Glossary and index of fluid power principles and components

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

H

HARDNESS
Resistance to indentation. See durometer hardness.

HEAD
The measure of pressure at the base or other reference point of a column of fluid. Normally measured in feet of water.

HEAT
The form of energy that has the capacity to create warmth or to increase the temperature of a substance. Any energy that is wasted or used to overcome friction is converted to heat. Heat is measured in calories or British Thermal Units (BTU's). Once BTU is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit. In the metric system one calorie is the amount of heat required to raise the temperature of one gram of water from 3.5 C to 4.5 C (called a small calorie). If the temperature change is from 14.5 C to 15.5 C, the unit is the normal calorie.

HEATER
An electro-mechanical device that converts electricity into heat, normally for use in raising the temperature of fluid stored in a reservoir or tank.

HEAT EXCHANGER
See COOLER.

HEAT RESISTANCE
The property or ability to resist the deteriorating effects of the elevated temperatures.

HELIX
A shape formed by spiraling a wire or other reinforcement around the cylindrical body of a hose; typically used in suction hose.

HORSEPOWER
The measure of energy used in description of the normal power level in a system. 1 horsepower = 550 lb.-ft./ min. of work.

HOSE
A passage used to transport fluid between components in a fluid power system. Normally a flexible conduit consisting of a tube, reinforcement, and usually an outer cover

HUNTING
Tendency for a system to oscillate continuously.

HYDRAULIC BALANCE
A condition of equal opposed hydraulic forces acting on a part in a hydraulic component.

HYDRAULIC CONTROL
A control which is actuated by hydraulically induced forces.

Hydraulic cylinder : An actuator driven by hydraulic fluid.

HYDRAULIC POWER
See FLUID POWER.

HYDRAULIC MOTOR
See FLUID MOTOR.

HYDRAULICS
Engineering science pertaining to liquid pressure and flow.

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

HYDROKINETICS
Engineering science pertaining to the energy of liquids in motion.

HYDROPNEUMATICS
Pertaining to the combination of hydraulic and pneumatic fluid power.

HYDROSTATICS
Engineering science pertaining to the energy of liquids at rest.

HYDROSTATIC TESTING
The use of liquid pressure to test a hose or hose assembly fro leakage, twisting, and/or hose change in length.

HYSTERESIS
The difference between the response of a unit r system to an increasing signal and the response to a decreasing signal.

HZ (HERTZ)
A measure of the number of cycles that occur in a specific period of time. Usually the time base is the second, but the time base may be any acceptable measure of time. Synonymous term for "cycles per second".