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.
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.
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.
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.
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.
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.
A circle indicates a component that primarily rotates (e.g. pumps and motors).
Diamonds are used to represent components that affect the hydraulic oil in a system. (Symbols for oil filters, heaters and coolers are diamond shaped.)
A square is usually a valve. Relief valves, pressure reducing valves and counterbalance valves are all examples of square schematic symbols. A series of squares together show the various positions of a directional control valve. More on this later.
Operators attach to components to indicate the methods by which that component is controlled. The most common examples:
Stacking operators end to end means that both have to be activated in order actuate (operate) the component. In this example, the valve must receive both a pilot signal and an electrical signal to the solenoid to act.
Operators placed side by side mean that either can be activated in order actuate the component. In this example, the valve must receive either a pilot signal or an electrical signal to the solenoid to act.
Accumulator symbol: The empty arrow indicates that it has a gas-filled bladder.
A standard cylinder symbol
An orifice/flow control
Tank/reservoir symbol: Commonly used to mean this line returns to the tank rather than drawing a long line across a schematic.
A diagonal arrow is used to indicate that a component is variable or adjustable. In this example the arrow is used to show an adjustable spring.
An curved arrow is used to show that a component rotates. They are primarily used on shafts, as in the example shown.
Cartridge/logic valve: The large "T" represents the poppet. There is also a spring above it.
Ball Valve Symbol: A white fill means that this valve is normally open while a black fill means the valve is normally closed.
Typical check/non returning valve symbol
Shuttle Valve: The horizontal line segments are the two lines whose pressures are being compared. The vertical line will carry the output of whichever line's pressure is greater.
Click and drag the symbol to its matching label.