Free Millwright Hydraulic Systems and Schematics Questions and Answers — Questions and Answers
Question 1: In a hydraulic schematic, what is the function of a symbol showing a rectangle with a spring line and an arrow drawn diagonally through it?
- A fixed displacement pump
- A variable pressure relief valve (Correct answer)
- A check valve
- A flow control valve
Correct answer: A variable pressure relief valve
This symbol represents a variable pressure relief valve. The rectangle is the valve body, the arrow indicates it's adjustable (variable), and the spring shows it is spring-loaded to open at a set pressure, protecting the system from over-pressurization.
Question 2: What is the primary function of an accumulator in a hydraulic system?
- To filter contaminants from the fluid
- To cool the hydraulic fluid
- To store hydraulic energy and absorb shocks (Correct answer)
- To convert hydraulic energy to mechanical motion
Correct answer: To store hydraulic energy and absorb shocks
An accumulator stores hydraulic fluid under pressure, typically using a compressed gas bladder. This stored energy can be used to absorb shocks, supplement pump flow for short periods, or maintain system pressure if the pump is shut down.
Question 3: A loud whining or screeching noise from a hydraulic pump is often a symptom of what condition?
- Excessive system pressure
- Fluid viscosity being too high
- Normal pump operation
- Pump cavitation (Correct answer)
Correct answer: Pump cavitation
Cavitation is the formation and collapse of vapor bubbles in the fluid, typically caused by a starved inlet (clogged suction strainer, low fluid level). This condition is very destructive to the pump and produces a characteristic high-pitched whining sound.
Question 4: According to Pascal's Law, if a 100 lb force is applied to a 1-square-inch piston, what is the maximum weight that can be lifted by a 10-square-inch piston in the same system?
- 100 lbs
- 1,000 lbs (Correct answer)
- 10 lbs
- 10,000 lbs
Correct answer: 1,000 lbs
Pascal's Law states that pressure is transmitted equally throughout a confined fluid (P = F/A). The pressure is 100 lbs / 1 sq. in = 100 PSI. This pressure acts on the larger piston, so the lifting force is 100 PSI * 10 sq. in = 1000 lbs.
Question 5: What does the designation '4/3' for a directional control valve indicate?
- 4 positions and 3 ports
- A maximum pressure of 400 PSI and 3 gallons per minute flow
- 4 ports and 3 positions (Correct answer)
- A 4-inch port size with 3 internal spools
Correct answer: 4 ports and 3 positions
The first number in a directional control valve designation indicates the number of ports (ways) for fluid to flow. The second number indicates the number of distinct positions the valve spool can be in to direct that flow.
Question 6: Besides lubrication, what is the most critical function of hydraulic fluid in a system?
- To transmit power (Correct answer)
- To prevent corrosion
- To clean the system components
- To provide electrical insulation
Correct answer: To transmit power
The fundamental purpose of the fluid in a hydraulic system is to transmit power. It does this by moving under pressure from the pump to an actuator, converting the fluid power into mechanical force or torque.
Free Millwright Hydraulic Systems and Schematics Questions and Answers
In a hydraulic schematic, what is the function of a symbol showing a rectangle with a spring line and an arrow drawn diagonally through it?