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How to Read Hydraulic Schematics

It is essential to learn how to read hydraulic schematics to fully understand how the hydraulic system operates and functions. Being able to identify what each symbol means enables you to troubleshoot and pinpoint operational issues and find their cause.

hydraulic pipes maintenance on heavy industry machineThe first time you read a hydraulic schematic and see the different hydraulic symbols, it can be quite confusing. This is because there are so many different lines, circles, squares, and other schematic symbols to decipher to determine what they are and what they mean.
The best way to learn how to read hydraulic schematics is through continued practice. It also helps if you have ‘cheat sheets’ that tell you what each hydraulic symbol and hydraulic component symbol is until you can memorise them.  You can download the one from our website: ISO Hydraulic Symbols
In addition, learning the basics of hydraulic system fundamentals is equally beneficial to help troubleshoot problems when they occur.

Hydraulic Symbols – Lines

The first types of hydraulic symbols you will encounter are lines. There are all different types of lines used in a hydraulic schematic. A solid line is used to identify the piping in the system. A dashed line is a pilot line.
You also need to distinguish between crossing lines and connected lines, which affect how the system operates. Lastly, there are dashed and dotted lines that indicate an enclosure like a directional control valve.

Hydraulic Symbols – Sawtooth Lines

Sawtooth lines on a hydraulic schematic represent various types of springs used in the hydraulic system. Additionally, the sawtooth lines can be connected to other components.

Hydraulic Component Symbols – Circles

Circles are used to distinguish between different types of hydraulic components, such as pumps and motors. A triangle or arrow in the circle indicates the direction of fluid flow. Other things to remember when looking at circles on a hydraulic schematic are:
  • Inward pointing triangles or arrows are used with hydraulic motors.
  • Outward pointing triangles or arrows are used with hydraulic pumps.

Hydraulic Component Symbols – Diamonds

Diamonds are used to identify hydraulic conditioning devices, such as filters, heat exchangers, and cooling devices. Arrows are used on exchangers to indicate the direction of the heat. For example, if the arrows point outwards, then the exchanger is a cooler.

On the other hand, if the arrows point inwards, then the component is a heater used in colder climates to ensure the hydraulic fluid is closer to the optimum operating temperature. An actual heat exchanger will have arrows pointing outwards inside the diamond. On the exterior will be an arrow pointing inwards, and then there will be a second arrow pointing out of the diamond.

Hydraulic Component Symbols – Rectangles

Rectangles are used to indicate the hydraulic fluid reservoir or tank. A completed rectangle represents a pressurised reservoir or tank. If the top of the rectangle is not present, so it looks like a flattened out ‘U’, it means the reservoir or tank is unpressurized.
If there is a line drawn vertically in the middle of the rectangle, this indicates where the fluid is returned to the tank. A line that connects at the bottom normally relates to the outlet from the tank to the pump or pumps.

Hydraulic Component Symbols – Ovals

Ovals are used to identify the different types of hydraulic accumulators used in the hydraulic system. Different symbols are used to identify the type of accumulator inside the oval.

Hydraulic Component Symbols – Squares

Squares are the hydraulic symbol used to identify different types of valves, including:
  • Pressure Valves
  • Directional Valves
  • Counterbalance Valves
  • Relief Valves
  • Pressure Reducing Valves
  • Sequence Valves
Each valve will have other identifying features based on the placement of arrows, springs, etc.,  on the square.

Other Hydraulic Symbols

We only touched on the basic elements of hydraulic symbols to be aware of and what they look like on hydraulic schematics. Other common symbols you need to know are:
  • Hydraulic Cylinders
  • Flow Control Valves
  • Pressure Gauges
  • Check Valves
  • Pilot Operated
  • Shut-Off Valves
  • Air Bleed Valves
  • Temperature Switches
  • Level Switches
  • Pressure Switches
  • Servo Valves
  • Quick Disconnects
  • Actuators

Steps to Deciphering Hydraulic Symbols

hydraulic elements symbolsIn general, when you first review a hydraulic schematic, you should use the following steps:
  1. Review the different types of lines.
  2. Determine where lines cross and where they connect.
  3. Identify each of the hydraulic components using our downloadable table: ISO Hydraulic Symbols
  4. Determine the fluid flow direction.
  5. Hypothesise what happens as the fluid flows through the system and moves through the various components, valves, etc.
  6. Hypothesise how the operation of valves would affect the fluid flow  through the actuators in the hydraulic system.
Most importantly, if you encounter a symbol you do not recognize or are unfamiliar with, it is best to find out what the symbol means and how the component functions within the hydraulic system.
Learning how to read hydraulic schematics takes time and practice. Remember to be patient and work through the schematic slowly. The more you practise reading schematics, the more you become familiar with each symbol.
Once you are familiar with reading schematic diagrams and deciphering hydraulic circuits, you will be able to apply your skills and knowledge to troubleshoot hydraulic system problems. Furthermore, you will be able to determine system efficiencies and create your own hydraulic systems.

Hydraulic System Components and Services

When you need hydraulic system components, repairs, and custom-built parts, White House Products, Ltd. is here to help. We offer one of the largest inventories of hydraulic pumps, motors, cylinders, and related components. Furthermore, we can custom-build hydraulic components to your exact specifications using high-quality materials.
For further information or assistance, please feel free to contact us at +44 (0) 1475 742500 today.

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