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Precautionary measures against condensation in a pneumatic system

Precautionary measures against condensation in a pneumatic system
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Precautionary measures against condensation in a pneumatic system - 1

Precautionary measures against condensation in a pneumatic system (Phenomena, process, prediction and preventive measures) In a pneumatic system, temperature drops may cause internal condensation under certain piping and operating conditions, leading to malfunction and reduced life time due to deterioration and the washing out of grease. This brochure provides useful information on countermeasures and preventive actions to be taken in this regard. P-E01-11B

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Precautionary measures against condensation in a pneumatic system - 3

Contents Page 1. Condensation phenomenaȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵ 1 What is condensation in a pneumatic system? What kind of problems can it bring about? 2. Process of condensationȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵ 2 2-1 Adiabatic expansion 2-2 Process of condensation 3. Condensation assessmentȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵ 5 3-1 Condensation assessment chart 3-2 Condensation assessment program 4. Countermeasures against condensationȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵ 7 5. Supplementȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵȵ 9 Dew point...

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Precautionary measures against condensation in a pneumatic system - 4

1. Condensation phenomena Ȝ What is condensation in a pneumatic system? In a pneumatic system, waterdrops sometimes form inside piping, affecting operation and the life of equipment. For this reason, compressed air is usually dehumidified with an air dryer before being supplied to the system. However, due to increasing demand for smaller, faster equipment, even the use of dehumidified air may result in condensation and consequent failure when a small actuator is used. Photo 1 shows condensation occurring inside a piping, and Photo 2 shows the dripping of condensation in a cylinder. Water...

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Precautionary measures against condensation in a pneumatic system - 5

2. Process of condensation The following is an example of a small cylinder drive system illustrating a condition under which condensation occurs inside a piping. 2-1 Adiabatic expansion Results of temperature measurement inside the piping Tl = (Ts+273) x ( 0.1 Ps+0.1 ) 0.286 –273 When the air at 27°C and 0.5 MPa undergoes adiabatic expansion to atmospheric pressure, theoretically the temperature will drop to nearly –93°C. Actual temperature measurements inside the piping in the right chart show that the temperature dropped to approximately –80°C. Temperature of supplied air: 20°C Gauge...

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Precautionary measures against condensation in a pneumatic system - 6

[Temperature drop -» Mist formation] The solenoid valve is switched and air inside the piping is instantly released. Then, the pressure inside the piping is reduced suddenly (adiabatic expansion), causing the temperature to drop. If the atmospheric dew point of the supply air is Tt (°C), and the temperature drop of the air Ti (°C) after adiabatic expansion falls below this value (77 < Tt), then mist formation occurs. Mist formation Cylinder Piping (tube) Solenoid Exhaust [Mist evaporation and small amount of residual mist] Most of the mist is discharged through evaporation by the...

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Precautionary measures against condensation in a pneumatic system - 7

[Volume of the piping is large (long piping) —> Mist accumulation] When the cylinder is small and the piping is long (that is, the volume of the piping is larger than that of the cylinder), air inside the cylinder cannot be exhausted at the time of release and remains inside the piping. Mist cannot be exhausted Piping (tube) Solenoid Exhaust If the volume of the piping is smaller than the volume of the cylinder, the mist will be exhausted with the exhausted air as shown in the figure below, and the mist will not accumulate inside the piping. As the cylinder cycles, the mist accumulating...

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Precautionary measures against condensation in a pneumatic system - 8

The probability of condensation is influenced mainly by the volume ratio, humidity and pressure of the supply air, etc. The following chart and program are provided for assessing more specific cases. 3-1 Condensation assessment chart I [condition] Switching intervals of solenoid valve: ON 1 sec, OFF 1 sec. Piping tube material: Polyurethane Range in which condensation occurs Range in which condensation does not occur Enlarged chart

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Precautionary measures against condensation in a pneumatic system - 9

How to use the chart (Refer to page 5) (1) Find the atmospheric dew point of inlet air ©. When the humidity of inlet air can be considered as relative humidity or a pressure dew point, the atmospheric dew point can be found according to the humidity conversion chart in "Humidity and conversion" page 10 of the supplement. (2) Find the volume ratio Kv ®. Find the volume ratio from the following equation for a volume ratio. Vt: Volume inside the piping [cm3] Ps : Gage pressure of supplied air [MPa] (3) Assess the probability of condensation. Extend lines from © to (?) and from © to © to find...

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Precautionary measures against condensation in a pneumatic system - 10

ketro-B-P07.qxd 10.12.27 1:31 PM Page 1 4. Countermeasures against condensation Based on the above-mentioned condensation example, the following preventive measures can be implemented. Ȝ Countermeasures against air quality Compressed air containing a large amount of moisture condenses easily and may cause the pneumatic equipment to malfunction. Therefore, it is recommended to install an air dryer before pneumatic equipment, based on the results of the Condensation Assessment Chart or the SMC Model Selection Software. For selecting the air dryer, refer to the SMC Pneumatic Energy Saving...

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Precautionary measures against condensation in a pneumatic system - 11

© By-pass circuit method Sufficient exchange of air can be achieved by providing one-way air supply and exhaust circuits with check valves and by-pass piping. By-pass piping installation position Li: it should be smaller than -g— x —QT~ and be installed as close to the cylinder as possible. Length of by-pass piping L2: approx. 20% of the total length of L Solenoid valve Check valve Sp : Piping cross-sectional area [mm2] Check Valve with One-touch Fitting Straight type (D Quick exhaust valve method Install quick exhaust valves close to the cylinder to exhaust air inside the cylinder directly...

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Precautionary measures against condensation in a pneumatic system - 13

The content of vapor in air is represented by the humidity or dew point. Absolute humidity : The mass ratio of vapor to dry air Relative humidity : The mass ratio of vapor to amount of saturated vapor Atmospheric pressure dew point : Temperature at which vapor reaches saturation when air is cooled under atmospheric pressure. Pressure dew point: Temperature at which vapor reaches saturation when air is cooled under fixed pressure. Humidity conversion diagram Relative humidity % How to use the humidity conversion chart Top-left chart: Top-right chart: Used for conversion between relative...

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