Positive Displacement Pumps
Progressive Cavity Pumps vs. Screw Pumps
In many industrial processes, the controlled and reliable transfer of liquids plays a crucial role. Especially when handling viscous media, products containing solids, or processes that require a constant volumetric flow, centrifugal pumps often fall short. In such situations, positive displacement pumps are usually the preferred solution.
Two commonly used types of positive displacement pumps are the progressive cavity pump (also known as an eccentric screw pump) and the screw pump. They are frequently compared and sometimes even considered interchangeable. In practice, however, there are clear differences in operation, application range, and maintenance requirements. In this article, you will read where these pumps are similar, how they differ, and when each solution is most suitable.
What are positive displacement pumps?
Positive displacement pumps move a fixed volume of liquid per revolution. This means that the flow rate is largely independent of the counterpressure in the system. This is a key difference compared to centrifugal pumps, where the flow rate varies significantly with changes in pressure.
Thanks to this principle, positive displacement pumps are highly suitable for applications where accuracy, process stability, and repeatability are important. Typical examples include dosing applications, pumping viscous products, or handling media with a variable composition.
Similarities between progressive cavity pumps and screw pumps
Despite their different designs, progressive cavity pumps and screw pumps share several important similarities.
Both pump types displace a fixed volume of medium per revolution, resulting in a highly predictable flow rate, which is essential in many process installations. In addition, both pumps can deliver a smooth, almost pulsation-free flow. This is particularly important for sensitive processes and for media that must not foam, separate, or be damaged.
Furthermore, both pumps are suitable for viscous liquids and are widely used in industry, water and wastewater treatment, and a broad range of process installations. These similarities are precisely what can make the choice between a progressive cavity pump and a screw pump complex in practice.
Progressive cavity pump
The progressive cavity pump operates with a metal rotor that rotates eccentrically within an elastomer stator. This motion creates sealed cavities that transport the medium in a controlled manner from the suction side to the discharge side.
This operating principle makes the progressive cavity pump highly suitable for demanding media, such as sludge, highly viscous liquids, and media containing solids. Abrasive particles can also generally be handled well, provided the correct stator material is selected.
One key advantage of progressive cavity pumps is their ability to generate high pressures at relatively low rotational speeds. This makes them suitable for applications with long pipe runs or high system resistance. At the same time, the low speed ensures gentle, product-friendly pumping.
A point of attention is the wear of the elastomer stator. Service life strongly depends on the medium, temperature, pressure, and rotational speed. Correct selection, proper maintenance, and timely overhaul are therefore essential to prevent unplanned downtime.
Screw pump
Screw pumps operate using one or more metal screws that mesh with each other. The medium is transported axially along the screws toward the discharge side. This process takes place with very tight tolerances and without the use of an elastomer stator.
As a result, screw pumps are particularly suitable for clean to lightly contaminated liquids with stable properties. Typical examples include oils, fuels, and various process liquids. Screw pumps can deliver relatively high flow rates and often operate at higher speeds than progressive cavity pumps.
A major advantage is their high efficiency and extremely smooth flow during continuous operation. This makes screw pumps popular in installations where long operating times and constant product flows are standard.
At the same time, screw pumps are less tolerant of solids and abrasive contaminants. Even small particles can cause damage to the screws. Proper filtration and good process control are therefore critical.
Technical and practical differences
Although progressive cavity pumps and screw pumps are both positive displacement pumps, their practical application differs significantly.
Progressive cavity pumps excel in flexibility. They can handle changing media, solids, and high pressures. This makes them highly suitable for water treatment, sludge handling, and industrial processes where the composition of the medium is not always constant.
Screw pumps, on the other hand, perform best in stable processes with clean liquids and higher capacities. In such applications, they are often more compact and energy-efficient.
Maintenance is also an important factor. With progressive cavity pumps, stator wear is a well-known point of attention, making regular inspection and overhaul essential. With screw pumps, the focus lies on preventing internal damage caused by contamination.
Common misconceptions
A frequently heard misconception is that progressive cavity pumps and screw pumps are easily interchangeable. In practice, an incorrect choice often leads to accelerated wear, higher energy consumption, or unplanned downtime.
It is also sometimes assumed that screw pumps are inherently fragile. Within their correct application range, however, they are highly reliable and efficient. Success lies in proper application and correct pump selection.
The role of IPG in pump selection and maintenance
When choosing between a progressive cavity pump and a screw pump, experience and independent advice are of great value. IPG supports you with brand-independent pump advice, based on your specific application and process conditions.
IPG does not only look at the pump type, but at the complete picture. The medium, operating conditions, desired service life, and total cost of ownership are all taken into account. This approach helps prevent situations where a pump functions technically, but causes unnecessary maintenance or downtime in practice.
In addition to advice and supply, IPG also supports maintenance and overhaul. Especially for progressive cavity pumps, overhaul is an essential part of the maintenance strategy. Wear of rotor and stator is unavoidable, but with timely and professional overhaul, service life can be significantly extended. IPG has the knowledge and facilities to overhaul progressive cavity pumps professionally and return them to reliable operation within your installation.
Thanks to this combination of advice, supply, and maintenance, IPG acts as a technical partner rather than just a supplier.