SACA Pneumatic and Hydraulic Systems 4 — Questions and Answers
Question 1: In a hydraulic system, what is the primary purpose of a pressure relief valve?
- To increase system pressure beyond rated capacity
- To protect the system from overpressure by diverting excess fluid to tank (Correct answer)
- To maintain constant flow rate regardless of pressure
- To filter contaminants from hydraulic fluid
Correct answer: To protect the system from overpressure by diverting excess fluid to tank
A pressure relief valve protects hydraulic circuits by opening and diverting fluid back to the reservoir when system pressure exceeds a preset limit.
Question 2: Which type of hydraulic pump is most commonly used in industrial automation systems due to its variable displacement capability?
- Gear pump
- Vane pump
- Piston pump (Correct answer)
- Screw pump
Correct answer: Piston pump
Piston pumps are preferred in industrial automation because they offer variable displacement, high efficiency, and can operate at high pressures.
Question 3: A pneumatic system uses a 5/2 directional control valve. What do the numbers 5 and 2 represent?
- 5 bar pressure and 2 second response time
- 5 ports and 2 switching positions (Correct answer)
- 5 liters per minute and 2 actuators
- 5 connections and 2 pilot signals
Correct answer: 5 ports and 2 switching positions
In pneumatic valve nomenclature, the first number indicates the number of ports and the second indicates the number of switching positions.
Question 4: What is cavitation in a hydraulic pump, and what causes it?
- Excess oil temperature caused by high operating pressure
- Formation and collapse of vapor bubbles due to localized low pressure at the inlet (Correct answer)
- Contamination of fluid by metal particles from worn components
- Reverse flow caused by a faulty check valve
Correct answer: Formation and collapse of vapor bubbles due to localized low pressure at the inlet
Cavitation occurs when the pump inlet pressure drops below the fluid's vapor pressure, causing vapor bubbles that implode violently and damage pump components.
Question 5: In a pneumatic circuit, a flow control valve with a check valve bypass is used to control actuator speed. Which function does this configuration perform?
- Meter-in control — restricts flow entering the actuator
- Meter-out control — restricts exhaust flow leaving the actuator (Correct answer)
- Pressure compensation regardless of load
- Bidirectional speed control in both directions
Correct answer: Meter-out control — restricts exhaust flow leaving the actuator
A flow control valve with a bypass check valve provides meter-out control by restricting exhaust air while allowing free flow in the supply direction.
Question 6: What is the function of a hydraulic accumulator in an automation system?
- To filter particulates larger than 10 microns from hydraulic fluid
- To store pressurized fluid for supplementing pump flow during peak demand (Correct answer)
- To convert hydraulic pressure into electrical signals for PLC feedback
- To reduce fluid viscosity during cold startup conditions
Correct answer: To store pressurized fluid for supplementing pump flow during peak demand
Hydraulic accumulators store pressurized fluid energy and release it during peak demand cycles, reducing pump size requirements and smoothing pressure fluctuations.
Question 7: In pneumatic systems, what does the ISO symbol for an FRL unit represent?
- Flow Rate Limiter — restricts maximum airflow to safe levels
- Filter-Regulator-Lubricator — conditions compressed air for downstream use (Correct answer)
- Frequency Response Linearizer — compensates for valve hysteresis
- Fail-safe Return Latch — holds actuator position on power loss
Correct answer: Filter-Regulator-Lubricator — conditions compressed air for downstream use
An FRL (Filter-Regulator-Lubricator) unit conditions compressed air by removing contaminants, regulating pressure, and adding lubrication for pneumatic components.
SACA Pneumatic and Hydraulic Systems 4
In a hydraulic system, what is the primary purpose of a pressure relief valve?