Question

(a) Explain the necessity of intercoolers on a multi-stage compressor. What attention is required to keep them safe and in good working order? Sketch and describe an intercooler suitable for a 2400 kPa compressor and state the materials used.

(b) What attention is needed before opening up for inspection? What faults are likely to develop in an air compressor and how are they remedied.

Answer 1

Part (a)

Necessity of Intercoolers on a Multi-Stage Compressor:

Compressing air generates heat, and intercoolers reduce the temperature of air before it enters the next stage, protecting components from heat damage.
Cooler air requires less work for compression in subsequent stages, improving overall efficiency.
By lowering operating temperatures, intercoolers reduce thermal stresses on components, enhancing durability.
Cooling condenses moisture in the air, preventing water accumulation in downstream equipment.

To Keep Intercoolers safe and in good working condition:

Ensure a continuous supply of cooling water.
Regularly clean the intercooler to maintain efficient heat exchange.
Drain accumulated oil and water frequently.
Verify that the intercooler drain line is clear.
Inspect and maintain the bursting disc to prevent failure under excessive pressure.

The sketch depicts a multi-tubular intercooler suitable for a 2400 kPa compressor. It uses a shell-and-tube design. The compressor's high-pressure air flows through numerous small-diameter copper tubes, maximizing the surface area for heat exchange. Cooling water circulates around the tubes in a cast iron jacket, absorbing the heat from the compressed air. A copper or brass bursting disc serves as a safety pressure relief device.

Materials Used:

Body: Cast iron (provides strength and corrosion resistance)
Tubes: Copper (excellent thermal conductivity)
Bursting Disc: Copper/Brass/Steel (depending on pressure requirements)

Part (b)

Attention Required Before Opening Up an Air Compressor for Inspection:

Ensure the electrical circuit is switched off and tagged with "Men at Work."
Fully drain the compressor, intercoolers, and air receivers to release residual pressure.
Verify that the discharge valve is not leaking air into the system.
Remove dirt and debris from around the compressor to prevent contamination during inspection.
Allow the compressor to cool if it has been in operation to prevent burns or thermal stresses.
Wear appropriate personal protective equipment (PPE), including safety glasses, gloves etc, depending on the conditions.

Likely faults and remedy:

The most effective way to prevent faults and ensure long-term reliability is through a rigorous preventative maintenance schedule (PMS) – including regular inspections, cleaning, component replacements, and lubrication as per the manufacturer's recommendations.

Maintenance Recommendations:

Overhaul suction and discharge valves every 1000 hours.
Replace air filters every 500 hours.
Inspect and test relief valves every 4000 hours.
Check IR for motor windings every 2000 hours.
Change lubricating oil every 2500 hours.

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