Hydraulic Terminology & Formula Reference
The most comprehensive and professional guide to hydraulic engineering terminology, formulas, and concepts.
Understanding Hydraulic Engineering
Hydraulic engineering is a specialized field that deals with the mechanical properties of liquids. It involves the study of fluid behavior under various conditions and the application of these principles in the design and operation of hydraulic systems. This guide provides an in-depth look at the key terminologies, formulas, and concepts that form the foundation of hydraulics.
Comprehensive Glossary
Over 200+ essential hydraulic terms with detailed explanations and diagrams.
Formulas & Equations
Essential mathematical formulas for hydraulic calculations and system design.
Practical Applications
Real-world examples and applications of hydraulic systems in industry.
Basic Hydraulic Terminology
Table 1-1: Fundamental Concepts in Hydraulics
Hydraulics is a branch of science and engineering that focuses on the mechanical properties of liquids. The following terms form the foundation of hydraulic technology and hydraulics definition.
Fluid Transmission
A method of transferring energy, control, and distribution through the use of pressurized fluids. Fluid transmission systems can be hydraulic or pneumatic, depending on whether they use liquids or gases.
Hydraulic Technology
A discipline that applies the principles of fluid mechanics to engineer systems that use liquid pressure to generate, control, and transmit power. Hydraulic systems are known for their high power density and precise control capabilities.
Hydrostatic Technology
The study of fluids at rest and the pressure distribution within them. Hydrostatic principles are fundamental to understanding hydraulic systems, particularly in relation to Pascal's Law, which states that pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel.
Nominal Pressure
The designated pressure rating for a hydraulic component or system under normal operating conditions. This value is used for design and specification purposes and does not necessarily reflect actual operating pressures.
Working Pressure
The actual pressure at which a hydraulic system or component operates during normal functioning. Working pressure can vary depending on load conditions, system demand, and other operational factors.
Pressure Range
The interval between the minimum and maximum pressures within which a hydraulic system or component is designed to operate safely and efficiently. Operating outside this range can lead to performance issues or system failure.
Inlet Pressure
The pressure of the fluid at the entrance of a hydraulic component, such as a pump, valve, or actuator. Inlet pressure is a critical parameter that affects component performance and efficiency.
Outlet Pressure
The pressure of the fluid at the exit of a hydraulic component. Outlet pressure is determined by factors such as system resistance, load conditions, and the design characteristics of the component.
Hydraulic Basics
- Based on Pascal's Law
- Transmits power through incompressible fluids
- High power-to-weight ratio
- Precise control capabilities
- Widely used in industrial and mobile applications
Basic Hydraulic Formulas
Force Calculation:
F = P × A
Force = Pressure × Area
Pressure Calculation:
P = F / A
Pressure = Force / Area
Flow Rate:
Q = V / t
Flow Rate = Volume / Time
Power Calculation:
P = (P × Q) / 600
Power (kW) = (Pressure (bar) × Flow (L/min)) / 600
Hydraulic Valve Terminology
Table 1-2: Terms Related to Hydraulic Valves
Hydraulic valves are essential components in hydraulic systems, used to control the direction, pressure, and flow rate of hydraulic fluid. The following terms describe various types of valves and their operational characteristics in hydraulic systems.
Valve
A device used to regulate, direct, or control the flow of a fluid (liquid or gas) by opening, closing, or partially obstructing various passageways. In hydraulic systems, valves play a critical role in managing system pressure, directing fluid flow, and controlling actuator movement.
Integral Valve
A type of valve where multiple similar valve functions are combined into a single housing or body. Integral valves are commonly used in compact hydraulic systems where space is limited and efficiency is prioritized.
Cartridge Valve
A modular valve designed to be inserted into a cavity within a manifold or block. Cartridge valves are known for their high flow capacity, compact size, and ease of integration into hydraulic systems. They are widely used in industrial and mobile applications.
Pilot Valve
A small valve that controls a limited-flow control feed to a separate, larger valve. Pilot valves are used to reduce the amount of force or power required to operate a main valve, making them ideal for high-pressure applications or systems requiring precise control.
Directional Control Valve
A valve used to control the direction of fluid flow in a hydraulic system. Directional control valves determine the path that hydraulic fluid takes as it moves through the system, enabling actuators to extend, retract, or remain stationary as required.
Spool Valve
A type of directional control valve that uses a cylindrical spool inside a valve body to control fluid flow. The spool has lands and grooves that align with ports in the valve body to direct fluid flow. Spool valves are widely used due to their simplicity, reliability, and ability to handle high flow rates.
Poppet Valve
A valve that uses a disc (poppet) to seal against a seat, controlling the flow of fluid. Poppet valves are known for their tight sealing capabilities, fast response times, and ability to handle high pressures. They are commonly used in applications requiring precise control and minimal leakage.
Four-Way Valve
A directional control valve with four ports: an inlet (pressure port), an outlet (tank port), and two working ports that connect to an actuator. Four-way valves are commonly used to control double-acting cylinders, providing bidirectional flow control for both extension and retraction.
Three-Way Valve
A valve with three ports that can be used to direct fluid flow between different paths. Three-way valves are commonly used for applications such as diverting flow, mixing fluids, or controlling single-acting cylinders.
Two-Way Valve
The simplest type of valve, with two ports (an inlet and an outlet) that can be opened or closed to control fluid flow. Two-way valves are commonly used as on/off valves or as pressure relief valves in hydraulic systems.
Valve Symbol Chart
Two-Way Valve
On/Off Function
Three-Way Valve
Diverting Function
Four-Way Valve
Bidirectional Control
Valve Application Examples
- Industrial machinery: controlling actuators in presses, conveyors, and material handling equipment
- Mobile equipment: steering systems, lift mechanisms, and braking systems in trucks and construction machinery
- Automation: precise control of robotic arms and positioning systems
- Marine applications: steering gear, winches, and cargo handling systems
Hydraulic Pump Terminology
Table 1-3: Terms Related to Hydraulic Pumps
Hydraulic pumps are essential components in hydraulic systems, responsible for converting mechanical energy into hydraulic energy by creating flow and pressure. The following terms describe various types of pumps and their operational characteristics in hydraulic systems.
Hydraulic Pump
A mechanical device that converts mechanical energy into hydraulic energy by creating flow and pressure in a hydraulic system. Hydraulic pumps are the heart of any hydraulic system, providing the power necessary to move fluid through the system and operate actuators.
Piston Pump
A type of positive displacement pump that uses pistons reciprocating within cylinders to create flow. Piston pumps are known for their high efficiency, ability to generate high pressures, and precise control capabilities. They are commonly used in high-pressure applications such as industrial machinery and mobile equipment.
Fixed-Displacement Pump
A pump that delivers a constant volume of fluid per revolution or cycle, regardless of the pressure requirements of the system. Fixed-displacement pumps are simple, reliable, and cost-effective, making them suitable for applications with consistent flow requirements.
Variable-Displacement Pump
A pump that can adjust its displacement (the volume of fluid delivered per revolution) to match the system's demand for flow and pressure. Variable-displacement pumps are more energy-efficient than fixed-displacement pumps, as they only deliver the amount of fluid required by the system, reducing energy waste.
Gear Pump
A type of positive displacement pump that uses intermeshing gears to transfer fluid. Gear pumps are simple, compact, and reliable, making them suitable for a wide range of applications. They are commonly used in low- to medium-pressure systems where smooth, continuous flow is required.
Vane Pump
A type of positive displacement pump that uses vanes sliding in slots around a rotor to create flow. Vane pumps are known for their quiet operation, high efficiency, and ability to handle moderate pressures. They are commonly used in applications such as power steering systems and machine tools.
Axial Piston Pump
A type of piston pump where the pistons are arranged axially (parallel to the drive shaft). Axial piston pumps are known for their high efficiency, compact size, and ability to generate very high pressures. They are commonly used in high-performance applications such as aerospace, industrial machinery, and mobile equipment.
Radial Piston Pump
A type of piston pump where the pistons are arranged radially (perpendicular to the drive shaft). Radial piston pumps are known for their very high pressure capabilities, smooth operation, and durability. They are commonly used in applications requiring extremely high pressures, such as hydrostatic transmissions and high-pressure test equipment.
Hydraulic Servo Pump
A pump that uses a servo mechanism to control its output flow or pressure. Hydraulic servo pumps are capable of very precise control and are commonly used in applications requiring high accuracy and responsiveness, such as robotics, aerospace systems, and industrial automation.
Pump Efficiency Comparison
Pump Selection Criteria
- Pressure Requirements: Higher pressures typically require piston pumps
- Flow Rate: Gear and vane pumps are suitable for lower flow rates
- Efficiency: Piston pumps offer higher efficiency for high-power applications
- Control Requirements: Variable-displacement pumps for systems requiring flow adjustment
- Cost: Gear pumps are generally the most cost-effective option
Hydraulic Motor and Cylinder Terminology
Table 1-4: Terms Related to Hydraulic Motors and Cylinders
Hydraulic motors and cylinders are the actuators in hydraulic systems, responsible for converting hydraulic energy back into mechanical energy. The following terms describe various types of motors and cylinders and their operational characteristics in hydraulic systems.
Hydraulic Motor
A mechanical actuator that converts hydraulic pressure and flow into rotational mechanical energy. Hydraulic motors are used in a wide range of applications, including industrial machinery, mobile equipment, and aerospace systems, where they provide high torque and variable speed capabilities.
Cylinder
A mechanical actuator that converts hydraulic energy into linear motion and force. Hydraulic cylinders are used in a wide range of applications, including construction equipment, industrial machinery, and automotive systems, where they provide controlled linear movement and high force capabilities.
Piston Cylinder
A type of hydraulic cylinder that uses a piston inside a cylinder barrel to convert hydraulic pressure into linear motion. Piston cylinders are the most common type of hydraulic cylinder and are used in a wide variety of applications due to their simplicity, reliability, and high force capabilities.
Single-Acting Cylinder
A hydraulic cylinder that uses hydraulic pressure to move the piston in one direction only. The return stroke is typically accomplished by an external force, such as gravity, a spring, or another mechanical device. Single-acting cylinders are simple and cost-effective, making them suitable for applications where force is required in only one direction.
Double-Acting Cylinder
A hydraulic cylinder that uses hydraulic pressure to move the piston in both directions. Double-acting cylinders are more versatile than single-acting cylinders and are used in applications where force is required in both directions, such as lifting, pushing, and pulling operations.
Single-Rod Cylinder
A hydraulic cylinder with a piston rod extending from one end of the piston only. Single-rod cylinders are the most common type of hydraulic cylinder and are used in applications where the force and stroke requirements are the same in both directions. However, due to the different effective areas on each side of the piston, the force and speed capabilities will differ between the extend and retract strokes.
Double-Rod Cylinder
A hydraulic cylinder with piston rods extending from both ends of the piston. Double-rod cylinders provide equal force and speed capabilities in both directions, making them suitable for applications requiring precise control and symmetry in both directions of movement.
Differential Cylinder
A double-acting cylinder where the piston rod area is significant enough to affect the cylinder's performance. In a differential cylinder, the effective area on the rod side of the piston is smaller than the area on the cap side, resulting in different force and speed characteristics for the extend and retract strokes. Differential cylinders are commonly used in applications where rapid extension and slower, more powerful retraction are required.
Telescopic Cylinder
A hydraulic cylinder with multiple stages or nested tubes that extend and retract in sequence. Telescopic cylinders provide a long stroke while maintaining a relatively compact retracted length, making them ideal for applications where space is limited, such as dump trucks, forklifts, and aerial work platforms.
Cylinder Force Calculation
The force exerted by a hydraulic cylinder can be calculated using the following formula:
F = P × A
Force = Pressure × Area
Where:
- F = Force (N)
- P = Pressure (Pa)
- A = Piston Area (m²)
Motor vs. Cylinder Applications
Hydraulic Motors
- Conveyor systems
- Winches and hoists
- Rotary actuators
- Milling and grinding machines
Hydraulic Cylinders
- Material handling equipment
- Presses and stamping machines
- Automotive lifts
- Excavator arms
Hydraulic Accessories and Other Terminology
Table 1-5: Terms Related to Hydraulic Accessories and Components
Hydraulic accessories and components play critical roles in supporting the operation of hydraulic systems. The following terms describe various accessories, fluids, and other components used in hydraulic systems.
Hydraulic Circuit
A system of interconnected hydraulic components, including pumps, valves, actuators, and accessories, designed to perform a specific function. Hydraulic circuits can be simple or complex, depending on the application requirements, and are the foundation of all hydraulic systems.
Hydraulic Fluid
The medium used to transmit power in a hydraulic system. Hydraulic fluids must have specific properties, such as viscosity, lubricity, and chemical stability, to ensure efficient and reliable operation of the system. Common types of hydraulic fluids include mineral oil, synthetic oil, and water-based fluids.
Reservoir
A container that stores hydraulic fluid in a hydraulic system. The reservoir also provides space for fluid expansion, allows air to separate from the fluid, and helps cool the fluid by dissipating heat. Reservoirs can be open (vented to the atmosphere) or closed (pressurized).
Filter
A device used to remove contaminants from hydraulic fluid. Filters are essential for maintaining the cleanliness of hydraulic fluid, which is critical for the proper functioning and longevity of hydraulic components. Filters can be located in various parts of a hydraulic system, including the reservoir, pump inlet, and return lines.
Accumulator
A device that stores hydraulic energy in the form of pressurized fluid. Accumulators are used in hydraulic systems to store energy for peak demand situations, absorb shock and vibration, maintain pressure during pump downtime, and compensate for leaks and thermal expansion. Common types of accumulators include bladder, piston, and diaphragm accumulators.
Seal
A device used to prevent the leakage of fluid in a hydraulic system. Seals are critical for maintaining system efficiency and preventing contamination. They can be static (used between stationary components) or dynamic (used between moving components). Common types of seals include O-rings, gaskets, and lip seals.
Hose
A flexible tube used to convey hydraulic fluid between components in a hydraulic system. Hoses are designed to withstand high pressures and are typically made of an inner tube, reinforcement layers, and an outer cover. They are used in applications where flexibility is required, such as mobile equipment and machinery with moving parts.
Fitting
A component used to connect hoses, pipes, and other components in a hydraulic system. Fittings must provide a leak-free connection and be compatible with the hydraulic fluid and system pressures. Common types of fittings include threaded fittings, flanges, and quick-connect couplings.
Pressure Relief Valve
A safety valve that limits the maximum pressure in a hydraulic system by diverting excess fluid back to the reservoir when the pressure exceeds a preset level. Pressure relief valves are critical for preventing overpressure situations, which can damage components and pose safety risks.
Flow Control Valve
A valve used to regulate the flow rate of hydraulic fluid in a system. Flow control valves are used to control the speed of actuators, such as cylinders and motors, by adjusting the volume of fluid flowing to them. They can be fixed or adjustable and are an essential component in many hydraulic circuits.
Hydraulic Fluid Types
Mineral Oil
Most common type, good lubrication properties
Synthetic Oil
High-performance, suitable for extreme temperatures
Water-Based Fluids
Fire-resistant, used in high-risk environments
Biodegradable Fluids
Environmentally friendly, used in sensitive areas
Common Hydraulic Accessories
Filters
Remove contaminants from hydraulic fluid
Accumulators
Store hydraulic energy and absorb shocks
Pressure Gauges
Measure system pressure
Coolers
Maintain optimal fluid temperature
Mastering Hydraulic Engineering
Understanding the terminology and concepts outlined in this guide is essential for anyone working with hydraulic systems. Whether you're an engineer designing hydraulic circuits, a technician troubleshooting a system, or a student learning about fluid power, these foundational terms and principles will serve as a valuable reference.
Key Takeaways
Hydraulic Fundamentals
Based on Pascal's Law, hydraulic systems use incompressible fluids to transmit power.
Components
Pumps, valves, actuators, and accessories work together to create efficient systems.
Fluid Management
Proper fluid selection, filtration, and maintenance are critical for system performance.
Applications
Hydraulics are used in industrial machinery, mobile equipment, aerospace, and more.