How To Read Hydraulic Symbols

Hydraulic symbols are a standard designed to provide a clear representation of how each hydraulic component functions in a hydraulic system. 

Hydraulics engineers regularly encounter these diagrams, but these symbols can be daunting to interpret if you have limited experience with schematics and the fluid power industry.

On this page, Carr Lane ROEMHELD provides a comprehensive table outlining the definitions of each symbol used in a hydraulic diagram. Engineers can use this page as a reference to determine common schematic symbols used in fluid power, hydraulics, pneumatics, diagrams and circuits. 

Basic Symbols Representing Hydraulic Components

What do circles, semi circles, squares, rectangles, diamonds and lines represent in hydraulic schematics?

Circles and semi-circles are used to represent rotary devices such as pumps or motors. Triangular arrows represent the direction fluid takes in the pump or motor. 
•    When circles represent pumps, the arrow faces outwards. 
•    When circles represent motors, the arrow faces inward. 
•    Motors are often bi-rotational and have triangles at both the top and bottom of the circle. This represents fluid is able to enter at either port. 
•    Pumps can also have motors 
Diamonds represent conditioning devices such like filters, heaters, and coolers. 
Back-to-back semi circles and arrow heads represent flow control elements, either viscosity dependent or viscosity independent. 
Saw Tooth Symbols represent springs. 
In hydraulic power diagrams, lines are another commonly used symbol. 
•    Continuous lines represent flow lines. 
•    Dotted lines indicate pilot signals and drains
•    Dash-dot lines are used to show an enclosure outline that represents a grouping of components such as a directional control valve

How Hydraulic Symbols Work Together

Hydraulic symbols can work together in endless combinations representing actual machines. The above examples are only a sampling of commonly used symbols. Below is our hydraulic symbiology glossary outlining elements of specific Carr Lane ROEMHELD parts, including check valves, power units, relief valves, control valves, pressure gauges, hydraulic circuits, variable displacement pumps and more.