How To Design A Pneumatic Circuit

They’re reliable, efficient and cost-effective, and can be adapted to a wide variety of circumstances. While many business owners have their systems installed completely, it helps in managing the system if you understand the basic principles of pneumatic circuit design. 

This walk-through guide will take you step by step into the design environment for a basic pneumatic circuit. You’ll start by assessing your system requirements and then move on to selecting the necessary components. Once you’ve grasped the key principles of circuit design, you can go on to assemble a customised pneumatic system.

Step 1: Assessment

Before you begin to design your pneumatic circuit, you need to define your system requirements and decide what you want the system to accomplish. You can start with the following questions:

• What do you want your pneumatic system to do? In other words, will you be clamping, pressing, lifting or some other activity?

• How much force and speed do you think you’ll need to carry out that activity?

• How many actuators or cylinders will you need to achieve this?

• How often will you want to be performing this action; i.e. what is the system’s duty cycle?

• What will you need to do to make the system safe?

• What regulations and standards must you comply with when building this system?

You need to ensure that you define these parameters clearly in order to select the right components. Try and keep it as simple as possible and avoid overthinking it, but be sure that your design is capable of doing what you want it to.

Step 2: Choose The Right Type Of Actuation

The actuator is central to any pneumatic circuit. It’s the means by which you convert the static power of compressed air into the kinetic force of mechanical motion. You probably know that there are many types of pneumatic actuator, but you’ll have to take your application into account to determine which type will best suit its design. Two of the most commonly found actuators are the linear type and the rotary type.

Linear Actuators

These usually take the form of a cylinder, which travels in a straight line. They offer precise control in applications like materials handling, food processing and robotics. You have the option of either single- or double-acting cylinders:

• Single-acting cylinders are pushed out by compressed air and have a spring return.

• Double-acting cylinders are pushed in both directions by compressed air.

Which type you need will depend on how far the piston needs to travel, or its stroke length.

To work out how much force (F) the actuator will produce, you’ll also need to know:

• The surface area (A) of the cylinder piston or diaphragm in centimeters/inches squared.

• How much pressure (P) is being applied, in psi or bar. 

You then apply the following formula: F = P × A

For example, if the total area is two square inches and the air pressure is 100 psi, then the force generated will be 200 lbs. This is a simplistic calculation, but calculating the force requirements of a pneumatic cylinder can sometimes be a lot more complex.

Rotary Actuators

This type of actuator provides rotational movement, which is typically used for positioning, clamping and indexing applications. They come in various types, including:

• Vane

• Diaphragm

• Rack and pinion

• Scotch yoke

Step 3: Calculating Air Supply And Pressure

You’ll need an air compressor to supply the power for your pneumatic system. Key factors to consider when selecting an appropriate air compressor include:

• Capacity: you need a compressor that can supply a sufficient volume of air, measured in cubic feet per minute (CFM), at the pressure you need (typically 80 psi, or 5.5 bar).

• Storage: you can help stabilise pressure fluctuations with an air receiver tank.

• Filtration and lubrication: to make your compressed air system last longer, include a filter-regulator-lubricator (FRL) unit to improve the quality of your air supply.

Step 4: Control Valves

The next step you need to consider is picking out the right pneumatic control valves. These are critical for regulating the actuator movement and airflow. The most common types of control valve are:

Directional Control Valves (DCVs)

These are the valves that control the direction in which compressed air is supplied to the actuator. DCVs are divided into categories, according to how many ports they have and how many ways they provide for the air to travel. 

• A port is the physical opening in the valve’s body that allows the air in or out. They’re marked to show their function, like inlet, exhaust or return ports, though some are multifunctional.

• A way defines the path that air travels through the valve body. This way changes in accordance with the position of the valve, directing the airflow to different ports as required. Available valve combinations include:

• 2/2 valve: two ports, two positions, offering a single path through the valve. This means it can be either open or closed, and generally provides a simple on/off function.

• 3/2 valve: three ports, two positions, offering a choice of path through the valve. This is usually from the inlet pressure port to the actuator or from the actuator to the air exhaust port. This combination is frequently used for single-acting cylinders, which have a return spring.

• 4/2 or 4/3, 5/2 or 5/3 valve: four or five ports, two or three positions. These valves are usually used for double-acting cylinders, which use pneumatic force to move the cylinder in both directions. Two-position valves are for simply extending and retracting the cylinder, while three positions offer greater flexibility for precision operations like inching.

Other Valve Requirements

• Flow control valves adjust the airflow to regulate actuator speed.

• Pressure control valves regulate the system’s compressed air pressure.

• Check valves prevent any backflow from occurring in the circuit.

Selecting the right combination of valves for your pneumatic circuit ensures that the system will operate smoothly, and reduces the likelihood of excessive wear.

Step 5: Circuit Layout Design

Once you have determined what components you’ll need for your pneumatic system, it’s time to move on to circuit design. You can do this manually, or use one of the many software applications available online. Here are some guidelines to designing a pneumatic circuit:

• Draw a schematic, with pneumatic components represented by the universally understood standard symbols.

• Connect these components together in a logical order:

  • Compressor → FRL unit → control valves → actuators

  • Where required, add in flow control and/or pressure regulators.

• Ensure the airflow is as unimpeded as possible, by minimising restrictions and angles in hoses, fixtures and tubing.

• Incorporate essential safety features such as pressure relief valves and emergency shut-off valves.

A well-planned pneumatic circuit layout will help to reduce the likelihood of pressure drops and optimise system efficiency.

Step 6: Assemble The Circuit And Test It

Once you’re happy with your pneumatic circuit design, you can proceed to its assembly:

• Install all your components securely, using a solid framework on which to mount actuators, FRL units and valves.

• Connect up all hoses, using appropriately sized and typed pipes and tubing to avoid any risk of bottlenecks.

• Check your system for leaks, using de-ionised water or portable devices to detect air leaks in seals and fittings.

• Circuit testing: you’ll need to pressurise the system gradually, testing each function manually before you go ahead to fully automated operation. 

By testing the system carefully in all conditions before you begin operations, you can be sure it’s going to perform as you expected.

Step 7: System Optimisation

Once you have your pneumatic circuit up and running, you’ll want to fine-tune it for best performance. Look for any ways in which you can maintain the system for optimum reliability and improve its efficiency. Some of these might include:

• Monitor for wear and tear, so that issues can be caught before they cause a real problem. Make regular inspections of seals, lubricants and hoses. 

• Optimise energy consumption by adjusting air pressure and flow rates so no energy is wasted.

• Implement safety routines and make sure that operators are properly trained in emergency procedures.

Understanding Your Pneumatic System

Once you’ve designed your own pneumatic circuit, you’ll have a better understanding of how the system works. You’ll need to plan it carefully, select the correct components and assemble the whole thing systematically. By following the above seven steps, you’ll be able to create an efficient, cost-effective and reliable pneumatic system.

You can be an experienced engineer or a complete beginner, designing a complex automation process or just a simple actuator system. Grasping the fundamentals of pneumatic circuit design means that your mechanical applications and industrial automation processes will operate smoothly, so get designing today and create your own pneumatic solutions.