CPT Instrumentation & Equipment Maintenance 3 — Questions and Answers
Question 1: A centrifugal pump experiences cavitation. Which corrective action is most appropriate?
- Increase discharge pressure
- Reduce suction head or increase NPSH available (Correct answer)
- Decrease impeller speed
- Close the discharge valve partially
Correct answer: Reduce suction head or increase NPSH available
Cavitation occurs when NPSH available falls below NPSH required, so increasing suction pressure or reducing inlet losses eliminates vapor bubble formation.
Question 2: What instrument is used to verify that a rotating shaft is operating within acceptable vibration limits?
- Tachometer
- Manometer
- Accelerometer or vibration sensor (Correct answer)
- Pyrometer
Correct answer: Accelerometer or vibration sensor
An accelerometer or vibration sensor measures mechanical vibration amplitude and frequency to detect imbalance, misalignment, or bearing wear in rotating equipment.
Question 3: Which type of heat exchanger maintenance is performed to remove scale and fouling deposits from tube surfaces?
- Hydrostatic testing
- Tube plugging
- Chemical or mechanical cleaning (Correct answer)
- Retubing
Correct answer: Chemical or mechanical cleaning
Chemical cleaning (acid or solvent) or mechanical cleaning (rodding or high-pressure water jetting) removes fouling deposits that reduce heat transfer efficiency.
Question 4: What does the abbreviation 'P&ID' stand for in process plant documentation?
- Process and Instrumentation Diagram
- Piping and Instrumentation Diagram (Correct answer)
- Pressure and Instrument Data
- Plant and Inspection Document
Correct answer: Piping and Instrumentation Diagram
P&ID stands for Piping and Instrumentation Diagram, which shows the interconnection of process equipment, piping, and instrumentation.
Question 5: A safety relief valve (SRV) is leaking continuously at normal operating pressure. What is the most likely cause?
- Operating pressure too close to set pressure (Correct answer)
- Valve is incorrectly installed upside down
- Valve inlet is too large
- Spring tension is too high
Correct answer: Operating pressure too close to set pressure
When operating pressure is within 10% of the set pressure, the valve disk may 'simmer' or leak due to insufficient margin between operating and set pressure.
Question 6: Which sensor type measures level based on the weight of the liquid column above it?
- Ultrasonic level sensor
- Float-based level switch
- Hydrostatic pressure transmitter (Correct answer)
- Capacitance probe
Correct answer: Hydrostatic pressure transmitter
A hydrostatic pressure transmitter measures the pressure exerted by the liquid head above it, which is proportional to the liquid level and density.
Question 7: During a loop check on a new installation, what is the technician verifying?
- That the process fluid meets quality specifications
- That the instrument signal correctly reaches the control room and the associated device responds (Correct answer)
- That all pipe flanges are properly torqued
- That the equipment insulation is adequate
Correct answer: That the instrument signal correctly reaches the control room and the associated device responds
A loop check verifies end-to-end instrument signal integrity — from field transmitter or device through wiring to the control system — and confirms correct controller response.
CPT Instrumentation & Equipment Maintenance 3
A centrifugal pump experiences cavitation.
Which corrective action is most appropriate?