Hydraulic Power Variables 301

actual flow rate

The flow rate that a pump delivers during operation. Actual flow rate is measured when determining a pump's volumetric efficiency.

actual operating torque

The amount of torque required to power a hydraulic pump. Actual operating torque is used to calculate mechanical efficiency.

actuators

An active fluid system component at the end of the hydraulic circuit. Actuators, such as cylinders or hydraulic motors, convert hydraulic energy into mechanical energy.

A-weighted decibel scale

A scale for measuring noise production that reflects the exclusion of frequencies that humans do not normally hear. An A-weighted decibel scale is commonly used to measure workplace noise levels.

boundary layer

A layer of mostly stationary liquid that forms in the fluid closest to the inside wall of a conductor. A boundary layer forms during fluid flow.

burst pressure

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

cavitation

A condition caused by excess air that creates bubbles in hydraulic fluid. Cavitation can damage various system components, but it commonly affects the hydraulic pump because it results in an inadequate amount of fluid being delivered to the pump.

centimeters per second

cps. The number of centimeters that an object travels in one second. Centimeters per second is a unit used to measure the speed of linear components, such as a cylinder actuator.

clearances

The small space between components that allows for movement and lubrication. Clearances are necessary for the successful operation of many fluid system components.

component noise

Noise produced by the normal operation of a hydraulic component. Component noise is generated throughout a hydraulic system, particularly by the pump.

conductors

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

constant

A value or number that does not change. The mathematical constant 1714 is used when calculating hydraulic horsepower requirements.

control valves

An active fluid system component that controls fluid flow, direction, and pressure. Control valves function within given temperature and pressure ratings.

control valves

An active fluid system component that controls hydraulic fluid flow, direction, and pressure. Control valves include pressure relief valves and needle valves.

cubic centimeters

cm³ A metric unit of measurement used to measure volume. Cubic centimeters are used to measure the fluid displacement of a hydraulic pump.

cubic inches

in.³ An English unit of measurement used to measure volume. Cubic inches are used to measure the fluid displacement of a hydraulic pump.

cycle

One complete revolution or rotation of a rotary component. A cycle may also be one complete extension and retraction of a linear component.

cylinder actuator

An actuator that directs force in a straight line. Cylinder actuators may be single- or double-acting.

dBA

A noise level designation that indicates decibels measured on an A-weighted decibel scale. A dBA scale indicates the decibel output of a device.

decibels

dB. A unit of measurement that describes the intensity of a sound wave. Decibels below 80 are acceptable for a hydraulic system.

differential pressure

The difference in pressure measurements between any two points of a system or a component. Differential pressure is measured in pounds per square inch (psi) or pascals (Pa).

directly proportional

A constant ratio between two values in which one value changes in the same way as the other. The directly proportional values of hydraulic horsepower and flow rate mean that one increases or decreases as the other increases or decreases.

efficiency

A hydraulic system's work output divided by the pump's energy input. Efficiency ratings are used to determine the condition of a pump.

efficiency

The amount of power output a hydraulic system produces compared with the amount of power input. Efficiency ratings are used to determine operating conditions.

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.

flow capacity

A rating that indicates how much fluid a hydraulic pump moves into the system in a given amount of time. Flow capacity, also known as flow rate, is measured in gallons per minute (gpm) or liters per minute (lpm).

flow meter

An instrument used to measure the volume of fluid moving through a pipe or component. Flow meters are used to measure the actual flow rate of a pump.

flow rate

A rating that indicates how much fluid a hydraulic pump moves into the system in a given amount of time. Flow rate, also known as flow capacity, is measured in gallons per minute (gpm) or liters per minute (lpm).

fluid displacement

A pump rating that indicates the total volume of fluid a hydraulic pump moves into the system in one reciprocating or rotating cycle of the pump. Fluid displacement is measured in cubic inches or cubic centimeters.

fluid flow

The motion of a liquid or gas subjected to unbalanced forces or stresses. Fluid flow in a hydraulic system is subjected to resistance, which causes pressure to develop.

fluid noise

Noise produced by pressure surges in a hydraulic system. Fluid noise is produced by a hydraulic pump.

foot-pounds

ft.-lbs. An English unit of measurement used to measure work. One foot-pound indicates the amount of energy needed to move one pound a distance of one foot.

force

The push or pull that gives energy to an object. Force results from an object's interaction with another object.

force multiplication

The proportional increase in available power associated with hydraulic systems. Force multiplication allows a hydraulic system to produce an output force that is proportionally larger than the input force.

friction

A force that resists motion between two objects that are in contact with each other. Friction generates heat and increases wear in components.

gallons per minute

gpm. A unit used to measure the volume flow rate of fluid in a hydraulic system. Gallons per minute is an English unit of measurement.

gear pump

A fixed-displacement hydraulic pump that uses meshing gears that rotate to move fluid. Gear pumps are relatively inexpensive and compact.

gpm@rpm

gallons per minute@revolutions per minute. A term often used to describe a pump's flow rate. gpm@rpm describes how many gallons per minute of fluid a pump can move into the system at a specific driven speed.

hazard

Any source of potential damage, harm, or human health risk in the workplace. Hazards include noise pollution and extreme heat.

horsepower

hp. A unit used to measure power. One horsepower is equivalent to 33,000 ft.-lb. per minute.

hydraulic horsepower

HHP. The power required to drive a pump at a known flow rate and system pressure. Hydraulic horsepower is directly proportional to pump flow rate and system pressure.

hydraulic power

Energy derived from the movement of a liquid, such as oil or water, under pressure. Hydraulic power is converted into mechanical power when it leaves a hydraulic system.

hydraulic power variables

Any characteristic of a hydraulic system or component that can be measured and quantified. Hydraulic power variables include pump displacement, motor speed, and system efficiency.

hydraulic pumps

A mechanical power source that generates fluid flow. 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.

inches per second

ips. The number of inches that an object travels in one second. Inches per second is a unit used to measure the speed of linear components, such as a cylinder actuator.

inversely proportional

A constant ratio between two values in which one value changes in the opposite way as the other. The inversely proportional values of hydraulic horsepower and system efficiency mean that if hydraulic horsepower decreases, the system efficiency increases.

joules

J. A unit in the International System of Units (SI units) used to measure work. One joule equals 0.737 ft.-lb.

laminar flow

A type of fluid flow in which fluid particles move in continuous and parallel flow paths within fluid layers. Laminar flow minimizes friction.

linear motion

Movement that takes place along a straight line. Linear motion produces mechanical energy.

liters per minute

lpm. A unit used to measure the volume flow rate of fluid in a hydraulic system. Liters per minute is a metric unit of measurement.

load

The force that acts on an object and provides resistance. The load in a hydraulic system is pressurized fluid.

maximum allowable operating pressure

MAOP. A pressure rating that indicates the maximum amount of pressure a hydraulic system component can safely tolerate. The maximum allowable operating pressure is less than the maximum allowable working pressure (MAWP).

maximum allowable working pressure

MAWP. A pressure rating that indicates the pressure required for a component 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 pump. Mechanical efficiency can decrease due to friction between mechanical and fluid components.

newton-meters

N-m. A metric unit used to measure torque. Newton-meters may be used to express the torque of an electric motor.

noise

A sound that is typically unpleasant and interferes with a person's ability to hear. Noise is measured in decibels.

operating pressure

The pressure at which a system or component normally runs. Operating pressure is often used to specify the capabilities of specific hydraulic system components, such as control valves and actuators.

output horsepower

The horsepower a prime mover provides to a hydraulic pump. Output horsepower requirements determine prime mover selection.

overall efficiency

A pump rating that compares the total horsepower output to the total horsepower input. Overall efficiency is determined by multiplying volumetric efficiency by mechanical efficiency.

Pa

Pascals. A metric unit used to measure pressure. Pa units are used to express the pressure requirements for a hydraulic system.

Pascal’s Law

A physical law stating that pressure applied to a confined fluid at rest is transmitted equally throughout the fluid. Pascal's Law describes the relationship between force, pressure, and area.

pascals

Pa. A metric unit used to measure pressure. Pascal units are used to express the pressure requirements for a hydraulic system.

peak values

The point at which horsepower and torque are highest. After peak value is reached, speeds increase and horsepower and torque decrease.

personal protective equipment

PPE. Any clothing or device worn to minimize exposure to hazards and prevent injury. Personal protective equipment includes hearing protection and safety goggles.

positive-displacement pump

A hydraulic pump with a fixed fluid displacement per cycle or revolution. Positive-displacement pumps are used with a pressure relief valve on the outlet side.

pound-feet

lb.-ft. An English unit of measurement used to measure torque. Pound-feet may be used to measure the torque of an electric motor.

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.

power

The rate of work performed by a system. Power is expressed in units of horsepower.

pressure

The amount of force exerted upon a fluid or object per unit area. Pressure is commonly expressed in pounds per square inch (psi) or pascals (Pa).

pressure

The exertion of force upon a fluid. Pressure is measured in pounds per square inch (psi) or pascals (Pa).

pressure gauge

A mechanical instrument that measures the internal pressure of a vessel or system. Pressure gauges may have a dial display or a digital readout.

pressure rating

The range of pressure a hydraulic component can withstand during normal operation. Pressure ratings apply to various components of a hydraulic system.

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.

productivity rate

The amount of work performed in a particular time. Productivity rates depend on system variables such as flow rate and pressure.

psi

pounds per square inch. An English unit used to measure pressure. Psi units are used to express the pressure requirements for a hydraulic system.

resistance

The opposition to a force. Resistance can be created by friction.

revolutions per minute

rpm. A unit that indicates the number of rotations a cylindrical component completes in one minute. Revolutions per minute is a measurement of speed.

rotary motion

Spinning or turning movement that takes place around a fixed axis, without a change in linear position. Rotary motion produces mechanical energy.

rpm

revolutions per minute. A unit of measurement that indicates the number of rotations a cylindrical component completes in one minute. Rpm is a measurement of speed.

speed

The rate an object travels measured over a given period of time. Speed is used to measure both linear and rotational movement.

temperature ratings

A temperature range assigned to hydraulic components. The temperature rating of a hydraulic system is typically between 100°F and 125°F (38°C to 52°C).

theoretical flow rate

A pump's rated operating flow rate. Theoretical flow rate is higher than actual flow rate.

theoretical operating torque

The amount of torque a hydraulic component is capable of delivering. Theoretical operating torque is used when calculating the mechanical efficiency of a pump.

throttle

A control used to vary the speed of a mechanical device, such as a diesel engine. A throttle on an engine may be used to change the driven speed of a pump.

torque

A force that produces rotary motion. Torque is measured in pound-feet in the English system and newton-meters in the metric system.

turbulent flow

A type of fluid flow in which fluid particles move roughly and erratically within fluid layers. Turbulent flow can result from abrupt changes in the direction or diameter of a conductor.

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.

velocity

The speed with which fluid flows through a hydraulic conductor. Fluid velocity is measured in inches per second (ips) or meters per second (mps).

vibration noise

Noise produced in response to pressure surges. Vibration noise is produced by the hydraulic pump.

volume

The amount of space that a substance or object occupies within a container. Volume is measured in cubic inches or cubic centimeters.

volume flow rate

The total volume of hydraulic fluid that moves through a hydraulic system component in a given period of time. Volume flow rate is measured in gallons per minute (gpm) or liters per minute (lpm).

volumetric efficiency

An efficiency rating that describes the amount of leakage in a hydraulic pump. Volumetric efficiency is the most commonly used efficiency rating when determining the condition of a hydraulic pump.

work

The result of a force applied to an object and the distance through which the force travels. Work is expressed in foot-pounds or joules.

working pressure

A pressure rating that indicates the pressure required for a component to overcome the resistance of the applied load in a system component. Working pressure is sometimes referred to as the maximum allowable working pressure (MAWP).