September 2012
Description: Water is essential to the survival of most living things, and assuring clean water is a top priority for more than 50,000 community water
systems in the United States alone. This process begins with flowlines that take water from lakes, rivers and reservoirs and pump it to a treatment plant.
Bearing Applications: Housed bearing units are used in sluice gates and ball bearings in the pumps at pumping stations
Description: Water coming into the treatment plant goes through a coarse screen to keep out debris. Then coagulant (e.g. aluminum sulfate, iron chloride) is added to help solids agglomerate, or clump together. Air is pumped in to mix the coagulants at high speed.
Bearing Applications: Mixers typically use sleeve bearings, while fans and blowers feature housed bearing units (e.g. split-to-the-shaft). The pumps have ball bearings.
Items to Consider: Most submerged applications use sleeve bearings.
Description: The water is gently stirred in flocculators to help coagulated particles cling together to form larger particles, known as “floc.” This
is done with paddles (20 on a shaft is not uncommon) in one of five arrangements: horizontal paddle wheel, vertical paddle wheel, walking beam, oscillating, or impeller
Bearing Applications: Housed bearing units (e.g. split-to-the-shaft) connect paddle shafts in a series and provide vital support. These applications can require as many as 100 bearings. On vertical paddle wheels, where the bearings may be submerged, sleeve bearings are common.
Items to Consider: In some flocculators, such as the horizontal design, the bearings are submerged in the water and should use a lubricant that is moisture-repellant. Corrosion resistance is also important, especially as the use of ferric chloride as a flocculant becomes more common.
Description: Water and floc are pumped to a sedimentation tank, where the floc settles on the bottom so it can be discharged and thickened and
dried for disposal. Drag screens help separate the floc from the water, which exits through a sluiceway near the top of the tank.
Bearing Applications: The pumps use ball bearings, while the drag screens typically have chain-and- sprocket drives with sleeve bearings. The jack shaft, or support shaft, of a sludge collector has ball bearings or roller bearings..
Items to Consider: The drag screen drives are underwater, so their sleeve bearings are generally made of nylon or polyethylene.
Description: Any particles remaining in the water are filtered out thorough filter beds of sand, gravel and/or activated charcoal.
Bearing Applications: The pumps that move the water into and out of the filtration stage use ball bearings.
Description: Small amounts of chlorine are added to kill any bacteria or microorganisms. If the water will be used for drinking, fluoride is
added to fight tooth decay.
Bearing Applications: Ball bearings are used in the pumps at pumping stations.
Description: Purified water is pumped from the treatment plant to water towers or reservoirs, sometimes called clearwells, to be stored until needed. From there it enters the distribution system that takes it to local residences and business.
Bearing Applications: Ball bearings are used in the pumps at pumping stations.