Plant Operator Selection System Test Plant Operator Selection System Mechanical Concepts 2 — Questions and Answers
Question 1: A pump is operating at 1,800 RPM and moves 50 gallons per minute. If the speed is increased to 3,600 RPM, approximately how much fluid will the pump move per minute?
- 50 gallons
- 75 gallons
- 100 gallons (Correct answer)
- 200 gallons
Correct answer: 100 gallons
Pump flow rate is directly proportional to shaft speed, so doubling RPM doubles the flow rate from 50 to 100 GPM.
Question 2: Which type of valve is best suited for completely stopping or fully opening flow in a pipeline, but is NOT recommended for throttling?
- Globe valve
- Gate valve (Correct answer)
- Needle valve
- Ball valve
Correct answer: Gate valve
Gate valves are designed for fully open or fully closed service and can be damaged if used to throttle flow.
Question 3: A wrench with a 12-inch handle requires 30 lb of force to turn a bolt. What force would be needed if the handle were extended to 18 inches?
- 45 lb
- 30 lb
- 20 lb (Correct answer)
- 15 lb
Correct answer: 20 lb
Torque must remain constant, so force × distance = 30 × 12 = 360 lb-in; 360 ÷ 18 = 20 lb.
Question 4: In a hydraulic system, a small piston with an area of 2 sq in supports a large piston with an area of 20 sq in. If 10 lb is applied to the small piston, what load can the large piston support?
- 10 lb
- 20 lb
- 100 lb (Correct answer)
- 200 lb
Correct answer: 100 lb
Pascal's law states pressure is equal throughout, so 10 lb ÷ 2 sq in = 5 psi × 20 sq in = 100 lb.
Question 5: Which of the following best describes the purpose of a pressure relief valve in a piping system?
- To regulate normal operating flow
- To prevent system pressure from exceeding a safe limit (Correct answer)
- To measure differential pressure across a pump
- To control the direction of fluid flow
Correct answer: To prevent system pressure from exceeding a safe limit
A pressure relief valve automatically opens to vent excess pressure and protect equipment when system pressure exceeds a set point.
Question 6: A belt drives two pulleys. The drive pulley has a diameter of 6 inches and spins at 900 RPM. What is the speed of the driven pulley if its diameter is 3 inches?
- 450 RPM
- 900 RPM
- 1,800 RPM (Correct answer)
- 2,700 RPM
Correct answer: 1,800 RPM
Speed ratio is inversely proportional to diameter ratio: 900 × (6 ÷ 3) = 1,800 RPM.
Question 7: When a fluid flows from a wider pipe section into a narrower pipe section at constant volumetric flow, what happens to the fluid velocity?
- Velocity decreases
- Velocity stays the same
- Velocity increases (Correct answer)
- Velocity becomes zero
Correct answer: Velocity increases
By the continuity equation, the same volume must pass through a smaller area, so velocity must increase.
Plant Operator Selection System Test Plant Operator Selection System Mechanical Concepts 2
A pump is operating at 1,800 RPM and moves 50 gallons per minute.
If the speed is increased to 3,600 RPM, approximately how much fluid will the pump move per minute?