Hydraulic Terms
We have
compiled a comprehensive list of commonly used hydraulic terms which
may prove helpful in purchasing, troubleshooting and repairing your
hydraulic unit.
- Accumulator
- A container in which fluid is stored under pressure as a source
of fluid power.
- Actuator,
pneumatic/hydraulic - A device in which power is transferred from
one pressurized medium to another without intensification.
- Additive
- A chemical added to a 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 atmosphere
and the component in which it is installed.
- Cavitation
- A localized gaseous condition within a liquid stream which occurs
where the pressure is reduced to the liquids vapor pressure.
It is caused by an insufficient supply of oil.
- Circuit,
open - A circuit in which return fluid is directed to the reservoir.
- Contaminant
- Any material or substance which is unwanted or adversely affects
the fluid power system or components, or both.
- Cushion
- A device which provides controlled resistance to motion.
- Cylinder
cap - A cylinder end closure which completely covers the bore
area.
- Cylinder
capacity, extending - Volume required for one full extension of
the cylinder.
- Cylinder
capacity, retracting - Volume required by one full retraction
of the cylinder. (Generally, less than extending)
- Cylinder
force, theoretical - The pressure multiplied by the effective
piston area, ignoring friction. For double acting cylinders the
value must be given for both direction of stroke. (PSI x A²
= F)
- Cylinder,
bore - The internal diameter of the cylinder body.
- Fluid
power - Energy transmitted and controlled through use of a pressurized
fluid.
- Heat
exchanger - A device which transfers heat through a conducting
wall from one fluid to another. (Typically to cool a system.)
- Hose,
wire braided - Hose consisting of a flexible material reinforced
with woven wire braid.
- Hydraulic
motor - A device which converts hydraulic fluid power into rotary
motion.
- Hydraulic
motor, fixed displacement - A hydraulic motor in which the displacement
per unit output motion cannot be varied.
- Hydrostatic
transmission - Combination of one or more hydraulic pumps and
motors forming a unit.
- Line,
return - A pipe (conductor) to return the working fluid to the
reservoir.
- Intensifier
- A device which converts low pressure fluid power into higher
pressure fluid power.
- Manifold
- A conductor which provides multiple connection ports.
- Port
- A terminus of a passage in a component to which conductors can
be connected.
- Power
unit - A combination of pump, pump drive, reservoir, controls
and conditioning components to supply hydraulic power to a system.
- Pressure
- Force per unit area, usually expressed in pounds per square
inch (bar). PSI
- Pressure,
atmospheric - Pressure exerted by the atmosphere at any specific
location. (Sea level pressure is approximately 14.7 PSI absolute.
1bar = 14.5 PSI).
- Pump
- A device which converts mechanical torque and motion into hydraulic
fluid power.
- Pump,
fixed displacement - A hydraulic pump in which the volume displaced
per cycle cannot be varied.
- Pump,
variable displacement - A hydraulic pump in which the volume displaced
per cycle can be varied.
- Quick
disconnect coupling - A component which can quickly join or separate
a fluid line without the use of tools or special devices.
- Reservoir
(tank) - A container for storage of liquid in a fluid power system.
- Seal,
dynamic - A sealing device used between parts that have relative
motion.
- Seal,
static (gasket) - A sealing device used between parts that have
no relative motion.
- Switch,
pressure - An electric switch operated by fluid pressure.
- Transducer,
flow - A device which converts fluid flow to an electrical signal.
- Trunnion
- A mounting device consisting of a pair of opposite projecting
cylindrical pivots. The cylindrical pivot pins are at right angle
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 and material.
- Vacuum
- Pressure less than ambient atmospheric pressure.
- Valve
- A device which controls fluid flow direction, pressure or flow
rate.
- Valve,
directional control - A valve whose primary function is to direct
or prevent flow through selected passages.
- Valve,
flow control (flow metering) - A valve whose primary function
is to control flow rate.
- Valve,
flow dividing - A valve which divides the flow from a single source
into two or more branches.
Definitions
from 1994/1995 Fluid Power Handbook & Directory by the editors
of Hydraulics & Pneumatics
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