7.(a) Sketch a Chemical Filter tower supplying air suitable for breathing and diving, labelling ALL elements.(4)
(b) Explain the purpose of TWO of the filter elements sketched in part(a).
(a) Sketch – Chemical Filter Tower for Breathing / Diving Air (4 marks)
Description of the sketch (text version):
A Chemical Filter Tower (also called a purification tower or breathing air purification unit) is fitted downstream of the air compressor and typically contains several stages housed in a vertical pressure vessel. The air flows upwards through filter elements arranged in the following sequence:
┌───────────────────────────────┐
│ Breathing Air Outlet │
├───────────────────────────────┤
│ Activated Carbon Cartridge │ ← Removes oil vapour & odours
├───────────────────────────────┤
│ Molecular Sieve (Desiccant) │ ← Removes moisture & CO₂
├───────────────────────────────┤
│ Coalescing / Particle Filter │ ← Removes oil mist & solid particles
├───────────────────────────────┤
│ Air Inlet from Compressor │
└───────────────────────────────┘
Labels to include:
- Air inlet (from compressor)
- Coalescing or particle filter
- Chemical drying cartridge (molecular sieve or desiccant)
- Activated carbon filter
- Air outlet (to breathing air storage or manifold)
- Drain valve at base for removal of condensed oil and water
(b) Purpose of TWO of the filter elements (4 marks)
- Coalescing / Particle Filter
- Purpose: Removes liquid oil droplets, condensed water, and solid impurities from the compressed air.
- Explanation: Prevents these contaminants from entering downstream filters, thereby protecting chemical elements and improving air purity.
- Activated Carbon Filter
- Purpose: Removes oil vapours, odours, and traces of hydrocarbons by adsorption.
- Explanation: Ensures the air is free from harmful vapours and smells, making it safe and pleasant for breathing.
Alternative acceptable explanations:
- Molecular Sieve / Desiccant Cartridge: Removes moisture and carbon dioxide, ensuring the air is dry to prevent corrosion, freezing, or regulator malfunction during diving.
- Final Dust Filter: Captures fine dust from the desiccant or carbon bed before air leaves the tower.