Air Compressor - Basic

Air Compressor is a device which is convert energy (like electrical motor, diesel engine or gasoline engine) by storing pressurized air into potential energy. Working method on an air compressor is store the air in tank by more forces and shut off after reaching its higher pressure limit. This pressurized air used in various work by a pneumatic system, when the tank pressure reaches a certain limit, compressor start again to fill the air tank. Electrical and Air pressure are the two power source which are mostly use in many industries all over the world.

Air Compressor Types

There are several types of air compressors according to the design and principle of operation:

Reciprocating compressors: Using a reciprocating piston which is moved up and down by a rotating crankshaft, like a car engine. Single Stage and Two Stage Reciprocating compressors are commonly used.

Rotary Screw air compressors: Using two meshed screw drives that constantly rotate to force air to down the shaft from the larger, from least-compressed grooves to more compressed grooves. Mainly used in Industrial purposes.

Rotary Vane Compressors: A rotor with a number of spring-loaded blades are using here. This rotor is set inside a cylinder, spins to move air from the larger area of the cylinder into the smaller side. By the movement of this rotor from large area to small area compresses the air.

There are other types of compressor, but these are the very common.

How Reciprocating Air Compressors Work?

All air compressors working principle are same, moving air from a larger area to a smaller area. Here we discuses about Reciprocating Air Compressor.

These types of compressor working like a car engine. An electric motor (sometimes a gas engine) rotates a crankshaft that moves the connecting rod, which causes the piston to move up and down inside the compression chamber. 

On the down stroke, the inlet valve opens and air comes from the outside. Piston compressors have a weakness from dirt, so an air filter is using to remove the dirt from air. 

On the upstroke, the inlet valve shut-off, and the unload valve opens, passing the compressed air to the air tank. When the piston moves down, this discharge valve remains close. Air come into compression chamber, trapping the compressed air in the storage tank and the inlet valve opens, repeating the cycle. 

Important Parts of an Air Compressor

Pressure Switches

The pressure switches use for measuring the pressure amount which is building inside the tank and control the motor. This pressure switch use to ensure motor run at low air pressure and cut-off at high air pressure. It is a safety device to ensuring the safety of device as well as user. When motor start, air goes to the tank and a pressure is building up. At a set pressure point, pressure switch give a high pressure signal and switch off the motor. After some use of air from the tank, pressure is going low and a start signal goes to the motor to start.

This difference between the low pressure point and the high pressure point is called the “pressure differential.”

Overload Valve

Overload valve is another safety device to protect the air storage tank from explosion. Every air compressor’ tanks must have a certain standards. An overload valve’s parameter adjust by tanks standard to control the over pressure.

Air Regulator

There are two gauges used in air compressor, one in air tank for showing the pressure of the tank. Another one for measuring how much air flowing out, this gauge is regulated by a knob to adjust air pressure how much you need.

Drain Valve

A drain valve is using in air tank to remove water component from compressed air. When air is compressed, air is going lose its temperature and some moisture is gain in the air.

Terms and Specifications for Air Compressor

Now talk about some terms and specification to understand the nameplate of an air compressor.

Horsepower: This terms using mainly for motor or engine which is run the air compressor. It may be written in horsepower or kilowatt (KW). This term is for showing how much power consummated by a compressor.

Pressure: Low and high pressure range is given by this term. The unit of this pressure is given in Pounds per Square Inch or PSI.

Power Source: As run by electric power, air compressors need 3 phase or single phase electrical power. For large volume air compressor 3 phase motor is using. Small compressor runs by single phase motor.

Air Tank: This specification is varying for users to user. Air tank will depends on how much air you need for your work.

Working Principle Of Inductive Sensor

By applying a voltage to the oscillator coil an alternating inductive field is created in front of the active surface of the unit.

When a metallic object (steel, aluminum, copper, brass etc.) enters this field from any direction and the state of the oscillator is modified until the threshold of the trigger is inverted this induces a change in the final stage and the subsequent command of an external load. The intervention distance depends on the type of metal and as described earlier, in the reduction factors. All the sensors are protected against inversion of polarity and electrical disturbances of inductive sources and can be supplied with short circuit protection in the D.C. version. The main advantages offered by proximity sensors in relation to normal limit switches are mainly unlimited duration as they have no moving parts (wheels, springs etc.) lack of maintenance requirement and elimination of possible false contacts due to contact movement.

Quality Systems (a Reference to IS0 9000)

Making of the Quality Systems

Many countries have framed guidelines and standards. The earliest standard was issued in 1959 by the US Department of Defense for large contracts (MIL-Q 9858. ‘Quality program requirements’). The long interval between Taylor‘s description of Quality Management in 1911 until 1959. When the US Defense Department laid down its quality requirements for the first time, was perhaps due to an increase in global interest that developed only in the late 1950s. Since then, there has been a continuous application of these standards to contractors and manufacturers worldwide. For civilian use in the United States. ANWASQC. Standard C and ZI, I5 were published in 1968. Since then, many countries and large organizations have been publishing their own quality control systems. For civilian reference, ‘A Guide to Quality Assurance’ was first published in 1972 (BS 4891). This was soon replaced by BS 5 179, ‘Guide to Operation and Evaluation of Quality Assurance Systems’. This was upgraded by BS 5750 in six parts. To ensure consistency in all standards and to make them universal a technical committee, TC/I 76, of the International Standards Organization (ISO), Switzerland, was entrusted with the task of drawing up such a set of standards. They have by now introduced the following standards:

IS0 8402

Quality Vocabulary.

IS0 9000

Quality Management and Quality Assurance Standard. Guidelines for selection of Standards in the series and use of the same for the management of quality systems.

IS0 9001

Model for Quality Assurance in Design or Development, Production. Installation and Servicing.

Applicable to those who design, produces, install and service their products or carry out such activities.

IS0 9002

Model for Quality Assurance in production, installation and servicing.

Applicable to those who make their products on the basis of some proven designs, or work as ancillaries for standard products.

IS0 9003

Model for Quality Assurance in Final Inspection and Test.

Applicable to those who are engaged in third-party inspection and testing.

IS0 9004

Quality Management and Quality System Elements - Guidelines.

Applicable to quality assurance for services, such as hotels and hospitals etc.

All these standards have since been adopted by the member countries as their national standards, fully or in slightly modified forms, to suit their own requirements and working conditions. These standards define and clarify the quality norms and aim at in-house quality disciplines, to automatically and continually produce a product, provide a service or program to the stipulated specifications, quality norms and customer needs. They guarantee a product or service with a minimum quality. The envisaged quality systems thus aim at a work culture that pervades all those involved in different key activities or processes, to achieve the desired goal through carefully evolved systems.

Maintenance of bearings

Reasons for high bearing temperature

This may be due to

• Excessive quantity of grease causing churning
• Inadequate grease due to deterioration or leakage
• Misalignment, causing friction and excessive axial forces
• Loose fit of the bearing housing, causing both inner and outer races of the bearing to rotate inside the housing
• Corrosion or the presence of foreign matter in the bearing.

Any of the above reasons may result in noise and an increase in temperature and must be corrected. Critical installations such as a refinery, a petrochemical plant, a chemical plant or a petroleum pipeline may require special precautions and control to avert any excessive heating of the bearings, which may become fire hazards. For these installations, bearing temperature detectors with a relay and alarm facility may also be installed in the control circuit of the switching device to give warning or trip the motor if the temperature of the bearing exceeds the preset safe value.

Maintenance of bearings

Grease may leave skin effect on the races of the bearings if the motor is stored idle for a long period. This may cause noise during operation and overheating of the bearings. After a long period of storage grease may also dry and crack, and produce these effects. To detect this, bearing covers may be opened and the condition of the grease and any skin effects checked. If such marks are visible, the bearings must be taken out and washed thoroughly in petrol or benzene to which is added a few drops of oil, and then re-greased with a recommended grade and quantity of grease. Quantities of grease above recommended levels may cause heat the same way as quantities below recommended levels.

Cleaning bearings

For cleaning bearings and bearing housings, before applying the grease, only the following fluids should be used: benzene, white petrol and benzole (white petrol is the most recommended).