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The Invisible Power Source of the Factory
인쇄용 교육자료이수 확인란 포함Learn about the roles of compressors, FRL units (filter, regulator, lubricator), cylinders, and valves.
Looking up at the factory ceiling, you can see blue or gray piping running along the entire line. Compressed air flows through these pipes. Impact wrenches, clamp jigs, air guns, painting booths, and transfer cylinders — more than half of the automation used in the Buulgyeong Machinery and Automotive Parts Factory gets its power from here. That's why compressed air is sometimes referred to as the "fourth utility" following electricity, water, and gas.
The problem is that compressed air is a secondary energy source made using electricity. During the process of converting electricity to compressed air, most of the energy is lost as heat. Therefore, it is much more expensive than using an electric motor for the same task.
> Compressed air makes a noise when it leaks, but it doesn't fall to the ground. So no one feels in a hurry. However, that noise is charged to the monthly electricity bill.
[Compressor] → [Aftercooler] → [Air Tank] → [Air Dryer] → [Line Filter]
Compresses Primary cooling and Absorbs pulsation Removes moisture Removes dust and oil
condensate separation pressure storage
↓
[Cylinder] ← [Speed Controller] ← [Solenoid Valve] ← [FRL 3-Point Set]
Performs work Adjusts speed Changes direction Filter, Regulator, Lubricator| Device | Function | If Left Unattended |
|---|---|---|
| Compressor | Compresses air from the atmosphere to 0.7~0.8 MPa | Inlet filter clogging → reduced output, power waste |
| Aftercooler | Cools the hot compressed air | Hot air remains in the piping → entire downstream system condenses |
| Air Tank | Responds to sudden demand, prevents frequent compressor operation | Increased pressure fluctuation, shortened compressor lifespan |
| Air Dryer | Lowers dew point to remove moisture | Water reaches the valve and cylinder |
| Line Filter | Removes dust and oil mist | Valve spool sticking |
| FRL 3-Point Set | Final adjustment just before the usage point | Pressure instability, cylinder wear |
| Type | Characteristics | Used In |
|---|---|---|
| Reciprocating (Piston) | Inexpensive and easy to withstand high pressure, noisy and pulsating, intermittent operation | Small factories, maintenance workshops |
| Screw | Strong for continuous operation, quiet, can be controlled with an inverter | Standard in factories with production lines |
The discharge pressure is usually set to 0.7~0.8 MPa, and it is reduced to about 0.4~0.6 MPa at the usage point using a regulator. If you use pressure higher than necessary, the force increases, but so do shock, noise, leakage, and electricity costs.
Industrial areas near the sea have high humidity. The moisture in the air drawn in by the compressor is mostly converted to water during compression. Let's calculate how much.
30 kW screw compressor (inlet 5 m³/min = 300 m³/h)
Summer inlet air temperature 30℃, relative humidity 80%
① Moisture drawn in
Saturated water vapor amount at 30℃ is about 30.4 g/m³ × 0.8 = 24.3 g/m³
300 m³/h × 24.3 g = 7,290 g/h ≈ 7.3 kg/h
② Moisture in the air after compression and cooling
When compressed to 0.7 MPa (about 8 atmospheres), the volume is reduced to about 1/8
300 ÷ 8 = 37.5 m³/h
At the cooler outlet, 40℃ saturated vapor is 51.1 g/m³ × 37.5 = 1,916 g/h ≈ 1.9 kg/h
③ Amount of water that falls out = 7.3 − 1.9 = 5.4 kg/h
If operated for 8 hours → about 43 liters per dayThis means that more than 40 liters of water per day is coming out of the piping somewhere. If not drained, this water will go to the valve and cylinder.
| Where the Water Goes | What Happens |
|---|---|
| Valve | Spool rust and sticking → poor operation, malfunction |
| Cylinder | Internal rust, seal damage, reduced output |
| Paint Booth | Water spots on the paint film → full re-painting |
| Winter outdoor piping | Freezing causes blockage, pipe damage |
Even with an automatic drain trap, it can get clogged with foreign matter. The most reliable method is to open the manual drain valve once every morning. Check the color of the water that comes out. If it looks milky or has an oily sheen, it's a sign that compressor oil is mixing in.
This is a set of three components attached right before the usage point.
| Symbol | Name | Function | Inspection Points |
|---|---|---|---|
| F | Filter | Removes moisture and foreign matter (standard 5 µm) | Water accumulation in the drain ball, replace element if pressure drop exceeds 0.1 MPa |
| R | Regulator | Reduces and stabilizes pressure to the required level | Secure the locking ring to prevent the setting pressure from changing arbitrarily |
| L | Lubricator | Supplies lubricating oil in mist form | Oil flow rate (usually a few drops per minute), remaining oil amount |
> The reason the filter is first and the regulator is second is because if dust and water get into the regulator's precision parts, the pressure becomes unstable. The lubricator is last because the oil needs to be introduced into the stabilized flow to spread evenly.
Most modern valves and cylinders are non-lubricated (non-lube) specifications. Manufacturers include special grease during assembly.
"How many kilograms can this cylinder push?" is the most common question on the factory floor. The calculation is simple.
Double-acting cylinder φ50, rod diameter φ20, operating pressure 0.5 MPa
※ 1 MPa = 1 N/mm², so 0.5 MPa = 0.5 N/mm²
[Forward] The entire piston front area receives the pressure
A = π × (50 ÷ 2)² = π × 625 = 1,963 mm²
F = 0.5 × 1,963 = 982 N ≈ 100 kgf
[Backward] The area occupied by the rod is subtracted
A = π × (25² − 10²) = π × 525 = 1,649 mm²
F = 0.5 × 1,649 = 825 N ≈ 84 kgf
→ The same cylinder has about 16% less force in the backward directionYou should not use the calculated force at 100%. Friction, back pressure, and pressure fluctuations are the reasons.
| Use | Recommended Load Factor | Actual Capacity of the Above Cylinder |
|---|---|---|
| Static Load (Clamp, Press, Holding in Place) | 70% or less | Approximately 70 kgf |
| Dynamic Load (Transfer, Pushing) | 50% or less | Approximately 50 kgf |
> When the force is insufficient, it's common to increase the regulator pressure, but the proper method is to increase the cylinder diameter. Since area is proportional to the square of the diameter, doubling the diameter increases the force by 4 times. Increasing pressure slightly increases the force but significantly increases shock, leakage, and noise.
This is the most common type of compressed air accident. Thinking that it's safe because the valve is closed, people pull out the tube or disassemble the cylinder, but pressure remains in the downstream piping and inside the cylinder.
Valve locking is "cutting off the supply," not "removing the pressure."
> The Industrial Safety and Health Standards Regulation requires that when performing maintenance, cleaning, or repair work on machinery, the operation must be stopped and a lockout tag and warning sign must be installed on the control device. This is not a formal procedure, but it is intended to actually prevent people from getting hurt.
It is common to use an air gun to brush off dust from work clothes, but this is prohibited. If compressed air enters a wound or skin, it can cause an air embolism, and foreign matter can enter the eyes. When brushing off clothes, use a dust collector or brush instead.
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