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1. Positive Displacement Pump: A pump that uses the movement or change of the enclosed volume of a housing and its internal moving parts to pressurize liquid from the intake to the discharge port.
2. Fixed Displacement Pump: A pump with a constant theoretical displacement per revolution.
3. Variable Displacement Pump: A pump with a variable displacement.
4. Gear Pump: A pump that uses two (or more) gears within a housing to pressurize liquid from the intake to the discharge port.
5. Vane Pump: A pump that uses vanes within the rotor grooves to contact the pump housing (or stator ring), pushing the liquid from the intake to the discharge port.
6. Plunger Pump: A pump that uses a piston or plunger to move between a swash plate and a cam. A pump that uses a piston or crank to reciprocate, forcing liquid from the suction side to the discharge side.
7. Axial Piston Pump: A pump in which the piston or plunger reciprocates parallel to the cylinder axis.
8. Radial Piston Pump: A pump in which the piston or plunger reciprocates perpendicular to the drive shaft.
9. Screw Pump: A pump in which a spiral rotor rotates within the housing, forcing liquid from the suction side to the discharge side.
10. Hydraulic Seizure: When liquid flows through a conical annular gap, if the valve core is eccentric within the valve body bore, the valve core may be subjected to a hydraulic lateral force. If the hydraulic lateral force is sufficiently strong, the valve core will press against the wall of the valve bore, causing seizure.
11. Hydraulic Shock: In a hydraulic system, a sudden, instantaneous increase in liquid pressure due to some reason, resulting in a high pressure peak, is called hydraulic shock.
12. Cavitation: In a hydraulic system, if the pressure at a certain point falls below the air separation pressure at the hydraulic fluid’s temperature, air previously dissolved in the fluid separates, rapidly forming a large number of bubbles within the fluid. This phenomenon is called cavitation. When the bubbles are introduced into the high-pressure fluid flow, they rapidly burst or shrink under the pressure and condense back into liquid. The space previously occupied by the bubbles forms a local vacuum, which is then filled by surrounding liquid particles at extremely high speeds. The collisions between these particles generate localized high pressure, creating a pressure shock. If this localized hydraulic shock acts on the metal surface of a component, it can cause corrosion. This corrosion caused by cavitation is called cavitation.
13. Displacement: The theoretical volume of fluid that a hydraulic pump should displace per revolution; the volume of fluid required for one output shaft rotation of a hydraulic motor, assuming no leakage.
14. Self-priming pump: A pump whose suction chamber volume automatically increases.
15. Variable displacement pump: A hydraulic pump whose displacement can be varied.
16. Constant-power variable displacement pump: A variable displacement pump in which the product of the outlet pressure p and the output flow rate q is approximately constant.
17. Oil trapping: When a hydraulic pump is operating, a dead volume forms between the suction and pressure chambers. The size of this volume changes with the rotation of the drive shaft, leading to pressure shock and cavitation, a phenomenon known as oil trapping.
18. Differential connection: A connection method in which pressurized oil flows simultaneously to both the left and right chambers of a single-piston-rod hydraulic cylinder is called a differential connection.
19. Reciprocating speed ratio: The ratio of the piston velocity v2 when oil flows into the small chamber and returns to the large chamber in a single-piston-rod hydraulic cylinder to the piston velocity v1 when oil flows into the large chamber and returns to the small chamber.
20. Spool valve neutral position function: The connection method of the oil ports of a three-position spool valve when it is in the neutral position, which reflects the control function of the reversing valve.
21. Pressure-Flow Characteristics of a Relief Valve: After the pre-compression of the relief valve’s pressure-regulating spring is set, the fluctuation of the relief valve’s inlet pressure with changes in the relief flow rate after the valve is opened is called the pressure-flow characteristic or opening-closing characteristic.
22. Throttle Valve Stiffness: When the throttle valve opening area A is constant, the ratio of the change in the pressure differential Δp across the throttle valve to the change in the flow rate through the valve is the throttle valve’s stiffness T.
23. Throttle Speed Control Circuit: A hydraulic system that uses a fixed-displacement pump for oil supply and a flow control valve to vary the flow rate to the actuator to achieve speed control is called a throttle speed control circuit.
24. Volumetric Speed Control Circuit: A hydraulic system that uses a variable displacement pump for oil supply and varies the flow rate to the actuator by varying the pump’s displacement to achieve speed control is called a volumetric speed control circuit.
25. Power Adaptive Circuit (Load-Sensitive Speed Control Circuit): A hydraulic system in which the output pressure and flow rate of a variable displacement pump meet the load requirements is called a power adaptive circuit.
26. Speed stiffness: The ability of a speed control circuit to resist speed changes when the load changes.
27. Back pressure: The pressure acting on the return side of a hydraulic circuit, or in the direction opposite to the pressure-applying surface. It can improve certain operating characteristics of a hydraulic system, but it can also damage its performance. Therefore, it is necessary to conduct analysis and research to properly address back pressure issues.
28. Hydraulic circuit: A component of a hydraulic device that performs a specific function and is composed of various hydraulic components.
29. Circuit diagram: A diagram of a hydraulic circuit represented using hydraulic symbols.
30. Hydraulic station: A hydraulic source device or a hydraulic device that includes a control valve and consists of a hydraulic pump, a drive motor, a fuel tank, and a relief valve.
31. Rated pressure: The maximum pressure that can be used continuously.
32. Surge pressure: The maximum pressure that rises during a transient process.
33. Opening pressure: The pressure at which a check valve or relief valve, for example, begins to open when pressure rises to a certain level and a certain flow rate is reached.
34. Closing pressure: The pressure at which a check valve or relief valve, for example, begins to close when pressure drops to a certain level and the flow rate decreases below a certain level.
35. Rated flow: The guaranteed flow rate under certain conditions.
36. Flow rate: Generally refers to the volume of fluid delivered by a hydraulic pump per unit time.
37. Displacement: The volume of fluid delivered (or delivered) per revolution of a positive displacement hydraulic pump (or motor).
38. Fluid power: The power possessed by a fluid. In hydraulics, this is expressed as the product of flow rate and pressure.
39. Pipeline: The pipes and piping systems that carry the working fluid.
40. Main line: Includes suction, pressure, and return lines.
41. Drain line “Line”: refers to the return line for draining oil, or the line that directs it to the oil tank.
42. “Channel”: a passageway that conducts fluid through the interior of a component or is machined or cast within it.
43. “Port”: the opening of a channel on a component that conducts fluid.
44. “Throttle”: a mechanism that reduces the cross-sectional area of flow by creating resistance within a pipe or channel. Examples include long-bore throttles and thin-edge throttles.
45. Sliding valve core (cylindrical valve core): a component that engages a cylindrical sliding surface and opens and closes the flow path as it moves axially.
46. Oil Leakage: The return of oil from a channel (or pipe) within a hydraulic component to a tank or manifold, or the phenomenon of such oil returning.
47. Oil Leakage: A small amount of oil that escapes from a normally sealed area.
48. Static Seal: Used to prevent fluid leakage in stationary parts.
49. Dynamic Seal: Used to seal relatively sliding parts.
50. Fluid jamming: Within a spool-type valve, uneven flow creates an unbalanced pressure distribution about the central axis, forcing the valve core against the valve body (or sleeve), preventing it from actuating.
51. Flow Jump: In a speed control valve (pressure-compensated flow control valve), the flow rate momentarily exceeds the set value when fluid begins to flow.
52. Chatter: A high-frequency vibration applied to a spool-type valve to reduce the effects of friction and fluid seizures and improve its performance.
53. Hydraulic balancing: Using hydraulic pressure to balance loads (including the equipment itself)
54. Fluid transmission: A device that uses fluid as a medium to transmit power
55. Meter-in: A throttle valve installed in the piping on the inlet side of the actuator controls the speed of movement by throttling the flow rate
56. Meter-out: A throttle valve installed in the piping on the outlet side of the actuator controls the speed of movement by throttling the flow rate
57. Meter-bypass: A portion of the flow to the actuator is diverted back to the tank via a throttle valve installed in a bypass line to adjust the actuator’s speed
58. Electro-hydraulic: A method in which electrical components such as solenoids are integrated into the hydraulic actuator
59. Pilot control: A method in which control is achieved by pressure introduced by a pilot valve or other device
60. Hydraulic transmission: A device that uses the pressure energy of a fluid to transmit power. This system uses a positive displacement hydraulic pump and a hydraulic actuator (hydraulic cylinder or hydraulic motor).
61. Pascal’s Principle (Principle of Hydrostatic Pressure Transmission): In a closed container, pressure applied to a stationary liquid is transmitted simultaneously and equally to all points in the liquid.
62. System Pressure: The discharge pressure of the hydraulic pump in the system.
63. Servo valves and proportional valves: Both valves infinitely adjust hydraulic valve outputs, such as pressure, flow, and direction, by modulating an analog input electrical signal. (Servo valves also have pulse-width modulation inputs.) However, their structures are completely different. A servo valve relies on modulating an electrical signal to control the action of a torque motor, deflecting the armature, which in turn actuates the pilot valve. The pilot oil from the pilot valve enters the main valve, pushing the valve core. A proportional valve modulates an electrical signal to displace the armature, actuating the pilot valve core. The resulting pilot oil then pushes the main valve core.
64. Kinematic viscosity: The ratio of dynamic viscosity μ to the density ρ of the liquid.
65. Hydrodynamic force: The force exerted by a flowing liquid on a solid wall that changes its flow rate.
66. Laminar flow: A flow state characterized by distinct layers of fluid, where viscous forces dominate and liquid particles are constrained by viscosity, preventing them from moving freely.
67. Turbulent flow: Inertial forces dominate, and at high speeds, the viscosity between liquid particles no longer constrains them, resulting in a completely chaotic flow state.
68. Along-the-line pressure loss: The loss caused by viscous friction when a liquid flows through a pipe.
69. Local pressure loss: When a liquid flows through bends, joints, sudden changes in cross-section, and valve openings in a pipe, the magnitude and direction of the flow rate change dramatically, generating vortices and strong turbulence, resulting in pressure loss.
70. Control Valve: A general term for valves that change flow conditions to control pressure or flow.
71. Pressure Control Valve: A general term for valves that control pressure.
72. Flow Control Valve: A general term for valves that control flow.
73. Directional Control Valve: A general term for valves that control flow direction.
74. Sequence Valve: A valve that controls the sequence of actuator operation in a system with two or more branch circuits based on circuit pressures and other factors.
75. Balancing Valve: A pressure control valve that maintains back pressure to prevent load drop.
76. Pressure Reducing Valve: A pressure control valve that adjusts the outlet pressure of this type of valve to a value lower than the inlet pressure, independent of flow rate or inlet pressure.
77. Unloading Valve: A valve that can unload a hydraulic pump under certain conditions.
78. Throttle Valve: A valve that restricts the flow of fluid by throttling. Typically refers to a flow control valve without pressure compensation.
79. Flow control valve: A flow control valve that maintains the set flow rate regardless of back pressure or pressure changes caused by load.
80. Flow control valve with temperature compensation: A flow control valve that maintains the set flow rate regardless of liquid temperature.
81. Diverter Valve: When dividing fluid flow between two or more hydraulic lines, this valve enables flow to be divided proportionally, regardless of the pressure in each line.
82. Directional Control Valve: A directional control valve with two or more flow patterns and two or more oil ports.
83. Cover (or Lap): The overlap between the land and window of a spool valve. The value is called the overlap.
84. Relief Valve: When the circuit pressure reaches the set value, some or all of the fluid flows back to the tank through the valve, maintaining the circuit pressure at the set value.
85. Safety Valve: A pressure valve designed to prevent damage to components, piping, etc. A valve used to limit the maximum pressure in a circuit.
86. Zero cover: When the spool of a spool valve is in the neutral position, the window is completely closed. With a slight displacement of the spool, the window opens, allowing fluid to flow through.
87. Positive cover: When the spool of a spool valve is in the neutral position, a certain (not large) displacement is required for the window to open.
88. Negative cover: When the spool of a spool valve is in the neutral position, the window is already open.
89. Servo Valve: Controls flow or pressure as a function of an electrical signal (or other input signal).
90. Valve Position: Used to determine the flow state within a directional valve.
91. Normal Position: The valve position when no operating force is applied
92. Neutral Position: The fixed center position of a directional valve
93. Offset Position: All valve positions of a directional valve except the neutral position
94. Locked Position: The valve position of a directional valve held by a locking device
95. Three-way Valve: A directional valve with three valve positions
96. Two-way Valve: A control valve with two oil ports
97. Four-way Valve: A control valve with four oil ports
98. Spring Return Valve: A valve that returns to its normal position under the action of a spring.
99. Closed Center: When the directional control valve is in the neutral position, all oil ports are closed.
100. Open Center: When the directional control valve is in the neutral position, all oil ports are open.
101. Normally Open: In the normal position, the pressure port and the outlet port are open.
102. Normally Closed: In the normal position, the pressure port is closed.
103. Spring-Centered Valve: A three-position directional control valve whose normal position is neutral. It is a type of spring-return valve.
104. Spring-Offset Valve: A directional valve whose normal position is offset. It is a type of spring-return valve.
105. Number of Oil Ports: The number of oil ports connecting the valve to the pipeline.
106. Shoulder: The sliding surface of the spool during movement.
107. Spool valve (or spool valve): A valve using a cylindrical spool.
108. Shuttle valve: A valve with one outlet and two or more inlets, where the outlet selects the inlet on the side with the highest pressure.
109. Solenoid valve: A general term for solenoid-operated valves and solenoid-operated pilot-operated directional valves.
110. Check valve: A valve that allows fluid to flow in one direction only, preventing it from flowing in the other direction.
111. Throttling directional valve: A directional valve whose flow rate can be continuously varied depending on the valve’s operating position.
112. Solenoid-operated valve: A valve that uses electromagnetic control to operate the valve.
113. Manually operated valve: A valve operated manually
114. Cam-operated valve: A valve operated by a cam
115. Pilot valve: An auxiliary valve used to operate the control mechanism in another valve or component
116. Hydraulically operated directional valve: A directional valve operated by pilot fluid pressure
117. Hydraulically controlled check valve: A valve that can reverse the flow of a check valve by controlling fluid pressure
118. Two-position valve: A directional valve with two valve positions
119. Electro-hydraulic directional valve: A hydraulically operated directional valve integrated with a solenoid-operated pilot valve
120. Actuator: A hydraulic component that uses fluid energy to perform mechanical work
121. Hydraulic motor: An actuator used in hydraulic circuits capable of continuous rotational motion
122. Positive displacement motor: An actuator that achieves continuous rotational motion by shifting or changing the enclosed space between the movable components within the housing as fluid flows from the inlet to the outlet.
123. Vane motor: A hydraulic motor in which the vanes within the rotor slots contact the housing (stator cup), rotating the rotor under the action of the inflowing fluid.
124. Hydraulic cylinder: A hydraulic motor in which the output force is proportional to the effective area of the piston and the pressure differential across it. Linear Motion Actuator
125. Double-Acting Hydraulic Cylinder: A hydraulic cylinder that can receive pressure oil from both sides of the piston
126. Single-Acting Hydraulic Cylinder: A hydraulic cylinder that can receive pressure oil from only one side of the piston
127. Single-Rod Hydraulic Cylinder: A hydraulic cylinder with a piston rod on one side of the piston
128. Double-Rod Hydraulic Cylinder: A hydraulic cylinder with a piston rod on both sides of the piston
129. Differential Hydraulic Cylinder: A hydraulic cylinder that utilizes the difference in effective area on both sides of the cylinder
130. Cushioned Hydraulic Cylinder: A hydraulic cylinder with a cushioning function
131. Fixed-Mount Hydraulic Cylinder Variable displacement motor: A hydraulic motor with a constant theoretical input displacement per revolution.
132. Variable displacement motor: A hydraulic motor with a variable theoretical input displacement per revolution.
133. Gear motor: A hydraulic motor in which pressurized fluid is input to rotate two (or more) meshing gears within the pump housing.
134. Piston motor: A hydraulic motor in which the pressure of the incoming fluid acts on the end face of the piston or plunger, rotating the motor shaft via a swash plate, cam, crank, or other mechanism.
135. Swing actuator: An actuator that rotates reciprocatingly within a 360° rotation angle.
136. Telescopic actuator [Hydraulic] Cylinder: A hydraulic cylinder with a multi-stage, sleeve-shaped piston rod that allows for a long working stroke.
137. Hydraulic Cylinder Thrust: The theoretical fluid force acting on the piston area.
138. Hydraulic Cylinder Stroke: The stroke length of the piston rod. For hydraulic cylinders with a cushioning device, this includes the cushioning length.
139. Servo Actuator: A combination of a servo valve and an actuator used in automatic control systems.
140. Booster: A hydraulic component that converts input pressure to a higher output pressure.
141. Filter: A component that removes solid particles from a fluid through filtering.
142. Pipeline Filters: Filters used in pipelines
143. Fuel Tank Filters: All filters fall into this category, except those used in pressure and vent lines.
144. Accumulator: A container that stores pressurized liquid; this stored liquid can be used as a temporary power source, for example.
145. Pressure Relay: A component that activates electrical contacts when fluid pressure reaches a predetermined value.
146. Hose Assembly: A pressure-resistant hose with connectors at both ends.
147. Pipe Fitting: A removable connector used to connect pipelines or to attach them to hydraulic components. A general term for hydraulic fluid.
148. Oil tank: A container for storing hydraulic fluid.
149. Base plate: A panel with pipe connections concentrated on one side, control valves mounted on it with seals, and an auxiliary panel for piping.
150. Oil circuit board (integrated block): A mounting plate with internal channels that function as pipes, external hydraulic components, and numerous connections.
151. Working oil: A fluid used in hydraulic equipment or systems.
152. Hydraulic fluid: Oil or other fluid used in hydraulic equipment.
153. Flame-retardant hydraulic fluid: This type of hydraulic fluid is flame-retardant and offers maximum fire protection.
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