If discharge from a positive displacement pump is consistently changing between high and low volumes, what is the most likely cause?

When a positive displacement pump exhibits varying discharge volumes, one key factor to consider is the alignment of the pump shaft. If the shaft is out of alignment, it can create friction and resistance during operation, leading to inconsistent performance. As the pump cycles through its operational process, the misalignment can cause fluctuations in the volume it can effectively discharge, resulting in that observed variability between high and low output.

Furthermore, proper shaft alignment is critical for maintaining the integrity and efficiency of pump operation. Misalignment can also lead to further mechanical issues, such as wear and tear on components, ultimately affecting the pump's overall reliability.

In contrast, other factors like a clogged discharge line or an overheating motor would result in pressure build-up or operational failures rather than changes in discharge volume. Similarly, using the wrong pump size typically leads to inadequate performance based on the system requirements but should not inherently cause fluctuations in the discharge rate if the system components are functioning within their limits.