The metering pump is a reciprocating pump of variable volume that accurately controls the displacement by adjusting the effective stroke length or changing the number of strokes. It is also called proportional pump, adjustable displacement pump, dosing pump and so on. Commonly used to accurately pressure (or no pressure) of the system or process continuous dosing quantitative liquid can also be used for small flow, high pressure liquid delivery. Magnetic pump, high temperature magnetic pump, stainless steel magnetic pump, pipe pump, vertical pipe pump, horizontal pipe pump, pneumatic diaphragm pump, electric diaphragm pump metering pump flow is usually from 10 to 15000L / h, discharge pressure from a few bar to 1000bar , Pump equipped with motor power from 0.12 ~ 55kW, greater flow is often used to achieve multi-pump. As an ideal device for accurate measurement and dosing of fluid, metering pumps can be used to quantitatively transport various media such as flammable, explosive, corrosive, abrasive and slurry, and widely used in chemical and petrochemical plants and water treatment. With the continuous application of new materials and new processes, the new metering pump can almost accurately transport any media requirements. First, the measurement accuracy Measurement accuracy is the stability of the steady-state accuracy Es, repeatability ER (linearity) and linearity (1inearity) in general, is a measure of the metering pump metering accuracy and product quality is important in accordance with. Stability Accuracy Es is the percent change in pump flow relative to the average flow rate under a fixed system condition. The stability accuracy is for the entire range of regulation. That is, under the condition of stable operation of the pump, the percentage of deviation between each flow obtained by continuous measurement and the average value of these flows is not changed. Qmax is the maximum measured value in a set of flows, L / h Qmin is the minimum measured value in a set of flows, L / h Qavr is the arithmetic mean of a set of flows, L / h . Repeatability ER refers to the reproducible performance of the pump flow at a given set of conditions, after adjusting the flow set point and then back to the original set point, expressed as a percentage of the nominal flow rate. That is, within the required adjustment range, under the condition of steady operation of the pump, repeatedly "change the pump flow point and then back to the original set point to measure the flow at this point", the maximum deviation of a set of flow obtained is relatively Pump rated flow (usually 100% flow set point under the flow) percentage. Qmax is the maximum measured value in a set of flows, L / h; Qmin is the minimum measured value in a set of flows, L / h; and QRated is the rated flow of pumps, L / h. Linearity EL refers to the degree of linear deviation between the actual measured flow and the corresponding calibrated flow line, expressed as a percentage of the nominal flow rate. That is, Qi is the measured value of a set of flow measured at a certain flow set point, L / h, Qc is the flow rate corresponding to the same flow set point on the flow calibration curve, L / h ; QRatd - pump rated flow, L / h. Since the purpose of linearity measurement is to measure the accuracy of linear scaling of pump flow, in practice it is common practice to linearly fit different flow values ​​at multiple set points actually measured in the product test to obtain the measured flow directly The maximum deviation of the value from this line calculates the percentage of the deviation relative to the pump nominal flow, which is typically the flow at 100% flow setpoint. SH / T 3142-2004 and AP1675 stipulate that the pump is in operation, its flow rate should be within the regulation of the entire regulation range can be adjusted, the pump rated flow should be at least 110% of the maximum flow rate of the process requirements, the adjustment ratio (turndownati0 , Refers to the ratio of nominal flow to minimum flow) of at least 10: 1. Within the specified regulation range, the stability accuracy should not exceed ± 1%. Repeatability and linearity should not exceed ± 3%. Note: When the metering pump operates below 10% of the rated flow rate, the metering accuracy drops a lot. Therefore, it is generally not advisable to operate at 10% of the rated flow rate. Selection is best to consider the pump operating point at 30% of the rated flow above.
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