Water Pumps: Are You A Lumper or A Splitter

Written by Diane M. Calabrese | Published December 2024

 

Fire may have given civilization a big boost, and we can’t overlook the wheel, but the water pump is linked to broad improvements in quality of life. (Take sanitation for one.)

We know how myriad water pumps serve our industry. That use, though, stands as just a small example of the functions that water pumps provide.

In fact, so diverse are water pumps that classifying them—constructing a taxonomy of water pumps—tends to make lumpers or splitters out of us. Lumpers might start with two broad categories: positive displacement and centrifugal.

Splitters, though, want to clarify at the onset (positive displacement as reciprocating or rotary, centrifugal as axial or radial). Doing so brings precision in naming, and the precise naming recognizes the many outcomes of decades of innovation.

Before getting back to a sampling of the staggering array of water pumps and the diverse needs they meet, let’s back up to our industry. Water pumps are so much a part of the day for contractors they sometimes suffer from the same sort of benign neglect as other useful tools.

A water pump requires the same diligence in operation and maintenance as any other piece of equipment. It must be used according to its manufacturer’s instructions.

Ask a representative of an OEM [original equipment manufacturer] what he or she wishes every contractor better understood. We put just that question to Keith Linton, a member of the sales team at Giant Industries Inc. in Toledo, OH.

“The more a pump is in bypass, the quicker the unloader will wear out is something every contractor should understand,” says Linton. [For a refresher on pump problems see “Troubleshooting Pumps” https:// www.cleanertimes.com/magazine/ cleaner-times-articles-2/trouble shooting-pumps/.]

Is there a general breakdown of pump applications that correlates with pump types? “Centrifugal pumps are commonly used for water, solvents, and other low-viscosity fluids while positive displacement pumps are commonly used for high-viscosity fluids like oil, paints, and resins,” says Linton.

As refined as water pumps get when engineers match the design to the task, their basics reduce to nudging water (with air or more water) or stirring up water to tap its inherent (kinetic) energy. Whether we notice them or not, we see water pumps in every direction.

Take simple, positive displacement pumps. A toilet plunger is a manual pump that functions when it gets a push, forms a seal, and concentrates air to force the movement of water (and clogs). A hand-operated water pump relies on a lever to move the plunger.

Look to a water-saving washing machine, which likely works with an impeller (instead of an agitator), to see an everyday function being carried out by a centrifugal pumping action.

Equipment-focused manufacturers, distributors, and contractors know that the direction in which pump elements move is not the determinant of how a pump is defined. Some positive displacement pumps are built on a cog system in which two interlocking (toothed) moving cogs (“gears” to some) push water (or other fluids). And some pumping systems combine both displacement and centrifugal components.

One method for delineating subcategories of centrifugal pumps involves the direction in which water flows in relation to the impeller. For instance, an axial flow pump flows in alignment with the impeller, while a radial flow pump generates a flow that is perpendicular to the impeller. Yes, the two types can be combined, which results in a mixed flow.

In the detailed nomenclature of positive displacement pumps, the toilet plunger and water hand-pump would be reciprocating pumps. And the washing machine with the impeller would be a basic rotary pump.

One problem with naming pumps is that monikers may be assigned according to function instead of structure. For example, submersible pumps may include different designs. Many (but not all) submersible pumps have a centrifugal design.

Make It Flow

Pumps are designed to get water to flow. Hydraulic engineers look at pumps as devices that add energy to water. They encourage water to move. The deployment of water pumps is up to the user.

Filtration, cooling, irrigation, drainage, and wastewater treatment are

Short, medium, and longer introductions to water pumps abound. One of the best, if not the best we have seen, is an opensource document from the U.S. Department of Energy’s Energy and Renewable Energy division. It is titled Improving Pumping System Performance—A Sourcebook for Industry . The Sourcebook was written by members of the Hydraulic Institute. (To get a copy of the document in pdf format, use the link https:// www.energy.gov/sites/prod/files/ 2014/05/f16/pump.pdf .)

A model of clarity, the Sourcebook explains that centrifugal pumps are the most popular type of pump because of their longevity and low maintenance, features that in turn make them less costly to operate. A caution is that the size of the pump must not be larger than required because it is inefficient and also bad for the long-term performance of the pump.

Cavitation may occur in centrifugal pumps when the pump operates at a high flow rate. (Pumps have an optimal performance curve, and if pushed too far out of optimum range, pressure differences in the fluid lead to bubble formation in the water. The bubbles move and collapse, acting as destructive entities when they hit the impeller or casings.) At too low a flow rate, vortices can develop in the water (or any fluid), and they too can create damage akin to cavitation. If water intake to a pump is restricted for whatever reason, it can lead to cavitation.

To hydraulic engineers, centrifugal pumps are known also by the name rotodynamic pumps, which aptly describes the circular movement of the

impeller and the basics of the pump. Water (or other fluid) is rotated by the impeller, a mechanism by which energy is added to the water. Energized water enters a chamber attached to discharge piping. The chamber (diffuser) is the source of water for the piping to the wand and nozzle.

Relatively safe to operate when properly maintained (e.g., scheduled seal replacement), centrifugal pumps also tolerate a wide range of ambient conditions. They work well in pressure washers.

(Positive displacement pumps meet needs for high pressure and low flow of viscous liquids. They have more controls, such as valves for pressure release.)

In addition to the document from the DOE, there’s another valuable open-source resource available. The Water Handling Equipment Guide from the National Wildfire Coordinating Group at the Forest Service of the U.S. Department of Agriculture (https://www.fs.usda. gov/Internet/FSE_DOCUMENTS/ stelprd3819991.pdf) includes, for instance, a list of criteria to consider when choosing a fire pump. The list applies equally well to choosing a pressure washer pump or, more specifically, for getting to know the pump of a pressure washer as well as the other components. A contractor should list needs for flow (gpm), weight limitations, length of hoses, environment where pump will be used (e.g., summer heat of Arizona), hours of service pump will have each week, type of water in the region contractor provides service (e.g., are there abrasives in it), and altitude (e.g., is the contractor working at sea level or in a mile-high region).