When selecting the three-screw pump, we should know as much as possible about the operating conditions of the pump. In addition to the operation flow and pressure, we also need to know the characteristics of the transport medium, such as whether the medium is corrosive or not, whether it contains solid solution, And the ratio of the solid solution and the size of the solid particles, as well as the working temperature, viscosity, specific gravity of the medium, the corrosiveness of the material, the suction conditions of the pump unit, and the installation conditions, according to our experience.
Three screw pump selection should pay attention to the following points:
1. Selection of pump speed
(1)Determination of the range of rotational speeds based on the medium viscosity and specifications of the pump.When conveying high viscosity medium, the pump should select low rotational speed, if the viscosity is low, the corresponding high rotational speed:medium viscosity > 20 °E, for the pump with large specifications (60mm above the main rod diameter), 970rpm or 720rpm is the appropriate rotational speed. If the viscosity is higher (viscosity > 80 °E) such as viscose, can reduce the speed of use, recommended 200-500rpm. For small size of pump, when the medium viscosity is more than 20 °E, 1450rpm or 970rpm is the best speed. If the viscosity is higher (viscosity > 80 °E), the rotational speed can be reduced, 300-600rpm is recommended.
2.Because the higher the rotational speed of the pump, the smaller the volume of the pump under the same performance parameters. However, because of the high rotational speed and high friction power, the pump has a large wear and short life, if the lubricity of the conveying medium is poor or contains trace impurities, Lower speed should be selected to keep the pump longer life, recommended below 1450rpm.The selection of the structure can be carried out according to the installation and operation conditions of the pump, referring to the series and type of the three-screw pump.
(1) conveying lubricating oils, with a temperature below 80 °C and a pump with a built-in bearing structure;
(2) when the temperature exceeds 80 °C or the lubricity of the conveying medium is poor, the pump with external bearing structure is selected;
(3) the medium with poor fluidity and high viscosity or the pump with double-layer heating pump structure should be selected when heating or heat preservation of the medium is needed;
(4) when conveying at high temperature, the pump made of high-temperature resistant material should be selected, please contact our sales people.
3. Matching motor
After the type selection of the pump is determined, the shaft power N of the pump can be found according to the sample data, and after the shaft power is added to a certain power reserve, it can be used as the basis for selecting the motor. The general motor power Nm should not be less than pump shaft power N times the power reserve coefficient K, K value can refer to the following table values:
In addition, because the pump performance parameters provided by the sample are in the form of table form or specific viscosity, the performance curve at rotational speed is given, and the required pump performance value can not be read out directly, which can be roughly estimated according to the following principles. For more accurate data, consult with ourprofessional people.
The flow rate of the three-screw pump is approximately linear when the pressure is at the same speed and viscosity. The higher the pressure, the smaller the flow rate.
Under the same viscosity and pressure, the flow rate of the pump is approximately proportional to the rotational speed.
Under the same viscosity and pressure, the shaft power is approximately proportional to the rotational speed.
When viscosity increases, both flow rate and axial power increase, but due to the complexity of the relationship, we can consult professional people if necessary.
As long as the selection of appropriate, reasonable maintenance, the three-screw pump can ensure satisfactory operation.