Factors to Take into Consideration When Buying Air Compressor

How to Choose Air Compressors

          Factors that should be taken into consideration to get the suitable air compressors can be separated into nine things: pressure, outlet air volume, electricity distributor, environmental restriction, installation method, cooling method, sound restriction, management, and efficiency restrictions.

          1. Pressure :
          Air compressor’s pressure (kg/cm2) other than using real usage as indicator, pressure lost in pipe and purifier system must also be taken into consideration.                                                                                                                              Pipe decreased pressure: Pressure decreased by pipe is like when a car is traveling through a wide, straight, and short road, it will reach the destination faster and reduce wasted energy. Normally pipe pressure lose rate is around 0.5 kg/cm2. Air compression is usually coupled with air purifying, heat exchanging, and drying through pipes or filter. To purify the air, pressure is often lost by 0.3-0.5 kg/cm2 (Filter and Dryer).

          2. Outlet Air Volume :
          Real Air Volume: Is the result from using standard equipment to measure the air volume from air compressor after the process.
Piston Position Changing Amount: It is the theorical air volume from calculating according to theory without taking efficacy factors and machine energy lost into account. Normally one stage would multiply it by 0.65 and two stage would be 0.8 which is almost the same amount of real air volume; as a result, choosing outlet air volume should consider these following factors:
         (A) Current Demand (100%)
         (B) Possible Leakage from Pipe (10%)
         (C) Future Expansion Plan (20%-50%)
         (D) Usage Range (10%-30%)
Which means that projected outlet air volume should be = (A+B+C) x (1+D) and when C is increased, D will be decreased proportionally. It should be noted that, standard measurement is from “Real Air Volume”

Other factors to consider :

          1. Electricity Distribution :
          Each country and each region throughout the world has different type of electricity distribution: one phase or three phases.                                                      One phase: Normal voltage are 110V and 220V for convenience and safety. If it’s less than 1hp, 110V will be used and 220V otherwise. 5hp or more is not suitable for one phase.
          Three phase: Voltage of this phase are often 220V, 380V or 440V. It is often used on machines with high horsepower.
Every country has their own power supply, voltage, and frequency. These elements and electric phase must be specified so that suppliers can assemble the compressors correctly. Before the machine starts, it should be checked and ensured that the air compressor motor and the voltage can be used together.

          2. Environmental Restrictions :
          Depending on the structures, compressors can be separated into two types: oiled and oil-free.
           Oiled: If compressors require oil to lubricate the inside of machine and compressing part, it is an oiled compressor. As a result, the output air will be slightly tainted with oil; though, it can still be used in mandatory industry. Excess oil can also be filtered out by installing filter in certain industry.
           Oil-free: Mechanical parts that do not use oil are made from special self-lubricating material which can substitute the lubricant in compression. Consequently, air is not contaminated by oil and can meet the demand of oil-free high precision industries: medical, food, semiconductor, and coating. Usually, oiled compressors come with oil waste and oil contaminated air and drainage water which requires the correct procedure to take care of as stated by environmental law.

          3. Installation :
          Installation method can be chosen by referring to usage state:
          Portable: small compressors are all portable which uses two to four wheels to move around as user needs.
          Stationary: Bulky compressors unfit for moving around with needs for permanent piping while reducing vibration and noise, mostly use stable installation. Need to take caution in foundation and water level.

          4. Cooling method :
          Various function of cooling are as following:
Cool the machine temperature to increase machine lifespan and decrease oil spread. Cool the outlet air temperature and improve drying quality.
Provide safety by preventing machine temperature to be too high.
          Water Cooling: Cooling cycle tower must be installed. Uses water flow to induce heat exchange between the pump and outlet pipe. This method is suitable for high horsepower machine due to its high efficiency in spreading heat.
          Air Cooling: Cool the machine by utilizing air cycle made from fan to induce heat exchange between the pump and the air outlet pipe. This is a convenient and simple method. It has just also been designed to be more efficient recently thus becoming the mandatory cooling system for both low and high horsepower machines.
Caution for air compressor installation:                                                                The area air ventilation should be good with sufficient area to install the machine. The distance from reciprocating air compressor and wall should be at least 30 centimeters, 1 meter for screw type, and 1.5 meter from the roof.

          5. Noise Specification :
          Air compressors will produce noises from the following:
          Operational Noise: When the machine is compressing, the operation will create machine noises, air intake and discharge noise, air flow noise, friction noise, cooling fan noise, and power sources noise: electric motor or the compressor’s driver noise.
          Air Compressor Instability: If the balancing is bad or the installation isn’t considering the water level enough, the vibration from the machine and the metal plate will cause noises and air leakage which can also create noise at high pressure.

          Due to the different in both component formation and operation in each model, noises will also vary. For the open suction chamber type, since the chamber is unobstructed, the noise frequency wave will spread onto the environment. Low horsepower machine will yield lower noise and will not affect the environment; though, high horsepower will create enough noise to affect the environment, unless it is properly managed.
          Cube Piston Type: The inside of open and cube type are the same but metal plates for cube type are specially designed with high quality soundproof, noise absorbing, and impact cushioning material which can properly reduce vibration and noise appropriately.
          Screw Type: Due to its difference in operation, the noise frequency is different from reciprocating type. It usually comes in cube type with high quality noise absorbing, soundproof, and impact cushioning material resulting in less noise than reciprocating type.

          Noise protection is not able to provide complete silence but can reduce noise just enough to tolerable or amicable level of the environment. Normally the noise should be lower than 75 decibels. After considering usage and economy, when there’s only a few restrictions and environmental restrictions, open chamber type is more preferred; on the other hand, cube type is more preferrable when taking workplace quality of life into account or that restrictions is present.

          6. Control Method :
          Air compressor control should be managed properly depending on various air volume demand to maximize the compression efficacy and machine lifespan. For example, currently, small air compressors with air cooling system are separated into two types: semi-automatic and full-automatic.
          Semi-Automatic: Automatic Unloading System is used for air compressor at zero and maximum load. The mechanism is that when the gas pressure exceeds the designated maximum, the automatic unloading valve will drive the piston to expel the gas allowing inlet valve to remain open and show zero load status.
          Full-Automatic: This type utilize the Pressure Switch System to control motor. When air pressure exceeds designated pressure set on the switch, the switch relay will cut all electricity from motor resulting in suspension of machine. When the pressure touches the lowest designated value, the relay switch will turn the motor on and resume the operator. This method is suitable for low horsepower machine that are seldom used to support another main machine.
To be more flexible in your operation, here is a few more suggestions:

◆ Full Manual/Semi-Automatic – Use hand to control the system
◆ Full Switch Control/Semi-Automatic – Use microcomputer to automatically choose controlling schematics depending on the site situation