container which stores fluid under pressure. Used as an energy source
or to absorb hydraulic shock. Common types are piston, bladder and
BLEEDER (BLEED VALVE): A device for removal of pressurized fluid. Used to bleed air from system.
A gaseous condition within a liquid stream caused when pressure is
reduced to the vapor pressure. To be avoided due to destructive effects
on pumps and motors.
CIRCUIT; PILOT: Used to control a main circuit or component.
CIRCUIT; REGENERATIVE: Used
to increase cylinder speed by directing rod end discharge to the piston
side of the cylinder. Can be incorporated into directional control
valve as fourth position.
CYLINDER: A device which converts hydraulic energy into linear mechanical motion and force.
CYLINDER; DOUBLE ACTING: A cylinder which can apply force and motion in either direction.
CYLINDER; SINGLE ACTING: A cylinder which can apply force in one direction only.
CYLINDER; DEPTH CONTROL: A mechanical or hydraulic device, adjustable, for limiting cylinder stroke.
A cylinder design which permits the use of two or more cylinders in
series, automatically synchronizing cylinder position at the end of
DETENT: A spring device which maintains the spool of a directional control valve in position.
DETENT RELEASE: A mechanical, hydraulic or electrical device for releasing the detent.
FILTER: A device incorporated into a hydraulic system to remove contaminants from the oil.
FITTING: A device for connecting hose or pipe to hydraulic components.
FLOAT SPOOL (POSIT10N):
A spool valve design which connects all ports to the tank (return)
port, usually in a detented fourth position, allowing a cylinder or
motor to "float".
FLOW RATE: The volume of fluid passing through the system or component in gal. per min. (or 11m)
FLUID POWER SYSTEM: The transmission and control of power through the use of fluid pressure.
MOTOR: A device which converts hydraulic energy into rotary motion, either fixed or variable.
PORT: The internal or external terminus of a passage. The point where the fitting is attached.
PRESSURE: The force per unit area, expressed in pounds per square inch (psi), bars, or atmospheres.
PRESSURE; BACK: The pressure encountered on the downstream or return side of a component.
PRESSURE; CRACKING: The pressure at which a pressure operated valve begins to pass fluid.
PRESSURE; MAXIMUM RATED: The
maximum pressure at which a component should be operated on a
continuous basis, usually the relief valve setting at maximum flow
PUMP: A device which converts mechanical energy into hydraulic. energy, either fixed or variable.
RESERVOIR: A container which stores the liquid in a fluid power system.
SEAL: A device which prevents or controls the escape or passage of hydraulic fluid.
VALVE: A device which controls fluid flow rate, direction, or pressure.
VALVE; DIRECTIONAL CONTROL: A device for directing or preventing the oil flow in a system.
OPEN CENTER (TANDEM) TYPE: Has the inlet port connected to the outlet (tank) port in neutral.
CLOSED CENTER TYPE: Has the inlet port blocked from the outlet and work ports in neutral.
TWO-WAY: A 2 port valve with inlet and outlet ports.
THREE-WAY: A 3 port valve (in, out ~r,d work) normally used with a single acting cylinder or uni-directional motor.
FOUR-WAY: A 4 port valve (in, out and 2 work) used with double acting cylinders, bi-directional motors.
TWO, THREE, FOUR POSITION: The number of positions in which a valve can be positioned.
A multiple spool valve in which the return oil from the first spool is
directed to the inlet of the second spool (and from the second to the
third, etc.). This type valve permits simultaneous operation of two or
more functions with the same oil flow. However, the total pressure
requirements of all functions are accumulative.
A multiple spool valve in which the inlet oil is connected to all
spools simultaneously. If more than one spool is actuated, the function
requiring the lowest pressure will operate first.
SERIES-PARALLEL TYPE: A
multiple spool valve which has all spools connected to the open center
passage in neutral. However, when actuated, the upstream valve takes
full priority. The return oil is directed to downstream spools as in a
series type valve.
POWER BEYOND (HIGH PRESSURE CARRYOVER):
A sleeve attachment which permits the oil flow from one valve (when in
neutral) to be used by another valve downstream. Hence, a 3-spool valve
cou1d be connected to a 2-spool valve to create a 5-spool valve, The
first valve takes priority and thrust have a separate outlet port to
return oil from an activator back to the reservoir.
LOAD CHECK (LIFT CHECK):
A device which prevents a load from dropping when a valve is shifted,
until ample pressure and flow is available to hold or move the load