Utilities that extract water from pit wells often have a persistent repair issue: Debris and sand that accumulates at the pit’s base. When pumping occurs, these abrasive elements get stirred up.
To protect equipment from damage and minimize lead intrusion into drinking water, a Texas utility tested various grades of plastic for vertical spindle pump line shafts and bowl bushings.
Bowl bushings are usually made of bronze or rubber. In addition to containing lead, bronze can’t withstand dry startup conditions and must be prelubricated. That means the pump must have a lubrication system, which increases costs. Rubber experiences high friction and can tear out of the housing.
At least one grade of plastic swelled and made the pump seize. A year ago, the water utility found something that doesn’t and began replacing bronze and rubber pump components.
Vesconite Hilube is a thermoplastic made by the Vesconite Bearings division of Vesco Plastics, a South African manufacturer of self-lubricated polymer bearings and bushings with U.S. offices in Cleveland and Denver. The material doesn’t swell in water, has a low co-efficient of friction, is ideal for dry startup, and demonstrates a low wear rate compared to many other materials.
Ninety percent of dry startup specifications require one minute of running time. The Hilube bearings and bushings survived 5.7 psi and surface velocities of 1,152 fpm for much longer without damage.
Vesconite Bearings provided an alternative design that enabled the utility to incorporate the plastic into its pumps. Line shaft bushings had a 3-inch outside diameter, 1.94-inch inside diameter, and were 4.5 inches long.
“The line shaft bushings were made longer than the retainer hub, and a chamfer was machined on to the protruding bushing to deflect the particles that might end up between the shaft and the bushing,” says Vesconite Bearings' Charlie Simpson. “The size of the grooves of the bushing were also increased to allow debris easier passage through the bushings.”
For more on this application, call Simpson at 866-635-7596. For a technical manual, visit http://www.vesconite.com/industry/pumps/pump.htm.