Understanding pump types can reduce downtime and improve efficiency in solids-laden applications. Eric Lawson from Vaughan Co. has some insights.
Pumps are arguably the most important and prevalent piece of equipment for any facility. The ability to transport fluids reliably and efficiently is critical to the modern world. However, we hardly ever have the luxury of transporting a pure liquid like clean water.
Pumping reliability is not solely based on mechanical performance but also on solids-handling performance. Clogging and binding represent system downtime, while plugging upstream piping and fittings can be even more troublesome. Given this reality, the need for solids-handling pumps becomes clear. So, why not design pumps to reliably pass solids?
Unsurprisingly, Vaughan Company does! Non-clog centrifugal and positive displacement pumps are extensively used in solids handling applications, generally with a specified maximum solids size, or ‘ball pass’, that can reliably pass through the pump. This may work for applications with larger pumps and smaller solids sizes, but this is rarely the case. Wastewater pumping commonly experiences unpredictable and/or large solids sizes, which may require active solids handling technology that does not just passively allow solids to pass through the pump but actively reduces and conditions them.
Pump types
There are three main types of active solids handling pumps: chopper pumps, cutter pumps, and grinder pumps. Unfortunately, the industry can be confused by the lack of a universal definition and manufacturers’ hybridisation. So, Vaughan would like to propose definitions that are simple to apply and provide a meaningful distinction. In a chopper pump, the hydraulic surfaces are integral to the solids handling, directly ‘chopping’ the solids using the impeller.
Cutter pumps use stationary and rotating elements to handle solids. The core concept of a chopper pump is that it is impossible to separate the chopping from the pumping, whereas, with a cutter pump, the cutting feature is distinct. This allows cutter pumps to utilise various non-clog impeller types, but the added features increase power requirements.
A more specialised version of a cutter pump is a grinder pump, which integrates a grinding mechanism into the pump’s suction. This can significantly increase power consumption and reduce pump capacity but provides the most controlled discharge solids size. Grinder pumps are well suited for septic systems, where smaller piping and dependability are more important than efficiency. However, grinder pumps will rarely be seen in higher-capacity pumping applications due to their poor efficiency.
Pump terms
In practice, manufacturers use the terms chopper pump and cutter pump interchangeably, while the term grinder pump is used rather consistently. However, most contemporary chopper and cutter pumps are hybridized variants of the two styles. For example, Vaughan chopper pumps use the impeller to cut against a stationary cutter bar. This provides the chopping action, but several cutters are also integrated into the pump.
There is an external cutter that cuts fibres and prevents items from bridging the suction, an upper cutter behind the impeller that prevents fibres from wrapping around the mechanical seal and shaft, and an insert cutter in the backplate that keeps the pump-out vanes on the back of the impeller from binding. So, while it is marketed as a chopper pump, it does have cutters, which, without the chopping impeller, would make it a cutter pump.
Alternatively, a manufacturer’s pump might not feature a chopping impeller, or it might be a secondary feature to a primary cutter system and marketed as a cutter pump.
Regardless of labelling, the decision to use which type of pump should be based on the application’s needs.
