compressor engineer Interview Questions and Answers

1. What are the different types of compressors?

   • Answer: Compressors are broadly classified into positive displacement compressors (reciprocating, rotary screw, rotary vane, scroll, lobe) and dynamic compressors (axial, centrifugal). Each type has its own advantages and disadvantages regarding capacity, pressure, efficiency, and application.

2. Explain the working principle of a reciprocating compressor.

   • Answer: A reciprocating compressor uses a piston moving back and forth in a cylinder to compress gas. During the intake stroke, the piston moves away from the cylinder head, drawing in gas. During the compression stroke, the piston moves towards the cylinder head, compressing the gas. Finally, the compressed gas is discharged through a valve.

3. What is the difference between centrifugal and axial compressors?

   • Answer: Centrifugal compressors use rotating impellers to increase the gas pressure by accelerating it radially outwards. Axial compressors use a series of rotating and stationary blades to increase gas pressure by gradually increasing its axial velocity and then converting it to pressure.

4. Explain the concept of polytropic compression.

   • Answer: Polytropic compression is a thermodynamic process where both heat transfer and work are involved. It's represented by the equation PVⁿ = constant, where 'n' is the polytropic index, varying between adiabatic (n=k) and isothermal (n=1) processes.

5. What is compressor surge? How can it be avoided?

   • Answer: Surge is a violent pressure fluctuation in a compressor that occurs when the flow rate is reduced below a critical value. It can damage the compressor. Surge can be avoided by proper compressor selection, using surge control systems (blow-off valves, variable inlet guide vanes), and maintaining optimal operating conditions.

6. What is compressor efficiency? Explain different types.

   • Answer: Compressor efficiency measures how effectively the compressor converts input power into compressed gas. Types include adiabatic efficiency (ideal adiabatic compression), isentropic efficiency (ideal isentropic compression), and volumetric efficiency (actual vs. theoretical volume).

7. What are the common causes of compressor vibration?

   • Answer: Vibration can be caused by unbalance in rotating parts, misalignment, bearing wear, resonance, fluid pulsation, and faulty foundations.

8. How do you troubleshoot a compressor that is overheating?

   • Answer: Overheating can result from insufficient lubrication, clogged air filters, faulty cooling systems, excessive load, or internal leakage. Troubleshooting involves checking lubrication, filter condition, cooling system functionality, load demands, and internal compressor seals.

9. Explain the role of intercoolers and aftercoolers in a multi-stage compressor.

   • Answer: Intercoolers cool the gas between stages to reduce the work required for subsequent compression stages and increase efficiency. Aftercoolers cool the final compressed gas to reduce its temperature and volume, improving downstream system performance.

10. What are the safety precautions to be taken while working with compressors?

    • Answer: Safety precautions include lockout/tagout procedures, personal protective equipment (PPE) usage, regular inspection and maintenance, proper ventilation, and awareness of high-pressure hazards.

11. What is the purpose of a pressure relief valve in a compressor system?

    • Answer: A pressure relief valve protects the compressor and system from overpressure by automatically releasing excess pressure if it exceeds a set limit.

12. Explain the concept of capacity control in compressors.

    • Answer: Capacity control allows adjusting the compressor's output to match the demand, preventing wasted energy and improving efficiency. Methods include inlet guide vanes, variable speed drives, and multiple compressor units.

13. What are the different types of compressor seals?

    • Answer: Common types include mechanical seals, labyrinth seals, and stuffing box seals. The choice depends on the application, pressure, temperature, and gas properties.

14. How do you perform a compressor performance test?

    • Answer: Performance tests involve measuring parameters like pressure, flow rate, power consumption, temperature, and efficiency at various operating points. These data are then compared to the manufacturer's specifications.

15. What is the role of lubrication in a compressor?

    • Answer: Lubrication reduces friction between moving parts, minimizing wear and tear, preventing overheating, and ensuring smooth operation. The type of lubricant depends on the compressor type and operating conditions.

16. What is the significance of compressor instrumentation?

    • Answer: Instrumentation provides real-time data on compressor performance, allowing for monitoring, troubleshooting, and preventative maintenance. It improves safety and efficiency.

17. Explain the importance of regular compressor maintenance.

    • Answer: Regular maintenance extends the lifespan of the compressor, improves efficiency, reduces downtime, enhances safety, and ensures reliable operation.

18. How does the design of a compressor differ for different gases?

    • Answer: The design considerations vary based on the gas's properties such as molecular weight, viscosity, and chemical reactivity. Materials selection, sealing systems, and lubrication requirements are adjusted accordingly.

19. What are the common problems encountered in screw compressors?

    • Answer: Common issues include oil contamination, bearing failure, timing gear problems, and rotor wear. Regular maintenance and monitoring are crucial.

Thank you for reading our blog post on 'compressor engineer Interview Questions and Answers'.We hope you found it informative and useful.Stay tuned for more insightful content!