Different operating conditions of AB centrifugal pumps under the same working conditions
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There are two identical AB-type centrifugal pumps, and after adjusting the process, the inlet pressure was reduced to 1.5 kilograms. According to maintenance calculations, a inlet pressure of 1.6 kg is normally required to ensure proper operation. But now one unit is operating properly, with no abnormal noises, and its vibration levels are also within the required range. But the other unit makes abnormal noises (aerodynamic erosion is the preliminary diagnosis), and its vibration is also unstable. The inlet pressure disappeared when it rose to 1.6 kilograms. How can improvements be made without changing the inlet pressure or the pipelines?
The following methods can be tried to address the issues of abnormal noises and unstable vibrations: 1. Check and clean the pump’s filter and inlet pipes to ensure there are no blockages or impurities. 2. Check whether the pump’s impeller and seal are worn or damaged, and carry out necessary replacement or repair. 3. Check and adjust the internal clearances of the pump to ensure they are within the manufacturer’s recommended values. 4. Properly lubricate and maintain the pump to ensure that all components function properly. By following the above steps, it may be possible to resolve the operational issues caused by a decrease in inlet pressure, without having to increase the inlet pressure or modify the pipelines. .
1. Add an induction wheel； 2. Reduce the inlet temperature (difficult) ；
Reducing the inlet pressure changes HPSHa, failing to meet the pump’s HPSHr and resulting in cavitation. Since the poster has specified that the inlet pressure and piping cannot be changed, other measures include: appropriately reducing the temperature of the medium at the inlet, decreasing the pump flow rate, lowering or removing the precision of the filter screen at the pump inlet, altering the physical properties of the medium to increase the vaporization pressure, reducing the viscosity of the medium, operating two pumps in parallel to raise the pressure at the inlet of each pump’s impeller, and using valves with lower resistance, among others. That is, to analyze each factor affecting the net positive suction head one by one to see if it is feasible.
First, it is necessary to determine whether the flow rate or outlet pressure of the two pumps is the same.
Since the pumps are all cast, even two identical pumps may not have exactly the same performance, which is why the question raised by the original poster arises. Since the inlet pressure has already been reduced, the pipeline design cannot be changed; thus, the following options remain: 1. Reduce the resistance in the inlet pipe, including the inlet filter (by changing its type and reducing the mesh size of the filter), valves (those with low resistance), reducers, and elbows (elbows with a larger diameter). 2. Lower the temperature of the medium; this is a bit difficult ； 3. Reducing the flow rate – to determine whether this can lower the required net positive suction head of the pump, it is necessary to examine the pump’s performance curve. 4. Smooth the lower inlet of the impeller as well as the pump inlet as much as possible, which can reduce the required net positive suction head slightly ； 5. Check whether it is possible to replace the impeller; since one of the pumps does not experience cavitation, this indicates that the net positive suction head required for the impeller of that pump is sufficient – it’s just possible that a defective casting caused it to fail to meet this requirement.
The abnormal one may have been running online for a longer time.