How do rotary air compressors work

Unlike reciprocating air compressors that use a cylinder and piston arrangement in a linear compression process, rotary screw air compressors use a pair of intermeshing screws rotors contained in a stator housing airend , with an inlet port on one end and a discharge port on the other end.

The male and female rotors are cut to very tight tolerances and intermesh together as they turn. As the tips of the male and female rotors come together on the inlet port side of the airend, there is a vacant space volume where atmospheric air is sucked into the compression chamber. There are three basic units of measure to consider when talking about a compressed air system…flow, pressure, and power.

Technically, end users do not pay for compressed air, they pay for the energy kW required to produce the desired flow and pressure. The challenge for the end user is to determine the most efficient way to produce the required volume of compressed air at the required pressure. Take me to the webinar. A single-stage rotary screw air compressor contains a single set of rotors in a single stator housing and is typically driven directly by the motor shaft, through a set of gears, or by a belt and pulley arrangement.

Two-stage rotary screw air compressors are typically direct or gear drive. The difference between the two is not the end result, rather the energy required to produce the end result. A simple analogy: If you were asked you to push your car from point A to point B on a level parking lot, it would require a certain amount of energy on your part to do so.

If you had a friend help push the car the same distance, the end result would be the same, but it would require less energy overall because the work is being done by two people instead of one!

The intent of this discussion is to demonstrate the differences between single-stage and two-stage compression and is not based on actual applications. There are pros and cons to everything, and air compressors are no different. Both single-stage and two-stage rotary screw air compressors have their place in industry and plant managers are charged with making the right choice based on their unique needs and requirements. Single-stage air compressors offer multiple options such as tank mount, integral dryer, open or enclosed, and a choice of micro-processors controller.

As with two-stage, multiple control methods are available on single-stage air compressors. All single-stage air compressors use pressure at the discharge of the air compressor to control the operation of the machine. Variable Speed Drive VSD technology senses the discharge pressure and varies the speed of the main motor, delivering the best part-load efficiencies of all the control methods.

The most widespread type of screw compressors are lubricated compressors with oil injection. For sensitive processes regarding the quality of compressed air non-lubricated compressors are used. The compression process, in case of a lubricated compressor, proceeds as follows:. The air circuit: Air is drawn through the filter and an open inlet valve, into the compressor element and gets compressed. The air is discharged through an outlet valve via a minimum pressure valve and the air cooler.

During loaded operation, a minimum pressure valve keeps the pressure in the separator tank above a minimum value, required for lubrication. An integrated check valve prevents the compressed air downstream the valve from being vented into the atmosphere during unloaded operation. When the compressor is stopped, the check valve and inlet valve close, preventing compressed air and oil to be vented into the air filter. The remaining oil is removed by the oil separator. The oil system is provided with a thermostatic bypass valve.

When the oil temperature is below its set point, the bypass valve shuts off the supply to the oil cooler and the oil cooler is bypassed. The bypass valve starts opening the supply from the cooler when the oil temperature has increased to the set point.

At approx. An oil stop valve prevents the compressor element from flooding with oil when the compressor stops. MultiAir Italia S. Read more below from rotary air compressor expert Kaishan. Rotary compressors contain two helical rotors within the housing that interlock. Ambient air comes into the compressor through the inlet valve. Air is then trapped between the two rotors.

There, the screws turn, and this increases the pressure of the air by reducing its volume. Some rotary screw air compressors do consist of only one screw, but these are not as widely used in the industrial realm, where the full power of two screws is essential for large-scale productions. Single-screw rotary models are more often used in refrigeration. In the design of these compressors, the assembly that consists of the housing and rotors is known as the air end.

In all types of rotary compressors, the air end is where incoming ambient air is compressed. Some rotary screw compressors use oil while others do not, but all compressors need to filter out the oil present in the ambient air. In compressors that use oil, the motor drives the male rotor, which in turn drives the female rotor. Fortunately, the latest compressor controls contain troubleshooting diagnostics and fault indicators.

There are generally five areas of the compressor that require maintenance: airend, motor, drive train, lubricants, and filters.

Airends and their bearings are damaged by contamination in the air and lubricants and by excessive heat. Inspect for unusual noises and vibrations. Monitors should be able to detect impending problems and sound alarms. Motor bearings should always be lubricated with the right amount and type of grease. Replace bearings on a conservative schedule.

Periodically check ampere draw to ensure the motor is not overloaded. Providing proper ventilation and ambient temperature in the compressor room increases motor life. Drive train systems must be kept aligned. If the frame or mounting block settles, misalignment will damage the coupling. Gear drives must always be properly lubricated. Inspect and adjust the tension on V-belt drives at least every operating hours.

Worn or frayed belts should be replaced. Lubricants cool, seal, protect, and remove contaminants in a compressor. Always drain all existing lubricant before refilling to ensure maximum service life. Change oil on a schedule recommended by the manufacturer for the application.

Regular oil sampling helps maximize lubricant life. Avoid lubricants not specifically designed for a particular compressor; they may impact service life. Filters protect the compressor from wear and damage. Proper filtration is more cost effective than repairing damaged equipment. Inspect and replace air inlet filters on a regular basis about every hr.

This timing reduces component contamination and airend wear, which improves operating efficiency. Oil filters should be changed and strainers cleaned about every hr. Keep the compressor clean. Fouled compressor and intercooler surfaces increase the compressed air temperature. This increase has the effect of reducing output, but not total energy input.

This added energy per unit output shows up as higher temperature of the discharge air. The aftercooler and dryer must reduce this temperature. The result is less compressed air output and increased energy input. Foszcz, Senior Editor, , jfoszcz cahners. Colder temperature increases and warmer temperature decreases efficiency. Less than 15 hp Reciprocating Reciprocating Reciprocating Reciprocating.