Gear pump conveying high viscosity liquid should output more flow under lower power consumption, less leakage and larger pressure. When determining the medium to be transported, we should strictly follow the provisions of the product manual, try to use the fluid medium recommended by the manufacturer, and pay attention to the working temperature range of the system. When you want to use in a wide temperature range, the viscosity index of the conveying medium should be higher.
When the viscosity of the conveying liquid is high, or when the system works in a cold environment, it is necessary to ensure that the conveying medium can flow smoothly. Many oils contain waxy components, which are easy to crystallize at low temperature, and the pour point of transportation medium should be lower than the expected lower operating temperature. In addition, the medium to be transported must be compatible with the rubber materials such as seals, gaskets and hoses in the system. If they are not compatible, the medium to be transported must be redefined.
Transport medium is not only the medium of energy transfer, but also the medium of lubrication, sealing and heat transfer. If the liquid viscosity is too high, it will increase the internal friction resistance, reduce the output power, waste energy, and produce too high system temperature. The outlet pipeline of high viscosity gear pump should also be equipped with safety valve and other protection devices, so that once the outlet channel of the pump is blocked, the safety valve can be opened to relieve pressure. The inlet and outlet of high viscosity gear pump need safety valve.
1. Selection of working pressure
The rated pressure of pump refers to the higher allowable pressure when the pump works continuously, and its working pressure is determined by the external load. The service life of pump is directly related to its working pressure. For the gear pump that does not work frequently, its working pressure can be taken as the rated pressure of the pump. Considering the different product quality, the rated pressure is reduced by 20% ~ 30%. For the gear pump which often works under higher pressure, its working pressure should be 1 ~ 2 pressure levels lower than the rated pressure of the pump. Petrochemical equipment is often 24-hour continuous operation, when the pump working pressure 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 high viscosity gear pump is adjusted too high, the gear pump will run under overload.
2. Installation and commissioning
The support or flange of high viscosity gear pump and its driving motor shall be installed on the same foundation. The foundation, flange or support shall have enough rigidity to reduce the vibration and noise of gear pump during operation. The motor and gear pump shall be connected by elastic coupling, the coaxiality shall be less than 0.1 mm, and the inclination angle shall not be more than 1 degree. When installing the coupling, do not knock it with hammer to avoid damaging the gear and other parts of the gear pump. If driven by pulley, sprocket, etc., bracket support should be set to prevent the driving gear bearing from radial force. When fastening the foundation screw of gear pump and motor, the stress of the screw shall be uniform and the connection shall be reliable. When rotating the coupling by hand, you should feel that the gear pump can rotate easily without clamping and other abnormal phenomena, and then you can pipe. The inner diameter of oil suction pipe of high viscosity gear pump should be large enough, narrow passage or sharp turning should be avoided, elbow should be reduced, unnecessary valves and accessories should be removed, the installation height of pump should be reduced as much as possible, and the length of oil suction pipe should be shortened to reduce pressure loss. The sealing of pipe joints and other components should be good to prevent air intrusion, so as to control the occurrence of cavitation and cavitation. Before starting operation, fill the shell of gear pump with liquid to be transported, so as to start safely. If the ambient temperature is lower than freezing point, hot steam should be injected into the pump in advance for preheating treatment, and then the gear pump can be started. The rotation direction of gear pump should be consistent with the oil inlet and outlet. If the pump is idle or idle for a long time, use it for the first time and then close it for an hour. 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 gear pump should also be equipped with safety valve and other protection devices, so that once the outlet channel of the pump is blocked, the safety valve can be opened for pressure relief. For the high viscosity gear pump that needs forward and reverse rotation, the inlet and outlet pipelines need to be equipped with safety valves.
3. Noise problem
In the fluid transportation system, the rapid changes of liquid flow velocity, flow rate and pressure, the rupture of bubbles and alternating load are the common causes of noise. The gear pump transporting high viscosity liquid is the main source of system noise.
Reasonable determination of the working speed of the gear pump can avoid the meshing resonance frequency of the rotation of the gear and the shaft, which can prevent the aggravation of the noise. Because when the meshing frequency is close to the natural frequency of the gear train, resonance is easy to occur. Appropriate vibration isolation technology can prevent the vibration from transmitting to adjacent structures. Therefore, the gear pump and the drive motor should be connected by flexible coupling and installed on the same base plate to ensure the coaxiality. The base plate is installed on the elastic support, which can further improve the vibration isolation effect. It is an effective way to control the noise of high viscosity gear pump to set an expansion cavity or accumulator on the outlet pipe of gear pump to absorb the pressure pulsation of pump or buffer the sudden change of pressure in pipe.
