Why can’t this pump deliver any flow?
Thread Content
Our plant’s catalytic cracking unit is equipped with a diesel pump, model 200AYⅡ-150. When the inlet is not fully open, the current almost exceeds the limit; at the same current level, the backup pump can achieve a flow rate of 320, while this pump only manages 280. It is suspected to be an internal leakage issue; checks show that all clearances are within the standard range, with only the impeller mouth ring clearance at 1.1 mm (the standard should be 0.8–1.0 mm for hot oil pumps). I have two questions: First, if it’s not an internal leak in the pump—since a thorough inspection has been conducted and most of the components have been replaced—what could be the possible cause? Second, is there a formula to express the effect of the mouthpiece gap on pump flow rate?
It’s very likely that the problem lies with the clearance between the wear ring and other components. We’ve encountered a similar issue here before: one pump failed to deliver any flow, even though it had just been serviced. Upon inspection, we found that the clearance exceeded 0.5 mm; it then had to be reworked by the machining department before it started working properly. In your case, there’s still some flow coming out of the outlet, whereas we got absolutely no flow at all back then
Check whether the sizes of the pump impellers are the same
A large gap in the mouth ring does not cause overcurrent; it only results in low flow rate and low pressure (due to internal leakage). The reasons for high current are, firstly, issues with the motor, and secondly, worn parts within the pump itself.
There’s no need to worry about the clearance of the mouth ring; we have a pump of the same model, and the corrosion of its mouth ring is unimaginable. It still operates at full capacity, just with reduced output, but it won’t cause overcurrent.
Check whether the center of the impeller flow channel is offset.
When the inlet isn’t fully open, the current is about to exceed the limit??? Is a centrifugal pump used for inlet regulation? ? ?
How to adjust the flow rate of a centrifugal pump using the inlet valve? For overcurrent, please check whether the three phases of the motor are balanced.
Please, the original poster, explain in detail: Is it a newly installed pump or one that has been in operation for some time? What were the previous operating conditions (current)?
When the pump is in operation, the inlet valve should be fully open, and the outlet gate valve should be used to regulate the flow rate. Additionally, please check whether the inlet pipelines for the backup pump and the overcurrent pump are arranged in the same way, and whether insufficient flow of the medium entering the pumps could be causing a reduction in their flow rate (check for blockages in the inlet pipelines and gate valves) ； Check whether the inlet of the pump impeller or the flow channel is blocked, as this can also prevent an increase in flow rate ； Friction occurs inside the pump due to the excessive current, resulting in high power consumption and overcurrent in the motor. Please check!