The Basics Of Pneumatic Circuits

Post By: John Rowse On: 20-12-2022 Read Time: 3 minutes - Guides - Pneumatics

Pneumatic devices have been found that are almost 4,000 years old. More than 2,000 years ago, the Han Chinese were already using a fairly complex system of hydraulics to operate a bellows. A double-action piston was part of this system, with inlet and outlet valves; these are the fundamentals of any air pressure system. Subsequently, the basics of pneumatic circuits developed to include vacuum pumps and then electricity.

Further developments in the 20th century refined the components of a pneumatic circuit to include items such as solenoids. The number of ports and valves can be varied, and the essential pneumatic components combined in different ways to perform different tasks. The bottom line, however, is that basic pneumatic circuits can be configured to suit most processes in machine automation.

Designing a Pneumatic Circuit

Designing a pneumatic circuit means combining the pneumatic cylinder or actuator with a number of supporting components like air preparation devices, flow controls, hoses and tubes. The actuator converts compressed air into mechanical motion and usually comes with a cylinder and a piston.

  • Compressor
  • FRL
  • Valves
  • Cylinders

Air Preparation

Compressor

The first thing you need in a pneumatic circuit is an air compressor. All pneumatic devices need consistent air pressure and flow to operate optimally, so any good pneumatic design starts with the supply of air pressure. The compressor takes in ambient air, compresses it so that it’s at a higher pressure, and then delivers it from its storage tank to the operating parts of the system.

FRL

This air supply first needs to be prepared before it can feed compressed air through to any other pneumatic circuits. Ambient air contains all kinds of contaminants like dirt and dust that need to be filtered out, and compressing it adds moisture. Once these elements are removed, the air pressure and flow are regulated to the correct levels. If necessary, it will also be lubricated so as to protect the downstream equipment. The elements of filtering, regulating and lubricating the compressed air are often combined in a single FRL unit.

Airflow

Valves

You need a controlled airflow to run a pneumatic device efficiently, so a pneumatic circuit contains a number of ports and valves that supply and remove air in a given rate or direction. Simple valves are open or closed, to turn the air supply on or off. Directional valves control which way the air flows, and can reverse the air supply to make the actuator travel in the opposite direction. Other types of valve in a pneumatic circuit may include a manual shut-off relief valve, a check valve and a soft start or dump valve.

The first item in the circuit connected to the air supply is usually a pneumatic isolation/lockout valve or manual shut-off relief valve. Mounted upstream of the FRL unit, this enables maintenance of the unit at the machine. Other designs show it mounted downstream of the FRL unit, so that airflow through the valve is already clean and dry. However, this makes filter maintenance more difficult and could have a knock-on effect on other equipment when the air is dumped for servicing.

Pneumatic Circuits

A good pneumatic circuit design will also incorporate some type of flow control valve to restrict excess motion in the cylinder, such as needle or ball valves. A properly sized cylinder with appropriate flow control uses the air more efficiently, and consequently moves faster and is more stable. Cushioning built into the cylinder also limits its impact at the end of travel. Both these components in a pneumatic circuit design can help protect the cylinder from noisy banging and possible impact damage.

Simple Cylinder Circuits

Cylinders or Actuators

Pnxeumatic cylinders can be single acting or double acting. In the simpler, single acting cylinder, piston rod extension is activated by compressed air and retraction by means of an open coiled spring. Double acting cylinders have two ports, so that the piston rod can be both extended and retracted by means of compressed air. It can also be done using a 4-way solenoid valve, mounted after the air preparation unit and controlled by a PLC. It’s commonly operated by a pilot valve, using minimal air pressure to move a spring-return valve that controls the flow of air.

Components & Configurations

The design of pneumatic systems is clearly very flexible, but these basic pneumatic circuits combine the most common components to carry out many useful automation functions. Cylinders, flow controls, FRLs, valves, buttons, and any number of other components can be added in various configurations, so that almost any kind of pneumatic system is covered.