| accumulator |
A fluid system component that stores pressurized hydraulic fluid from the pump as a source of fluid power. Accumulators release hydraulic fluid as necessary at the required system pressure. |
| active components |
Any fluid system component characterized by being a source of activity. Active components, such as hydraulic pumps, perform an explicit action on hydraulic fluid. |
| actuator |
An active fluid system component at the end of a hydraulic circuit. Actuators, such as cylinders or hydraulic motors, convert hydraulic energy into mechanical energy. |
| additives |
A substance added to another substance or material to improve its chemical and physical properties. Additives in crude oils can protect against rust and improve flow. |
| air-cooled heat exchanger |
A component in a hydraulic system that uses cold air to relieve excess heat. Air-cooled heat exchangers dissipate heat from the hydraulic fluid. |
| axial piston pump |
A hydraulic pump that has pistons arranged in a circle and parallel to the drive shaft centerline. An axial piston pump uses an angled swashplate that maintains contact with the piston shoes to reciprocate pistons. |
| backflow |
The movement of pressurized fluid opposite its intended or desired direction. Backflow causes fluid to return to its source. |
| balanced vane pump |
A hydraulic pump that consists of extendable blades attached to a rotor that is centered in an elliptical cam ring. A balanced vane pump is a fixed-displacement pump. |
| bearings |
A device that minimizes friction between moving parts. Bearings allow for linear or rotational movement, and may also prevent movement by controlling forces that act on moving parts. |
| bladder |
An expandable flexible bag that can be filled with air or liquid. The bladder in a bladder accumulator separates compressed gas from pressurized liquid. |
| bladder accumulator |
A hydropneumatic accumulator that uses a flexible elastic bag to separate the hydraulic fluid from the compressed gas. A bladder accumulator transfers power from the compressed gas to the hydraulic fluid. |
| boosters |
A component of a hydraulic system that converts low-pressure fluid power into high-pressure fluid power. Boosters, also referred to as hydraulic intensifiers, typically receive pressure from oil. |
| cam ring |
An external rotor casing. The cam ring in a vane pump remains stationary as the rotor turns. |
| check valves |
A directional control valve that allows fluid flow in one direction and blocks flow in the reverses direction. Check valves prevent backflow. |
| conductors |
A passive fluid system component that conveys fluid through a hydraulic system. Conductors include pipes, tubes, and hoses. |
| contamination |
The presence of any unwanted substances in a fluid system. Contamination is the primary cause of problems in a fluid system. |
| control valves |
An active fluid system component that controls fluid flow rate, direction, and pressure as fluid moves through the system. Control valves include pressure relief valves and needle valves. |
| corrosion resistance |
A fluid's ability to stop the formation of rust within the components of a hydraulic system. Corrosion resistance in a hydraulic fluid prevents fluid deterioration. |
| crescent pumps |
An internal gear pump consisting of an internal gear that is separated from an external gear by a metal seal. Crescent pumps are fixed-displacement pumps. |
| crescent seal |
The stationary component in a crescent pump that separates the internal gear from the external gear. A crescent seal is machined into the pump where there is maximum clearance between the gears. |
| crude oils |
Unrefined petroleum oil. Crude oil is often refined and mixed with additives for use as hydraulic fluid. |
| cylinder block |
A solid unit that houses the pistons in a piston pump. The cylinder block in an axial piston pump rotates and the pistons maintain contact with the angled swashplate in order to reciprocate. |
| cylinders |
A hollow bore that houses a movable piston attached to a piston rod. A cylinder applies force in a straight line. |
| demulsibility |
A fluid's ability to release water. Demulsibility in a fluid means that the fluid will separate from water. |
| diaphragm accumulator |
A hydropneumatic accumulator that uses a metal partition to store compressed gas and pressurized liquid. Diaphragm accumulators are similar to bladder accumulators. |
| directional control valves |
A fluid system component that determines the path hydraulic fluid takes in a hydraulic system. Directional control valves start, stop, and control the direction of fluid flow. |
| double-acting cylinder |
A hydraulic linear actuator that applies force in both directions as the piston reciprocates. Double-acting cylinders use fluid pressure to extend and retract the piston. |
| drive gear |
A gear that transmits power. A drive gear is attached to a drive shaft, which is driven by the prime mover. |
| drive shaft |
A driving mechanism that rotates to transfer motion. A drive shaft is powered by a prime mover, such as an electric motor. |
| driving mechanism |
A component that rotates to transfer motion. The driving mechanism in a positive-displacement pump is typically a drive shaft. |
| efficiency |
The amount of power output a hydraulic pump produces compared with the amount of power input. Efficiency ratings are used to determine the condition of a pump. |
| electric motor |
A machine that converts electricity into mechanical energy or motion. An electric motor is a type of prime mover for a hydraulic system. |
| external gear pump |
A fixed-displacement hydraulic pump that moves fluid using two meshing gears that rotate. An external gear pump is available in single or multiple configurations. |
| filter |
A device that separates and retains insoluble contaminants from a fluid. A filter for a hydraulic system has a maximum flow rate and pressure rating. |
| fire-resistant fluids |
A hydraulic fluid that is very difficult to ignite. Fire-resistant fluids do not support combustion once the ignition source is removed. |
| fittings |
A fluid component that connects, redirects, extends, or terminates the run of a fluid conductor. Fittings that are installed improperly can result in external leakage. |
| fixed displacement |
A hydraulic pump with a fluid displacement value that stays the same from cycle to cycle. Fixed-displacement pumps are not as common in industrial settings as variable-displacement pumps. |
| flammability |
The ability or tendency to ignite or burn when exposed to an open flame or ignition source. The flammability of petroleum-based oils can present a fire hazard in hydraulic systems used near high temperatures or open flames. |
| flow capacity |
The total volume of fluid that a pump moves into the hydraulic system in a given period of time. Flow capacity is also known as flow rate and is measured in gallons or liters per minute. |
| flow control valves |
A fluid system component that controls the rate of fluid flow through a hydraulic system. Flow control valves make it possible to control other system components, such as the speed of an actuator. |
| flow rate |
The total volume of fluid that a pump moves into the hydraulic system in a given period of time. Flow rate is also known as flow capacity and is measured in gallons or liters per minute. |
| fluid displacement |
The total volume of fluid a hydraulic pump moves in one reciprocating or rotating cycle. Fluid displacement is measured in cubic inches or cubic centimeters per revolution. |
| fluid flow |
The motion of a fluid, usually a liquid or a gas, subjected to unbalanced forces or stresses. Fluid flow in a hydraulic system is subjected to resistance, which allows pressure to develop. |
| force |
The push or pull that gives energy to an object. Force results from an object's interaction with another object. |
| force multiplication |
The increase in available power associated with power transmission systems. Force multiplication allows a hydraulic system to produce an output force that is larger than the input force if the same pressure is applied to differently sized areas. |
| friction |
A force that resists motion between two moving objects that touch. Friction between the moving components in a fluid system can lead to excess wear. |
| gallons per minute |
gpm. A unit of English measurement that is used to measure the flow capacity or flow rate of a hydraulic pump. Gallons per minute is a unit of volumetric flow. |
| gear motor |
A hydraulic rotary actuator with two or more meshing gears. A gear motor has a fixed displacement. |
| gear pumps |
A fixed-displacement hydraulic pump that uses meshing gears that rotate to move fluid. Gear pumps are relatively inexpensive and compact. |
| glycol |
An organic compound belonging to the alcohol family. A glycol and water solution forms a fire-resistant hydraulic fluid. |
| gpm |
gallons per minute. A unit of English measurement that is used to measure the flow capacity or flow rate of a hydraulic pump. Gpm is a unit of volumetric flow. |
| heat exchanger |
A hydraulic system component that helps relieve excess heat in the hydraulic fluid. Heat exchangers may use water or air to cool a system. |
| heat transfer rating |
The rate at which thermal energy is exchanged between physical systems. The heat transfer rating of a heat exchanger describes its effectiveness in transferring thermal energy. |
| horsepower |
hp. A unit of power. One horsepower is equivalent to 33,000 foot-pounds per minute. |
| hoses |
A type of flexible fluid conductor that joins components of a hydraulic fluid system, usually in a nonlinear fashion. Hoses are made from rubber and often include wire braiding for reinforcement. |
| hydraulic actuator |
A hydraulic system component that converts hydraulic energy from the pump into mechanical energy. Hydraulic actuators can direct linear or rotary force. |
| hydraulic fluid |
A liquid, typically oil, that transfers the power in a hydraulic system. Hydraulic fluid generally has high viscosity. |
| hydraulic intensifiers |
A component of a hydraulic system that converts low-pressure fluid power into high-pressure fluid power. Hydraulic intensifiers, also referred to as boosters, typically receive pressure from oil. |
| hydraulic motors |
A device that converts hydraulic energy into mechanical energy. A hydraulic motor is a rotary actuator that can rotate continuously. |
| hydraulic pump |
A mechanical power source that creates fluid flow and moves fluid through a hydraulic system. Hydraulic pumps receive energy from a prime mover, such as a motor or engine. |
| hydraulic system |
A type of power transmission system that uses oil or another liquid under pressure to transmit mechanical power. A hydraulic system can transmit large amounts of power using a small input force. |
| hydropneumatic accumulator |
A type of accumulator that uses compressible gas to keep stored hydraulic fluid pressurized. Hydropneumatic accumulators use a device, such as a piston, bladder, or diaphragm, to separate the hydraulic fluid from the compressed gas. |
| idler gear |
A gear that is driven by the drive gear in a gear pump as the two gears mesh. The idler gear in an internal gear pump is typically smaller than the drive gear. |
| ignition source |
Any process or event capable of causing a fire or explosion. Ignition sources include an open flame, hot metal, or sparks. |
| incompressible |
Relatively incapable of losing volume in response to pressure. Liquids are incompressible, while gases are compressible. |
| inlet port |
An opening on the side of a hydraulic pump through which fluid enters the pump. Multiple inlet ports can be included in one pump. |
| in-line check valve |
A directional control valve with the inlet and outlet port located directly opposite each other. An in-line check valve can completely allow flow in one direction while blocking flow in the reverse direction. |
| internal combustion engine |
A type of engine that internally produces heat energy and mechanical energy. Internal combustion engines used for hydraulic systems commonly run on gasoline or diesel. |
| internal gear pump |
A fixed-displacement hydraulic pump with an internal gear that is smaller than the external gear. An internal gear pump is available in single or multiple configurations. |
| kilopascals |
kPa. An SI unit used to measure pressure. Kilopascals may be used to express pressure requirements for a hydraulic system. |
| leakage |
The movement of fluid out of a hydraulic system or from one hydraulic system component to another. Leakage decreases efficiency and can lead to system failure. |
| linear actuators |
An actuator that directs force in a straight line. Linear actuators include double- and single-acting cylinders. |
| liters per minute |
lpm. A unit of metric measurement that is used to measure the flow capacity or flow rate of a hydraulic pump. Liters per minute is a unit of volumetric flow. |
| loads |
The amount of force or pressure placed on a hydraulic system. The load exerted on a system must be compatible with the hydraulic pump and other system components. |
| lpm |
liters per minute. A unit of metric measurement that is used to measure the flow capacity or flow rate of a hydraulic pump. Lpm is a unit of volumetric flow. |
| lubricant |
A substance used to reduce friction between moving components. Lubricants often include oil and grease. |
| lubricity |
The ability of a fluid to reduce friction and provide lubrication. High lubricity in a hydraulic fluid indicates an effective lubricant. |
| mechanical properties |
The collection of properties that describe a liquid's ability to lubricate and flow. Mechanical properties of a hydraulic fluid include viscosity, lubricity, and demulsibility. |
| metal-forming presses |
A machine that uses hydraulic power to generate compressive forces. Metal-forming presses often use hydraulic intensifiers to produce increased pressure. |
| needle valve |
A flow control valve that adjusts fluid flow rate by changing the size of the outlet port. A needle valve consists of a sharp conical obstruction that extends or retracts to enable variable flow. |
| normally closed |
A valve position in which the valving element is unactuated and covering a port. A normally closed valve opens when a specific pressure is reached. |
| normally open |
A valve position in which the valving element is unactuated and not covering a port. A normally open valve closes when it actuates. |
| outlet port |
An opening on the side of a hydraulic pump through which fluid is expelled into the hydraulic system. Multiple outlet ports can be included in one pump. |
| outlet pressure |
The pressure of the fluid at the hydraulic pump's outlet port. Outlet pressure is typically measured in pounds per square inch (psi) or kilopascals (kPa). |
| oxidation |
A material's chemical reaction with oxygen. Oxidation causes rust to form on metal surfaces and can lead to deterioration. |
| passive components |
Any fluid system component characterized by inactivity. Passive components, such as conductors, do not perform an explicit action on fluids, but they allow fluids to act upon them. |
| petroleum-based oil |
A thick hydraulic fluid developed from petroleum. Petroleum-based oils provide good lubrication and are compatible with most seal materials. |
| pipes |
A fluid conductor that joins components of a fluid system. Pipes typically convey fluid in a straight line and on a permanent basis. |
| piston accumulator |
A hydropneumatic accumulator with a liquid section and a nitrogen-charged gas section. A piston accumulator has a piston separating the liquid chamber from the gas chamber. |
| piston motor |
A rotary actuator that uses the reciprocating motion of pistons to produce torque. A piston motor can have a fixed or variable displacement. |
| piston pumps |
A hydraulic pump that uses the reciprocal motion of pistons to move fluid through the pump. Piston pumps can have a fixed or variable displacement. |
| piston rod |
A movable, cylindrical component attached perpendicularly to a piston. A piston rod is housed in a cylinder. |
| piston shoes |
The swiveling end portion of a piston that contains ball and socket joints. The piston shoes in an axial piston pump maintain contact with the angled swashplate to reciprocate the pistons. |
| poppet |
A conical valving element that opens and closes in response to variations in pressure. Poppets are used in some directional control valves. |
| port |
An opening on a valve or cylinder through which fluid can flow. A port allows for inlet or outlet flow. |
| positive-displacement pumps |
A hydraulic pump with a given fluid displacement per cycle or revolution. Positive-displacement pumps are used with a pressure relief valve on the outlet side. |
| pounds per square inch |
psi. A unit used to measure pressure. Pounds per square inch units are used to measure pressure requirements for the hydraulic system and for system components. |
| power source |
A device that generates the energy needed to power a tool or system. The power source in a hydraulic system is the hydraulic pump. |
| power transmission system |
A grouping of components that work together to move energy from a source to an output device in order to perform work. Power transmission systems include hydraulic and pneumatic systems. |
| pressure |
The exertion of force on a confined liquid. Pressure is a function of resistance to fluid flow. |
| pressure compensator |
A device used with variable-displacement pumps. Pressure compensators automatically control a pump's displacement. |
| pressure control valves |
A type of control valve that regulates pressure in a hydraulic system. Pressure control valves are active elements of a hydraulic system. |
| pressure intensification ratio |
A specification that indicates how much pressure a hydraulic intensifier can deliver to the hydraulic system. The pressure intensification ratio is inversely proportioned to the area ratio of the cylinders. |
| pressure rating |
The amount of pressure a hydraulic system can withstand without increased leakage or damage. Pressure ratings are typically expressed in pounds per square inch (psi) or kilopascals (kPa). |
| prime mover |
The component in a hydraulic system that provides mechanical energy to power the hydraulic pump. Prime movers for hydraulic systems include electric motors and internal combustion engines. |
| prime mover |
The component in a hydraulic system that provides mechanical energy to the hydraulic pump. Prime movers for hydraulic systems include electric motors and internal combustion engines. |
| properties |
The physical and mechanical characteristics of a material that distinguish it from other materials. Properties determine how a material will perform in different environments. |
| psi |
pounds per square inch. A unit of English measurement used to measure pressure. Psi units are used to measure pressure requirements for the hydraulic system and for system components. |
| pumping chambers |
A compartment in a hydraulic pump between gear teeth or vanes. Pumping chambers trap fluid and push it to the outlet port. |
| radial piston pump |
A type of piston pump with a radial arrangement of pistons within a cylinder block. In a radial piston pump, the pistons are perpendicular to the drive shaft centerline. |
| radially |
Having parts arranged in straight lines coming from the center of a circle. Radial arrangements of pump components are found in vane pumps and some piston pumps. |
| ratio of areas |
A physical law stating that a given pressure exerted in a larger cylinder can be intensified when transferred to a smaller cylinder. The ratio of areas in a hydraulic intensifier is the area of one piston compared with the area of a second piston. |
| reciprocating |
The repeated back-and-forth movement of a component. Reciprocating mechanisms in some hydraulic pumps push fluid through the pump. |
| relief valve |
A pressure control valve that allows pressurized fluid to drain back into the reservoir if the hydraulic system reaches a critical pressure. A relief valve is typically the first control valve after the hydraulic pump. |
| reservoir |
The main storage container for fluid in a hydraulic system. A reservoir may be pressurized or nonpressurized. |
| resistance |
The opposition to force. Resistance in a hydraulic system results in pressure. |
| revolutions per minute |
rpm. A unit of measurement that indicates the number of complete rotations a cylindrical component makes in one minute. Revolutions per minute is a measurement of speed. |
| right-angle check valve |
A directional control valve with an inlet port and an outlet port located at right angles to each other. A right-angle check valve can divert the direction of fluid flow. |
| rotary actuator |
An actuator that directs force in a circular motion. Rotary actuators include hydraulic motors and limited-rotation devices. |
| rotating |
Spinning or turning movement that takes place around an axis, without a change in linear position. Rotating motion is a type of mechanical energy. |
| rotor |
A rotating part of an electrical or mechanical device. A rotor is the driven component of most hydraulic pumps. |
| rpm |
Revolutions per minute. A unit of measurement that indicates the number of complete rotations a cylindrical component makes in one minute. Rpm is a measurement of speed. |
| sealant |
A material or liquid that provides an airtight or watertight barrier. Sealants protect moving components in a hydraulic system from leaks and contamination. |
| seals |
A device in a fluid power system that prevents fluid leakage and blocks contaminants from entering the system. A seal that is in contact with hydraulic fluid must be compatible with the fluid. |
| sequence valves |
A pressure control valve that allows hydraulic fluid to flow into a secondary part of the circuit after a critical pressure is reached in the primary part of the circuit. Sequence valves can control two operations performed in sequence. |
| single-acting cylinder |
A linear actuator that directs force in one direction as the piston extends. Single-acting cylinders use an external force to retract the piston back into the cylinder. |
| sludge |
A form of contamination. Sludge is gummy liquid matter that forms in the reservoir when contaminated hydraulic fluid mixes with water. |
| spill-containment |
An area where chemical, oil, or sewage spills are closed off with barriers or by a drainage system. Spill-containment areas can present potential hazards, particularly if petroleum-based oils are used. |
| spool |
A cylindrical valving element that alternately allows and blocks flow depending on its linear position. A spool slides to block and open valve ports. |
| steel |
A metal consisting of iron and carbon, usually with small amounts of other elements. Steel is a common metal in manufacturing. |
| stroke |
The length of travel of a piston when it moves into or out of a cylinder. The stroke of a piston helps to determine a piston pump's displacement. |
| swashplate |
A flat, angled component of an axial piston pump that maintains contact with the piston shoes to cause the pistons to reciprocate. The swashplate angle determines an axial piston pump's displacement. |
| synthetic oils |
A hydraulic fluid developed without petroleum. Synthetic oils are manufactured using chemicals and additives not found in nature. |
| thin wall steel |
A strong steel material with high thermal properties. Thin wall steel tubing is a conductor that can bend or flex. |
| throttle |
A control used to vary the speed of a mechanical device. A throttle on an internal combustion engine allows operators to adjust the speed of the hydraulic pump. |
| torque |
A force that produces rotation. Torque is measured in foot-pounds in the English system and newton-meters in the metric system. |
| tubing |
A fluid conductor that joins components of a fluid system, usually in a nonlinear fashion. Tubing is easily bent and eliminates the need for fittings and connection points. |
| unbalanced vane pump |
A hydraulic pump that consists of extendable vanes and a rotor mounted off-center in a circular cam ring. An unbalanced vane pump can have fixed or variable displacement. |
| vacuum |
The state of negative pressure. A vacuum that forms in the inlet port of a hydraulic pump allows fluid to enter the pump. |
| valving mechanism |
The component of a valve that covers a port. Valving mechanisms include spools and poppets that cover or open a port to block or allow flow. |
| vane motor |
A rotary actuator with extendable blades attached radially to a slotted rotor. Vane motors used in hydraulic systems are typically balanced with a fixed displacement. |
| vane pumps |
A hydraulic pump that uses a series of flat protrusions that extend within a rotor to trap and move fluid. Vane pumps are efficient at fast operating speeds. |
| vanes |
A retractable mechanism that extends radially from the center of a rotor in a vane pump. Vanes rotate to move fluid through the pump. |
| variable displacement |
A hydraulic pump that can be adjusted to change the amount of fluid that is moved in one pump cycle. Variable-displacement pumps are generally more expensive than fixed-displacement pumps. |
| viscosity |
A fluid's ability to flow at a given temperature. The viscosity of a fluid decreases as temperature increases. |
| volume |
The amount of space that a substance or object occupies within a container. Volume is measured in cubic inches or cubic centimeters. |
| water glycol solutions |
A fire-resistant hydraulic fluid consisting of 40% water and 60% glycol. Water glycol solutions are compatible with many synthetic seal materials. |
| water-cooled heat exchanger |
A component in a hydraulic system that consists of a cylinder with pipes containing cold water. Water-cooled heat exchangers remove heat from hot hydraulic fluid by passing the fluid over the pipes. |
| water-in-oil emulsions |
A fire-resistant hydraulic fluid consisting of 40% water dispersed in an oil base. Water-in-oil emulsions are characterized by small droplets of water completely surrounded by oil. |