1. Common types and characteristics of metering pumps
Plunger metering pumps
1. Low price .
2. The flow rate can reach 76 m3/hour, the flow rate is in the range of 10% to 100%, the measurement accuracy can reach ±1%, and the maximum pressure can reach 350 MPa. When the outlet pressure changes, the flow is almost constant.
3. It can transport high viscosity medium, not suitable for transporting corrosive slurry and dangerous chemicals.
4. The shaft seal is a packing seal, and there is leakage. The packing needs to be adjusted periodically. The packing and plunger are easy to wear, and the packing ring needs to be pressure flushed and drained.
5. There is no safety relief device.
Mechanical diaphragm
1. The price is lower.
2. No dynamic seal, no leakage.
3. It can transport high-viscosity media, abrasive slurries and dangerous chemicals.
4. The diaphragm is subject to high stress and the life of the diaphragm is low.
5. When the outlet pressure is below 2 MPa, the applicable range of flow rate is small; the measurement accuracy is ±5%, and the flow rate can change up to 10% when the pressure changes from the minimum to the maximum.
6. No safety relief device.
Hydraulic diaphragm
1. No dynamic seal, no leakage, safety relief device, easy maintenance.
2. The pressure can reach 35 MPa; the flow rate is in the range of 10:1, and the measurement accuracy can reach ±1%; every time the pressure increases by 6.9 MPa, the flow rate decreases by 5% to 100% ten out of ten.
3. The price is higher.
4. It is suitable for medium viscosity medium.
Bellows
1. The price is lower.
2. No dynamic seal, no leakage.
3. It is most suitable for conveying vacuum, high temperature and low temperature medium, the outlet pressure is below 0.4 MPa, and the measurement accuracy is low.
Second, how to select the model of the metering pump
1. Determine the pressure: the rated pressure of the selected metering pump should be slightly higher than the actual maximum required Pressure, generally 10 to 20% higher. Do not choose too high, too high pressure will waste energy and increase equipment investment and operating costs.
2. Determine the flow rate: the flow rate of the selected metering pump should be equal to or slightly larger than the flow rate required by the process. The use range of the flow rate of the metering pump is preferably 30-100% of the rated flow range of the metering pump, and the repeatability of the metering pump is high at this time. Considering the economy and practicality, it is suggested that the actual required flow rate of the metering pump should be selected as 70-90% of the rated flow rate of the metering pump.
3. Determine the material of the pump head (hydraulic end): After the specific model and specification of the metering pump is determined, select the material of the over-current part according to the properties of the over-current medium. This step is very important. , it will cause the medium to corrode and damage the overcurrent components or the medium to leak and contaminate the system. In severe cases, it may also cause major accidents.
4. Other aspects: When choosing a metering pump, it is also necessary to consider the precision level of the metering pump required. The higher the precision level, the greater the investment. The general working temperature of the metering pump is -30 ~ 100 ℃, and the special metering pump has a wider working temperature range (such as a high temperature liquid metering pump with a thermal insulation jacket, the delivery temperature can reach 500 ℃). For the particle size of the medium, the requirement should be less than 0.1mm, and for the medium larger than 0.1mm, the flow structure of the pump can be changed to meet the needs. For the viscosity of the medium, it should generally be 0~1000mm/s, and the special metering pump can reach 6000mm2/s. The flow rate of the mechanical diaphragm metering pump is the maximum flow rate measured under the calibrated rated pressure (when delivering clean water at room temperature) ), if the pressure drops, the output flow will be higher than the calibration.
