CVA Shaft Alignment & Machinery Installation 1 — Questions and Answers
Question 1: Which type of shaft misalignment produces high vibration predominantly in the axial direction at 1× and 2× running speed?
- Parallel misalignment
- Angular misalignment (Correct answer)
- Soft foot
- Resonance
Correct answer: Angular misalignment
Angular misalignment causes the shaft ends to meet at an angle, generating strong axial forces that produce elevated 1× and 2× vibration in the axial direction.
Question 2: What is the most common vibration frequency signature associated with parallel (offset) misalignment?
- Dominant 1× with elevated 3× harmonics
- Dominant 2× radial vibration (Correct answer)
- Sub-synchronous vibration below 0.5×
- High-frequency random noise
Correct answer: Dominant 2× radial vibration
Parallel misalignment typically produces a dominant 2× radial vibration component because the coupling must correct twice per revolution to accommodate the offset.
Question 3: During a soft foot check, what is the maximum acceptable dial indicator reading before corrections must be made?
- 0.001 inch (0.025 mm)
- 0.002 inch (0.05 mm) (Correct answer)
- 0.005 inch (0.127 mm)
- 0.010 inch (0.254 mm)
Correct answer: 0.002 inch (0.05 mm)
The industry-accepted threshold for soft foot is 0.002 inch (0.05 mm); readings above this value indicate the machine frame is distorted and must be corrected before alignment proceeds.
Question 4: What is 'soft foot' in the context of machinery installation?
- A machine foot made of rubber to absorb vibration
- A condition where one or more machine feet do not make full contact with the baseplate when hold-down bolts are tightened (Correct answer)
- The flexing of a shaft coupling under load
- Looseness in the foundation anchor bolts
Correct answer: A condition where one or more machine feet do not make full contact with the baseplate when hold-down bolts are tightened
Soft foot occurs when tightening hold-down bolts causes the machine frame to distort because one or more feet do not sit flush on the baseplate, inducing internal stresses and misalignment.
Question 5: Which alignment method mounts two dial indicators on the coupling hub of each machine and measures runout as the shafts are rotated together?
- Rim and face method
- Reverse indicator method (Correct answer)
- Laser tracker method
- Straightedge and feeler gauge method
Correct answer: Reverse indicator method
The reverse indicator method places a dial indicator on each shaft pointing back toward the opposite machine, allowing both parallel and angular misalignment to be calculated simultaneously with high accuracy.
Question 6: Thermal growth must be accounted for during precision shaft alignment because:
- It changes the coupling stiffness during operation
- Machinery expands when it reaches operating temperature, shifting the shaft centerlines from their cold-aligned positions (Correct answer)
- Thermal growth only affects the baseplate, not the machine shafts
- It reduces vibration amplitude at running speed
Correct answer: Machinery expands when it reaches operating temperature, shifting the shaft centerlines from their cold-aligned positions
As machines heat up to operating temperature, differential thermal expansion between the driver and driven machine changes shaft centerline positions, so cold alignment must include a thermal offset to achieve true alignment at running conditions.
Question 7: What is the primary purpose of shims during machinery installation?
- To absorb vibration between the machine and baseplate
- To adjust the vertical position of machine feet to achieve correct shaft alignment (Correct answer)
- To prevent corrosion between the machine foot and baseplate
- To distribute the weight of the machine evenly across the baseplate
Correct answer: To adjust the vertical position of machine feet to achieve correct shaft alignment
Shims are precision metal spacers placed under machine feet to make fine vertical elevation adjustments that bring the shaft centerlines into proper alignment.
CVA Shaft Alignment & Machinery Installation 1
Which type of shaft misalignment produces high vibration predominantly in the axial direction at 1× and 2× running speed?