CPM Mechanical Systems Installation & Repair 2 — Questions and Answers
Question 1: When performing a reverse dial indicator alignment, a reading of +0.020 in. at the bottom of the coupling hub (zeroed at top) indicates what offset at that plane?
- 0.020 in.
- 0.010 in. (Correct answer)
- 0.040 in.
- 0.005 in.
Correct answer: 0.010 in.
Rim readings show twice the actual offset, so a 0.020 in. TIR equals 0.010 in. of offset.
Question 2: A soft foot condition on a motor is best detected by which method?
- Checking motor amperage under load
- Measuring the shaft runout with the coupling removed
- Loosening one hold-down bolt at a time while indicating foot movement (Correct answer)
- Measuring vibration at the outboard bearing only
Correct answer: Loosening one hold-down bolt at a time while indicating foot movement
Loosening each bolt with an indicator on that foot reveals movement greater than about 0.002 in., which signals soft foot.
Question 3: What is the primary purpose of grouting a pump baseplate?
- Provide a rigid, uniform load transfer between the baseplate and foundation (Correct answer)
- Seal the baseplate against corrosion only
- Allow thermal growth of the pump casing
- Electrically insulate the motor from the ground
Correct answer: Provide a rigid, uniform load transfer between the baseplate and foundation
Grout fills voids to create full contact and rigid support, reducing vibration and distortion.
Question 4: When installing a bearing with an interference fit on a shaft using induction heating, what is the generally recommended maximum bearing temperature?
- 150°F (65°C)
- 500°F (260°C)
- 350°F (177°C)
- 250°F (120°C) (Correct answer)
Correct answer: 250°F (120°C)
Most manufacturers limit heating to about 250°F (120°C) to avoid altering the bearing steel's hardness.
Question 5: A centrifugal pump is making a crackling, gravel-like noise at the suction and showing reduced head. What is the most likely cause?
- Excessive discharge pressure
- Cavitation due to insufficient NPSH available (Correct answer)
- Misaligned discharge piping
- Overgreased motor bearings
Correct answer: Cavitation due to insufficient NPSH available
Cavitation occurs when NPSHa falls below NPSHr, forming and collapsing vapor bubbles that sound like gravel.
Question 6: On a V-belt drive, what is the proper method to check belt tension?
- Measure the force required to deflect the belt a set distance at the span midpoint (Correct answer)
- Twist the belt 180 degrees and release
- Measure the motor current at no load
- Check that the belt rides at the bottom of the sheave groove
Correct answer: Measure the force required to deflect the belt a set distance at the span midpoint
The force-deflection method, typically 1/64 in. per inch of span, gives the correct tension.
Question 7: What is the main reason for replacing all belts on a multi-belt V-drive at the same time rather than just the broken one?
- New belts are cheaper in sets
- Old belts become electrically conductive
- Mixed new and stretched belts share the load unevenly (Correct answer)
- It is required for warranty on the motor
Correct answer: Mixed new and stretched belts share the load unevenly
Old belts are stretched, so new belts carry most of the load and fail prematurely; matched sets prevent this.
