Glossary

A  :  B  :  C  :  D  :  E  :  F  :  G  :  H  :  I  :  J  :  L  :  M  :  N  :  P  :  Q  :  R  :  S  :  T  :  V  :  W

A

AIR BLEEDER

A device for removal of air from a hydraulic fluid line.

AIR BREATHER

A device permitting air movement between atmosphere and the component in which it is installed.

AIR, COMPRESSED (Pressure)

Air at any pressure greater than atmospheric pressure.

AREA

A surface enclosed by a specific boundary.

B

BAR

A unit of pressure based on Newtons per square meter, approximately equal to 14.5 PSIG. This unit is not preferred in SI metrics.

BOYLE’S LAW

The absolute pressure of a fixed mass of gas varies inversely as the volume, provided the temperature remains constant.

BURST PRESSURE

The pressure which causes rupture. Also, the inside-out differential pressure that causes outward structural failure.

C

CAVITATAION

A localized gaseous condition within a liquid stream causing the rapid implosion of a gaseous bubble.

CELCIUS

A temperature scale. 0 Celsius (or ‘0’ Centigrade) is the freezing point of water (32ºF).

CIRCUIT

An arrangement of interconnected component parts.

CONTAMINATION LEVEL

A quantitative term specifying the degree of contamination.

CONTAMINANT

Any material or substance which is unwanted or adversely effects the fluid power system or components, or both.

CONTROL, SERVO

A control actuated by a feedback system which compares the output with the reference signal and makes corrections to reduce the difference.

CORROSION

The chemical change in the mechanical elements caused by the interaction of fluid or contaminants, or both. More specifically related to chemical changes in metals. The products of change may be introduced into the system as generated particulate contamination.

CUSHION

A device which provides controlled resistance to motion by use of a gradually reduced flow area.

CUSHION, CYLINDER

A cushion built into a cylinder to restrict flow at the outlet port thereby arresting the motion of the piston rod.

CYCLE

A single complete operation consisting of progressive functions starting and ending at the neutral position.

CYLINDER

A device which converts fluid pressure and flow into the linear mechanical force and motion. It usually consists of a movable plunger or ram, operating within a cylindrical bore.

CYLINDER, DOUBLE ACTING

A cylinder in which fluid pressure can be applied to the movable piston rod in either direction.

CYLINDER, DOUBLE ROD

A cylinder with a single piston and a piston rod extending from each end.

CYLINDER DUAL STROKE

A cylinder combination which provides two working strokes.

CYLINDER, NON-ROTATING

A cylinder in which relative rotation of the cylinder housing and the piston and piston rod, plunger or ram, is not recommended.

CYLINDER, ROTATING

A cylinder in which relative rotation of the cylinder housing and the piston and piston rod, plunger or ram, is recommended.

CYLINDER, SINGLE ACTING

A cylinder in which the fluid pressure can be applied to the piston in only one direction.

CYLINDER, SINGLE ROD

A cylinder with a piston rod extending from one end.

CYLINDER, TANDEM

Two or more cylinders with interconnected rod and piston assemblies.

CYLINDER, TELESCOPING

A cylinder with nested multiple tubular rod segments which provide a long working stroke in a short retracted envelope.

D

DENSITY

A unit of mass per unit volume.

DISPLACEMENT, VOLUMETRIC

The volume for one revolution or stroke.

DRIFT

The percentage above and below the operating pressure at a constant flow rate over a specified length of time.

E

EFFICIENCY

The ratio of the useful energy delivered by a dynamic system to the energy supplied to it.

ENCLOSURE

A housing for components.

ENERGY

The capacity for doing work. (See Joule.)

EROSION

The loss of material in mechanical elements caused by the impingement of fluid or fluid suspended particulate matter, or both. The product of erosion will be introduced into the system as additional generated particulate contamination.

F

FAHRENHEIT

The thermometric scale on which, under standard atmospheric pressure, the boiling point of water is at 212 degrees above the zero of the scale and the freezing point is 32 degrees above the zero.

FLANGE

A mounting device usually consisting of a plate or collar.

FLUID

A liquid, gas, or combination thereof.

FLUID FRICTION

Friction due to the viscosity of fluid.

FORCE

An energy or influence that if applied to a free body results chiefly in an acceleration of the body and sometimes in elastic deformation and other effects. (See Newton.)

G

GAGE

An instrument or device for measuring, indication, or comparing a physical characteristic.

GAGE, FLUID LEVEL

A gage which indicates the fluid level.

GAGE, PRESSURE

A gage which indicates the pressure in the system to which it is connected.

GRAVIMETRIC VALUE

The weight of suspended solids per unit volume of fluid. A method employing membrane filters for this determination is outlined in Society of Automotive Engineers Aerospace Recommended Practices -785.

H

HEAT

(1) Added energy that causes substances to rise in temperature, fuse, evaporate, expand, or undergo any of various other related changes, that flows to a body by contact with or radiation from bodies at higher temperatures, and can be produced in a body (as by compression). (2) The energy associated with the random motions of the molecules, atoms, or smaller structural units of matter is composed. (See Joule.)

HOSE

A flexible line or conduit.

HYDRAULIC(S)

Of or pertaining to the engineering science of liquid pressure and flows.

HYDRAULIC HORSEPOWER

Horsepower computed from flow rate and pressure differential.

HYDRODYNAMICS

Engineering science pertaining to the energy of liquid flow and pressure.

HYDROSTATICS

Engineering science pertaining to the energy of liquids at rest.

I

INDICATOR

A device which provides external visual evidence of sensed phenomena.

INTENSIFIER

- A device which converts low pressure fluid power o higher pressure fluid power.

J

JOULE

A unit of work, energy, or heat. 1J (joule)=1 Nm (Newton Meter).

JOULE PER SECOND

A unit of power, i.e. the rate of doing work.

L

LINE

A tube, pipe, or hole for conducting fluid.

LINE, DRAIN

- A line returning drain fluid independently to the reservoir or vented manifold.

LINE, EXHAUST

A line returning power or control fluid back to the reservoir or atmosphere.

LINE, PILOT

A line which conducts control fluid.

LUBRICATOR

A device which adds controlled or metered amounts of lubricant into a pneumatic system.

LUB (FOOT)

A mounting device consisting on a block extending past the basic cylinder profile. The block usually has a tapped or through mounting hole at right angles to the cylinder axis.

M

MANIFOLD

A conductor which provides multiple connection parts.

MASS

The property of a body that Is a measure of its inertia, that is commonly taken as a measure of the amount of material it contains and causes it to have weight in a gravitational field, and that along with length and time constitutes one of the fundamental quantities on which all physical measurements are based.

METER

A unit of length, 1 meter = 39.37 inches.

MUFFLER

A device for reducing gas flow noise. Noise is decreased by back pressure control of gas expansion.

N

NEWTON

A unit of force based on the unit of mass, Kg (Kilogram), multiplied by the acceleration, M/S² (meters per second per second) which produces KGM/S², called the Newton.

NEWTONMETER

A unit of torque.

P

PACKING

A sealing device consisting of bulk deformable material or one or more mating deformable elements, and maintain effectiveness. It usually uses axial compression to obtain radial sealing.

PHASE

A distinct functional operation during a cycle. Some typical sequential phases are: neutral, rapid advance, feed or pressure stroke, dwell and rapid return.

PIPE

A tubular shaped passage for fluid conduction.

PIPE, THREAD

Screw threads for joining pipe.

PIPE THREAD, DRYSEAL

Pipe threads in which sealing is a function of root and crest interference.

PIPE THREAD, TAPERED

Pipe threads in which the pitch diameter follows a helical cone to provide interference in tightening.

PNEUMATICS

Engineering science pertaining to gaseous pressure and flow.

PORT

An internal or external terminus of a passage in a component.

POWER

The time rate at which work is done. (See Joule per Second or Watt.)

POWER UNIT

A combination of pump, pump drive, reservoir, controls and conditioning components which may be required for its application.

POWER UNIT, HYDRAULIC

A combination of components to facilitate fluid storage and conditioning, and delivery of the fluid under conditions of controlled pressure and flow to the discharge port of the pump, including maximum pressure controls and sensing devices when applicable. Circuitry components, although sometimes mounted on the reservoir, are not considered part of the power unit.

PRECIPITATE

Particles separated from a fluid as a result of a chemical or physical change.

PRESSURE

Force per unit unit area, usually expressed in pounds per square inch in the English system.

PRESSURE, ABSOLUTE

The pressure above zero absolute, i.e., the sum of atmospheric and gage pressure. In vacuum related work it may be expressed in millimeters of mercury (mm Hg).

PRESSURE, ATMOSHPERIC

Pressure exerted by the atmosphere at any specific location. (Sea level pressure is approximately 14.7 pounds per square inch absolute.)

PRESSURE, BACK

The pressure encountered on the return side of the system.

PRESSURE, BURST

The pressure which creates loss of fluid through the component due to t the fracture of the component.

PRESSURE, CHARGE

The pressure at which replenishing fluid is forced into a fluid power system.

PRESSURE, CRACKING

The pressure at which a pressure operated valve begins to pass fluid.

PRESSURE, GAGE

Pressure differential above or below atmospheric pressure.

PRESSURE, OPERATING

The pressure at which a system is operated.

PRESSURE, OVERRIDE

The difference between the cracking pressure of a valve and the pressure reached when the valve is passing full flow.

PRESSURE, PILOT

The pressure in the pilot circuit.

PRESSURE, PRECHARGE

The pressure of compressed gas in an accumulator prior to the admission of a liquid.

PRESSURE, PROOF

The non-destructive test pressure, in excess of the maximum rated operating pressure, which causes no permanent deformation, external leakage, or other malfunction.

PRESSURE, RATED

The qualified operating pressure, which is recommended for a component or a system by the manufacturer.

PRESSURE, RATED FATIGUE

A pressure that a pressure containing component is represented to sustain 10 million times without failure.

PRESSURE, RATED STATIC

A pressure that a component can withstand without failure.

PRESSURE, SYSTEM

The pressure which overcomes the total resistances in a system. It includes all losses as well as useful work.

PRESSURE VESSEL

A container which holds fluid under pressure.

PRESSURE, WORKING

The pressure which overcomes the resistance of the working device.

PUMP

A device which converts mechanical force and motion into hydraulic fluid power. It produces flow.

Q

QUICK DISCONNECT

A coupling which can quickly join or separate a fluid line without the use of tools or special devices.

R

RATE CURRENT

The specified servovalve input current of either polarity to produce rated flow. Rated current must be specified for a particular coil connection differential, series, or parallel, and does not include null bias current.

RATED FLOW

The maximum flow that the power supply system is capable of maintaining at a specific operating pressure.

REDUCED PRESSURE RANGE

The adjustment range of the regulator.

RESERVOIR HYDRAULIC

A vessel or tank for storing and conditioning liquid in hydraulic system.

RESPONSE TIME

The time required for effective transition.

RESTRICTOR

A device which reduces the cross-sectional flow area.

RETURN LINE

The line conducting fluid from working devices to the reservoir.

RING, “O”

A ring which has a round cross-section usually used for sealing.

RING, PISTON

A piston sealing ring. It is usually one of a series and is often split to facilitate expansion or contraction.

RING, SCRAPER

A ring which removes material by a scraping action.

RING, WIPER

A ring which removes material by a wiping action.

S

SAE PORT

A straight thread port used to attach tube and hose fittings. It employs an “O” ring compressed in a wedge-shaped cavity. A standard of the Society of Automotive Engineers J514 and AJSI/B116.1.

SCORING

Scratches in the direction of motion of mechanical parts caused by abrasive contaminants.

SEAL, DYNAMIC

A sealing device used between parts that have relative motion.

SEAL, LIP

A sealing device which has a flexible sealing projection

SEAL, PRESSURE ACTUATED

A sealing device in which sealing action is aided by fluid pressure.

SEAL, STATIC

A sealing device used between parts that have no relative motion between them.

SECOND

A unit of time, 1/60 of a minute.

SHOCK WAVE

A pressure wave front which moves at a sonic velocity.

SI METRIC SYSTEM

A modernized and internationally standardized version of the metric system based on the meter, second, kilogram, amphere, degree Kelvin, and candela.

SILENCER

A device for reducing gas flow noise. Noise is decreased by tuned resonant control of gas expansion.

STOKE

The standard unit of kinematic viscosity in the cgs (centimeter-gram-second) system. It is expressed in square centimeters per second; 1 centistoke equals .01 stoke.

SWITCH, FLOW

An electric switch operated by a fluid flow.

SWITCH, PRESSURE

An electric switch operated by fluid pressure.

SYNTHETIC FLUID

Fluid which has been artificially compounded for use in a fluid power system.

SYNTHETIC FLUID, PHOSPHATE ESTER

A fluid composed of phosphate esters. It may contain additives.

SYNTHETIC FLUID, PHOSPHATE ESTER BASE

A fluid which contains a phosphate ester as one of the major components.

T

TANK

A container for the storage of fluid in a fluid power system.

TANK, AIR-OIL

A tank in which pressurized air is used to force oil into the outlet port.

TANK, VACUUM

A tank for storing gas at less than atmospheric pressure.

TEMPERATURE

See Celcius and Fahrenheit.

TIE ROD

An axial external cylinder rod which traverses the length of the cylinder. It is prestressed at assembly to hold the ends of the cylinder against the tubing. Tie rod extensions can be a mounting device.

TRUNNION

A mounting device consisting of a pair of opposite projecting cylindrical pivots. The cylindrical pivot pins are at right angles or normal to the piston rod centerline to permit the cylinder to swing in a plane.

TUBE

A conductor whose size is its outside diameter Tube is available in varied wall thickness.

V

VALVE

A device which controls fluid flow direction, pressure, or flow rate.

VALVE ACTUATOR

The valve part(s) through which force is applied to move or position flow-directioning elements.

VALVE, DIRECTIONAL CONTROL

A valve whose primary function is to direct or prevent flow through selected passages.

VALVE, FLOW CONTROL, DECELERATION

A flow control valve which gradually reduces flow rate to provide deceleration.

VALVE, FLOW CONTROL (FLOW MEETING)

A valve whose primary function is to control flow rate.

VALVE, HYDRAULIC

A valve for controlling liquid flow or pressure.

VALVE MOUNTING

The mounting characteristics of a valve.

VALVE, PILOT

A valve applied to operate another valve or control.

VALVE, PNEUMATIC

A valve for controlling gas flow or pressure.

VALVE, PREFILL

A valve which permits full flow from a tank to a “working” cylinder during the advance portion of a cycle, permits the operating pressure to be applied to the cylinder during the working portion of the cycle, and permits free flow from the cylinder to the tank during the return portion of the cycle.

VISCOSITY

A measure of the internal friction or the resistance of a fluid to flow.

VISCOSITY, ABSOLUTE

The ratio of the shearing stress to the shear rate of a fluid. It is usually expressed in centipoise.

VISCOSITY, KINEMATIC

The absolute viscosity divided by the density of the fluid. It is usually expressed in centistokes.

VISCOSITY, SAE NUMBER

The Society of Automotive Engineers arbitrary numbers for classifying fluids according to the viscosities. The numbers for classifying fluids according to their viscositiles. The numbers in no way indicate the viscosity index of fluids.

VISCOSITY INDEX

A measure of the viscosity-temperature characteristics of a fluid as referred to that of two arbitrary reference fluids. (ASTM Designation D2270-64).

W

WATER-GLYCOL FLUID

A fluid whose major constituents are water and one or more glycols or polyglycols.

WATT

A unit of power.

WORK

Moving a force through a distance. (See Joule.)