Types of Pumps: The Basics

When you need to transfer any type of fluid from one location to the other, your choice of pump will have a big impact on how efficiently and effectively you get the job done. Here’s a look at to the most common types of pumps and what they’re used for.

Centrifugal vs. positive displacement pump

Pumps are often categorized into two broad types: Centrifugal and positive displacement.

A centrifugal pump uses the energy created by an engine- or motor-powered rotating impeller to move fluid. Fluid enters the pump suction, then the impeller eye. As the impeller rotates, the fluid is moved either outward or upward, depending on the type of pump (radial or axial), increasing its velocity. The fluid then enters a diffuser or volute, where it gains pressure, and is pushed out through the discharge point. A centrifugal pump may have one impeller (single stage), two impellers (two stage) or three or more impellers.

A positive displacement pump uses suction to draw fluid into an intake chamber, then uses the mechanical power of a plunger or piston to force it into a discharge chamber and through the discharge point.

Centrifugal pumps: Types and advantages

Even at a small size, centrifugal pumps can move a lot of water fast. Another advantage: Because they don’t have a lot of moving parts, they require minimal maintenance.

The downsides: Centrifugal pumps can’t operate unless they have fluid in the system, so they must be primed before they are started. In addition, if there is no liquid to run through the pump, if too much air gets suctioned into the system or if gas bubbles form while the pump is operating, the pump can overheat or vibrate, which could lead to a pump breakdown.

Types of centrifugal pump

Centrifugal pumps come in many types, each of which is suited to different applications. Below are some of the most widely used centrifugal pumps.

Trash pump

Trash pumps are good at handling wastewater and fluids that contain debris, such as stones, leaves, sticks and mud, that can clog other pumps. They’re often used for dewatering and for removing clogs and solids from liquids.

Vacuum assisted pump

Vacuum assisted pumpsmake priming a centrifugal pump easier. The vacuum removes air from the pump and brings liquid into it so the pump can be started. Depending on the suction and discharge size, these pumps may be well suited to pumping graywater, muddy water, sludge and sewage.

Rotary wellpoint pump

Designed specifically for wellpoint and sock dewatering, rotary wellpoint dewatering pumps are efficient at handling high air and water volumes.

Positive displacement pump: Types and advantages

Positive displacement pumps are better than centrifugal pumps at handling high viscosity fluids, such as oils and glycerin. They are often used in wastewater treatment. These pumps maintain a steady flow, even when the pressure of the fluid changes. They are also more energy efficient than centrifugal pumps.

On the downside, positive displacement pumps operate at a slightly slower speed than centrifugal pumps and require more maintenance. That can make them more costly to operate. Running them dry can cause pump failure.

Positive displacement pump types

There are many types of positive displacement pumps. Here are two of the most common.

Diaphragm pumps

Diaphragm and double-diaphragm pumps propel liquids through their system with the use of one or two reciprocating diaphragms. They can run on condensed air, electricity or diesel. Depending on the material they’re made from, diaphragm pumps can handle liquids ranging from water to acids. They are often used for industrial, chemical and fuel transfer.

Wellpoint piston dewatering pumps

Like rotary wellpoint pumps, these pumps offer high suction lift and high air-handling capabilities. They are efficient and cost-effective for dewatering operations.

What is a submersible pump?

Some centrifugal pumps and positive displacement pumps are designed to be fully submerged in water. The motor of a submersible pump is located in a hermetically sealed compartment that keeps liquids out. Because the pump is submerged, there is no suction lift limitation and no need for a suction lift hose. Submersible pumps are often used for household flood dewatering, emptying wells and ponds and pumping sewage. They are quiet and efficient.

Today’s pump technology includes many variations on these basic pump types. If you’re not sure what type of pump will work best for your application, talk with a pump expert at your rental vendor or retail outlet. Choosing the right pump is key to getting the job done the first time.

Browse our pump selection or contact the United Rentals Fluid Solutions group for help with all your pump and filtration needs.