As the old joke goes, what should you do if your hammer isn’t suitable for a job? Get a bigger hammer! When managing clogging in wastewater pumps, the ‘bigger is better’ mentality often holds sway. But this is not correct. A recent whitepaper from Xylem, demonstrates that big is not the problem. The complexity of the object is.
Clogs are dangerous for wastewater pumps. A clogged pump shuts down operations, often requiring technicians to access the site. These interventions tend to be temporary, as a clog can quickly develop again after removing the obstructing materials. Often, the pumps don’t clog entirely but instead continue to operate at a sub-optimal level.
To explain what is going on, we must first address a mistaken assumption in the wastewater management world. The prevailing logic is that you need larger throughlet sizes to avoid clogging. If an object can navigate the throughlet feeding water into the impeller area, there shouldn’t be clogging.
This principle makes sense at face value, and when introduced over a century ago, it also suited operations of the day. Brute performance, not efficiency, was the main priority, and engineers assumed that a large object is the greatest danger to a pump’s continued operations.
Anatomy of a clog
Large objects don’t cause the majority of problems. Instead, long, stringy and fibrous objects are the real culprits. Large objects often don’t even reach the pump. Due to their size and weight, such objects often get deposited in low-flow and stagnant wastewater cycle areas. They rarely make it to the wastewater pumps.
But long and stringy materials — such as tissues, wipes, and dishcloths — are different. They can travel with the stream at leisure, and hook onto the leading edges of impellers. Just as a string quickly wraps around the moving parts of a lawnmower or cooling fan, these fibres start catching and entangling on the impeller. They then provide more surface areas for other materials to grab. This culmination is what eventually causes a pump to clog.
A clog results in two outcomes: either the impeller stops moving, so operations cease, or the pump has to use more power to keep the flow going. Other than the inconveniences of shutdowns, the pump’s components also become damaged.
Traditional wastewater impeller designs don’t address this. Vortex impellers and single-vane impellers are subject to reduced efficiency, damage to parts, and difficulties establishing balance for the throughput. There is a phenomenon with intermittent pumps where clog material can backwash in the pump sump, but this is temporary. Once operations resume, that clogging process quickly starts again.
If a bigger throughlet size isn’t doing the job, then what will? Since the early Nineties, Flygt — a Xylem brand — has engineered a solution that is now part of its market-leading wastewater pump family. These designs have since become the standard for addressing clog issues caused by both fibrous and large objects.
Flygt’s design tackles clogging at several levels. Its wastewater pumps manage the transport of liquid and solids by using a self-cleaning hydraulic. The new backswept impeller design stops materials from attaching to its leading edge. A relief groove pushes such materials to the chamber’s periphery, where they are subsequently flushed out.
This design is as effective as traditional pumps when handling large solid waste. It is dominatingly effective at avoiding clogs caused by stringy materials that can accumulate. The difference is a substantial saving in pump maintenance and total cost of ownership and significantly reduced operational and unplanned costs.
When it comes to clogging in wastewater pumps, bigger throughlet size isn’t better. In fact, it’s irrelevant. Smarter is better – a smarter pump design that manages clogging in a modern and efficient manner. Contact Xylem and Flygt, the creators of this breakthrough (and growing standard) in wastewater pump design, and learn how we can reduce breakdowns, improve performance, and make pump investments pay for themselves.