phc february 2011
www.phcnews.com
What type of grinder pump do you need? PLUMBING
On the job with Liberty Pumps 32
a public sewer main, then on to a treatment plant and ultimately returned to the environment, where it can lead a disinfected and productive second life. Sometimes a home or business’ sewer line is at a lower elevation than the sewer main. That’s where the sewage pump or a sewage grinder pump comes in. These pumps are traditionally put in some sort of tank and buried; either in the basement or outdoors. When water is used, wastewater is collected and stored in a holding tank. When it reaches a pre-set level, the pump is activated, pumping the waste out into the sewer system. But not surprisingly, pumps can be
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susceptible to certain problems. Regular “solids handling” sewage pumps simply try to pass solids along. What goes in, goes out… or at least it tries. Certain waste items like diapers or articles of clothing or towels will clog regular pumps. Even if the pump can pass along some of these things, if the solid is larger than the pipe diameter, then the items can clog the pipes. Grinder pumps are designed to
grind waste into a fine slurry. But many grinder pumps can also be susceptible to problems. Failure of these pumps can come in different forms, but they all cause the same outcome. Wastewater from the residence or building stops flowing, an alarm may go off, and back up can occur if the alarm is ignored. For obvious reasons, this is not desirable. There are three distinct grinder
pump products: •A single stage centrifugal
grinder pump uses a single impeller, spinning on a shaft, powered by a motor to create the pumping action. Wastewater is pumped through the cutters that grind, shred or cut the material that is being pumped out of the basin. Single stage centrifugal grinders are typically used in applications that require lower discharge heights (less than 90 feet). •A two stage centrifugal grinder
pump is basically the same as the single stage unit but it has two impellers instead of one. Two-stage centrifugal grinders are typically used in applications that require more discharge height, typically in
astewater from a building’s fixtures is supposed to be carried to
the 140 feet of lift range. •A semi-positive displacement
grinder is powered by a motor turning a stainless steel screw-type rotor that spins inside a rubber stator that creates a pumping action. This type of grinder pump allows for higher pumping heights as the material is squeezed inside the rubber stator pumping the wastewater through the pump and out of the basin. Semi-positive displacement grinders are typically used in applications that require higher discharge heights, typically in the 140 feet of lift range, sometime higher.
What are common problems of Grinder pumps? Different types of grinder pumps
can fail for different reasons. Here's the top 6 list: Wadding —Material can wad up
on the cutting mechanism, blocking the flow of water, overheating the pump and even burning out the motor. Jamming —Material can actually
get impacted inside the cutter mechanism to the point where it overcomes the torque of the motor and stops it. Clogging —Ground
material that gets past the cutting mechanism can clog up inside the pump housing blocking water or stopping the impeller. Rubber stator failure —
Macerated waste and pressure can wear on a rubber stator causing it to fail and render the pump useless. Motor burn out —
Some pumps must be applied to the right pressure and flow. Improperly applied pumps can overload and burn out the motor. Seal failure —A
common pump problem where the main seal fails, allowing water to get into the motor. This problem can be aggravated in a grinder pump because the ground material can actually wrap around the seal and cause it to fail.
How can I avoid these problems? One of the newest cutter
technologies on the market is the patented V-Slice®
by Liberty Pumps. It is designed to eliminate the
issues of wadding, clogging, and jamming that traditional cutters have. This new innovation provides superior shredding performance in demanding sewage applications. The hardened stainless steel cutting system provides in excess of 367,000 cuts per minute and aggressively shreds jeans, shop rags, diapers, sanitary napkins, and other difficult solids into fine slurry. Its special features allow it to do the shredding with minimum motor torque, and it has self clearing features, so it won't easily wad, jamb, or clog. Seals: Traditionally a double
mechanical seal arrangement is used because it is common for the first seal to fail since it is vulnerable to foreign/stringy material. This material gets wound around the shaft and can split the seal faces open. The Omnivore uses a Viton double lip seal for the lower seal in conjunction with a silicon carbide mechanical
Cutter Technology
*These curves show no minimum head requirement. e Continued on p 34
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