Question

(a) Define the essential conditions, which must be satisfied by the air supply for a pneumatic control system.

(b) Sketch a control air supply arrangement and give a reasoned explanation for positioning of dryers and filters.

Answer 1

Part (a)

Essential conditions for air in pneumatic control system:

Air must be free of dust and particles to prevent clogging or partial blockage of small orifices and piping.
Particles cause wear and tear on components and can lead to system inefficiency or failure.
Moisture in the air can lead to corrosion of metal components in the pneumatic system.
Condensed water can cause malfunctions by freezing in cold conditions or affecting the system's control stability.
Compressed air should not contain oil to prevent blockage of orifices and contamination of sensitive control components.
Air must be devoid of any foreign contaminants that could choke nozzles and orifices, impacting the accuracy and reliability of the system.
The air quality should meet the guidelines set by ISO 8573-1:2010, which specifies the maximum allowable levels for:
- Particles: 0.1–0.5 μm (≤20,000), 0.5–1.0 μm (≤400), 1.0–10.0 μm (≤10).
- Water Content: Dewpoint ≤-70°C.
- Oil Content: ≤0.01 mg/m³ (liquid, aerosol, and vapor).
Part (b)
The air used in pneumatic control systems must be clean and dry to prevent damage to pneumatic components. Air from the starting air receivers undergoes the following treatment
process:
- The high-pressure air from the main air receiver is passed through a pressure-reducing valve, lowering the pressure to a range of 7–8 bar suitable for pneumatic systems.
- The air is passed through a filter to remove oil and water carried over from the compressor. This step eliminates contaminants that could affect system performance.
- The filtered air is sent through a dryer containing materials like silica gel or activated alumina to remove residual moisture. Dry air prevents corrosion and freezing in control lines.
- Regular drainage of accumulated water, oil, and condensate is necessary to maintain the air quality and prevent blockages in the system.
Now the air is clean & dry enough to be suitable for use in pneumatic control systems.

✓ Verified Model Answer (Text Solution)

Essential conditions for air in pneumatic control system:

The air used in pneumatic control systems must be clean and dry to prevent damage to pneumatic components. Air from the starting air receivers undergoes the following treatment