There was a pump in that room, and the program said there would be a teardown.

Teardowns aren't uncommon in technical schools, but not at trade association meetings. This one was being held at the Refrigerating Engineers and Technicians Association (RETA) annual convention in soggy Florida. Most technical sessions that take place during association meetings use PowerPoint presentations, handouts, and maybe a tool or small component passed around the classroom. This particular RETA meeting included teardowns of a valve in addition to the pump.

The pump teardown was one of the technical session highlights, and crowded to the point that instructor Steve Hess of Cornell Pumps had to offer an unscheduled second class later in the day. It even bumped up attendance of his pump troubleshooting session, held before the teardown. It also got people's minds off the previous night's Molly Hatchet concert.

HANDS-ON

The first step was to loosen and remove the backplate bolts. "An external line connects to the reservoir," he said. Hess backed the unit out, pulled off the impeller, and pulled off the backplate.

"Use STP to lubricate seal elastomers, the shiny seal faces," Hess told his audience. Avoid getting finger oils onto the stationary element.

He removed the backplate from the second stationary element and turned the pump to the outboard side. "Look for the shiny side of the stationary element, the black elastomer," Hess said. "Make sure the backplate area is clean."

He noted that the line comes in, feeds oil to the pump, and goes into the fitting. When tearing down the unit for maintenance, "You need to avoid cutting the O-ring."

Hess applied a little more STP to the shaft sleeve. "The groove prevents leakage along the seal," he said. "The sleeve prevents wear to the shaft." The O-ring and sleeve then go over the shaft. "Put on the gland - try to avoid dragging it," he said.

The bronze rotating element and elastomer are put on next. "Without STP it sets a lot quicker," he said. However, there should be no refrigeration oil on mating surfaces. "It will take longer for them to wear in," Hess said.

He made sure the pumping ring was facing out, then installed the Teflon® spacer, first compression spring, and secondary compression spring (facing out). The final steps were to attach the impeller and tighten up the springs.

The exercise was missing a little of the ambience of an on-the-job or even a shop teardown; but the lights stayed on and there was no PowerPoint, for which the audience seemed very grateful.

TROUBLESHOOTING SCENARIOS

The operational, hierarchal method troubleshoots for cavitation, recirculation, and vapor entrainment. "Cavitation relates to net positive suction head," he said.

Vapor entrainment can be perceived as cavitation. It can result in: