Boiler Feed Pump Sealing
In boiler feed pumps, mechanical seals, packing and labyrinths are the seals of choice today. Feed water is sealed with mechanical seals and packing.
By Robert L. Matthews
In boiler feed pumps, mechanical seals, packing and labyrinths are the seals of choice today. Feed water is sealed with mechanical seals and packing. Bearing housings are sealed labyrinth or magnetic seals except in the case of older pumps that aren’t upgraded from lip seals. The single cartridge seal is the most popular and is still being improved with more aggressive pumping rings to circulate fluids for better cooling around the seal faces, which is where the most problems occur.
The API Flush Plan 23 can be a better choice than Flush Plan 21 that has supported many seals over time. The 21 piped fluid from the pump discharge through a cooler into the stuffing-box and out the throat bushing to cool the seal generated heat. Flush Plan 23 circulates stuffing-box fluid through a cooler and back. This didn’t always do well – but, today, seal suppliers are tightening throat bushing clearances to hold cooled fluids, and improving pumping ring efficiencies that give greater circulating fluid acceleration. This combination is increasing mean time between failures in boiler feed pumps. So, if you want to try and make a difference with little change, this might be just what helps your system.
We experience steamy hot water leaks to the atmosphere and water contamination in the bearing housings – and both are bad. The steamy high pressure water is big safety issue and the oil contamination is shortening the bearing life at a high rate of speed. Not all feed pumps have these issues, but too many do. Leaks in boiler feed pumps are much more common in older pumps than in newer installations. The technology and experience of the pump manufacturer is constantly improving and, with advancing seal technology, boiler feed pumps installed today are better than ever.
When the pump is operated at its BEP (best efficiency point), the chance of leaks is reduced. The piping, alignment, base condition, balance, drive and more can affect the pump and all should be as good as possible.
About the Author: Reliability manager for Houston-based Royal Purple Ltd., Bob Matthews has 35+ years of pump industry experience – from hands-on to supervision, in-plant maintenance management, consulting and training. He has taught advanced pump classes for Fortune 500 companies, universities, the Vibration Institute, ASME and FSA. Contact: www.royalpurple.com