American National Standards Institute

American Society of Agricultural Engineers (sets standards for many hydraulic components for agricultural use)

A container which stores fluids under pressure as a source of hydraulic power. It may also be used as a shock absorber.

A device which converts hydraulic power into mechanical force and motion. (Examples: hydraulic cylinders and motors.)

The presence of dispersed air bubbles in the system's hydraulic fluid. Aeration can result in severe erosion of pump components when the bubbles collapse as they suddenly encounter high pressure when entering the discharge area of the pump.

The pressure encountered on the return side of a system.

These valves are manual shut-off valves. They differ from needle valves in that they cannot meter the flow of oil. These valves can be used to shut off the flow of oil while repairs are made to the system or for shutting off the flow in one particular line of a circuit, etc.

The end of the cylinder opposite the rod end. Some device, such as a cross tube or a clevis, is welded directly onto the base plate and used to secure the cylinder.

The process by which air is removed from a hydraulic system.

The inside diameter of the cylinder tube.

The minimum pressure which starts moving an actuator.

A vent installed into a port on a hydraulic cylinder to allow a double-acting cylinder to be used in a single-acting application.

A secondary passage for fluid flow.

An external port used to drain off the small amount of oil that collects in the seal and bearing pockets of a hydraulic motor or pump. This oil has slipped through clearances between the gear sides and the housing. If the oil is not drained, the pressure inside the housing would blow out the shaft seal. This becomes a problem only when two or more hydraulic motors are connected in a series.

This is a style of piston seal that is a non-positive seal. It is made from cast iron and is like the piston rings on an engine piston.

A phenomenon which occurs when the pressure at a point in a hydraulic system is lowered below the vapor pressure of the oil in the system. This allows bubbles of oil vapor to form in the oil. If this occurs at the pump inlet, the quick pressure rise inside the pump forces these bubbles to collapse violently. This can cause erosion of metal parts, noise and vibration.

These valves are most often a ball, or poppet, and spring design. Oil is allowed to flow unrestricted in one direction by pushing the poppet off its seat. Oil is blocked in the other direction by forcing the poppet onto its seat and closing off the flow path. Applications include load holding, directing flow into other accessory valves, and any other application where backflow is unwanted.

A series of component parts connected to each other by fluid lines or passages. Usually part of a "system".

A "U" shaped bracket used for mounting a cylinder to an application. A clevis is either located at the rod end or on the end cap or both. The clevis is two narrow tangs that have a machined hole to receive a common pivot pin.

A hydraulic system in which the control valves are closed during neutral, stopping oil flow. Flow in this system is varied, but pressure remains constant.

A valve in which inlet and outlet ports are closed in the neutral position, stopping flow from pump.

Once the fluid has been circulated, much like an open loop system, the oil is recirculated at low pressure back to the pump inlet, rather than being returned to the reservoir. This type circuit is more adaptable to hydraulic motor applications.

A heat exchanger which removes heat from a fluid. (See "Heat Exchanger.")

A compound or material deposited as a film on a metal surface that either provides physical protection against corrosive attack.

A device to connect two hoses or lines, or to connect hoses to valve receptacles.

The pressure at which a relief valve, etc., begins to open and pass fluid.

Small pieces of pipe welded to the base plate or the rod of a cylinder which serve as a means to attach a cylinder to an application.

Cushion Valves (or crossover relief valve). These valves absorb pressure spikes caused if a motor or cylinder is brought to an abrupt stop while moving a heavy load. Both the inlet line and the outlet line are connected to each other inside the valve body by two relief valves, each facing opposite the other. If a spike occurs, the valve can discharge the flow to the opposite line. There are four ports on the cushion valve - two are connected to the cylinder or motor, and two are connected to the control valve, and slows down the piston.

A single complete operation of a component which begins and ends in a neutral position.

A device for converting fluid power into linear or circular motion. Referred to as an "actuator". Customers also refer to these as "pistons", "rams", and "pushrods."

A situation that occurs when pressure within a system is stopped or blocked with no place to relief. Pump flow continues to build pressure until something gives way within the system, resulting in damage.

A device which maintains a preselected spool position (either "in" or "out") on a directional control valve.

The difference in pressure between any two points in a system or a component. (Also called a "pressure drop.")

The armature is directly linked to the spool and provides the physical force for lifting.

A valve which directs oil through selected passages. (Usually a spool or rotary valve design.)

The volume of oil displaced by one complete stroke or revolution (of a pump, motor, or cylinder). Usually expressed as CIR (cubic inches per revolution). For example, if a motor rated is at 2.2 CIR, this indicates that for every revolution, the motor displaces or expels 2.2 cubic inches of fluid.

Two pumps in one housing. Two separate inlets and outlets are utilized. One shaft drives both pumps. There is a pump at the shaft end and one at the cover end.

A cylinder in which fluid power can be exerted on both sides of the piston. Sometimes referred to as "power up, power down". This cylinder can be controlled in both the extend and retract phases.

Motion of a cylinder or motor due to internal leakage past components in the hydraulic system.

The coils operate in a dry environment, protected by solenoid housing.

A removable device that protects the male tip half when disconnected from the female coupling half. Excludes contamination.

Capable of movement or motion.

This is a seal that seals a moving surface like a rod or a barrel.

Uses a locking ring that fits onto the outside of the bearing. When the ring is rotated up to 180 degrees, the shaft is secured to the bearing. The letters HC indicate eccentric collar.

A valve that is opened and closed by a solenoid.

The length of a cylinder measured from the center of the mounting hole on the rod end to the center of the mounting hole on the base end when the piston and rod are in the "out" position. The longest overall length of a cylinder.

A device which removes solids from a fluid.

An adapter designed to connect different types of hose, tubing or pipe together.

A pump in which the output per cycle cannot be varied.

This valve connects the "A" and "B" work ports to the tank port in a detented fourth position. This allows oil to flow from both ends of a double-acting cylinder which, in turn, allows the rod to extend or retract depending on the force applied to the rod. For example, a bulldozer blade or a snowplow blade.

A valve which controls the rate of flow.

A valve which divides the flow from one source into two or more branches. (Includes "priority" and "proportional" types.)

A testing device which gauges either flow rate, total flow, or both.

The volume of fluid passing a point in a given time.

Energy transmitted and controlled through use of a pressurized fluid.

A push or pull acting upon a body. In a hydraulic cylinder, it is the product of the pressure on the fluid multiplied by the effective area of the cylinder piston. It is measured in pounds or tons.

This valve is identical to four-way, three-position with the fourth position as "float" or "motor" position. Power up, gravity down.

Controls double-acting cylinders. Four-way denotes the flow pattern: (1) inlet, (2) "A" work port, (3) "B" work port, and (4) outlet. Three-position denotes the handle position: (1) forward or up, (2) neutral or middle, and (3) back or down. Power up, gravity down.

The resistance to fluid flow in a hydraulic system. (An energy loss in terms of power output.)

The pressure at which a valve is wide open and passes its full flow.

A device for measuring the pressure of a gas or liquid.

Uses two gears. The "drive" gear is keyed to the shaft and meshes with the "driven" gear. The oil flows around the outside diameter of each gear as they revolve. A suction is formed on the inlet side by the oil being carried away in the cavities formed beneath the teeth of the gears. The oil is then transported around and discharged into the cavity of the outlet port. The meshing of the teeth in the middle seals the inlet from the outlet. These are fixed displacement pumps. The output flow can be varied by changing drive speed.

This type of hydraulic motor also has two elements. As the inner gear rotates, rollers which form the displacement

This type of motor has two elements -- the inner being keyed to the shaft, which rotate and mesh together inside a housing. At top dead center the two elements come into full mesh. At bottom dead center, the two elements are completely out of mesh. The center element has one less tooth than the outer element, which causes cavities to form as each tooth of the inner element moves from one cavity to the next.