipe shall be shortened to reduce pressure loss. The sealing of pipe joints and other components shall be good to prevent air intrusion, so as to control the occurrence of cavitation and cavitation. Before starting the operation, fill the shell of the high viscosity pump with the liquid to be transported for safe start. If the ambient temperature is lower than the freezing point, the hot steam shall be introduced into the pump in advance for preheating treatment, and then the high viscosity pump can be started. The rotation direction of high viscosity pump shall be consistent with the oil inlet and outlet. If the high viscosity pump is operated for the first time or used after being idle for a long time, it is best to run for about one hour under no-load or small load. If abnormal temperature rise, leakage, vibration and noise are detected in advance in the running in stage, stop the machine for inspection. The outlet pipeline of high viscosity pump shall also be equipped with safety valve and other protective devices, so that once the outlet channel of the pump is blocked, the safety valve can be opened for pressure relief. For high viscosity pumps requiring forward and reverse rotation, safety valves shall be set on the inlet and outlet pipelines.

2. Selection of working pressure of high viscosity pump

The rated pressure of the pump refers to the maximum allowable pressure when the pump works continuously, and its working pressure depends on the external load. The service life of the pump is directly related to its working pressure. For high viscosity pumps that do not work frequently, the working pressure can be taken as the rated pressure of the pump. Considering the different product quality, it is best to reduce the rated pressure by 20% ~ 30%. For high viscosity pumps that often work under high pressure, the working pressure shall be 1 ~ 2 pressure levels lower than the rated pressure of the pump. Petrochemical equipment often operates continuously for 24 hours. At this time, the working pressure of the pump should be much lower than the rated pressure, and the working speed should also be lower than the rated speed. If the working pressure of the high viscosity pump is adjusted too high, the high viscosity pump will operate under overload.

3. Noise problem of high viscosity pump

In the fluid conveying system, the rapid changes of liquid flow velocity, flow and pressure, bubble rupture and alternating load are the common causes of noise. The high viscosity pump conveying high viscosity liquid is the main source of system noise. Reasonably determine the working speed of high viscosity pump to make the rotation of gear and shaft avoid meshing resonance frequency, which can prevent the aggravation of noise. Because resonance is easy to occur when the meshing frequency is close to the natural frequency of the gear train. Appropriate vibration isolation technology can prevent vibration from being transmitted to adjacent structures. Therefore, the high viscosity pump and the driving motor shall be connected through a flexible coupling and installed on the same base plate to ensure coaxiality. The base plate is installed on the elastic support to further improve the vibration isolation effect. Setting an expansion chamber or accumulator on the outlet pipe of the high viscosity pump to absorb the pressure pulsation of the pump or buffer the pressure sudden change in the pipeline is an effective means to control the noise of the high viscosity pump.

Application characteristics of variable frequency motor for high viscosity pump:

1. The insulation grade is generally grade f or higher. The strength of ground insulation and wire turn insulation shall be strengthened, especially the ability of insulation to withstand impulse voltage shall be considered.

2. For the vibration and noise of the motor, the rigidity of the motor components and the whole shall be fully considered, and its natural frequency shall be improved as much as possible to avoid resonance with each force wave.

3. Cooling mode: forced ventilation cooling is generally adopted, that is, the cooling fan of the main motor is driven by an independent motor.

4. Measures to prevent shaft current, bearing insulation measures shall be taken for motors with a capacity of more than 160kW. The main reason is that it is easy to produce magnetic circuit asymmetry and shaft current. When the currents generated by other high-frequency components act together, the shaft current will increase greatly, resulting in bearing damage. Therefore, insulation measures should be taken generally.

5. For constant power variable frequency motor, when the speed exceeds 3000r / min, special grease with high temperature resistance shall be used to compensate for the temperature rise of the bearing.

Especially with the increasingly wide application of frequency converter in the field of industrial control, the use of frequency conversion motor is becoming more and more widely. It can be said that because of the advantages of frequency conversion motor over ordinary motor in frequency conversion control, it is not difficult for us to see the figure of frequency conversion motor where frequency converter is used.