PUMP DESIGN UPGRADE IMPROVES MTBR FOR PAPER MILL

CHALLENGE

A paper mill in the USA was experiencing reliability issues with a third-party pump. They appointed ClydeUnion Pumps, part of Celeros Flow Technology, to investigate the cause and propose a solution.

The new design was based on increasing the margin between the first natural frequency and the running speed. This was achieved by changing the shaft diameter, the distance between bearings, and the distance from the radial bearing and coupling. The throat bushing was also upgraded to graphalloy and installed with mechanical seals. With these changes, we were able the increase margins considerably (see table 2).

SOLUTION

ClydeUnion Pumps found that the pump’s shaft was sheared under the impeller fi t and there was a crack in the hub of the impeller at the keyway. The impeller wear rings were exhibiting 360° rubbing and some case damage had been caused by a combination of erosion and rubbing of the impeller.

Analysis of the pump was undertaken to determine the cause of the broken shaft under the impeller. Calculations of the first and second dry natural frequencies were done on the original pump. The results showed that the pump’s first and second dry natural frequencies were running quite close to the x 1 and x 2 running speed. Factoring in the effects of the worn packing and wear rings, it was clear that the pump was operating at critical speed.

The new design was based on increasing the margin between the first natural frequency and the running speed. ClydeUnion Pumps achieved this by changing the shaft diameter, the distance between bearings, and the distance from the radial bearing and coupling. The throat bushing was also upgraded to a graphite/metal alloy and installed with mechanical seals.

OUTCOMES

The upgrades resulted in a considerable increase in operating margins, verified by ring tests. The data shows that the upgraded pump will run smoother and with fewer mechanical problems, resulting in an extended Mean Time Between Repairs (MTBR).

Following this demonstration of our engineering and diagnostic expertise, the customer requested that ClydeUnion Pumps upgrade all three of their pumps.