With respect to the operation of a two-stage reciprocating air compressor, explain:

The 2nd stage relief valve may lift occasionally due to:

1. A momentary over-pressure in the 2nd stage (e.g. if the 2nd stage delivery is blocked or the receiver is full and the pressure rises).
2. A fault in the 2nd stage (e.g. a sticking delivery valve or a faulty unloader) causing the pressure to rise.
3. Water or oil in the 2nd stage cylinder (from carry-over) causing a pressure spike.
4. The relief valve being set too low (incorrect setting).
5. A sudden increase in the load or a fault in the intercooler causing the 2nd stage inlet pressure to rise.

The valve plates (the reed/ring plates of the suction and delivery valves) may break due to:

1. Fatigue: the plates flex millions of times and can fail by fatigue, especially if they are worn or have a defect.
2. Overheating: if the compressor runs too hot (e.g. due to a faulty intercooler or insufficient cooling), the plates can overheat and fail.
3. Water or oil carry-over: liquid in the cylinder can cause a hydraulic shock that breaks the plates.
4. Foreign material: dirt or debris in the cylinder can damage the plates.
5. Incorrect valve spring tension or a misaligned valve.

The bursting disc of the 1st stage intercooler may puncture due to:

1. Over-pressure in the intercooler (e.g. if the 2nd stage is blocked or the intercooler is blocked, the pressure rises and the disc bursts).
2. A fault in the 1st stage (e.g. a sticking delivery valve) causing the pressure to rise.
3. Water or oil carry-over causing a pressure spike.
4. The disc being damaged or incorrectly fitted.
5. A sudden blockage of the intercooler or the 2nd stage inlet.

A noticeable reduction in the capacity (delivery) of the compressor over time is due to:

1. Wear of the piston rings and cylinder, causing blow-by and reduced compression.
2. Leaking valves (suction or delivery) allowing air to pass back, reducing the delivery.
3. Fouling of the intercooler and the filters, increasing the pressure drop and reducing the air flow.
4. Leaks in the piping and the valves.
5. Wear of the piston and the cylinder, increasing the clearance volume.
6. A faulty unloader or a sticking valve.

The capacity is restored by overhauling the compressor (renewing the rings, valves, and cleaning the intercooler and filters).