ABSOLUTE VISCOSITY

The ratio of shear stress to shear rate. It is a hydraulic fluid's internal resistance to flow.

ABSORPTION

The integration of one material into another.

ACCUMULATOR

A container which stores hydraulic fluid under pressure. Used as an energy source or to absorb hydraulic shock. Designed to increase or relieve pressure in the hydraulic system. Common types of hydraulic accumulator are: piston, bladder and diaphragm.

ACTUATOR

A device in which power is transferred from one pressurized medium to another without intensification; the hydraulic components such as hydraulic cylinders, hydraulic motors and hydraulic rotary actuators that directly help convert hydraulic energy into mechanical energy.

ADDITIVE

A chemical added to a hydraulic fluid to impart new properties or to enhance those which already exist.

AIR BLEEDER

A device for the removal of air.

AIR BREATHER

A device permitting air movement between the atmosphere and the hydraulic component in which it is installed while preventing contaminants from entering the hydraulic component.

AIR, COMPRESSED

Air at any pressure greater than atmospheric pressure

AIR INCLUSION

The ambient atmosphere forced or trapped into the hydraulic system during connection of quick-release coupling halves.

AIR-COOLED HEAT EXCHANGER

A hydraulic component in a hydraulic system that relieves excessive heat with cool air

AIR-OPERATED ACCUMULATOR

A hydraulic component used to store hydraulic fluid. The air-operated accumulator increases and relieves hydraulic pressure through the use of an inflatable bag. Also called a gas-loaded accumulator.

AIR-OVER-OIL INTENSIFIER

A hydraulic component that is powered by compressed air. Compressed air exerts force on a piston, which magnifies pressure as the hydraulic fluid escapes to smaller conductors and actuators.

ANTI-FOAM AGENT

One of two types of additives used to reduce foaming in petroleum products

ASPERITIES

Microscopic projections on metal surfaces resulting from normal surface-finishing processes.

ATMOSPHERIC PRESSURE

The weight of the atmosphere. Atmospheric pressure refers to the amount of pressure exerted by the air.

BALL VALVE

A hydraulic valve that uses a spherical obstruction to stop and start hydraulic flow. A ball valve is usually rotated 90 degrees; to open and close. Provides a rugged and reliable sealing surface. Metal to metal sealing resist injury from contamination.

BLEEDER (BLEED VALVE)

A device for removal of pressurized fluid. Used for the removal of air from an oil system.

BODY HALF

Other nomenclature "female half", "coupler", "socket". The receptacle portion of a quick-action coupling which normally includes the mechanism to lock the two quick-action coupling halves together.

BOOSTER

A hydraulic component that converts low hydraulic pressure from a large linear actuator into high pressure in a small linear actuator. Also called intensifiers, boosters are usually two different-sized hydraulic cylinders connected by a common piston.

BOUNDARY LUBRICATION

A form of lubrication between two rubbing surfaces without the development of a full fluid lubricating film.

BREAK AWAY

Automatic separation of a quick-action coupling when an axial separation force is applied.

BREAK-AWAY CLAMP

A clamping device that holds the quick-action coupling sleeve, allowing the body to move forward upon disconnect within either a single-acting or double-acting sleeve or backward upon connection within a double-acting sleeve.

BREATHER, AIR

A device permitting air movement between the atmosphere and the hydraulic component in which it is installed while preventing contaminants from entering the hydraulic component.

BRINELLING

Indentation marks (dimples) or grooves worn into the shoulder of the quick-action coupling male half by the locking (detent) balls in the female half.

BULK MODULUS

The measure of a hydraulic fluid's resistance to compressibility.

BURST PRESSURE

The pressure at which a device fails, loosing it's ability to contain pressure.

CAM

A circular component of a hydraulic piston pump that is mounted off-centre and moves pistons when rotated.

CAP, BLIND END

A hydraulic cylinder end closure that completely covers the bore area.

CAP, ROD END

The hydraulic cylinder end enclosure that covers the differential area between the bore area and the piston rod area.

CAVITATION

A circumstance that occurs in hydraulic pumps when existing space is not filled by available fluid. Cavitation will deteriorate the hydraulic oil and cause erosion of the inlet metal.

CENTRIFUGAL FORCE

A force directed outward and away from the centre of a rotating object.

CHECK VALVE

A hydraulic control valve that allows fluid to flow in one direction. Hydraulic check valves prevent backflow.

CIRCUIT, OPEN

A hydraulic circuit in which return fluid is directed to the reservoir.

CIRCUIT, PILOT

Used to control a main circuit or component.

CIRCUIT, REGENERATIVE

Used to increase hydraulic cylinder speed by directing rod end discharge to the piston side of the hydraulic cylinder. Can be incorporated into directional control valve as fourth position.

CLEVIS

A "U" shaped mounting device that contains a common pin hole at right angle or normal to the axis of symmetry through each extension.

CLOSED-CENTRE SYSTEM

A hydraulic system in which the hydraulic pump continually operates against a load, even in the neutral condition.

CLOSED CENTRE VALVES

This type of hydraulic valve is used in a hydraulic system where the hydraulic valve blocks the flow of hydraulic oil from the hydraulic pump into an accumulator. The accumulator is used to store the hydraulic oil under pressure. This hydraulic valve takes the pressure off the hydraulic pump and in neutral locks the hydraulic cylinder in place with no load on the hydraulic pump.

COMPLETE COUPLING

Other nomenclature hydraulic "coupling", "quick-action coupling". The two separate quick-action coupling halves connected together.

COMPRESSIBILITY

The change in volume of a unit of volume of a hydraulic fluid when subjected to a unit change of pressure.

CONDUCTOR

The hydraulic components such as pipes, tubes, and hoses that convey liquids throughout a hydraulic system.

CONNECT UNDER PRESSURE

Ability to connect coupling halves with internal pressure applied to either or both coupling halves.

CONTAMINANT

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

CONTROL VALVES

Used to harness the power of a hydraulic system. The three basic types of hydraulic control valves are tandem centre, open centre (motoring spool), and closed centre. Both the tandem centre and the closed centre types are available in a three-way or four-way valve. By opening or closing valves, you can control how much or in what direction a hydraulic piston moves. Valves can also control many pistons working with each other at the same time.

CORROSION INHIBITOR

Additive for protection of wetted metal surfaces from chemical attack by water or other contaminants.

CORROSION RESISTANCE

The ability of a hydraulic fluid to resist rust and deterioration within the hydraulic components of a hydraulic system.

COUPLING, FEMALE HALF

Other nomenclature "body half", "coupler", "socket".

COUPLING, MALE HALF

Other nomenclature "male tip", "nipple", "plug".

CRESCENT PUMP

A gear-within-gear pump that consists of an inner gear that is separated from the outer gear by a crescent-shaped component that provides both support and a seal.

CUSHION

A device which provides controlled resistance to motion.

CUSHION, CYLINDER

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

CYCLE

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

CYLINDER

A hydraulic actuator constructed of a plunger or piston inside a cylindrical housing. The piston or plunger operates because of pressurized liquid and converts fluid power into linear mechanical force and motion.

CYLINDER, ADJUSTABLE STROKE

A hydraulic cylinder equipped with adjustable stops at one end to limit piston travel.

CYLINDER CAP

A hydraulic cylinder end closure which completely covers the bore area.

CYLINDER CAPACITY, EXTENDING

Volume required for one full extension of the hydraulic cylinder.

CYLINDER CAPACITY, RETRACTING

Volume required by one full retraction of the hydraulic cylinder. (Generally, less than extending)

CYLINDER; DEPTH CONTROL

A mechanical or hydraulic device, adjustable, for limiting hydraulic cylinder stroke.

CYLINDER; DOUBLE ACTING

A hydraulic cylinder which can apply force and motion to the moveable element in either direction.

CYLINDER, NON-ROTATING

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

CYLINDER; REPHASING

A hydraulic cylinder design which permits the use of two or more hydrulic cylinders in series, automatically synchronizing hydraulic cylinder position at the end of each stroke.

CYLINDER; SINGLE ACTING

A hydraulic cylinder which can apply force to the moveable element in only one direction.

CYLINDER, TANDEM

Two or more hydraulic cylinders with interconnected piston assemblies.

CYLINDER THRUST

The push of a hydraulic cylinder in pounds: Thrust = Piston Area (in.) x Pump Pressure (PSI) or Thrust = bore diameter squared x .78 x PSI

DEAD-WEIGHT ACCUMULATOR

A hydraulic component used to store hydraulic fluid. The dead-weight accumulator increases and relieves pressure through the use of a weighted vertical piston.

DEMULSIBILITY

Ability of an oil to separate from water. The resistance of a hydraulic fluid to emulsification, or how well a hydraulic fluid resists mixing with water.

DETENT

A spring device which maintains the spool of a hydraulic directional control valve in position.

DETENT RELEASE

A mechanical, hydraulic or electrical device for releasing the detent.

DEWAXING

Removal of paraffin wax from lubricating oils to improve low temperature properties.

DIRT TOLERANCE

An indication of the internal clearance of a hydraulic pump. Hydraulic pumps with high dirt tolerance have the most clearance, are the least efficient, and allow the most backflow. Hydraulic pumps with low dirt tolerance have the least amount of clearance, are the most efficient, and allow little to no backflow.

DISPLACEMENT

The amount of liquid transferred from the inlet of the hydraulic pump to the outlet in a single revolution. Displacement can be fixed or variable.

DOUBLE-ACTING CYLINDER

A hydraulic cylinder which can apply force and motion to the moveable element in either direction.

DOUBLE-ACTING SLEEVE

Other nomenclature "two-way sleeve". Allows one hand push-to-connect or pull-to-disconnect convenience when the quick-action coupling female half is clamp or bulkhead mounted and connected to a hose.

DRIVE GEAR

The gear in a hydraulic gear pump that is attached to the driving mechanism. The drive gear turns the driven gear.

DRIVEN GEAR

The gear in a hydraulic gear pump that is rotated by the drive gear.

DRIVING MECHANISM

A component of a hydraulic gear pump that rotates the driving gear.

DUROMETER HARDNESS

A measure of elastomer hardness by use of a durometer.

DUST CAP

A removable device that protects the male tip half when disconnected from the female coupling half. Excludes contamination.

DUST PLUG

A removable device that protects the female body half when disconnected from the male tip half. Excludes contamination.

EMULSIFIER

An additive that promotes the formation of a stable mixture, or emulsion, of oil and water.

EMULSION

Intimate mixture of oil and water, generally of a milky or cloudy appearance.

EP ADDITIVE

Lubricant additive that prevent sliding metal surfaces from seizing under conditions of extreme pressure (EP).

FILTER

A device incorporated into a hydraulic system to remove contaminants from the hydraulic oil.

FITTING

A connector or closure for fluid power lines and passages.

FLOAT SPOOL

A spool valve design which connects all ports to the tank (return) port, usually in a detented fourth position, allowing a hydraulic cylinder or hydraulic motor to "float".

FLOW CHECKING

Other nomenclature "ball checking", "lock-up", "check-off". Occurs when the male tip half valve closes during high flow conditions, such as when quickly lowering a heavy loader.

FLOW CONTROL VALVE

A type of hydraulic valve consisting of a needle valve and a check valve placed in close proximity in a common body. Flow control valves regulate the flow of hydraulic fluid.

FLOW DEMAND

The amount of fluid movement in a hydraulic system that is required to perform a specific job or type of work.

FLOW RATE

The volume, mass or weight of a fluid passing through a given point in a given time. Flow rate is commonly measured in gallons per minute (gpm).

FLOW, TURBULENT

A flow situation in which fluid particles move in a random matter.

FLUID FRICTION

Friction due to the viscosity of fluids.

FLUID POWER

Energy transmitted and controlled through use of a pressurized fluid.

FLUID POWER SYSTEM

The transmission and control of power through the use of fluid pressure.

FLUID STABILITY

Resistance of a fluid to permanent changes in properties.

FIRE-RESISTANT FLUID

Hydraulic oil used especially in high temperature or hazardous applications.

FLOW, LAMINAR

A flow situation in which fluid moves in parallel laminar or layers.

FORCE MULTIPLICATION

The exponential increase in available power usually associated with tools and power transmission systems.

FOUR-WAY SPOOL VALVE

A spool valve that allows the reversal of hydraulic fluid flow. A four-way spool valve has five ports.

FULL-FLUID-FILM LUBRICATION

Presence of a continuous lubricating film sufficient to completely separate two surfaces.

GAS-LOADED ACCUMULATOR

A hydraulic component used to store hydraulic fluid. The gas-loaded accumulator increases and relieves pressure through the use of an inflatable bag. Also called an air-operated accumulator.

GATE VALVE

A hydraulic valve that either allows or prohibits the flow of hydraulic fluid. The gate valve consists of a plate-like obstruction that is raised and lowered into place to control the flow of hydraulic fluid.

GAUGE

An instrument or device for measuring, indicating, or comparing a physical characteristic, such as pressure or volume.

GEAR

A circular toothed component that engages, rotates, and transmits power to another circular toothed component when rotated.

GEAR PUMP

A hydraulic pump that uses meshed gears that rotate and move liquid through a hydraulic system.

GEAR-ON-GEAR PUMP

A hydraulic pump that creates pressure in a hydraulic system through the interaction of two toothed gears that are located adjacent to one another. One gear rotates and drives the other gear.

GEAR-WITHIN-GEAR PUMP

A hydraulic pump that creates pressure in a hydraulic system through the interaction of two toothed gears that are located one inside of the other. A gear with external teeth rotates and drives the internal gear.

GEROTOR

A gear-within-gear pump that consists of an inner gear with one less tooth than the outer gear.

GLOBE VALVE

A valve that adjusts the flow of hydraulic fluid between and including fully on and fully off. The globe valve consists of a circular plug and a tapered seat.