Basic Elements of Schematic Symbols

Objective

  • Interpret basic schematic elements as used in components and system drawings.

Introduction

Schematic symbols and schematic drawings are very popular in the field of hydraulics.

The schematic provides a symbolic way to show all of the components and connections in a hydraulic system.

A schematic also allows a skilled reader to understand much of the engineering and operating principles that the machine's designers intended.

At first glance a schematic can be overwhelming!

Schematic symbols are a visual language, and like any language, you need to understand the individual words before you can understand what is being said.

With that in mind, let's learn to speak schematic!

Line Styles

The basic building blocks of a schematic are the lines that make up the hoses, pipes, and tubes assemblies.


A solid line represents a main path for flow. The pipes or hoses between components and the flow channels within components.

Short dashed lines are return/drain/tank lines. A main path for flow to return to the reservoir.

On the other hand, long dashed lines are for pilot lines. Very little, if any, flow passes through most pilot lines. Many are only used to detect pressure.

A large bulge on an otherwise normal line is used to tell the reader that this particular line is a flexible hose line. This would imply that any line without large bulge on it would have to be a solid pipe. Sadly, that is not an assumption we can make.

White, or empty, arrows on a line indicate that this is a pneumatic line rather than a hydraulic line. This would only be seen on a schematic that has both pnuematic and hydraulic circuits.

So it goes without saying (almost) then that a black, or filled in, arrow on a line would be a hydraulic line. Generally only seen on schematics that have both pnuematic and hydraulic circuits.

A line that consists of both short and long dashes is an enclosure or manifold line. This is used to show that a group of separate components are actually all contained within a single block of metal.

Finally, a line can have these lightning bolt arrows on it. This indicates that this is an electrical line.

When Lines Collide

Hydraulic schematics can get pretty complicated. Lines can be crisscrossing all over the place. Some of these lines will be connected, some will be passing by unconnected.

It is important to be able to tell the difference!
Connected Lines
3 Way Line Connection
(without connection nodes)
3 Way Line Connection
4 Way Line Connection

If a line terminates on another line, as in the first example, those lines are connected. But using a connection node, as in the other two examples, is the preferred way to show that two lines are connected.

Crossing Lines

Line Crossing Over

Line Crossing Over (with hop-over)

Similarly, two lines crossing unconnected to each other can be shown as one line drawn over the second. But using a hop-over makes it explicitly clear that the two lines are not connected.

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We hope you enjoyed Basic Elements of Schematic Symbols

Vacuum Pressure
Atmospheric Pressure
Low Pressure
Medium Pressure
High Pressure
Ground/Common
Lowest Voltage
Medium Voltage
Highest Voltage
Magnetic Field
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