The Different Types of Pumps

Choosing the right pump is as important as choosing the right motor or inverter. The pump is the heart of many fluid-handling systems, and it is essential that all of the various types of pumps are understood to obtain reliable and economic performance.

This guide will take you through the major types of pumps and the major subtypes of pumps that are used in industrial applications. The benefits and characteristics of the various kinds of pumps, potential problems and limitations, and their uses have been included.

Classification Overview: Dynamic vs Positive Displacement

Before examining the various kinds of pumps, it is necessary to explain the two general classes employed by engineers, which are as follows: 

Dynamic (rotodynamic) pumps: pumps which use velocity and kinetic energy (through the agency of an impeller or blades) for the moving of fluids and convert velocity into pressure.

Positive displacement pumps: pumps which hold a given amount of liquid and which are then, mechanically, replaced or displaced from the inlet into the outlet, in given cycles.

Each class has its advantages, disadvantages and limitations, and many of the principal types of pumps belong to one of these classes.

Centrifugal Pumps

Centrifugal pumps are among the most commonly used industrial pumps. They use the kinetic energy imparted to the liquid by the rotating impeller to produce an increase in the pressure of that liquid as it leaves the impeller.

Variants & features:

End-suction / single-stage: Commonly used in general-service water, oil and chemical applications.

In-line (in-line centrifugal): The suction and discharge connections are in line, providing the most efficient design and compact construction for installation in small spaces.

Multistage centrifugal: Use of more than one impeller to increase the head developed.

Submersible centrifugal pumps: Installed in the liquid being pumped, usually in sumps, wells and for drainage.

Chopper/grinder (subtype of centrifugal): These have chopper devices to shred the solids before reaching the impeller, preventing clogging. They are used in wastewater, sludge and slurry handling applications.

Strengths & limitations:

• Well adapted for high flow and low-to-medium pressure service.
• Low pulsations and smooth running.
• Not suitable for very viscous fluids or slurries containing solids (except for special designs).

Gear Pumps

Gear pumps are a standard rotary positive-displacement type and consist of two or more intermeshing gears; fluid is trapped in the cavities and transported from the inlet around the housing to the outlet side.

Key points:

• Ideal for moderate pressures and clean fluids (oil, lubricants, chemical dosing).
• Good for moderate viscosity fluids.
• Simpler construction, compact, relatively predictable flow (for given speed).

Points to consider:

• As high clearance is required, abrasive or solids-laden fluids give wear.
• Not well suited to high viscosity slurries or shear-sensitive fluids.

Lobe Pumps

Lobe Pumps (Rotary Positive Displacement) Lobe pumps are pumps using lobed rotors that revolve without making contact. The fluid is moved over the casing as the lobes spin. 

Advantages: 

• Gentle pumping action, suitable for the working of shear-sensitive fluids (such as foods, biotechnological studies and pharmaceuticals). 
• Capable of handling a certain amount of solid particles without injuring the product due to their presence. 

Drawbacks: 

• It is impossible to obtain an accurate flow. If the pressure varies, the flow is irregular. May not be able to equal gear pumps for very high flow efficiency in clean fluids, etc.

Progressive Cavity Pumps 

Also known as screw pumps and Moineau pumps, they operate by having a helical rotor rotate within a flexible stator. This forms sealed cavities which advance toward discharge.

Advantages: 

• Excellent choice for viscous or shear-sensitive fluids, slurries, and fluids with entrained solids.
• Provides relatively pulsation-free flows along with good suction lift characteristics. 
• Can better handle multiphase flows (liquid + solids + gas) than many alternatives under some circumstances. 

Disadvantages: 

• Stator material may wear under abrasives or high temperatures. 
• It may be more complex and costly to maintain. 
• Efficiency may suffer under high differential pressures.

Diaphragm (Membrane) Pumps

These pumps have a flexible diaphragm that moves back and forth to draw fluid into it and push the fluid out again, usually through check valves.

Advantages: 

Self-priming, dry-running ability (on some designs). Good for corrosive, abrasive, or viscous fluids. Seal-less design helps greatly reduce the propensity to leak. 

Disadvantages: 

Not suited for very high flows or pressure ranges. Diaphragms and check valves can be wear points and require periodic maintenance.

How to Choose the Right Pump

When it comes to specifying a pump for an industrial system, particularly where your motor and inverter architecture control or power it, the following are items of prime consideration:

• The fluid or liquids with regard to: viscosity, solids content, abrasiveness, corrosiveness, temperature, etc. 
• Required flow and pressure/head. Suction lift or priming requirements. Duty cycles, run time, stroke speed/RPM constraints.
• Pulsation tolerance/need for smoothing. 
• Maintenance, availability of spare parts, and reliability. 
• Compatibility with motor & inverter control (variable speed, soft start, torque limits, overload protection). 

At RJW Engineering, we provide not only the pump but also the appropriate electric motor and inverter/drive solution that fits the application.