Second, the choice of matching motor
Pump output power P = ρgQH, where ρ-the density of the pump transport slurry, g-gravity acceleration, Q-pump flow rate, H-pump head.
The submersible sewage pump is designed according to the water density 1000kg/m3. The density of the mortar will be much higher than the water density. If the submersible sewage pump is used as a submersible dredge pump for pumping sand, the motor load is too large and it is easy to burn the motor. At this time, some manufacturers will use the method of reducing the diameter of their impeller to reduce the actual parameters of the pump type and avoid burning the motor.
The theoretically calculated output power of the pump is much smaller than the actual output power. The power of the submersible dredge pump is not only as simple as multiplying the power of the clean water pump motor with the slurry density, but also increases the safety by 1.3 to 2 times. margin. This is because the size of the slurry concentration is difficult to control when the sand pump is working, and the density of the transported slurry suddenly increases and decreases, causing the output power of the sand pump to change accordingly. In addition, when the sand pump is started and operated, the solid particles will impede the rotation of the impeller (the impeller will be caught in severe cases), which will further increase the output power of the sand pump. The larger the solid particles in the slurry, the greater the uncertainty. Therefore, when designing and matching the motor power of the sand pump, not only the rated output power of the water pump but also the maximum output power must be considered.
Submersible dredge pumps are generally equipped with four-stage or six-stage low-speed, high-torque motors, and submersible sewage pumps are generally equipped with two-stage motors with a speed of 2980 rpm. The high-speed motor has a high speed, so if the parameters are the same flow rate and head, the volume of the pump casing and impeller is small, but the higher the speed, the faster the wear rate, which causes the pump casing and impeller to wear when the submersible sewage pump is pumping sand soon, it is necessary to shut down frequently to replace accessories, and the maintenance cost is high.
- The structural characteristics of submersible dredge pump and submersible sewage pump are different.
When the water contains sediment, the main phenomena of pump damage are burning motor and impeller wear. The vast majority of them are burning the motor, the main reason is that the motor is overloaded or the motor enters the water. Motor overload can be solved by increasing the power of the supporting motor, or by increasing the cooling water circulation. The water intake of the motor is mainly a sealing problem, especially how to ensure that the mortar is completely isolated from the motor when pumping sand, and to avoid the water source containing the mortar from entering the motor. It has been a problem that needs to be solved in the manufacture of submersible sand pumps.
To extend the service life of submersible dredge pumps, the problems of sand pumping seal and sand pumping wear must be solved. The main problem here is the sand pumping seal problem. Tai’an PCEAN Pump Industry Co., Ltd. adopts a specially designed double-face cemented carbide mechanical seal to improve the reliability of the mechanical seal. The machine seal is lubricated with oil, and there is a large amount of engine oil in the machine seal cavity, which can further prevent the entry of the mortar liquid.
Furthermore, there is a separate oil chamber between the machine seal and the motor, which is the channel connecting the motor and the impeller. Even if the machine seal fails, a small amount of leaked slurry will flow to the machine oil chamber and will not contact the motor or the bearing, avoiding bearing grease Loss can extend bearing life.