Centrifugal pumps have low head and high flow rate; can changing the impeller alter the head?
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The reflux pump at the top of the distillation tower in the naphtha hydrogenation unit is model 65AYⅡ100. After the pump starts operating, the outlet pressure is 9 kilograms; when the outlet valve is opened two notches, the pressure drops to 8 kilograms. The flow rate is 15 cubic meters per hour, with an inlet diameter of DN80 and an outlet diameter of DN50. Currently, there are no issues with the reflux process. The liquid is sent to the feed pipeline network of the aromatization unit, where the pipeline pressure is 8 kilograms. The pump’s rated flow rate is 20 cubic meters per hour, with a head of 114 meters. At present, there are no problems with the flow rate when sending the liquid away. Given the low head required for transmission, it is now planned to replace the impeller with one of larger diameter. Upon inspection, it was found that the impeller had not been machined; the clearance between the ring and the impeller is 65 microns, the impeller diameter is 180 millimeters, it has three blades, and the width of the flow channel is 10 millimeters. Replacing the impeller with one of larger diameter is not feasible. Is it possible to use an impeller with more blades, a wider flow channel, and still a diameter of 180 millimeters? What is the relationship between the number of blades and the width of the flow channel? Is there any formula for this? I would appreciate detailed explanations from experts
The impeller can be replaced with a larger one. Since a margin is taken into account during selection, if the head increases while the flow rate remains unchanged, the manufacturer needs to calculate whether it is necessary to use a larger motor.
By \"large,\" do you mean the diameter of the impeller? The diameter of this impeller is 180; it hasn’t been cut, and that is its maximum size – any larger and the pump head won’t fit. It’s too troublesome to contact the manufacturer; you have to go through management first. Whenever we encounter pumps that require a high head, we calculate it ourselves – either by applying the impeller cutting formula or by removing some of the impeller stages. Given that the medium in question is naphtha with a density of around 68, and considering a rated head of 114, the actual pressure at the pump outlet is approximately 8 kilograms per square centimeter. Therefore, we plan to select a new pump or replace the impeller. I’m asking this question simply because I want to learn more about this topic; I hope the experts on this forum can have mercy on me and provide some information. Thank you:P
Don’t carry it all by yourself. The manufacturer is professional and can do a good job. You must be mistaken; production cannot proceed, and then you’re not far from getting laid off.
Solutions should be discussed with the manufacturer.
This post was last edited by “Only mediocrity is unacceptable” on October 7, 2016, at 22:27. Haha, it’s not just me; we’re a team, a maintenance workshop. Due to poor design and installation, there were quite a few issues with component selection. If we had to rely on the manufacturers to handle all these problems, the costs would have been enormous. Instead, we do all the designing and modifications ourselves. When ordinary components get damaged, we repair them or find suitable materials to make new ones. For more complex components, we submit purchase requests, and after receiving them, we install them ourselves. In our spare time, we’re practically professionals, haha ;P. All of us have years of maintenance experience, so you can rest assured
It can be replaced; the necessary actions need to be taken based on the current actual operating parameters and the required specifications. It is recommended to contact the pump manufacturer for discussion
Firstly, it seems that the gap between the sealing ring and the mouth ring is 0.65 mm, which is too large; this is probably the main reason for the low pressure and flow rate at the pump outlet. After addressing this issue, it is possible to negotiate with the manufacturer to replace the impeller with one of larger size. According to the similarity law, the pump outlet pressure is proportional to the square of the impeller’s outer diameter, while the pump outlet flow rate is proportional to the outer diameter of the impeller; therefore, the shaft power is proportional to the cube of the impeller’s diameter.
Let me give you a comprehensive response: 1. The AY pump is manufactured by domestic companies; its impellers are cast. Due to cost considerations, these domestic companies do not use precision-cast impellers. Ordinary sand-cast impellers cannot have a perfectly round outer diameter, so that diameter is processed afterward. If it really hasn’t been processed, I suspect you’re using a product from a small factory. 2. The gap at the mouth ring is 65 silk; if this is a one-sided gap, it’s too large. If it’s caused by wear over time, it needs to be replaced immediately. If the new pump already has such a gap, then there is a problem. 3. The reason for only three blades is that this pump is a low specific speed centrifugal pump designed for low flow rates and high head; having too many blades would cause blockage at the inlet and lead to a deterioration in performance. There are two possible solutions to your current situation: consult the original manufacturer to see if it’s possible to increase the diameter of the impeller ； Ask the manufacturer to change the impeller to have 6 blades, in a design of 3 long and 3 short blades, that is, a design with long and short blades.
The key is to look at the motor: as the head increases while the flow rate remains constant, by how much does the shaft power increase? Does the motor still have enough capacity?
Mouth ring clearance, 37.5 mm per side. The impeller diameter is already at its maximum; if it were any larger, the pump could not be installed. If the diameter and flow path remain unchanged, increasing the number of impeller blades can improve the head. Is there a calculation formula?