30 Questions
What is the power transmission medium in hydraulic systems?
Pressurized hydraulic fluid
What are electrohydraulic (EH) systems controlled by?
Electrical means
What are hydro-mechanical systems controlled by?
A combination of mechanical and hydraulic mechanisms
What is the main component for controlling the flow into the actuator in an EH system?
Main valve
What generates the command signal to the electronic control module (ECM) in electronically controlled hydraulic systems?
Sensors
What is the function of the electronic control module (ECM) in EH systems?
Controls the valves and pumps/motors
What is the function of proportional flow control valves in hydraulic systems?
Regulate fluid flow in terms of rate, direction, and pressure
What is the typical volumetric size of the reservoir compared to the flow rate of the pump in a hydraulic power supply unit?
3 to 5 times
What are the common power sources for hydraulic pump in industrial and mobile equipment applications?
Electric motors and internal combustion engines
Which type of design includes JIC style and overhead design for hydraulic power units?
Common hydraulic power unit designs
What must engineers understand about hydraulic components and their symbolic representations?
Physical construction and operating principles
What are the applications of hydraulic motion control systems?
Mobile equipment, industrial factory automation, aircraft and naval flight control systems, and military ground vehicles
What type of valves are used for applications requiring controlled flow to be turned ON or OFF?
Proportional and servo valves
What is the primary function of safety relief valves in hydraulic circuits?
To protect against excessive pressures at the pump and actuator sides
Which valves can achieve a finite number of desired speed or force control levels at a lower cost and with simpler design?
A few ON/OFF valves in parallel
What is a characteristic of ON/OFF valves in discrete speed or flow rate control applications?
Limited flow metering capabilities
What can be used in real-time as part of a closed loop control algorithm in hydraulic systems?
Measured quantities
What do EH control systems operate to track and can be used in hydraulic motion systems for safety-related additions?
Commanded output power level
What are the main components to be identified in a hydraulic circuit diagram?
Main power supply, actuators, flow control valves, safety valves, and power flow paths
What are the types of command signal sources in a hydraulic system?
Operator-generated, automatically generated, or remote by an electronic control module (ECM)
What are the steps involved in the design of an electro-hydraulic motion control system?
Specifications, system concept design, component sizing and selection, control algorithm design, modeling and simulation, and hardware testing
What can be used as measured variables in an electro-hydraulic (EH) system for control purposes?
Load position, speed, pressure, force, torque, spool displacement, flow rate, pump output pressure, pump displacement, and pump speed
What types of variables can be derived from the measured variables in an EH system and regulated?
Intermediate variables
What kind of logic should be identified and studied in hydro-mechanical built-in priority and over-ride type logic, as well as control logic software?
Hydro-mechanical built-in priority and over-ride type logic, as well as control logic software
What is the hydraulic analogy of an electrical system battery or capacitor?
The accumulator
Which component reduces the open loop natural frequency of the EH system?
Accumulators
What is the purpose of parallel bypass valves in hydraulic filters?
Safety measure in case of clogging
What type of control is used in the electrohydraulic circuit for the motion of a rotary hydraulic motor for a service truck?
Closed-loop speed control
In a simple hydraulic system utilizing lever motion for hydraulic power, what is the function of check valves in fluid movement?
To prevent backflow
What is the function of the fixed displacement gear type pump in a hydraulic system?
To circulate flow from the pump port to tank port
Study Notes
Hydraulic System Components and Concepts
- ON/OFF valves can operate in three different speed ranges by controlling both or either one of the valves, providing simple and low-cost motion control solutions for discrete speed or flow rate control applications.
- The accumulator, which is the hydraulic analogy of an electrical system battery or capacitor, serves as a pressurized fluid storage component and aids in transient response and shock absorption.
- Accumulators reduce the open loop natural frequency of the EH system and are available in weight loaded, spring loaded, and hydro-pneumatic types, with the latter utilizing dry nitrogen as the compressed gas.
- Accumulators are rated based on hydraulic fluid volume, maximum and minimum operating pressures, precharge pressure, and maximum shock pressure they can tolerate, with the compression ratio representing the ratio between maximum and minimum operating pressure.
- Filtration is crucial in removing solid particles from hydraulic fluid, with filters located at different points in the system and replaceable elements to remove particles above a certain size, such as 3-micron.
- Filters have parallel bypass valves as a safety measure in case of clogging due to excessive dirt accumulation, which can lead to unfiltered fluid causing component failure.
- Specifications for a filter include the minimum size of particles it can filter, maximum pressure it can withstand, and maximum flow rate it can support.
- A simple hydraulic system utilizing lever motion for hydraulic power is shown, illustrating the conservation of power and the function of check valves in fluid movement.
- Another simple hydraulic system with a fixed displacement gear type pump and a manually actuated open-center valve is depicted, with the valve circulating flow from the pump port to tank port in the neutral position.
- Components of a hydraulic circuit for the motion of a cylinder in an excavator, powered by an internal combustion engine and controlled by a manually operated directional valve, are illustrated.
- An electrohydraulic circuit for the motion of a rotary hydraulic motor for a service truck, with speed control through a directional flow control valve and operator input switch, is shown, featuring closed-loop speed control using a tachometer speed sensor as feedback.
- Hydraulic circuits play a crucial role in various applications, from simple lever-operated systems to complex electrohydraulic systems in heavy machinery and equipment.
Test your knowledge of hydraulic system components and concepts with this quiz. Explore ON/OFF valves, accumulators, filtration, and different types of hydraulic circuits, from simple lever-operated systems to complex electrohydraulic systems in heavy machinery and equipment.
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