Gas Compressors and Systems

Gas compressors and systems are used to pressurize and circulate gas through a process, enhance conditions for chemical reactions, provide inert gas for safety or control systems, recover and recompress process gas, and maintain correct pressure levels by either adding and removing gas or vapors from a process system. Gas compressors work in two stages. In the first stage, gas flows through the inlet check valve and fills the larger diameter first-stage cylinder. Pressurized hydraulic fluid, acting on the hydraulic piston, strokes the piston assembly to the left compressing the gas in the first-stage cylinder. Gas in the first-stage cylinder flows through the check valves into the smaller diameter second-stage cylinder.

At the end of the first stage, the four-way valve changes position and directs pressurized hydraulic fluid to the left side of the hydraulic piston. The piston assembly moves to the right compressing gas in the second-stage cylinder. Gas flows out of the second-stage cylinder into the discharge gas line. The piston assembly reverses direction at the end of the second-stage stroke and the cycle repeats.

There are four broad categories of compressor types. There are many variations within each type: reciprocating compressor, fan / blower compressors, rotary compressors, and ejector compressors.

In reciprocating compressors, the thrust of a positive displacement pump, within the cylinder, moves the gas through the system. This thrust enhances both the pressure and the density of the gas being transported. Examples of reciprocating gas compressors include piston compressors, lubricated and non-lubricated, and metal diaphragm compressors. In general, reciprocating pumps offer low rational and piston speed, leading to a high reliability factor with a minimum of maintenance.

Fan / blower compressors contain high-speed impellers through which a dynamic head is imparted to the gas. This category of gas compressors includes axial flow, radial, centrifugal and fan-blower compressors. They may also be referred to as turbomachinery.

Rotary compressors and rotary screw compressors move gas through the system by the positive displacement of two rotating lobes or by oscillating vanes confined in an eccentric cylinder. Rotary screw compressors are well known for their robustness, compactness and reliability. They are designed for long periods of continuous operation, needing very little maintenance. The smooth running action of the rotors enables the screw compressor to handle the most difficult of gases, contaminants, or liquid slugs without vibration.

Ejector compressors move gas via kinetic energy induced through high-velocity nozzles. The advantage of ejector gas compressors over mechanical pumping machinery is that it has no moving parts and as such requires very low maintenance.