Jim Elsey on the mysteries of the twilight zone
by Jim Elsey
June 5, 2019

Solution: One-way pump
The mechanic was 100 percent correct. The pump was operating in the correct direction. The essential information left out of conversations and drawings was that the system had multiple pumps in parallel with the subject pump. The discharge check valve for this pump would randomly and intermittently stick in the open position. When this pump was not operating under power, it was forced in the reverse direction by flow or pressure from the other pumps. The impeller and casing were now acting as a hydraulic turbine. Because most ANSI pumps use an impeller that is screwed on, the impeller would back off and seize to the casing during reverse operation.


I have a long list of pump issues that fit into this twilight zone, but these are some of my favorites. These show that inexperienced personnel are frequently assigned to startup. Assumptions are made, no instructions are ever read, nor is any OEM consulted with prestart questions. Almost no pump installation is “plug and play.” There are alignments to conduct, driver rotational checks to make, mechanical seals to set, oil to add and piping to vent. Educate yourself and avoid that dimension in time and space known as the twilight zone.

Read more Common Pumping Mistakes articles here.