A positive displacement (PD) pump moves fluids with a forward pumping action by trapping a fixed amount of liquid and forcing (displacing) it from the inlet to the outlet with each cycle. This process enables the displacement of dense, thick, or sensitive fluids at a steady flow. Positive displacement pumps are used in industries such as pharmaceuticals, paints, ceramics, food & beverage and water treatment.
There are broadly two types of positive displacement pumps: rotary and reciprocating.
Rotary pumps displace liquids by rotating components like gears, screws, or vanes. With each revolution, a fixed amount of liquid is moved. Gear pumps, screw pumps, progressive cavity pumps (single screw pumps), vane pumps and lobe pumps come under the subset of rotary pumps.
To elaborate further, screw pumps use screws to rotate axially clockwise or counterclockwise, moving fluids of all viscosities along an axis. Gear pumps use a driving and a driven gear which mesh and unmesh while revolving in opposite directions, allowing the liquid to be carried along in the gaps and displaced. Vane pumps have blades that are pushed to the walls of the housing (of the pump) by rotating rotors. Lobe pumps use two rotors, each with two or three lobes, to direct fluid flow.
Reciprocating pumps, on the other hand, displace fluids by using a to-and-fro motion generated by pistons or diaphragms. The cyclical motion is referred to as reciprocation. These pumps include air-operated double diaphragm (AODD) pumps, electronically operated double diaphragm pumps, piston pumps and plunger pumps. Reciprocating pumps are known for their ability to work around high pressures and displace viscous, abrasive, or corrosive fluids. These pumps are ideal for scenarios where steady and controlled flow is essential.
How do positive displacement pumps work?
Positive displacement pumps are all about creating a cavity chamber between the pump’s suction and the discharge side of the pump. The steps typically involve:
- Suction Phase: In this phase, the chamber in the pump expands as a result of moving pistons/gears/diaphragms. This creates a vacuum that draws fluid into the chamber through the inlet.
- Trapping Fluid: Once the fluid is in the chamber, the pump traps it and isolates it from the inlet.
- Displacement and Discharge: The trapped fluid is then displaced as the pump’s moving part continues its cycle/revolution, reducing the volume within the chamber. Displacement is controlled as per the decided flow rate.
What are some of the advantages of a positive displacement pump?
- Constant flow rate – Positive displacement pumps offer precise control over the volume of liquid displaced per cycle, even if the pressure changes.
- Can handle fluids with high viscosity – Positive displacement pumps are popular in several industries because of their ability to handle thick, viscous fluids that are difficult to pump with centrifugal pumps.
- Accurate Metering – These pumps are ideal for applications in chemical processing industries where precise and repeatable fluid dosing is a top requirement.
How to select the right positive displacement pump?
When selecting a positive displacement pump, one must consider factors such as fluid viscosity, pressure requirements, flow rate, and maintenance needs. Factors aside, it is also important to choose the right brand, a name that is well-known in the pumps domain and trusted by a wide range of industries.
Innovative Pumps & Valves by IDEX India
Cognito’s positive displacement pumps
Cognito pumps are designed to handle the world’s most challenging fluid transfer applications. The brand’s EODD pumps are known for their reliability, performance and efficiency. With over 30 years of experience designing and manufacturing industrial products, including pumps of all kinds, Cognito offers its customers unparalleled reliability, ease of use, and maintenance simplicity. Below are a few reasons why Cognito’s pumps are best in class.
- They are long-lasting – Cognito’s patented diaphragm with a larger diameter and shorter stroke ensures its pumps operate for the longest time without several maintenance sessions. The hardened seat and stopper cage design add to the pump’s durability quotient.
- They are leakproof – Cognito’s EODD pumps feature secondary static seals, which prevent fluid contact, protecting the pump in case of diaphragm failure. Not just that, the leak detector sensors of the system also raise the alarm to stop the pump in case any leak is noticed.
- They save on energy – Cognito pumps are known to use less energy than AODD pumps. The brand won the Most Innovative Energy Saving Product award by CII 2023-24.
- They incorporate smart technology – Cognito’s EODD pumps feature smart technology that enables operators to remotely connect and monitor the pump. The generated data can be used to optimise pump performance and determine if any updates are required.
Besides these features, Cognito offers its customers world-class before-sales and after-sales service. From selecting the right pump for their needs to tech support and taking feedback from the client, the Cognito team is always there.
To learn more about Cognito’s positive displacement pumps, click here –
https://www.cognitopump.com/ 
