Parts of the Reciprocating Compressor

Now that we have seen the principle of working of the reciprocating compressor, let us see the various parts of the compressor. The important parts of the reciprocating compressor are: cylinder, piston, piston rings, connecting rod, crankshaft, suction valve, discharge valve, suction port, discharge port etc. All these parts have been described in details below (refer the image below):

In small compressors the cylinder is made by directly boring into the main body of the compressor, which is usually made up of cast iron. In case of the large multi-cylinder compressors, the cylinder is made separately and it is fitted into the main body of the compressor. This type of cylinder is also called as the liner or sleeve. In such compressors if any of the cylinders gets worn out or damaged, it can be replaced easily by the new liner, without having to replace the whole compressor.

The piston performs upwards and downwards motion inside the cylinder, which is also called as the reciprocating motion. During its motion the piston enables suction and compression of the refrigerant. The piston is made of cast iron or aluminum. During its motion inside the cylinder the refrigerant should not leak through the gap between the cylinder walls and the piston to the crankcase, hence piston is covered with the piston rings. The piston rings are not required in the smaller compressors. The gap between the piston and the cylinder is also filled with the lubricating oil, which also prevents the leakage of the compressed refrigerant to the crankcase.

The piston rings are circled around the piston. When the piston performs reciprocating motion inside the cylinder, it is the piston rings that come in contact with the walls of the cylinder. There is lots of friction between the cylinder walls and the piston rings, thus they have to be replaced from time-to-time for proper functioning of the compressor. This helps increasing the life of the piston and prevents replacement of the complete piston.

The piston can perform reciprocating motion inside the cylinder because of the rotary motion of the crankshaft. The crankshaft is the main shaft of the compressor. On one side it is connected to the electric motor directly by the coupling or by the belt and pulley arrangement. The rotation of the motor shaft brings about the rotation of the crankshaft. On the other side the crankshaft is also connected to the connecting rod, which is then connected to the piston at it other end. The rotary motion of the crankshaft is converted into the reciprocating motion of the piston by connecting rod. In case of the multi-cylinder compressors, the number of connecting rods connected to the crankshaft is same as the number of cylinders.

The connecting rod is the connecting link between the piston and the crankshaft. On one side the connecting rod is connected to the piston by piston pin and on the other side it is connected to the crankshaft by connecting rod cap. Both these connections of the connecting rod enable converting the rotary motion of the crankshaft into the reciprocating motion of the piston inside the cylinder. The connecting rod is usually made up of carbon steel forging.

Through the suction valve the low pressure refrigerant is sucked inside the cylinder and through the discharge valve the compressed high pressure refrigerant is discharged to the discharge line, from where the refrigerant goes to the condenser. The operation of the suction valve is such that is opens when the piston moves downwards and closes when the refrigerant is being discharged. The discharge valve opens only when piston reaches to certain level inside the cylinder and refrigerant has reached to the desired level of pressure. When the refrigerant is delivered from the cylinder, the discharge valve closes.

Through the suction piping the low pressure refrigerant is taken inside the cylinder via suction valve. The high pressure compressed refrigerant is delivered though the discharge line.

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