- Ed Tondra
How Do I Know if a Progressing Cavity Pump Is the Best Solution for My Application?
All images courtesy of www.pumps.netzsch.com and www.continentalultrapumps.com
The progressing cavity pump, also referred to as a “progressive cavity pump,” “pc pump,” or “pcp pump,” has been around since the early 1930s. During the last several years, the evolution of the progressing cavity pump has made it a reliable alternative in many positive displacement pump applications.
In this blog, we will highlight how the progressive cavity pump operates, spotlight some of its new design features, and discuss some of its applications.
How Does the Progressing Cavity Pump Work?
A progressing cavity pump is a positive displacement pump that uses a metal helical rotor typically connected to the drive- or power-end of the pump through a shaft with a pin or gear joint connection. The rotor operates within a fixed stator to create “pockets of fluid” that progress from suction to discharge, creating a consistent low pulse flow. The pump can deliver repeatable and accurate flow up to within +/- 1%.
Unlike a centrifugal pump that “throws” the fluid away from the impeller vanes, a progressive cavity pump enables the fluid to move from one cavity to the next, “pushing” the fluid forward. In return, this makes the flow constant at a given pump speed regardless of the discharge pressure required. This is uniquely different from centrifugal pumps since pressure continues to build to the point of pump failure, at its weakest point. Since the fluid continues to progress through the progressive cavity pump, it will build up pressure quickly if a valve or blockage occurs downstream. Therefore, it is required to have a pressure relief valve to avoid this type of situation.
Viscosity defines a fluid's resistance to flow. Fluids with higher viscosity are thicker, producing a greater resistance to flow. This phenomenon has a dramatic impact on centrifugal pumps as they cannot handle these types of applications. Conversely, progressive cavity pumps can! The progressive cavity pump can push the viscous fluid through its cavities, pumping the fluid forward.
Best Practices When Selecting a Progressive Cavity Pump
Estabrook Corporation is a leading regional sales and service organization that distributes high-quality pumps, valves, seals, controls, and repair for a Total System Solution approach. As a pump specialist in Ohio and upstate New York, we can help you properly select the correct pump for your application. Below are items to think about when searching for a progressing cavity pump.
Points to Consider
If a fluid is very abrasive, oversize the pump and reduce its speed
If a fluid is viscous, reduce the speed of the pump
— 1000 cp = 150 rpm
— 100 cp = 700 rpm
Size the pump to maintain 4-7 ft/sec velocity through the stator
Size the motor large enough to cover the highest temperature (i.e., expansion of stator)
The stator material compatibility
The rotor finish (e.g., chrome, black chrome oxide, etc.)
Points to Watch Out For
As with most pumps, they cannot be run dry
Low viscosity fluids “slip,” causing the pump to be inefficient
Deadheading the pump can cause heat build up and destroy the rotor/stator
Possible high start-up torque
New Design Features of the Progressive Cavity Pump
There have been recent advancements in progressing cavity pumps designed to increase reliability and ease of maintenance. Some of these design features for the stator include adjustability, spiral stator technology, and advancement in materials. For the rotor, the utilization of coatings has increased life and reliability. Additional developments that now allow full service in place capabilities make it much easier to repair and replace parts as needed. Let’s discuss some of these features in more depth.
This feature allows you to adjust the stator to compensate for wear, reestablish efficiencies, extend its service life, and minimize downtime.
Full Service In Place
Up- or sideward-removal of the rotor-stator unit reduces installation space and downtime with conventional and adjustable stators. The ability to service the unit in place allows for decreased downtime, lower inventory cost, and a much easier maintenance experience.
Spiral Stator Technology
The spiral stator differs from the traditional round stator in that it has a compressed and thinner lining with an even thickness. This difference allows for a more rigid and tighter pump, with the spillover and wearing minimalized, versus a standard stator. This leads to the ability to use the same rotor at a greater temperature.
Increased Available Geometries
Increased geometries allow for the simple change of rotors and stators to modify the flow and/or pressure of the pump. The outside dimensions, including the suction and discharge size, remain the same. All parts are identical, except for the rotor and stator, allowing you to address any operational changes in your system.
Market and Application Fits
The largest progressing cavity pump market installations worldwide typically include fluids with higher viscosities or products sensitive to shear. Here are some of the markets where you will find progressive cavity pumps.
Oil & Gas: Primarily seen in well streams with combined crude, water, gas, and sand.
Water and Wastewater: Abrasive slurries, sludges, and metering applications.
Food & Beverage: Pump applications for shear sensitive, thick, and abrasive fluids.
Chemical & Petrochemical: Can pump highly abrasive, viscous, and toxic fluids with minimal wear when compared to other positive displacement pumps.
Continuing, below are various applications where using progressing cavity pumps may be beneficial over other types of centrifugal pumps.
High Viscosity: With a higher viscosity fluid, the progressive cavity pump’s mechanical and volumetric efficiencies are favorable over centrifugal pumps.
Abrasive Solids: Unlike gear or vane pumps, the internal fluid velocity is much lower and causes less wear.
Low NPSH(a): Progressive cavity pumps can be used with as little as 28” Hg suction pressure
Shear Sensitive Fluids: Low velocity through rotor/stator, such as oil/water separators
Where Varying Flow Is Required: The flowrate is directly proportional to the speed of the pump, so changing the speed whether through a VFD or other means will easily adjust the flow rate
— When using air entrained fluids
— If the application requires the pump to be vertically mounted
— If multiphase applications with gas and solids in suspension
— Any self priming applications
— Where bi-directional operation is required
With the advancement of technology over the last several years and some of their inherent design benefits, progressing cavity pumps may now be the answer to your tough positive displacement applications. Please feel free to contact your Estabrook pump subject matter expert. We are here to understand your application and desired goals and then create a custom, impactful solution.
Estabrook has been a quality provider of Industrial Fluid Handling Solutions for over 55 years. To learn more about our broad range of Industrial applications and pump solutions that we can provide to your organization, please click on the Contact Us Now link: