Types of Pumps in Piping Engineering – Complete Guide with Interview Questions and Answers
Pumps are one of the most important rotating equipment used in piping systems and industrial plants. Without pumps, fluid transportation from one location to another would not be possible. Pumps help move liquids through pipelines, increase pressure, and maintain continuous process flow in industries.
In industries such as oil & gas, petrochemical, power plants, chemical plants, water treatment plants, pharmaceutical industries, and food processing units, pumps play a major role in plant operation. Different types of pumps are used depending on the fluid properties, pressure requirements, temperature, viscosity, and operating conditions.
In this article, we will study different types of pumps used in piping engineering, their working principles, applications, advantages, disadvantages, and important interview questions with answers.
What is a Pump?
A pump is a mechanical device used to transfer liquids from one place to another by increasing the pressure and flow of the fluid. Pumps convert mechanical energy into hydraulic energy.
The main purpose of a pump is:
- Move fluid through pipelines
- Increase fluid pressure
- Maintain continuous process flow
- Transfer liquids between tanks or equipment
- Circulate cooling or heating fluids
Classification of Pumps
Pumps are mainly classified into two major categories:
- Dynamic Pumps
- Positive Displacement Pumps
Each category contains several types of pumps used for different industrial applications.
1. Centrifugal Pumps
Centrifugal pumps are the most commonly used pumps in industrial piping systems. These pumps convert rotational kinetic energy into hydrodynamic energy using an impeller.
A centrifugal pump mainly consists of:
- Impeller
- Casing
- Shaft
- Bearings
- Mechanical Seal
- Suction Nozzle
- Discharge Nozzle
Working Principle of Centrifugal Pump
The impeller rotates inside the casing with the help of a motor. As the impeller rotates, centrifugal force pushes the fluid outward from the center toward the casing. This movement creates low pressure at the suction side, allowing more liquid to enter the pump continuously.
The fluid gains velocity and pressure energy before leaving through the discharge nozzle.
Applications of Centrifugal Pumps
- Water supply systems
- Cooling water circulation
- Chemical plants
- Oil refineries
- Firefighting systems
- HVAC systems
- Wastewater treatment plants
Advantages of Centrifugal Pumps
- Simple design
- Low maintenance
- Continuous flow
- Compact size
- High efficiency
- Suitable for large flow rates
Disadvantages of Centrifugal Pumps
- Not suitable for very high viscosity fluids
- Priming may be required
- Flow varies with pressure
2. Oil Derrick Pumps (Beam Pumps)
Oil Derrick Pumps are commonly called Beam Pumps or Pumping Jacks. These pumps are widely used in oil fields for crude oil extraction.
The pump works using a crank and beam mechanism. The rotating motor moves the beam up and down, which drives a piston inside the well. This reciprocating movement lifts oil from underground reservoirs to the surface.
Applications
- Oil drilling operations
- Crude oil extraction
- Petroleum production fields
Advantages
- Reliable operation
- Suitable for deep wells
- Efficient for low production wells
Disadvantages
- Large installation area required
- High maintenance
- Mechanical wear due to continuous movement
3. Positive Displacement Pumps
Positive displacement pumps transfer a fixed quantity of fluid during each operating cycle. Unlike centrifugal pumps, these pumps provide almost constant flow regardless of discharge pressure.
These pumps are highly efficient for handling viscous fluids, chemicals, oils, slurries, and high-pressure applications.
Positive displacement pumps are divided into:
- Rotary Positive Displacement Pumps
- Reciprocating Positive Displacement Pumps
Rotary Positive Displacement Pumps
1. External Gear Pumps
External gear pumps contain two meshing gears rotating inside a casing. Fluid enters through the suction side and gets trapped between gear teeth and casing before moving toward the discharge side.
Applications
- Lubrication systems
- Fuel transfer
- Hydraulic systems
- Chemical dosing
- Resins and solvents
Advantages
- Simple design
- High pressure capability
- Accurate flow control
- Compact size
Disadvantages
- Not suitable for abrasive fluids
- Limited handling of highly viscous materials
2. Internal Gear Pumps
Internal gear pumps consist of an inner gear and an outer gear rotating together. These pumps are highly suitable for handling viscous fluids.
Applications
- Bitumen transfer
- Heavy oils
- Chocolate and syrup industries
- Polymer processing
Advantages
- Handles high viscosity fluids
- Smooth flow
- Low noise operation
3. Lobe Pumps
Lobe pumps use rotating lobes instead of gears. The lobes do not touch each other, making these pumps suitable for sanitary and sensitive applications.
Applications
- Food industry
- Beverage plants
- Pharmaceutical industry
- Paper industry
- Slurry handling
Advantages
- Gentle fluid handling
- Can handle solids
- Easy cleaning and maintenance
4. Vane Pumps
Vane pumps contain rotating vanes mounted on a rotor. As the rotor turns, the vanes slide in and out, creating suction and discharge.
Applications
- Automobile hydraulic systems
- Power steering systems
- Air conditioning systems
- Hydraulic power units
Advantages
- Compact design
- Low noise
- Good efficiency
Reciprocating Positive Displacement Pumps
1. Piston Pumps
Piston pumps use a piston moving back and forth inside a cylinder. This reciprocating action creates suction and discharge.
Applications
- Hydraulic systems
- Pressure washing
- Oil transfer
- High-pressure applications
Advantages
- Very high pressure capability
- Accurate flow rate
- Efficient operation
Disadvantages
- High maintenance
- Pulsating flow
- Complex design
2. Plunger Pumps
Plunger pumps are similar to piston pumps but use a plunger instead of a piston. They can generate extremely high pressures.
Applications
- Boiler feed systems
- Reverse osmosis plants
- Chemical injection
- Industrial cleaning systems
Advantages
- High suction capability
- Suitable for high pressure
- Durable design
3. Diaphragm Pumps
Diaphragm pumps use a flexible diaphragm for pumping action. These pumps are excellent for handling corrosive and hazardous fluids.
Applications
- Chemical industries
- Pharmaceutical plants
- Slurry handling
- Corrosive chemical transfer
- Food processing
Advantages
- Leak-free operation
- Handles corrosive fluids
- Can run dry
- Good suction capability
Disadvantages
- Lower flow rate
- Moderate pressure range
Importance of Pumps in Piping Engineering
In piping engineering, pumps are considered heart of the process system because they maintain continuous fluid circulation. Proper pump selection directly affects plant efficiency, operating cost, safety, and reliability.
Piping engineers must understand:
- Pump types
- Pump curves
- NPSH requirements
- Suction and discharge piping
- Pressure drop calculations
- Cavitation prevention
- Pump alignment
- Material compatibility
Pump Selection Criteria
The following factors are considered during pump selection:
- Fluid type
- Flow rate requirement
- Pressure requirement
- Temperature
- Viscosity
- Presence of solids
- Corrosive nature
- Operating environment
- Maintenance requirements
Common Pump Problems
1. Cavitation
Cavitation occurs when vapor bubbles form and collapse inside the pump due to low pressure.
Effects of Cavitation
- Noise and vibration
- Impeller damage
- Reduced efficiency
- Mechanical failure
2. Seal Leakage
Mechanical seal failure may cause fluid leakage due to wear, improper alignment, or dry running.
3. Overheating
Insufficient lubrication or blocked flow can cause pump overheating.
Interview Questions and Answers on Pumps
Q1. What is the main function of a pump?
Answer: The main function of a pump is to transfer fluid from one place to another by increasing pressure and flow.
Q2. What are the two main classifications of pumps?
Answer: Pumps are classified into Dynamic Pumps and Positive Displacement Pumps.
Q3. What is a centrifugal pump?
Answer: A centrifugal pump converts rotational energy into hydraulic energy using a rotating impeller.
Q4. What is cavitation?
Answer: Cavitation is the formation and collapse of vapor bubbles inside a pump due to low suction pressure.
Q5. Which pump is best for high viscosity fluids?
Answer: Positive displacement pumps such as gear pumps are suitable for high viscosity fluids.
Q6. What is the difference between centrifugal and positive displacement pumps?
Answer: Centrifugal pumps provide continuous flow with variable pressure, while positive displacement pumps provide fixed flow regardless of pressure.
Q7. What are the applications of diaphragm pumps?
Answer: Diaphragm pumps are used for corrosive chemicals, slurry handling, pharmaceuticals, and food processing.
Q8. Why are lobe pumps used in food industries?
Answer: Lobe pumps provide gentle handling and maintain hygienic conditions without damaging the product.
Q9. What is NPSH in pumps?
Answer: NPSH stands for Net Positive Suction Head. It is the minimum pressure required at the suction side to avoid cavitation.
Q10. Which pump is commonly used in oil fields?
Answer: Beam pumps or pumping jack systems are commonly used in oil fields.
Conclusion
Pumps are extremely important equipment in piping engineering and industrial process systems. Different types of pumps are selected based on process requirements, fluid characteristics, and operating conditions.
Centrifugal pumps are widely used for general fluid transfer, while positive displacement pumps are suitable for high-pressure and viscous fluid applications. Understanding pump types, working principles, applications, and troubleshooting methods is essential for every piping engineer and mechanical engineer.
A strong knowledge of pumps helps engineers design safe, reliable, and efficient piping systems for industrial applications.