Centrifugal Pump vs Positive Displacement Pump: What's the Difference?

It sounds easy to select the right pump. However, a single wrong decision can bring everything to a halt. Wrong pump. Wrong job. Big problem. It may seem that centrifugal pumps and positive displacement pumps do the same thing. But they don't. They operate in different ways, they work with different fluids and fit different jobs.

Choose the correct one and your system works like magic. Get the wrong one and you either have pressure issues, leaked fluids or a pump that just cannot keep up.

This is where this guide comes in. We are going to make a comparison of centrifugal pumps and positive-displacement pumps in the easiest way possible. At the end, you will know which pump will fit your job and why.

What is a Centrifugal Pump?

The centrifugal type is the most popular in homes, factories, and industrial plants all over the world. It transfers fluid by a rotating part known as an impeller.

Its impeller has a high speed of rotation and forces the fluid outwards by centrifugal force. This movement generates pressure, which causes the fluid to be pumped out of the inlet to the outlet. Easy, quick and highly efficient, particularly when dealing with large amounts of thin liquids.

Centrifugal pumps can be found in water treatment plants, irrigation systems, HVAC, and mining.

How Does a Centrifugal Pump Work?

In the centrifugal pump, fluid moves with the help of a spinning component referred to as the impeller.

Here's how it goes:

1. Fluid is fed in by the inlet: the rotating pump forces it to flow into the rotor by creating low pressure at the center.

2. The impeller rotates and expels the fluid at a very high velocity.

3. Speed becomes a pressure when the fluid strikes the pump casing and slow down.

4. The pressurized fluid exits via the discharge port into your system.

The most important point to consider: the greater the pressure in the system, the lower the flow rate. The two are directly linked. This is why centrifugal pumps excel in high-volume and continuous work. But fight when a high degree of accuracy and consistency is required.

What is a Positive Displacement Pump?

A positive displacement pump operates in a very different manner.

Rather than spinning liquid, it entraps a fixed volume of liquid and forces it through the system. It doesn’t rely on speed. It relies on volume movement.

When accuracy, control and the need to work with thick or delicate fluids is required, this is the pump to turn to. It does not really mind pressure. It just keeps pushing.

The most common types of positive displacement pumps are:

• Progressive Cavity Pumps (PCP)

• Gear Pumps

• Diaphragm Pumps

• Peristaltic Pumps

• Lobe Pumps 

How Does a Positive Displacement Pump Work?

We can take an example of a Progressive Cavity Pump (PCP). It is one of the most popular types that exist:

• Its rotor is helical (a screw-shaped object) that spins around a stator made out of rubber.

• As it turns, it creates sealed pockets that trap the fluid.

• These pockets travel between the inlet and outlet pushing the fluid.

• It is a continuous flow that is steady and smooth throughout.

The key victory here: flow rate remains unchanged irrespective of pressure. That is why positive displacement pumps are popular in dosing, metering and handling thick or delicate fluids.

Key Differences Between Centrifugal Pump & Progressive Cavity Pump

A progressive cavity pump (PCP) is a type of positive displacement pump. It is commonly employed in the companies that work with thick and abrasive liquids. Here is a side-by-side analysis of the factors that are most significant:

Pump Performance Comparison of Centrifugal Pump & PCP Pump

Here's how they compare when the real work starts:

In case your fluid is thick or sensitive, PCP is a definite winner.

When to Use a Centrifugal Pump?

When it comes to pumping high volume of thin fluid (fast and efficiently), centrifugal pump comes to your rescue.

Go centrifugal when:

• The fluid is oil, light chemicals or water.

• You require high flow, not accuracy dosing.

• There are low or medium pressure requirements.

• The pump will operate continuously with low maintenance requirements.

• The liquid is either clear or contains little solid matter.

The best industries are water treatment, agriculture, HVAC, mining, light petrochemicals, and general manufacturing.

Bonus: less moving parts will result in lower maintenance invoices and increased time between services.

When to Use a Positive Displacement Pump?

A positive displacement pump is a solution when the most important things to you are precision, thickness and pressure.

Go positive displacement when:

• You are transporting heavy or syrup like fluids.

• Flows have to be accurate and consistent.

• This is a shear-sensitive fluid: pharma, cosmetics, food products.

• The fluid has a high solid composition.

• It is required to operate under high pressure.

• You require suction lift without external priming.

Leading industries: oil and gas, food and beverage, wastewater, chemicals, pharmaceutical, paper mills.

These pumps can cope with pressure variation, viscosity fluctuations, and awkward situations without affecting the flow. Extremely dependable where the conditions are not optimal.

Buying Quality Centrifugal & Positive Displacement Pumps From LEPU

You know the difference. Now get the right hardware.

LEPU is a competent manufacturer of high-performance pump components. LEPU provides exactly what you need when it comes to replacement parts of a PCP system or an entire pump unit and at a reasonable cost. 

A great example is LEPU’s screw pump replacement part. Built to exact specs. Minimal downtime. Maximum reliability.

Explore LEPU's full product range here.

Why LEPU?

• Professional manufacturer: strict quality control.

• Spare parts for major pump brands.

• Matches or beats OEM specs.

• Fast shipping at competitive prices.

• Engineer and procurement technical support.

Running a PCP system? LEPU is equipped with stators, rotors and wear parts to keep its running effortlessly.

The strength of a good pump is only as good as its parts. Performance and downtime hugely depend on the selection of the right supplier.

The Bottom Line

Both pump types are excellent, but in the right situation. Match the pump to the job and you'll have no problems.

Need high volume, thin fluid, low maintenance? Go centrifugal. Need precision, thick fluid, high pressure? Go positive displacement.

And when it's time to source parts (especially for PCP and screw pump systems), LEPU delivers quality you can count on, at a price that makes sense.

FAQs

Q1. What is the key distinction between the two types of pumps?

Centrifugal pump is one that involves a spinning rotor that gives the liquid speed, which is converted to pressure. A positive displacement pump entraps a certain amount of fluid and pushes it through mechanically.

Q2. What type of pump is best to use with thick fluids?

The positive displacement pumps always win. Centrifugal pumps become inefficient quickly when the viscosity increases.

Q3. Is it possible to handle solids with a centrifugal pump?

Yes. A vortex impeller allows some solid handling. But for fluids with high solid content, a positive displacement pump is the better call.

Q4. Is a progressive cavity pump a positive displacement pump?

Yes. A PCP is a type of rotary positive displacement pump. It uses a helical rotor inside a stator to carry fluid from inlet to outlet in sealed pockets.

Q5. What happens if you run a PD pump against a closed valve?

Don't do it. Unlike centrifugal pumps, positive displacement pumps maintain pressure even with a closed valve. That can cause serious damage. Always install a pressure relief valve in the system.

Q6. Which type is easier to maintain?

Centrifugal pumps win on maintenance: fewer parts, lower cost, longer service intervals. Positive displacement pumps need more regular attention: rotors, stators, and seals all wear over time.