Reciprocating Air Compressor-Explained.


The reciprocating air compressor is the most commonly used type everywhere in the world. The theory and design of a reciprocating air compressor have been discussed in my previous articles. In this article, let us discuss the detailed explanation on various components of a reciprocating air compressor along with its operation.

Suction Filter:

It is one of the most important components of any air compressor. The main aim of an air suction filter is to filter out the dirt from the ambient air and allow clean air for compression. The suction filter must be of correct size, that is it must be big enough not to get chocked frequently and fine enough to filter out minute dirt particles. Usually the filter will be of mesh type or viscous impingement type. A slight coat of lube oil must always be present in the filter to attract the dirt particles towards the filter. It must be positioned in such a way that it must be sucking the parts of the operator when he is taking rounds around it. The filter is enclosed inside a casing which is often detachable. The casing is made of plastic or sometimes aluminum or a light weight metal. It has a mouth which forms a passage for the ambient air to be sucked into the filter. It is highly essential to have the filter positioned in such a way that there is free air movement or adequate air availability for the usage of compressor. The usual path of air movement via the filter is the air gets filtered by the outer chamber of the filter and then enters the inner part of the filter. From the inner part, the air enters the clearance space (compression chamber) of the compressor.

Air Suction Filters

Cylinder Head:

2-Stage Air Compressor

The cylinder head of an air compressor is one of the most important components, which is usually heavy and strong enough to withstand the compression force of air and excessive heat of compression. The head has pockets for the intake and delivery valves, pipelines for intercooler and after cooler, and cooling water connections (inlet and outlet). The number and type of connections depend on the type of compressor. The cylinder head is usually made of cast iron, with cast cooling chambers. The head is connected to the compressor body by a number of studs. The cylinder head is assembled upon the compressor body, exactly matching the studs. There is usually a copper joint between the compressor body and the cylinder head. This copper joint expands as the temperature increases and thus seals effectively. The cylinder head is held tight against the body of the compressor, by the nuts on the studs, which are tightened against the compressor body with the cylinder head. This makes the cylinder head stable against the compression gas pressure inside the compressor. Air cooled compressors have cooling fins, where the surface area of exposure is more increased than the head without the fins.


Air Compressor Valve Assembly

Depending upon the number of stages, the compressor’s intake and delivery valves are positioned accordingly. For a 2-stage water cooled compressor, there are low pressure stage valves and high pressure stage valves respectively. The Low pressure or the 1st stage has one intake valve and one delivery valve. Similarly the high pressure or the second stage has one intake and one delivery valve. The valves are similar in operation but different in sizes. As discussed earlier in some of my previous articles, the low pressure or the first stage is bigger in size when compared to the high or the 2nd stage. Similarly, the 1st stage valves are bigger in size when compared to the 2nd stage. But both the valves have same parts of varying sizes. The valve unit contains valve seat with a center bolt and a locating pin. The valve seat has numerous concentric circles which form a perfect sealing with the valve plate. The locating pin positions all the valve units at a same place without any movement during operation. There is a guide washer, which helps in guiding the valve plate and other plates of the valve unit. The valve plate rests on the valve seat. Upon the valve plate, the damper plate is positioned. There are 3 to 4 set of spring plates which act as spring during valve operation. The spring plate is covered by a buffer plate and all these plates are locked in position by the castle nut and a split pin. The location of the valve plate and the spring plate vary depending upon whether the valve is used for intake or delivery.

In my next article, we will discuss other components, their functions, and the operation of a reciprocating air compressor.

This post is part of the series: Reciprocating Air Compressor-Explained – 1

Read here to know about the detailed explanation of suction filter, cylinder heads, valves, casing, compressor crankshaft and bearings, lubrication system, bumping clearances, maintenance, unloading operation etc.
  1. Reciprocating Air Compressor Explained-1
  2. About Reciprocating Air Compressors Explained – II
  3. Reciprocating Air Compressors