Centrifugal pumps are reliable and versatile pieces of light construction equipment for the do-it-yourself homeowner as well as the light construction contractor. To choose the right pump for your job, it's important to understand the basic differences between pumps' designs, costs and features.

Centrifugal pumps are classified into three categories - submersible, dewatering and trash.

Submersible pumps offer contractors versatility on the job site. These pumps are, by definition, submersible in water containing solids up to one-quarter inch in diameter and less than 10 percent by weight. Submersible pumps are relatively inexpensive, can run unattended, and are lightweight and quiet. They can pump unwanted water from well casings, tunnels, shafts, flooded basements, manholes, vaults, swimming pools and field drainage collection systems. They can also supply water to water fountains, waterfalls and small irrigation projects.

Dewatering pumps are also somewhat inexpensive but do not contain high-quality components. Centrifugal dewatering pumps feature high-volume flow capabilities, are lightweight and have a compact design. The water being pumped must be relatively clean, containing solids up to one-quarter inch in diameter and less than 10 percent by weight. These units are best suited for pumping water from manholes, flooded basements, utility vaults, swimming pools, lakes and barge holds. Dewatering pumps can also supply water to rural fire trucks, water trucks and small irrigation projects.

In contrast, trash pumps cost more, but they contain high-quality components. The construction and rental industries often prefer this type of pump, which has high-volume flow capabilities, is lightweight and compact, and has a pump housing that you can easily open for cleaning. These pumps can handle clean, muddy, mucky, and sandy or gravelly water with solids up to 2 inches in diameter and between 10 to 25 percent by weight. Trash pumps can remove unwanted water from excavations less than 20 feet deep, flooded basements, manholes, utility vaults, mining work, swimming pools, lakes and barge holds.

Before Buying A centrifugal pump utilizes the energy created by the rotation of an impeller to move liquids through the pump. Some of the major components of a centrifugal pump include the prime mover, mechanical seal, impeller, pump housing, volute and diffuser. When selecting a pump, consider the ease of reducing the distance between the wear plate and the impeller face. Cavitation and abrasive debris causes wear and ultimately increases the space between the impeller and the wear plate.

Most pumps need to be shimmed via the impeller, pushing it forward to decrease this gap, which means disrupting the costly mechanical seal. Some centrifugal trash pumps offer a shimmable wear plate made of stainless steel. This type of wear plate allows for easy shimming by moving the volute closer to the impeller without compromising the integrity of the mechanical seal. In addition to a shimmable wear plate, some centrifugal trash pumps offer an oil-lubricated mechanical seal. The seal remains cool, even during dry runs, and you can easily check for the presence of oil from the outside of the pump via the oil reservoir.

High-quality pumps require preventative maintenance and proper operation to maintain high performance levels. To ensure hours of trouble-free pump usage, remember these basic guidelines:

* Position the pump close to the source and use a short suction hose. Long hoses produce more friction and less volume. The shorter the distance a pump has to move liquids, the higher the volume the pump will deliver.

* Check the suction hose for leaks and secure all fittings. Most pumping problems are caused by faulty suction hose connections.

* Make sure the discharge hose is not kinked. If the hose is pinched or clogged, air cannot escape and the pump will not prime.

* Use a reinforced suction hose to avoid collapsing.

* Run the pump at the manufacturer's specified rpm. Running the unit at higher speeds can result in engine damage and cavitation, while lower speeds can decrease pressure head and flow rates.

* Use the proper strainer to avoid clogging and damage.

* Make sure flapper valves are operational.