Refrigeration & Equipment Engineering

Unit 3 - Parts of refrigeration systems

3.1.2.1.2.Different parts of the Reciprocating compressor
Piston
The piston is made of cast-iron and is mechanically well polished. It has a drilled hole to fit the piston or wrist pin. This pin is fitted for joining the connecting rod to the piston. Piston it fitted with close tolerance in cylinder. The function of the piston is only to compress the refrigerant in an enclosed cylinder.

Piston rings
Piston rings are made of cast-iron which are fitted on pistons but some piston rings are made of bronze metal also. This metal works for long time and not rubbed. These rings are installed in grooves on the piston. Generally piston has two or more rings. The main function of the piston ring is to maintain the proper lubrication and to prevent the gas from escaping between the piston wall and cylinder wall.

Crank shaft
Crank shaft is a moving lever. It is used for inducing the torque. When it is used with the connecting rod it moves with the reciprocating motion. Crank shafts are made of carbon steel, cast steel or nickel chromium steel. Crank shafts are equipped with counter weights and are carefully balanced to ensure smooth and vibration less compressor operation. This counter weight is made of cast-iron.

Connecting rod
Connecting rod is used for connecting the piston and crank shaft. One end is connected to the piston by means of hardened, ground and highly polished steel wrist pin. It is made of cast steel or cast-iron. The wrist pin upper end of the connecting rod have an oscillating or reciprocating motion while the lower end of the connecting rod combines a reciprocating and rotary motion.

Rings
There are two types of rings i.e, compression rings and oil scrapper rings. The compression ring is provided on the top of the piston and is used to seal the difference between the piston and the cylinder wall. The oil scraper ring is provided below the piston.

Suction and discharge valve
The valve that controls the flow of refrigerant from the suction line into cylinder head is known as suction valve. The valve that discharges the compressed gas towards the discharged line is called discharged valve. These valves are named according to the function they perform.