Top 50 Pump Piping Interview Questions and Answers – Part 2B (Pump Layout, Supports & Maintenance)
Pump Piping Interview Q&A (Part - 2B) Pump Layout, Supports & Maintenance
(Continuation of Part 2A)
Source: KnowPipingField.com
II JAY SHRI KRISHNA II
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Pump Piping Interview Q&A (Part 2B): – Pump Layout, Supports & Maintenance |
In the previous section, we discussed the importance of pump discharge piping, Net Positive Suction Head (NPSH), and the basic principles of cavitation. In this section, we will continue with practical interview questions covering cavitation prevention, Positive Displacement (PD) pumps, relief valves, pulsation dampeners, piping supports, equipment layout and maintenance practices.
These are among the most frequently asked topics during piping engineering, mechanical engineering, commissioning and maintenance interviews.
Question 21. How can pump cavitation be prevented?
Answer
Preventing cavitation begins with maintaining sufficient pressure at the pump suction so that the liquid remains in its liquid state while entering the impeller.
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Pump Cavitation Prevention - Engineering Best Practices |
Several engineering practices help reduce the possibility of cavitation:
- Ensure that NPSH Available (NPSHA) is always greater than NPSH Required (NPSHR).
- Keep suction piping as short and straight as practical.
- Increase the suction pipe diameter where required to reduce friction losses.
- Use the correct eccentric reducer orientation to prevent air pockets.
- Avoid operating the pump significantly away from its Best Efficiency Point (BEP).
- Maintain adequate liquid level in the suction vessel.
- Reduce liquid temperature whenever practical because hotter liquids have higher vapor pressures.
Applying these practices greatly improves pump reliability and service life.
Practical Example
A cooling water pump repeatedly experienced cavitation during summer months. Investigation showed that higher water temperatures increased vapor pressure, reducing the available NPSH. After increasing the suction pipe diameter and lowering friction losses, the cavitation problem was eliminated.
Question 22. Why is pump suction pressure so important?
Answer
The pump cannot create liquid.
Instead, it relies on the available suction pressure to continuously supply liquid to the impeller.
If suction pressure becomes too low:
- Flow becomes unstable.
- Cavitation may develop.
- Pump capacity decreases.
- Vibration increases.
- Mechanical seals may fail.
- Bearings experience higher loading.
Maintaining adequate suction pressure is therefore essential for reliable pump operation.
Question 23. What is the Best Efficiency Point (BEP) of a pump?
Answer
The Best Efficiency Point (BEP) is the operating condition at which a pump achieves its highest hydraulic efficiency.
At the BEP:
- Hydraulic losses are minimized.
- Internal recirculation is reduced.
- Shaft deflection remains low.
- Bearing loads are minimized.
- Mechanical seal life is improved.
- Energy consumption is optimized.
Whenever possible, pumps should operate close to their BEP for maximum reliability.
Question 24. Why should pumps not operate far from their Best Efficiency Point?
Answer
Operating far away from the BEP creates unstable hydraulic conditions inside the pump.
Possible consequences include:
- Increased vibration
- Internal recirculation
- Higher shaft loading
- Cavitation
- Noise
- Seal failures
- Reduced bearing life
Selecting the correct pump size during the design stage helps keep normal operation near the BEP.
Positive Displacement Pumps
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Centrifugal Pump Piping Layout and Maintenance Guidelines |
Question 25. What is the major piping requirement for a Positive Displacement (PD) pump?
Answer
Every Positive Displacement (PD) pump must have a pressure relief device installed on its discharge line.
Unlike centrifugal pumps, PD pumps continue delivering nearly the same volume of liquid regardless of discharge pressure.
If the discharge valve is accidentally closed while the pump continues operating, pressure rises rapidly and may exceed the design pressure of the piping system.
To prevent equipment damage, a properly sized relief valve or bypass valve is mandatory.
Practical Example
A gear pump transfers lubricating oil to process equipment.
If the downstream isolation valve is accidentally closed while the pump remains in operation, pressure will continue increasing.
The installed relief valve automatically opens and safely returns excess liquid to the suction side, preventing damage to the pump and piping.
Question 26. Why are relief valves mandatory for Positive Displacement pumps?
Answer
Positive Displacement pumps move a fixed volume of liquid during each operating cycle.
Unlike centrifugal pumps, they cannot simply reduce flow when discharge pressure increases.
Without a relief valve:
- Pipe rupture may occur.
- Pump casing damage may result.
- Mechanical seals may fail.
- Equipment safety is compromised.
For this reason, industry standards and good engineering practice require discharge pressure protection for Positive Displacement pumps.
Question 27. What is the purpose of a pulsation dampener?
Answer
Reciprocating pumps produce pulsating flow instead of continuous flow.
- Excessive vibration
- Pressure spikes
- Fatigue failures
- Instrument inaccuracies
- Increased pipe support loading
A pulsation dampener absorbs these pressure fluctuations, producing a smoother and more stable flow.
Question 28. Where are pulsation dampeners installed?
Answer
Pulsation dampeners are normally installed close to the pump.
Depending on the application, they may be located on:
Their exact location depends on the pump manufacturer, process requirements and pulsation analysis.
Proper placement significantly reduces vibration throughout the piping network.
Practical Example
A chemical dosing system using a diaphragm pump experienced severe pressure fluctuations that repeatedly damaged pressure transmitters.
Installing a pulsation dampener immediately downstream of the pump stabilized the pressure and eliminated instrument failures.
Pump Layout and Maintenance
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Essential protection requirements for Positive Displacement pumps to prevent overpressure and manage flow pulsations. |
Question 29. What is the recommended minimum spacing between adjacent pumps?
Answer
Pump layout should provide sufficient space for operation, maintenance and equipment removal.
A commonly accepted minimum clearance between adjacent pumps is approximately 1200 mm (4 feet).
However, the final spacing depends on:
Adequate spacing improves accessibility and enhances plant safety.
Question 30. Where should isolation valves be installed around a pump?
Answer
Isolation valves are generally installed on both the suction and discharge piping.
These valves allow maintenance personnel to safely isolate the pump without shutting down the entire process system.
Isolation valves simplify activities such as:
- Mechanical seal replacement
- Bearing inspection
- Pump removal
- Routine maintenance
- Equipment replacement
Whenever maintenance is required, both valves are closed before draining the pump.
Practical Example
A refinery process pump requires mechanical seal replacement during a scheduled shutdown.
Because isolation valves are installed on both the suction and discharge lines, maintenance personnel isolate the pump quickly without interrupting the remainder of the process unit.
Engineering Tips
Experienced piping engineers generally follow several practical guidelines to improve pump reliability:
- Keep suction piping short and direct.
- Avoid unnecessary fittings near the suction nozzle.
- Support piping independently from the pump.
- Verify nozzle loads during piping stress analysis.
- Install check valves in the correct orientation.
- Follow the pump vendor's installation recommendations.
- Maintain proper pipe alignment during installation.
- Confirm pump rotation before commissioning.
- Perform alignment checks after hydrotesting and piping installation.
- Monitor vibration regularly during plant operation.
These practices significantly reduce long-term maintenance costs.
Common Interview Tip
Many interviewers ask practical questions rather than theoretical ones.
Instead of memorizing definitions, understand why engineering practices are followed.
For example:
Instead of simply saying,
"An eccentric reducer is used on suction piping."
A stronger interview answer would be:
"Placing an eccentric reducer flat side up (FSU) in horizontal suction piping prevents trapped air accumulation. Eliminating trapped air reduces the risk of cavitation and helps provide smooth flow into the pump impeller."
Providing the engineering reason behind the practice demonstrates practical understanding.
Part 2A and 2B Summary
In Part 2A and Part 2B, we covered several critical pump piping concepts, including:
- Pump discharge piping arrangement
- Isolation valves
- Net Positive Suction Head (NPSH)
- Cavitation prevention
- Best Efficiency Point (BEP)
- Relief valves
- Pulsation dampeners
- Pump layout and spacing
- Pump maintenance considerations
Understanding these principles helps engineers design safer piping systems, improve pump performance, enhance equipment reliability and troubleshoot common operating problems.
Continue to Part 3A and Part 3B
In Part 3A and Part 3B, we will complete this interview guide with the remaining 20 practical interview questions, covering:
- Foundation and grouting
- Pump alignment
- Flexible connectors
- Thermal expansion
- Commissioning checks
- Frequently Asked Questions
Together, Parts 1, 2, and 3 provide a complete practical reference for pump piping engineering and interview preparation.
Suggested Further Reading
Top 50 Pump Piping Interview Questions and Answers – Part 2A (Discharge Piping & Cavitation)
Top 50 Pump Piping Interview Questions and Answers – Part 1 (Complete Practical Guide for Engineers)
Top 50 Piping Engineering Interview Questions and Answers (Complete Practical Guide for Engineers)
Corrosion Under Insulation (CUI): Design and Inspection Strategies
Advanced Offshore Piping Considerations for FPSO Vessels
Progressive Cavity Pump: A Versatile Solution for Challenging Fluids
Allowable Nozzle Loads – API 610 & WRC 107/297 Guide
All About Pump: Efficiency, Selection, Maintenance, Safety, Placement and Future Trends
Advanced Pump-Piping Interactions and Troubleshooting
Effect of Piperack Piping: Enhance Overall Plant Performance
Common Support Details Generally Used in Piping
Complete Guide: Control Valve Installation and Maintenance Best Practices
Multistage Centrifugal Pump P&ID Symbol Explained (Engineering Guide)
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