Pump impeller cutting issue?
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Regarding the cutting of pump impellers, relevant books explain that cutting leads to a decrease in flow rate, but sometimes I hear from technicians that the flow rate increases after cutting, which confuses me.
The flow rate should decrease, and the head will drop as well.
The flow rate of a pump is generally proportional to the diameter of its impeller; as the impeller size decreases, the flow rate certainly decreases as well.
Sometimes cutting the impeller can change the net positive suction head and thus adjust the performance of the pump. The theories presented in books are limited; many pump manufacturers rely on numerous experiments to modify the performance of pumps. Therefore, it’s not necessary to follow the procedures outlined in books strictly – it’s better to do more practical experiments. :lol thanks
“The concept of flow rate decrease as described in relevant books refers to the general situation; in reality, it should be considered as follows: first, obtain the performance curve and then determine at which area of that curve the pump is operating. Only by doing so can one predict the subsequent trend, because for some pumps, the head also increases as the flow rate increases:handshake
For pumps with relatively constant medium to low specific speed, the relationship between impeller cutting and flow rate, head, and shaft power is as follows: Q1/Q = (D1/D)², H1/H = (D1/D)², N1/N = (D1/D)⁴. The so-called increase in flow rate is likely due to the fact that the actual head required by the pump is lower than the head specified at the pump’s original design conditions, which results in excessive current during operation. After impeller cutting, at the same current level, the flow rate can be higher than before.
What was said on the 6th floor makes sense; we perform cutting in order to reduce excessive head. According to the performance curve, this allows for operation at high flow rates with low head, thereby saving energy, and the results are significant
The operating point must fall within the high-efficiency range (the area within 7% of the maximum efficiency) after the impeller is cut, under this premise
Calculated according to the pump impeller cutting law
It’s a conceptual issue; from your question, it can be inferred that you are not very familiar with the performance characteristics of pumps, as well as their regulation features. If you’re interested, please contact qq1211407944
1. Referring to the original pump’s performance curve, it is required that the operating point after cutting be within 7% of its high-efficiency point. 2. The relationships between the theoretical parameters flow rate Q, head H, and shaft power N and the diameter: Q1/Q = (D/D1)², H1/H = (D1/D)², N1/N = (D1/D)⁴. There are also percentage values: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%. Flow rate Q: 1.020, 1.04, 1.06, 1.08, 1.1, 1.12, 1.14, 1.17. Head H: 0.9801, 0.964, 0.941, 0.922, 0.903, 0.884, 0.845, 0.846. Power N: 0.96, 0.94, 0.89, 0.85, 0.81, 0.781, 0.75, 0.72. 3. The purpose of cutting the impeller is to change the head value at the rated operating condition, thereby causing excessive current flow. After the impeller is cut, the flow path in the pump volute actually changes. The data shown in the table above only reflect the change in the impeller’s performance; therefore, adjustments are necessary to ensure that the requirements of the manufacturing process are met. The amount of each adjustment is determined by the chief process engineer.