Terminology

A

• Accumulator: In a closed system, the accumulator stores the pressurized oil \ A container which stores fluid under pressure. Used as an energy source or to absorb hydraulic shock. Common types are piston, bladder, or diaphragm.

• Actuator: Device which converts hydraulic power into mechanical force and motion.

• Aeration: The presence of air bubbles in hydraulic oil in a hydraulic system.

• ANSI: American National Standards Institute

• ASAE: American Society of Agricultural Engineers

B

• Back Pressure: The pressure encountered on the downstream or return side of a component.

• Ball Valve: A type of manual shut off valve.

• Base Plate: The end of a cylinder opposite the rod end. Typically, a clevis end or cross tube is welded to a plate to help secure a cylinder.

• Bleed: The process of removing air from a hydraulic system.

• Bleeder/Bleeder Valve: A device for removal of pressurized fluid. Used to bleed air from system.

• Barrel: The metal housing of a cylinder designed to protect the internal workings of the cylinder and to keep the hydraulic fluid inside of the cylinder.

• Breather Plug: A plug that can be installed in a hydraulic cylinder's port to help relieve pressure.

• Bore: The interior diameter of a cylinder barrel.

• Bypass: A secondary passage for fluid flow.

C

• Case Drain: A port to drain excess internal oil from a motor

• Cavitation: 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.

• Check Valve: A valve that allows fluid to flow in one direction only. Requires a certain pressure to open the valve and closes when that pressure isn't met to prevent the backflow of fluid.

• Closed Center Type: Has the inlet port blocked from the outlet and work ports in neutral.

• Cracking Pressure: The pressure at which a pressure operated valve begins to pass fluid.

• Cylinder Depth Control: A mechanical or hydraulic device, adjustable, for limiting cylinder stroke.

• Cylinder: The chamber within which a rod and piston move back and forth under the influence of fluid pressure, gravity, or mechanical force.\ A device which converts hydraulic energy into linear mechanical motion and force.

D

• Dead Head: Operating a hydraulic system when the fluid can't flow properly due to a valve being closed or blockage in the system.

• Detent Release: A mechanical, hydraulic or electrical device for releasing the detent.

• Differential Pressure: Difference in pressure between two given points.

• Detent: A catch or lever that locks the movement of the valve handle and spool in place.\ A spring device which maintains the spool of a directional control valve in position.

• Displacement: The volume of fluid that a pump can move in a single cycle.

• Double Acting Cylinder: A cylinder which can apply force and motion in either direction.

• Drift: Refers to when a cylinder is under load and the rod slowly starts to retract without any input from the operator.

• Dust Cap: A cover for a quick coupler to prevent dust and other debris from enter a hydraulic system.

E

• Extended Length: The overall length of a cylinder when the chrome rod is fully extended.

F

• Filter: A device incorporated into a hydraulic system to remove contaminants from the oil.

• Fitting: Commonly referred to as an adapter fitting it is a device for creating a seal within a hydraulic system. A device for connecting hose or pipe to hydraulic components.

• Float Spool (Position): 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 Meter: A device that measures the flow of fluid in a hydraulic system

• Flow Rate: The volume of fluid passing through the system or component in gal. per min.

• Fluid Power System: The transmission and control of power through the use of fluid pressure.

• Four Way Valve: A 4-port valve (in, out and 2 work) used with double acting cylinders, bi-directional motors.

G



• Gland: Also known as the cylinder head, its primary function is to ensure that the pressure chamber stays pressurized. It is the part on the rod end of a cylinder that, depending on the type of cylinder; screws into the barrel, is welded on to the end of the barrel, or is secured in place by tie bolts.

• GPM: Gallons Per Minute

H

• Heat Exchanger: Regulates the temperature of a hydraulic system and removes any excess heat 

I

• ID: Internal Diameter

L

• 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.

M

• Manifold: Regulates fluid flow between pumps, actuators, and other components.

• Maximum Rated Pressure: The maximum pressure at which a component should be operated on a continuous basis, usually the relief valve setting at maximum flow rate.

• Motor: A device which converts hydraulic energy into rotary motion, either fixed or variable.

N

• Needle Valve: A regulating valve the allows for fine adjustments to be made to the flow of oil

O

• OD: Outside Diameter

• Open Center (Tandem) Type: Has the inlet port connected to the outlet (tank) port in neutral.

P

• Parallel Type: 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.

• Pilot Circuit: Used to control a main circuit or component.

• Piston: A fitting within a cylinder that moves back and forth with the rod.

• Port: The internal or external terminus of a passage. The point where the fitting is attached.

• Positive Displacement Pump: A pump that displaces an exact amount of fluid per revolution, such as a gear, vane, or piston pump.

• 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.

• Pressure: The force per unit area, expressed in pounds per square inch (psi), bars, or atmospheres.

• PSI: Pounds Per Square Inch

• PTO: Power Take Off

• Pump: A device which converts mechanical energy into hydraulic. energy, either fixed or variable.

R

• Ram: A term commonly used to refer to the rod and piston within a cylinder.

• Regenerative Circuit: 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.

• Re-phasing Cylinder: A cylinder design which permits the use of two or more cylinders in series, automatically synchronizing cylinder position at the end of each stroke.

• Reservoir: A container which stores the liquid in a fluid power system.

• Rod: A bar which drives the piston back and forth through the chamber of the cylinder.

S

• Seal: A device which prevents or controls the escape or passage of hydraulic fluid.

• Seal: A tight closure that prevents the passage of hydraulic fluid.

• 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.

• Series Type: 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 of valve permits simultaneous operation of two or more functions with the same oil flow. However, the total pressure requirements of all functions are accumulative.

• Single Acting Cylinder: A cylinder which can apply force in one direction only. 

• Spool: The internal passageways within a hydraulic valve. The standard spool has two ports that are blocked when the system is in neutral.

• Stroke: The movement, in either direction, of the piston and rod within a cylinder.

T

• Thread: Ribbing within a pipe or fitting that allows it to create a seal with another pipe or fitting. 

• Three Way Valve: A 3-port valve (in, out ~r,d work) normally used with a single acting cylinder or uni-directional motor.

• Two Way Valve: A 2-port valve with inlet and outlet ports.

• Two/Three/Four Position: The number of positions in which a valve can be positioned.

V

• Valve: A device which controls fluid flow rate, direction, or pressure.