Hydraulic Principles and System Design 391

bar

A metric unit of measurement that may be used to measure pressure. One bar is equal to 100,000 pascals.

beta ratio

A filter rating that indicates a filter's ability to remove particles of a specific size or smaller at a constant flow rate. Beta ratio is calculated during a multipass test by counting particles upstream and downstream of the filter.

bore

The interior of a cylindrical object. The bore of a cylinder actuator contains the movable elements within the cylinder barrel.

burst pressure

A rating that indicates the pressure at which a conductor fails during a pressure rating test. Burst pressure is higher than the working pressure.

cap end

A closure on one end of a cylinder actuator that covers the bore area to protect interior elements from damage. The cap end of a cylinder actuator is opposite the rod end.

clearance

A specified amount of space or distance between two objects or areas. Clearance between the hydraulic cylinder and machine components is necessary.

computer-aided design

CAD. A computer software program that aids in the design and drawing of a part, process, or building. Computer-aided design programs allow designers to evaluate how components can be used in a particular system.

conductors

A passive fluid system component that conveys fluid through a hydraulic system. Conductors include pipes, tubes, and hoses.

contamination

The presence of any foreign material in a hydraulic or pneumatic fluid that has a negative effect on the fluid system. Contamination may be material or a form of energy.

control valves

An active fluid system component that controls the flow rate, direction, and pressure of fluid as it moves through a fluid system. Control valves are placed strategically throughout a system.

cylinder actuator

A fluid power actuator that directs force in a straight line. Cylinder actuators include a movable piston and rod that reciprocate in response to fluid pressure.

diameter

The distance from one edge of a circle that passes through the center to the opposite edge. The diameters of the piston and rod in a cylinder actuator affect its force output.

effective piston area

The surface of the piston at the cap end or rod end of a cylinder actuator. The effective piston area depends on whether the cylinder exerts force during extension or retraction.

emergency cut-off valve

A safety device that halts all fluid action immediately. An emergency cut-off valve is located between the pump and the master valve.

factor of safety

A ratio of a component's absolute strength compared to the theoretical applied load it will experience. A factor of safety indicates the reliability of a component.

filters

A fluid conditioning device that removes solid contaminants from hydraulic fluid. Filters may be classified by micron rating, beta ratio, and filtration efficiency.

filtration efficiency

A filter rating that indicates the amount of particles of a given size a filter is able to trap. Filtration efficiency is calculated using the beta ratio and is expressed as a percentage.

flow rate

The total volume of fluid that moves through a hydraulic system or individual component in a given amount of time. Flow rate is expressed in gallons per minute (gpm) or liters per minute (lpm).

formulas

A representation of a known mathematical equation using numbers, letters, and variables. Formulas for fluid power systems include calculations for flow rate, pressure, and horsepower.

friction

The resistance to motion between two components that are in contact with each other. Friction can alter a cylinder actuator's theoretical output force.

horsepower

hp. A unit of power used to describe motor strength. One horsepower equals 746 watts.

hp

Horsepower. A unit of power used to describe motor strength. One hp equals 746 watts.

hydraulic fluid

A thick liquid, typically oil, that flows through a hydraulic system to transmit power. Hydraulic fluid is stored in the reservoir in a hydraulic system.

hydraulic motor

An actuator that rotates to convert hydraulic energy into mechanical power. A hydraulic motor can rotate continuously.

hydraulic pump

A mechanical power source that creates fluid flow and pushes fluid through a hydraulic system. A hydraulic pump receives energy from a prime mover, such as an electric motor or engine.

hydraulic safety valve

A safety device that relieves pressure in a hydraulic system. A hydraulic safety valve is used in conjunction with a rotating cylinder and a check valve.

inch-pounds

in-lb. A unit in the English system used to measure torque. The inch-pound's International System of Units equivalent is the newton-meter.

injection injury

A small puncture of the skin or body tissue caused by high-pressure fluid. Injection injuries usually occur while operating or inspecting pressurized hydraulic equipment.

inlet strainers

A coarse surface-type filter installed on a hydraulic pump inlet line to filter fluid entering the pump. An inlet strainer has a micron rating of 75 or higher.

inner diameter

ID. The interior surface of a hole or cylindrical feature. The inner diameter of a conductor hose is a critical measurement when sizing conductors for a fluid system.

job specifications

A document containing the essential components of a job or function. Job specifications include a summary of the work to be performed, the primary duties, and the minimum qualifications needed to perform the essential functions of the job.

linear actuator

A fluid power actuator that directs force in a straight line. Linear actuators are at the end of a hydraulic circuit and include single- and double-acting cylinders.

load

The force or pressure placed on a system or component. The load in a hydraulic system is pressurized fluid.

manifolds

A conductor in a fluid system that provides multiple connection ports. Manifolds reduce the number of separate fittings and connections in a fluid system.

MAWP

Maximum allowable working pressure. A pressure rating that indicates the highest pressure a component can experience during operation in order to overcome the resistance of the applied load. MAWP may be referred to as the working pressure.

maximum allowable working pressure

MAWP. A pressure rating that indicates the highest pressure a component can experience during operation in order to overcome the resistance of the applied load. Maximum allowable working pressure may be referred to as the working pressure.

mechanical efficiency

An efficiency rating that describes the amount of energy loss in a hydraulic component. Mechanical efficiency decreases due to friction between mechanical and fluid components.

micron ratings

A filter rating that indicates the largest size particle that can pass through the filter. Micron ratings are based on a filter's pore size.

microns

µ. A metric unit of measurement equal to one thousandth of a millimeter. Microns are often used to measure particles and pore sizes of hydraulic filters.

motor displacement

The volume of fluid a motor requires for one complete rotation of its output shaft. Motor displacement is measured in cubic inches or cubic centimeters.

multipass test

A test that measures filter performance under controlled operating conditions and at the filter's specified flow rate. A multipass test evaluates if a filter can achieve the cleanliness rate needed for the system.

newton-meters

N-m. A unit in the International System of Units used to measure torque. The newton-meter's English equivalent is the inch-pound.

nominal size

The stated dimensions or ideal dimensions of a part. Nominal size is different from the actual size of a part.

nomograph

A graph containing parallel scales gradated for different variables so that when a straight line connects values of any two scales, the related value is indicated. Nomographs assist in estimating data that normally would require calculations.

operating pressure

The pressure at which a system normally runs. The operating pressure of a fluid system may be used when specifying the capabilities of fluid system components.

outer diameter

OD. The exterior diameter of a cylindrical or round feature. The outer diameter of a conductor tube is a critical measurement when selecting a conductor for a fluid system.

output shaft

A shaft that rotates to transmit torque. An output shaft is mechanically linked to a motor or actuator.

pi

A mathematical constant that relates the diameter of a circle to its circumference. Pi equals 3.14 when used to calculate the area or circumference of a circle.

pounds per square inch

psi. An English unit used to measure pressure. Pounds per square inch units are used to express the pressure requirements for a hydraulic system or a hydraulic system component.

pressure

The force exerted on a fluid or object per unit area. Fluid pressure may be expressed using pounds per square inch (psi) or bar units.

pressure drops

The difference in pressure measurements between any two points of a system or component. A pressure drop occurs when force acts on a fluid as it flows through a hydraulic system component.

pressure gages

An instrument that measures fluid pressure. Pressure gages in a fluid system are installed throughout conductor lines to indicate pressure levels.

pressure ratings

An indication of the amount of pressure a fluid conductor can withstand. Pressure ratings generally depend on a conductor's wall thickness.

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.

psi

Pounds per square inch. An English unit used to measure pressure. The psi unit is used to express the pressure requirements for a hydraulic system or a hydraulic system component.

pull force

The force a cylinder exerts upon retraction. Pull force occurs when pressure acts on the rod end of a cylinder.

push force

The force a cylinder exerts upon extension. Push force occurs when pressure is introduced to the cap end of a cylinder.

radius

The distance from the center to the edge of a circle. Twice the length of a circle's radius equals its diameter.

rod end

The portion of a cylinder actuator containing the piston rod that extends out of the barrel. The rod end of a cylinder actuator is opposite the cap end.

rotary actuator

An actuator that rotates in fixed degrees to convert fluid energy into mechanical power at the end of a hydraulic circuit. A rotary actuator develops rotational force.

schedule number

A number that describes the thickness of a pipe wall. Schedule 40 is the most common metal pipe size.

square

The product of a number multiplied by itself. Square numbers may be used to calculate the area of a circle.

square centimeters

cm². A metric unit of measurement that is equal to a square with sides that are one centimeter long. Square centimeters are found by multiplying the square's length and height.

square inches

in.² A unit of area measurement that is equal to a square with sides that are one inch long. Square inches are found by multiplying the square's length and height.

stroke

The length of travel of a piston rod when it moves into or out of a cylinder. Stroke length is adjustable in some cylinder actuators.

theoretical output force

The rated push or pull an object exerts. The theoretical output force of a cylinder actuator depends on the effective piston area and the supplied fluid pressure.

theoretical torque

The amount of rotational force produced at the output shaft of a motor, assuming 100% operating efficiency for the motor. Theoretical torque may be expressed in inch-pounds or newton-meters.

torque

A twisting or turning force that produces rotation. Torque is produced in a rotary actuator as a result of the pressure drop across the motor.

volume

The amount of space contained within a three-dimensional shape. Volume may be measured in cubic inches or cubic meters.

wall thickness

A value that indicates the thickness of the wall of a conductor. Wall thickness may remain unchanged as outside diameter and inside diameter change.

working pressure

A pressure rating that indicates the highest pressure a component can experience during operation in order to overcome the resistance of the applied load. Working pressure may be referred to as the maximum allowable working pressure, or MAWP.

working pressure

A pressure rating that indicates the highest pressure a component can experience during operation in order to overcome the resistance of the applied load. Working pressure may be referred to as the maximum allowable working pressure.