Centrifugal pumps and positive displacement pumps are the two main categories in pump technology. They work fundamentally differently, and the distinction determines which type best suits a specific application.

Operating principle: the fundamental difference

Centrifugal pump: the fluid is accelerated by a rotating impeller. Kinetic energy is converted into pressure energy in the pump casing. Flow rate varies with system back-pressure.

Positive displacement pump: a mechanical component (gears, screws, pistons, diaphragms or plungers) displaces a defined volume of fluid per stroke or revolution. Flow rate is virtually independent of back-pressure.

When to choose a centrifugal pump

A centrifugal pump is the logical choice when the fluid is low-viscosity (water, thin process streams), large flow rates are needed, the duty point is relatively stable, continuous pulsation-free flow is desired, and low purchase and maintenance costs are important.

When to choose a positive displacement pump

A positive displacement pump is the better choice when the fluid is highly viscous (oil, resin, bitumen, syrup), dosing accuracy is required, high pressures are needed at relatively low flow rates, and flow must remain independent of system pressure.

Common selection mistakes

Using a centrifugal pump for high-viscosity media.
As viscosity rises, centrifugal pump efficiency drops drastically, energy consumption increases and the pump can overheat. Above approximately 300 cP, a positive displacement pump is typically more efficient.

Selecting a positive displacement pump where a centrifugal pump suffices.
For low-viscosity fluids and large flow rates, a centrifugal pump is more compact, cheaper to purchase and simpler to maintain.

Quick decision framework

1. Viscosity above 300 cP? Positive displacement pump.
2. Dosing accuracy required? Positive displacement pump.
3. Flow rate above 50 m3/h? Centrifugal pump is likely more efficient.
4. High pressure (>10 bar) at low flow? Positive displacement pump.
5. Pulsation-free flow needed? Centrifugal pump.

Gorman-Rupp Europe supplies centrifugal pumps and membrane/gear pumps (positive displacement) for viscous media.

Frequently asked questions

Want to know which centrifugal pump best fits your application? Share your application data (flow, head, medium, solids, installation type) and we will advise the right configuration. Contact Gorman-Rupp Europe.

When choosing a pump station, the installation type plays an important role: above ground (dry installed) or underground (wet well with submersible pumps). In this article, we compare both configurations on maintenance, safety, costs and uptime — so you can make an informed decision for your sewage, wastewater or water management situation.

What is an above-ground pump station?

An above-ground pump station, also known as a dry-installed pump chamber or dry-installed pump station, positions the pumps above liquid level. The liquid is drawn in via a suction line. Maintenance, inspection and repair take place above ground, without personnel needing to enter a wet well or confined space.

With an underground configuration, submersible pumps are placed directly in the liquid in a wet well. Maintenance requires the pump to be hoisted up, including the associated safety measures for working in confined spaces.

Comparison: above ground vs underground

Advantages of above-ground pump stations

Safety and working conditions
The most important advantage are safety and hygiene. Maintenance on pumps in a wet well requires working in a confined space — with risks of gas exposure (H₂S), slipping and drowning. An above-ground installation eliminates these risks. Personnel work at ground level in a dry, easily accessible space. Also, since the above ground installed pumps remain clean on the outside, the inspection and maintenance work adds to pleasant and hygienic working conditions.

Faster maintenance, higher uptime
At an above-ground pump station, pumps are directly accessible. Inspection covers, shimless adjustment and cartridge seals make maintenance fast and simple. No crane or hoisting equipment is needed. The result: shorter maintenance stops and higher uptime of the pump station.

Lower Total Cost of Ownership
Although the initial investment in an above-ground installation is sometimes higher, the TCO over the service life is often lower. This is due to shorter maintenance time, less deployment of specialist equipment and fewer emergency measures during failures. Read more in the article on costs and TCO of self-priming pumps.

Condition monitoring and early detection
An above-ground pump is not only easier to maintain, but also easier to monitor. Vibrations, temperature and noise are directly observable. And with the addition of suction and discharge gauge reading, pump operation and efficiency can be monitored real-time. This makes early detection of wear or deviations simpler than with a pump that is submerged.

When to choose above ground?

An above-ground pump station is in many cases the best choice for:

• Permanent sewage pump stations and lift station applications
• Locations where safety and working conditions are a priority
• Applications with high uptime requirements
• Situations where TCO outweighs purchase price

An underground wet well may be preferred when above-ground space is very limited, noise is unacceptable (and attenuation is insufficient), or when the application is simple enough to serve with a submersible pump.

Gorman-Rupp solutions for above-ground pump stations

Gorman-Rupp Europe supplies self-priming pumps designed for dry-installed installations. The Super T-Series®, Super U-Series® and Ultra V-Series® are suitable for wastewater, sewage and industrial applications.

The Reliasource / SCS system offers a complete modular pump station concept with self-cleaning sump, maintainable above ground and suitable as a replacement for traditional wet wells. View the full overview of self-priming pumps.

In addition, Gorman-Rupp Europe provides support with the selection, design and commissioning of above-ground pump stations, from system analysis to pre-assembled delivery.

Frequently asked questions

Want to know more about above-ground pump stations for your situation? Our pump specialists are happy to assist. Contact us.

On 4, 5, 6 and 7th of May 2026, Gorman-Rupp will be present at IFAT Munich 2026, the leading international trade fair for water, sewage, waste, and raw materials management.

You can find us in Hall B1, Booth 423, where we will show our latest pump solutions for municipal, sewage and wastewater applications.

We will also make a presentation at the Green Stage of IFAT on Reliability That Drives Efficiency and Lowers Costs: A Self-Priming Approach to Wastewater Pumping by Jeff Hannan, our Product Manager at Gorman-Rupp Company.

This session will be held on 4^th of May 2026 between 16:00-16:20 hours in Hall C4.427

Do not miss it and join us to get a closer look at how this approach works in practice.

Our team will be available throughout the exhibition – if you are planning to visit IFAT, feel free to get in touch in advance or stop by our stand.

If you need a ticket for IFAT visit or you have further questions, you can send an e-mail to nesibe.tuncer@gormanrupp.com. We will be happy to support.

We look forward to seeing you in Munich.