The crankshaft can be called the spine of any reciprocating machinery. The size and length of the crankshaft depends on the type of the air compressor. The crankshaft has three important parts jointed together or fabricated from the same piece. They are
- Crank web
Looking at the attached image, the main journal is the one which rests on the main bearing. It forms the center line of the crankshaft. The crank web are the appendices, projecting outside the center line of the crankshaft, giving way to support the crank pins, which are connected to the connecting rod.
The crankshaft has one end connected to the drive, which may be either an electric motor or diesel engine. The other end is usually a blind with a shaft seal and a journal bearing. The end which is connected to the drive usually has a flywheel attached to it. The flywheel in turn is attached to a flexible coupling.
This system is applicable only to those types of compressors that employ forced lubrication. The compressor crankcase forms an inherent oil sump; where some calculated amount of oil is available as a reserve even after the oil is under work, i.e. lubrication. The lube oil is drawn by the lubricating oil pump, which is driven or an attached pump with the crankshaft. The pump takes suction from the inherent lube oil sump of the compressor, and it supplies oil under pressure to a common manifold, from where the oil is routed to each main journal bearing and enters the drilled hole on the crankshaft after lubrication of the main bearing. After entering the drilled hole, the oil moves towards the crank pin, via the crank web, and thus lubricates the bottom end bearing of the connecting rod. After lubrication, some of the oil climbs up the drilled hole in the connecting rod and thus reaches the small end bearing, thus lubricating the gudgeon pin and related moving parts. The oil after lubrication falls down into the crankcase sump.
In my next article, we will discuss the other important components and systems of a reciprocating air compressor.