Overcoming Wastewater Challenges with a Centrifugal Grinder Pump
The best type of grinder pump is one that wastewater professionals can install and never have to touch for maintenance or repairs. It manages solids seamlessly without clogging, keeping residential, low-pressure sewer, industrial, commercial, or municipal wastewater systems up and running. It stands up to the modern “flushable” products that often wreak havoc on most systems. It also offers the fluid velocity needed to pull solids into the cutting mechanism and effectively pass them instead of allowing them to settle in the bottom of the tank.
A grinder pump’s inlet and discharge velocity, grinding mechanism, and other features can deliver long-term benefits and maximum uptime for wastewater management.
Centrifugal grinder pumps with radial cutting mechanisms offer more effective and reliable fluid velocity and cutting power than other options, including positive displacement pumps or centrifugal grinder pumps with axial cutters. Centrifugal pumps with radial cutting mechanisms overcome the modern challenges wastewater professionals face.
Clogging and Fluid Velocity
Challenge: Clogging at Inlet or Discharge
Solution: Better Fluid Velocity
Debris settling in lines or getting stuck at a pump’s intake are major challenges for wastewater operations. When solids are not drawn into a grinder pump’s cutting mechanism, it is a sign of a weak inlet velocity. This is a common issue with positive displacement pumps, which have lower fluid velocity on the discharge. This can result in solids accumulating against the intake, tank edges, and sewer line.
The EPA’s Alternative Wastewater Collection Systems manual states a fluid velocity with a minimum of two feet per second is required to scour solids in a low pressure sewer line. Centrifugal grinder pumps provide superior fluid velocity when compared to positive displacement grinders, keeping solids in suspension within the sewer system. Franklin Electric centrifugal grinder pumps provide higher fluid velocity while scouring lines without generating cavitation or limiting the operating range.
Solids Handling Capability
Challenge: Cutter Binding
Solution: Patented Radial Cutters
Centrifugal grinder pumps can come equipped with axial or radial cutting systems. Axial cutters can struggle with fibrous materials, especially as shear gaps increase. Over time, the distance between the cutters will open, allowing premature failure or clogging to occur.
Radial cutting mechanisms are cast parts designed to shred materials using a rotating and stationary cutter and do not rely on wear parts to establish shear gap. Radial cutters provide higher shearing force and retain tighter tolerances over time. They are superior to axial cutters, which require adjustment throughout the pump’s life as separation occurs, causing resistance in tension as material does not break in shear.
A powerful centrifugal grinder motor torque is critical to grind material when in a locked rotor condition. Higher locked rotor torque from the motor results in a higher shearing force applied by the cutters. This ensures that incoming solids, including difficult fibrous materials, are drastically reduced to allow successful passage.
High force and tight shear are key attributes to manage various stringy solids and fibrous materials found in today’s wastewater streams. A floating radial cutter paired with a powerful motor delivers the performance needed to grind tough materials while providing the shear needed to pulverize the waste.
Total Cost of Ownership
Challenge: Undersized and Inferior Materials
Solution: Quality Design and Components
Centrifugal grinder pumps must exert enough force to shred difficult materials, and the pump motor shaft must be able to withstand radial loads without bending. A short motor shaft will decrease the amount of leverage a radial load will have against the shaft at the bearings, and increased thickness will provide the shaft more cross sectional area to resist deflection. Both of these traits are critical to withstanding shaft deformation and premature
motor or bearing failure in grinding applications.
Axial cutters usually establish shear gap with shims which can shift during operation, causing wear and reduced grinding efficiency. In contrast, radial cutters are cast with tolerances set and provide the cutting performance needed without pulling the pump to adjust for proper clearance.
Binding at the End of a Cycle
Challenge: Motor Damage
Solution: Longer Run Cycle
Grinder pumps can have material lodged in the cutting mechanism at the end of a cycle. When the cycle restarts, the material will become wedged between the cutters and bind the system. A floating radial cutter can attack this problem, but ideally, the goal should be to reduce the number of starts and stops.
Centrifugal grinder pumps usually have longer run cycles with increased flow to clear more waste in less time than positive displacement pumps. Longer run cycles with fewer starts and stops extend pump life by reducing wear on the start components.
Reliability Against Non-Dispersable Solids
Challenge: Roping
Solution: Notched Components
Roping occurs when long, fibrous materials get tangled together, forming rope-like strands that can clog pipes and impede the function of pumps. Stringy materials often wind around the grinder blades or along the pump shaft. When the cutting surfaces cannot break a continuous stream of matter, the material will wrap around the shaft between the rotating and stationary cutters or around the shaft seal. Notches incorporated in the cutter and volute can distribute the flow against the cutters and balance the pressure to minimize radial forces that contribute to roping.
Challenges Met, Solutions Delivered
Wastewater professionals should choose a centrifugal grinder with robust construction and radial cutters to improve fluid velocity and shear force. This design boosts pump performance, extends run cycles, and reduces the total cost of ownership by ensuring more reliable operation.
