Corporate Buyers Guide

A reciprocating air compressor uses a piston to compress air. They are positive displacement machines, which means that they increase the pressure by reducing the volume of the air. Reciprocating compressors use a a piston driven by a crankshaft which is in turn driven by an external motor. The piston moves up and down in a cylinder to compress the air. As it moves down, a valve, the inlet valve, opens to allow air into the cylinder. When this downward movement stops, this valve closes and the the upward movement of the piston begins. This is where the air is compressed. When it nears the top of it’s movement, another valve, the outlet valve opens allowing the now compressed air to leave the cylinder.

Reciprocating air compressors can be single stage, two stage, or multi-stage. Single stage compressors compress the air using only one cylinder. Two stage compressors have two cylinders and take the compressed air from the first cylinder and feed it into the second to compress it further. When the first cylinder’s outlet valve opens, the second cylinder’s inlet valve also opens to allow the compressed air to enter the second cylinder. Multi-stage compressors have more than two cylinders in series, with each one taking the compressed air from the cylinder before it and compressing it further.

To select a dryer for compressed air, three important parameters have to be considered. 1. The desired dew point (humidity) of the air, 2. The cost to purchase, 3. The operating costs.

For refrigerated air dryers:

1.      The dew point goes to approximately + 35 F. To operate hand tools and for many applications this is sufficient. Also, in humid climates or for very dry air, the refrigerated air dryers is used as a pre dryer to ease the load on follow up desiccant dryers

2.      The initial cost to purchase a refrigerated air dryer is lower than for desiccant dryers. The installation cost is simpler and less expensive.

3.      The refrigerated air dryer uses large amounts of electricity. This makes the operating costs high..

One advantage of these dryers is that they can operate at higher inlet temperatures and pressure. Therefore, for plastic molding machines plus in many food and pharmaceutical applications the refrigerant pretreatment is an advantage.