Hydraulic Cylinder Guide: Hydraulic Terminology

Check out our list of common hydraulic terminology used in the manufacturing, automotive, heavy equipment, aerospace, and construction industries.

A-C

Accumulator

A pressurized container that stores fluid, which will then be used as a source of hydraulic power or to absorb mechanical shock.

Bleed Valve

A mechanical component that can be opened or closed to relieve pressure or to provide tight shut-off or isolation of fluids or liquids from a closed system.

Closed Center System

A closed center system is a type of hydraulic system. In this type of system, flow can vary while pressure remains constant when control valves are closed or neutral.

Cylinder

A device that converts fluid power into linear or circular motion or force. Types of cylinders include vane, rotary, piston, and double-acting.

D-F

Detent Release

A hydraulic, mechanical, or electrical component that releases a detent device, which helps maintain the position of the directional control valve. 

Fitting

A mechanical piping component that is used to tightly connect hoses or pipes in a hydraulic system.

Float Spool

A spool valve that connects and holds multiple ports of a tank (normally in a detented fourth position) to allow a cylinder or motor to float.

Flow Rate

A measurement of the volume of fluid (typically in gallons per minute) that passes through a system point or component.

Fluid Power System

A system that utilizes the power of fluids under pressure to control and transmit energy.

L-P

Load Check

A component that prevents the dropping of a load when a valve is shifted, until enough pressure and/or flow is available to hold or move the load.

(Hydraulic) Motor

An electromechanical assembly that converts hydraulic energy into fixed or variable rotary motion. The different types of hydraulic motors include piston, vane, and gear.

Pilot Circuit

A valve or circuit used to prevent the machine from self-starting after a circuit breaker trip or power failure.

Port

The open end of a hydraulic fluid line.

Pressure

The measure of fluid force per unit area as expressed in pounds per square inch (psi), bars, or atmospheres. In hydraulic terms, pressure converts a small force into an appreciable multiple of itself. There are various types of pressure, including back, breakout, cracking, differential, full-flow, operating, pilot, rated, static, suction, surge, system, and working.

Pressure Cracking

The amount of pressure it takes to open a relief valve or other pressure-operated valve.

Pump

A mechanical assembly that converts mechanical force into fixed or variable hydraulic fluid power. The different types of hydraulic pumps are gear vane, and piston.

R-V

Regenerative Circuit

A hydraulic circuit in which pressure fluid is discharged from a component and returned to the system to reduce flow input requirements. These circuits are used to increase cylinder action by directing discharged oil from the rod end to the piston end.

Reservoir

An open vessel or closed container that holds a supply of working fluid in a hydraulic system.

Seal

Gasket-like, non-metallic rings that block or control the escape or passage of hydraulic fluid.

Two-Way

A two-directional, or two-port valve or component that has inlet and outlet ports.

Valve

A mechanical component that can control the amount of pressure of a fluid, the direction of fluid flow, or the rate of flow. The main types of valves include bypass flow regulator, check, closed center, directional control, electro-hydraulic, flow control, flow divider, needle, open center, pilot, pilot-operated, poppet, pressure control, pressure reducing, pressure sequence, priority flow divider, proportional flow divider, relief, rotary directional, selector, shuttle, spool directional, thermal relief, and volume control.