What is a pneumatic system? 

A pneumatic system is a system of interconnected devices that use the pressure of compressed air to move cylinders, motors, or other mechanical devices. 

Standardized pneumatic system diagram in the factory includes: 

• Air compressor
• Cooler
• Gas tank 
• Main filter 
• Dryer 
• Fine filter 
• Ultrafine filter 
• Pipeline 
• Automatic drain 
• FRL combination kit (filter, regulator, oiler, 3/2 ON/OFF valve) 
• Pressure sensor 
• Solenoid valve 
• Throttle valve 
• Air cylinder 
• Sensor  

Basic pneumatic system diagram in factory

All the devices in the diagram above are essential, if one of the above devices is missing, the pneumatic system will not operate well or even cannot operate at all. 

The diagram above includes many pneumatic devices, divided into 4 groups of devices, including: (1) Production group, (2) Cleaning group, (3) Transmission group, (4) Consumption group.  

I. Production group 

The production group includes equipment: air compressor, cooler, air tank. 

The air compressor sucks in air from the environment and then compresses it into high-pressure compressed air for use. After the air is compressed, it will generate heat and there will be fluctuations in pressure. The air will then be passed through a cooler to lower the temperature. The compressed air will continue to be led through the air tank to store and stabilize the fluctuations in compressed air pressure for the following stages. 

Equipment in production group

1. Air compressor

The air compressor is the first device in the pneumatic system, which has the function of sucking in air from the environment and then compressing it into high pressure compressed air for use. There are many different types of air compressors, but the two common types are piston air compressors and screw air compressors.  

Piston air compressors and screw air compressors

A piston air compressor is a type of air compressor that converts the rotary motion of the engine into the reciprocating motion of the piston. The piston draws air into the cylinder through the suction valve, compresses it, and then releases the air through a check valve. This type of air compressor is commonly used in systems that require air pressure of about 3 to 7 bar.  

Screw air compressors operate on the principle of volume change, high-speed rotation from the motor helps 2 screws rotate in parallel and in opposite directions, making the gap volume of the screw and the compression chamber gradually smaller, thereby creating compressed air. This type of air compressor is often used in systems requiring pressure up to 10 bar.  

When comparing these two types of air compressors, screw air compressors produce more stable flow, operate with less noise but the initial investment cost is higher than piston air compressors. Therefore, screw air compressors are often widely used in industry, while piston air compressors are often used in civil use. 

2. Cooler 

After the gas is compressed, it will generate heat and there will be fluctuations in pressure. The gas will then be passed through a cooler to lower the temperature of the hot gas to about 40°C.  

The cooler has the function of cooling hot compressed air from 80-100°C or more to about 40°C before use. 40°C is the ideal temperature, in practice it will depend on the inlet temperature and give the corresponding outlet temperature. The condensed water vapor during the cooling process will be discharged through the automatic drain.  

The cooler has 2 types: HAA series air cooler and HAW series water cooler 

Air cooler: Hot air is led through the main pipe and distributed through the small pipes at the same time. The cooling fan will blow the outside air through the small pipes and the radiator fins to lower the temperature of the hot compressed air to about 40°C. During the process of lowering the temperature of the hot compressed air, a certain amount of condensed water will be discharged through the automatic drain. 

Notes when using air cooler: 

• The air cooler should be placed in a cool, well-ventilated place. Place it at least 20cm away from walls or other machines.
• If using the air cooler in a dusty environment, a dust filter should be installed in a dusty environment.
• For cooling pipes need to be cleaned periodically and check the automatic drain once a day 

Water cooler: Hot compressed air entering the inlet port will indirectly contact with the cooling water inside the metal water pipe, lowering the temperature of the hot compressed air. The cooling water will be circulated and cooled by the cooling tower. The condensed water will be discharged through the automatic drain. 

Notes when using water cooler: 

• The factory must equip itself with additional cooling towers. 
• Make sure the coolant is clean and has the required water level. 
• Check the automatic flusher once a day 

3. Gas tank

Compressed air will continue to be led through the air tank to store and stabilize the fluctuations of compressed air pressure. 

Uses of air tanks: In addition to the function of storing compressed air, air tanks also help stabilize fluctuations in compressed air pressure. You should choose an air tank with a volume 6-10 times the volume of the air compressor produced in 1 second, this will help ensure stable output pressure. At the same time, it is necessary to equip additional safety valves, pressure gauges and automatic discharge devices. 

There are 2 types of gas tanks: AT series with large capacity (100 – 3000 L) is often used to store gas for the entire factory, and VBTA series with small capacity (5 – 38 L) is often used to store gas for 1 machine line or 1 machine. This type of gas tank has an additional base on top to combine the use of a booster. 

There are 2 types of gas tanks: AT series and VBAT series.

The automatic drain has the function of automatically draining water according to the float mechanism, which is a device that is always present in air compressors, coolers, air tanks and some equipment or certain locations in the factory. Using an automatic drain is one of the drainage solutions for compressed air systems. 

II. Cleaning group 

The cleaning group in the compressed air system includes filters and air dryers, in which the filters have three main levels: coarse filter – fine filter – ultra-fine filter with the function of removing dirt, impurities, water and rust from the pipeline out of the compressed air system. The air dryer plays a key role in removing water vapor from compressed air.

The three positions of the cleaning group in the compressed air system are as follows: The coarse filter is placed before the air dryer, after the air dryer are the fine filter and the ultra-fine filter. 

Why is it necessary to clean compressed air before use? If compressed air is not cleaned, it will contain a lot of dirt and impurities: 

• Because compressed air is drawn from an outside air source, it will contain dust, impurities and moisture.
• There is oil when compressed air passes through the air compressor
• The head of the pneumatic transmission line is usually metal, which can have rust.

Thus, to have clean compressed air for the equipment and subsequent cycles, a compressed air cleaning system is needed, including filters with different levels and an air dryer. 

The standard for compressed air is determined based on ISO 8573-1:2010  

1. General filter

When passing through the filter levels, compressed air will be cleaned of dust, impurities, water and oil. 

Filters generally function to remove most of the dirt, impurities, water and oil from the compressed air system, helping to increase the efficiency of the air dryer, prolong the life and prevent problems for equipment in the compressed air system. Filtration levels include coarse filtration, fine filtration and ultra-fine filtration. In which, coarse filtration does not filter oil.  

Compressed air filtration process

The air filter has a simple operating principle: compressed air enters the Input port and enters the filter core. Dust and solid impurities will stick to the filter core wall and be retained there in amounts depending on the filtration level. Water and oil will accumulate at the bottom of the filter and be periodically discharged by the automatic drain.  

Operating principle of compressed air filter

When the output gas pressure drops compared to the input gas at a specified level, the color indicator will be pushed up, making it easy for the operator to detect when to replace the filter. 

When to replace the filter

So when should you replace the air filter element?  There are two cases where you need to replace the air filter element: 

• Filter core used for 2 years should be replaced once.  
• After a period of use, the air filter has an output pressure drop (output pressure is reduced compared to input pressure) of up to 0.1 MPa.  

However, the operating time of each factory is different, so depending on the maintenance conditions of the factory, you can flexibly choose the warranty time for the air filter to suit your factory. In addition, SMC air filters also have a color indicator to easily identify when to replace the filter element. When the color indicator turns red, it is time to replace the filter element. 

How to replace the filter cartridge: 

• Use the Allen key to remove the 4 screws on top of the filter cover. 
• Rotate the filter body to separate the filter body and cap. 
• Take out the old filter core and replace it with a new one. 
• Reinstall in reverse order of filter removal.  

2. Air dryer 

Air dryer is a device that removes water and steam from the compressed air system. Air dryer helps improve the quality of air source, thereby meeting the operating requirements of machinery and equipment, contributing to ensuring the production capacity of the factory. 

Depending on the system, environment and different products, choose an air dryer with different principles and capacities to suit the needs of use. Currently on the market, we distribute three product lines of SMC air dryers that work stably and reliably: refrigerated air dryers, membrane air dryers and adsorption air dryers, with different flow rates and dew points. 

Types of air dryers

Refrigerated air dryers use a closed-circulation system to cool the compressed air source so that the steam condenses into water and is discharged through an automatic discharge system. This type of air dryer has a large drying air flow range and a dew point of 3-10°C, consuming only electricity and almost no compressed air during the drying process. Refrigerated air dryers with large flow rates are usually placed in the air compressor room to process the source.  

Adsorption air dryers use desiccant materials to remove water vapor from compressed air. This type of air dryer has an output flow of less than 800 liters/minute and a low dew point of -30°C to -50°C. 

Membrane air dryer uses a special membrane containing hollow fibers inside to dry compressed air due to the pressure difference between the moisture inside and outside the membrane. This type of air dryer has a maximum flow rate of 1000 liters/minute, and a very low dew point from -15°C to -60°C. 

Adsorption air dryers and membrane air dryers have negative dew points and therefore have a very high air drying capacity, so they are often used for applications requiring high air quality such as in the food, pharmaceutical, and clean room industries, specifically for machine tools, measuring machines, food processing machines, packaging machines, semiconductor manufacturing equipment, and in electrostatic painting applications. 

III. Conduction group 

The transmission group includes the pipeline and the automatic discharger .

1. Pipeline 

There are three types of piping systems: metal piping, rubber piping and plastic piping.

• The metal piping at the source on the main line usually connects the equipment in the air compressor room together. 
• Rubber pipe connecting main line and branch line 
• Plastic pipes connect the devices on the branch line together. 

Two types of piping systems in factories

There are two types of piping systems in the factory: straight piping systems and loop piping systems. Compared to straight piping systems, loop piping systems are more stable in pressure but have higher initial investment costs. 

According to recommendations in installing gas distribution pipeline systems in factories, there are 3 following notes: 

• Every 100m of pipe should be installed 1m through, the purpose is to allow water to drain out easily. 
• At the end of the line, an automatic drain should be installed to automatically drain the water. 
• From the main line to the branch line, a gooseneck pipe should be installed to prevent water from splashing back into the device. 

2. Automatic discharge

Automatic dischargers are installed at the end of each line using compressed air in the factory. Automatic dischargers of the transmission group have 3 types: 

• Float type: simple, easy to operate with low drainage, about 100-400cm³/cycle 
• Electric type: drainage volume >400cm³/cycle.
• Timer type: phrase timer control with medium to high drainage cycle, when using this type, the drainage cycle can be set in the range of 0.5 – 45 minutes and the drainage time of one cycle can be adjusted in the range of 0.5-10 seconds 

This is the location of the automatic drains in the compressed air system at the factory, in which the float type automatic drains with low water discharge AD series are usually located at the end of the line or after the filters. The float type automatic drains with medium water discharge ADH series and electric type ADM series, along with the timed automatic drains with medium to high water discharge are usually installed after the air compressor, air tank, air dryer and upstream filters. 

IV. Consumer groups 

The consumption group consists of three parts: FRL unit , control device is valve and actuator is pneumatic cylinder. 

1. FRL set

The FRL is a combination of 3 devices: filter (filters out dirt, impurities, rust from pipes, filters water and oil), pressure regulator (adjusts pressure to suit usage requirements and helps stabilize output oil pressure) and oiler (lubricates the rear equipment).

The FRL unit has the function of removing dirt, impurities, water and adjusting the stable output pressure, lubricating the pneumatic equipment behind to operate smoothly. After the compressed air is processed, it can be used by the machines, valves, actuators, etc. behind. Depending on the type of production, each factory can choose to use different types. 

• The FRL unit combines 3 units: filter, regulator and oiler (AC) 
• FRL unit with integrated filter and pressure regulator, together with oiler, saves installation space (AC_A)
• For applications requiring higher air quality, in addition to the coarse branch filter, a fine filter (AC_C, AC_D) is also used.
• For factories in the food, pharmaceutical or clean room sectors that require no oil, only use a filter and a pressure regulator, or use the integrated version of a filter and a pressure regulator (AC_B).   

Let’s take a look at each device in the FRL set: 

Branch filter: Branch filter has the function of removing steam and water from the system, filtering dust, impurities and other air pollutants, filtering rust from the pipeline out of compressed air with a filtration level of 5µm.

Pressure regulator: The pressure regulator has the function of adjusting and stabilizing the output pressure to suit the requirements of the equipment, minimizing pressure fluctuations that affect the operation of the machine. 

Lubrication kit: provides lubrication for valves, cylinders and other hand-held pneumatic tools. Most SMC equipment supplied by Temas is pre-lubricated with specialized grease and does not require any further lubrication. 

2. Control valve 

Valve is a control device in the pneumatic system that controls the pneumatic cylinder, in addition to some other functions such as: opening and closing the air line, releasing excess air and blowing air. 

A directional valve is a device that receives an external signal (by force, pneumatic or electromagnetic) usually to release, stop or redirect the compressed air flowing through it. In a pneumatic system, valves are often used to open and close the air line for air blowing applications or to control cylinders depending on different applications.  

Directional valves are classified according to their type of action: 

• Hand/foot operated: The internal valve is operated by a mechanism such as a push button, pedal or knob. When released, the valve returns to its original position by a return spring. 
• Mechanical actuator: a valve that is actuated by a mechanical linkage, a camshaft or roller that comes into contact with the moving object. 
• Electrically actuated: An electromagnet coil generates magnetic force that pushes the valve core to change state. 
• Pneumatic actuator: The valve operates by sending a pneumatic signal to both ends of the valve core and causing the valve core to move. 

Applications of valves: 

• Two-port valve : Two-port valve is used to open and close the air line or blow air. 
• Three-port valve : Used to control a single-action cylinder or open and close to discharge excess air in the pneumatic system. 
• Five-port valve : used to control double-acting cylinders 

3. Pneumatic cylinder 

A pneumatic cylinder is an actuator that converts the energy of compressed air into mechanical motion. The motion here can be linear motion (pull or push), rotary motion (turn left or right), clamping motion depending on the type of cylinder. 

Some basic types of cylinders: Reciprocating cylinders, rotating cylinders, clamping cylinders 

Types of cylinders

Pneumatic cylinders are widely used in industries such as automobile industry, machine tool industry, wood industry, semiconductor industry, especially in hygiene and safety fields such as electronic assembly, food processing – pharmaceuticals, classifying and packaging products in automatic production lines. In addition, cylinders are also used in other fields such as: construction, transportation, mining, minerals, aviation, etc.