Why factories use compressed air
One compressor can feed the whole plant through a pipe network. The parts are inexpensive, easy to install and fast, and actuators such as cylinders carry no electricity, so they suit wet or dusty areas.
The trade-off is less force than hydraulics and less precise mid-stroke stopping than electric motors. Heavy pressing usually goes hydraulic; multi-position work usually goes to electric actuators.
The path the air takes
- The air compressor compresses air into a receiver tank
- An air dryer and main-line filters remove water and dust
- An FRL unit at each machine filters again and holds the pressure steady
- A directional control valve, such as a solenoid valve, sends air into and out of the cylinder
- A speed controller sets how fast it moves
- The cylinder or another actuator, such as an air gripper, turns air pressure into work
Air tubing and fittings connect every step.
1. Compressors and vacuum pumps
The power source of the system, sized by the total air the plant uses (litres per minute) and the working pressure. Food, pharma and electronics plants that need oil-free air use oil-free compressors; vacuum pumps handle suction gripping.
2. Filter regulator lubricator (FRL) units
FRL stands for Filter, Regulator and Lubricator. One sits in front of every machine to catch water and dust from the pipes and to hold a steady pressure, because main-line pressure swings with plant demand.
Most modern pneumatic parts need no lubrication, so a filter regulator alone is common. Once a system has been lubricated, keep lubricating it.
3. Directional control valves (solenoid, air-pilot and manual)
A valve is the switch for the air: it feeds one side of the cylinder and exhausts the other. A figure such as 5/2 means 5 ports and 2 positions.
- 5/2: for double-acting cylinders, the most common type
- 5/3: adds a centre position — closed centre (holds position), exhaust centre or pressure centre
- 3/2: for single-acting cylinders or simple on/off air
By actuation there are solenoid valves (electric, e.g. 24 VDC from a PLC), air-pilot valves (for areas without power) and mechanical or manual valves (roller, plunger or push button). A single solenoid has one coil and springs back when power is cut; a double solenoid has two coils and holds its last position.
4. Air cylinders
The main actuator, turning air pressure into straight-line motion. Two sizes matter: the bore, which sets the force, and the stroke, which sets how far the rod travels.
- ISO 15552 standard cylinders: standard mounting dimensions, interchangeable across many brands
- Compact cylinders: short bodies for jigs and clamping
- Small round cylinders: light pushing and pressing
- Twin-rod cylinders: two non-rotating rods that take side load better
- Slide tables and rodless cylinders: long travel in tight spaces
Models with a magnet in the piston work with an auto switch on the barrel that tells the PLC the stroke is complete. The model code shows it — for example SMC adds D after C (CDQ2) and Airtac adds S at the end (ACQ20X20S).
5. Speed controllers
A flow control valve that sets cylinder speed. The usual choice has a built-in fitting that screws straight into the cylinder port, set to meter-out for smoother motion.
6. Fittings, tubing and accessories
Push-in fittings lock the tube as soon as it is inserted and release when the collet is pressed. Several brands, Airtac among them, use letter prefixes for the shape.
| Prefix | Shape |
|---|---|
| PC | Straight, male thread |
| PL | Elbow, male thread |
| PU | Straight union, tube to tube |
| PE | Union tee |
| PY | Union Y |
Polyurethane (PU) tubing is flexible; nylon tubing takes more pressure and heat. Tubing is sized by outside diameter, e.g. 4, 6, 8, 10 and 12 mm. Common accessories are pressure switches (to flag low pressure), gauges and silencers.
How to read a model code (real examples)
| Code | Part | Meaning |
|---|---|---|
| TN32X80S | TN | Airtac TN twin-rod cylinder series |
| 32 | 32 mm bore | |
| 80 | 80 mm stroke | |
| S | Magnet for position sensing | |
| 4V210-08 | 4V | Airtac 5-port solenoid valve |
| 210 | 200 series, 5/2 single solenoid (220 = double solenoid) | |
| 08 | 1/4 in thread | |
| PC603 | PC | Straight fitting, male thread |
| 6 | 6 mm tube | |
| 03 | 3/8 in thread |
The same code is often written several ways, such as 4V210-08 and 4V21008, or PC603 and PC6-03. Send it however you have it.
Quick cylinder force calculation
Theoretical force = air pressure × piston area (F = P × A).
Example: a 32 mm bore at 0.5 MPa (5 bar). Piston area = 3.14 × 16 × 16 ≈ 804 mm², so the push force ≈ 0.5 × 804 ≈ 402 N, about 41 kgf.
The return stroke gives less force because the rod takes up part of the area. Size the cylinder so its theoretical force is about 1.5–2 times the load, to allow for friction and pressure drop.
Common problems and first checks
- Cylinder weak or short of full stroke: check the regulator pressure first. If pressure is fine but air leaks at the rod, the seals are usually worn — fit a seal kit or replace the cylinder.
- Solenoid valve not switching: check the coil has power and the air pressure is within spec. With power present and no shift, suspect the coil or water and dirt inside the valve.
- Water in the air lines: drain the filter bowls and receiver regularly or fit auto drains; if water persists, add an air dryer.
- Cylinder slamming at the end of stroke: slow it with the speed controller, or adjust the end cushion if the model has one.
Frequently asked questions
- What is the difference between pneumatics and hydraulics?
- Pneumatics uses compressed air, typically up to about 1 MPa (10 bar); it is fast, clean and cheaper. Hydraulics uses oil at pressures tens of times higher, so it gives far more force for pressing and heavy lifting.
- What air pressure do factories normally use?
- Usually about 0.4–0.7 MPa (4–7 bar) at the machine. Most pneumatic parts are rated to a maximum of about 0.7–1.0 MPa — check the rating on the part or in the catalogue.
- Can I use another brand instead?
- Often yes. Same-size ISO 15552 cylinders interchange across most brands, but valves and compact cylinders differ in mounting and threads between brands. Send us the original model and we will check a replacement.
- I don't know the model. What should I do?
- Photograph the part so the printing or nameplate shows and send it on LINE. If the printing has worn off, measure the bore, stroke and thread, and send a photo of how it is mounted.
Get a price on pneumatic parts
We source SMC, Airtac, CKD, Festo, Koganei, Parker, ASCO, Burkert and Anest Iwata parts, exact or equivalent. Send these details on LINE for the fastest quote.
- The full model code printed on the part or its nameplate (a photo is fine)
- Cylinders: bore, stroke and mounting style
- Valves: coil voltage (e.g. 24 VDC or 220 VAC), port thread and 5/2 or 5/3
- Fittings: tube size (mm) and thread size
- Quantity and the date you need it
Pneumatic Cylinder, Valve and Air Unit