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Compressed Air System Controls

Types of Controls

Library Monitor CategoryFlow Controllers
The advantages of adding controls to your air system include:

  • Reduced energy costs (10 to 25 percent)
  • Reduced maintenance

Controls reduce energy costs by improving pressure control and improving multiple compressor operation. The reduction in constant pressure spikes reduces the number of leaks and stress on the entire air system. Monitoring the compressor's condition also reduces maintenance costs.

To identify the proper control system for your air system, first determine the level of automation, reporting, and monitoring you need. Do you require:

  • Analog compressor condition monitoring?
  • Electronic pressure control?
  • Multi-compressor system pressure control?
  • Condition trending reports?
  • An interface for system monitoring?
  • The ability to remotely control the air system at multiple locations?

AutoDual Control
Dual Control is a combination of Constant Speed Control and Automatic Start/Stop Control. Automatic Start/Stop is the simplest form of compressor control. At a set low pressure point a signal is sent to start the compressor. The compressor runs until the pressure reaches the upper set point. This cycle repeats as the pressure fluctuates. Care must be taken to limit the numbers of starts to less than 6 per hour. More than 6 starts per hour can damage the electric motor. Constant speed control keeps the motor running continuously and as the pressure falls to a lower set point the compressor is put into a loaded position. In a loaded position the inlet valve is closed allowing air to be compressed. Once the upper pressure set point is reached the compressor goes into an unloaded condition where the inlet valve is kept open and the entering air is bypassed to atmosphere. This eliminates the problem of frequent starts on the electric motor. A manual switch allows selection of the mode that best suits the demand for compressed air.

A compressor that runs in constant speed control during periods of low demand wastes energy. A compressor that operates under auto start/stop during high air demand periods can damage the compressor's electric motor. An Auto Dual Controller such as the AutoTrol can automatically alternate to the appropriate mode to save energy. The unit works with any reciprocating compressor with head unloaders or a rotary screw compressor that has on/off control. The AutoTrol quickly pays for itself in energy savings.

In addition to managing pressure, many controllers monitor or control:

  • Automatic drain valves
  • Low oil emergency shutdown sensors
  • Inlet air temperature
  • Outlet compressed air temperature
  • Hours of operation


Flow controllers supply consistent air pressure, making pneumatic devices more efficient while optimizing the compressors operation. Flow controllers reduce a plant's costs two ways:

  • Reduced horsepower consumption saves on electricity.
  • Efficient operation of the compressor reduces maintenance expenses.


Intermediate Controls (Demand Expansion)

A proper compressed air system must provide a minimum amount of compressed air at a minimum pressure to satisfy all demands at all times. Those systems that perform without an intermediate control cost more to operate because it is forced to operate at a higher pressure than actually required to meet demands. At higher pressures the cost to compress the air is higher and any leak will lose more air. This is referred to as artificial demand. Artificial demand is wasteful and very costly. An intermediate controller with proper air storage will dramatically reduce the operating cost of a compressed air system.

The intermediate controller is located at the intermediate point of the system. This is downstream of the filtration and drying equipment (supply side) and upstream of the main piping distribution system (demand side).

An intermediate controller should:
1. Establish a stable pressure without a large pressure drop
2. Operate over a wide range of pressures and flows
3. Be responsive to handle system dynamics while maintaining the balance pressure
4. Ensure it will not shut down production in the event of a malfunction or control failure

Intermediate controllers operate by monitoring deviations in pressure on the demand side in relation to the set balance point pressure. A signal is sent to the controller that quickly increases or decreases flow to correct the demand side pressure. This keeps the pressure at the lowest possible pressure and supplies proper flow.

Storage is an important part of a system. Storage isolates the compressors from the demand side. Peak air demands in a properly sized system will use the storage air that allows the compressors to function in a more stable environment.

Microprocessor Based Controls

Microprocessor control systems utilize pressure transducers. The pressure accuracy allows pressure differential to be as low as 2 PSIG (0.13 bar). These models offer users the ability to program the controller to sequence multiple compressors. The system operates all of the compressors in a common pressure range, allowing for the highest energy savings. According to the manufacturer and model, between 2 and 16 compressors can be combined. These controllers either work off of several pressure transducers or one, depending on the particular controller.

The controller balances the load, distributing it evenly across all of the compressors. By managing multiple compressors, controllers eliminate compressors working against each other. This ensures constant pressure to the compressed air users and equipment. While improving the plant's compressed air delivery, controllers save the plant money by reducing electric costs and minimizing compressor maintenance.

Controllers also monitor intake air temperature, outlet compressed air temperature, outlet flow (cfm), and other critical measurements. You can access this information at a touch of a button from the LCD screen. And, the controller saves this information and allows you to retrieve it to produce reports. From these reports you can track how your compressor is operating to plan preventive maintenance.

A Microprocessor control with remote monitoring has all of the features of a Multiple Compressor Flow Controller and allows users to manage compressors from remote locations. For example, an operator in California can manage compressors in Georgia.

Controller Energy Efficiency
Flow controllers reduce a plant's energy consumption by keeping the compressed air system running efficiently. A compressor's electric motor runs less when a flow controller manages the air distribution, which reduces electric consumption. The flow controller shuts down the compressor when demand is low and automatically restarts the compressor when demand increases. The savings can be significant.

Cost Savings Example:
This example represents one 220 HP (1000 cfm) compressor at 100 psig running one shift; a shift equals 2,920 hours.

KW Conversion Factor = .746
Motor Efficiency = .93
Electric Cost a KWH = .07
Horsepower x KW Conversion Factor / Motor Efficiency x Operating Hours x Electric Cost a KWH = Power Cost

220 x .746 / .93 x 2,920 x 0.07 = $36,071

If you add a flow controller to the compressor package and reduce how long the compressor runs a day by 2 hours, you eliminate 730 hours of operation a year.
2,920 - 730 = 2,190

220 x .746 / .93 x 2190 x .07 =$27,053

$36,071 - $27,053 = $9,018
This is an annual savings of $9,018

Dew Point Monitor

Installed downstream of a dryer, a dew point monitor enables you to monitor the compressed air dew point and alerts you when dew point is out of specification. Dew point monitors help you manage your compressed air system and ensure proper air dryer operation.





Carbon Monoxide Monitor

A carbon monoxide monitor is recommended for all compressed air breathing systems. Colorless, odorless, and tasteless, carbon monoxide is typically the most toxic common contaminant in compressed air. An accurate and dependable carbon monoxide monitor protects against potential carbon monoxide poisoning. The monitor has an alarm feature, which is set by the user. If carbon monoxide exceeds the level an alarm sounds. A digital display continuously indicates the level of carbon monoxide detected in ppm.




Installation and Maintenance
Most controllers can be wall, track or panel mounted. All require electricity. Most accept 120/240 VAC 50/60 Hz. They are generally available in NEMA 4, NEMA 12 and NEMA 7 enclosures. Installation requirements vary from model to model. For more information, while specifying a controller on eCompressedair, check the catalog pages for the models you are interested in. A .pdf of the manufacturers' literature is also available from the catalog page.