February 1, 2009

Converting a Pump to Use Mechanical Seals

Andy Becker

Wear and leakage are common maintenance problems that result in pump discharge pressure dropping below optimum levels and reduced pump efficiency. Converting pumps to mechanical seals eliminates fretting or grooving of the shaft and provides for easier pump maintenance. By converting to mechanical seals, a plant also avoids incurring expenses associated with the replacement of sleeves and shafts.

Preparing large circulating pumps for this conversion can be challenging because of the size of the pumps or space restrictions. Sometimes it’s impossible due to the extent of repairs that may be required beforehand if the pipe has severe corrosion. Fortunately, field service crews are finding they can overcome these challenges by making repairs on site using portable machining tools developed for precision, power, and their ability to work in restricted spaces.

Portable machine tools are proving to be valuable assets in the drive to reduce plant downtime and streamline the repair process, which was the case recently at a coal-fired generation facility in northeast Oklahoma.

Circulating pumps at the coal-fired facility were to be converted to mechanical seals from traditional packing to prevent wear on pump shafts and better control leakage (Figure 5). Over time, traditional packing caused wear on the pump shaft because there was contact while the shaft was rotating. The packing then required frequent maintenance — either adjustment and/or frequent replacement — so the pump could achieve maximum efficiency without reduction in head. Converting the pumps to mechanical seals was expected to extend mean time between pump maintenance schedules and provide for more trouble-free maintenance.

5. OK pump needs work. A power plant located in Oklahoma decided that upgrading its circulating water pumps to mechanical seals would be less expensive than replacing sleeves and shafts. Courtesy: Climax Portable Machine Tools