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An air compressor control system matches the compressed air supply with system demand and is one of the most important determinants of overall system energy efficiency. Proper control of an air compressor system is essential to be able to ensure that the system is acting as efficiently as possible as well as providing high performance.

This article will provide you with all the relevant information necessary about air compressor control systems and the varying types of control strategies.

Table of Contents

Air Compressor Control Systems

Compressors draw low-pressure gas from auxiliary storage as raw input. Then, the output high-pressure gas is either for storage or to feed other processes. A compressor system is fundamentally made up of three main components.

These components are the compressor unit, the control system, and the driver. The driver provides mechanical power to the compressor. The driver is typically an AC-driven electric motor in most modern-day compressors.

The choice of the driver depends on the power and torque requirements of the compressor. The compressor unit consists of three parts: the first is a compressing mechanism enclosed in a tight metal casing, followed by the inlet and outlet plumbing, and then the cooling and lubrication systems.

Most compressors use water as a coolant, but for very low operating temperatures, they use better refrigerant lubricants. The lubricating system covers the contact surfaces of moving parts with oil. This reduces the wear and overheating of key components. The system works similarly to an engine’s oil system in that it pumps, filters, cools, and recirculates oil within the air compressor.

Compressor control systems are thereby vital in maintaining the stable operation of a compressor. The purpose of these controls is to guarantee safe working for both the compressor and its operators. Control systems offer the ability to improve the efficiency and durability of the compressor.

These control systems are composed of a collection of sensors and electrical components. All controls can typically be commanded from a central terminal. The larger the compressor, the more the computerized control systems they have.

Uses of Compressor Control System Strategies

Few compressed air systems generally operate at full-load all of the time. Part-load performance is therefore critical and is primarily influenced by the type of compressor and the control strategy in place. The type of control specified for a given system is largely determined by the type of compressor being used and the facility’s demand profile.

If a system has a single compressor with a very steady demand, a simple compressor control system will be adequate. On the other hand, a complex system in a factory setting with multiple compressors, varying demand, and many types of end-uses will require a more sophisticated strategy in place.

In any case, careful consideration should be given to both compressor and system control selection because they can be the most important factors affecting system performance and efficiency. This brings us to the following 7 critical system control operations:

  • Start/Stop
  • System Information
  • Driver Control
  • Stable Operation
  • Modulating Controls
  • Alerts and Alarms
  • Automatic Shutdown in Unsafe Conditions

Let’s take a look at each in more detail!

Start/Stop

Starting and stopping compressors must follow a series of careful steps to ensure that the compressor starts and stops safely. During startup, the operator must conduct preliminary checks and preparations which include valve checking, auxiliary checks, and purging if necessary. The lubricant and coolant systems must be checked too.

Sensors report on the status of the compressor and all the auxiliaries. The compressor initially starts at a low speed to warm up while it is carefully monitored. As the speed increases gradually to the ramp speed which is the lowest speed threshold for minimum compression. The compressor eventually reaches full speed and its peak performance.

The hutting down process is equally involving. The compressor is gradually slowed down while its inlet supply is slowly constricted. Eventually, the inlet supply is completely cut off from continued deceleration. The compressor is then brought to a complete halt.

During these start/stop processes, the compressor controls vary the compressor speed to ensure safe and successful startups and shutdowns. Intelligent control systems can perform these tasks near enough automatically, or with little human interaction.

System Information

Real-time information from sensors is crucial in determining the status and conditions of the compressor. For instance, low oil levels are likely to indicate an oil leak. High temperatures may be indicative of worn-out parts or insufficient lubrication leading to parts rubbing against each other.

Crucial sensors on compressed air systems include:

  • Pressure sensors
  • Temperatures sensors
  • Level sensors
  • Flow sensors
  • Overload sensors

Sensor systems on auxiliary components are parts of the overall compressor control system. They monitor environmental variables outside the compressor and this information can also be critical to the compressor’s operation.

Every compressor is rated for specific working conditions or environmental factors. Deviations or adjustments of certain variables away from the specified level may reduce the compressor’s efficiency. Inefficient machines will tear and wear quicker while also consuming far more energy.

This is why monitoring and reporting are so important. This collection of data can help operators observe the rate of wear of the compressor’s parts so that maintenance procedures and schedules can be prepared accordingly.

Driver Control

Most air compressors use electric motors as their driver because they’re efficient, clean, and capable of delivering large figures of torque. Electric motors do, however, need motor controls to help protect them and manipulate operations.

Here are some of the well-known motor control devices:

  • Pilot devices
  • Motor starters
  • Intelligent controllers
  • Variable drive and speed controllers
  • Miniature circuit breakers

Let’s take a look at each in more detail!

Pilot Devices

Pilot devices are the most common motor control device. They comprise various types of selector switches, pushbuttons, signal beacons, toggle switches, and pilot lights. They can be described as indication devices or actuation devices, depending on their design.

Typically used as a part of a control system, automated process, or a control panel, pilot devices provide information on condition and control monitoring of different types of processes, machinery, and equipment. They are mainly used in commercial or industrial applications where the human-to-machine interface is required.

Motor Starters

Manual motor controls will typically have a push-button starter connected to the power panel. Starting and shutting down the motor is a matter of operating a switch on the starter or operating it remotely. Larger motors will need more sophisticated start/stop controllers. These controllers mostly regulate the electrical power feed into the motor from the mains or power supply.

The assembly of a contactor and overload relay is described as a motor starter. Transformers and additional controls, may vary the frequency, amplitude, and voltage of the AC waveform going into the motor to ensure a safe start and shut down.

A relay is a controlled switch that works by responding to an external signal and is mainly used to control high-powered circuits. Both contactors and relays are electromagnetic switching components. Contactors usually operate at a higher control voltage and have overload protection.

Intelligent Controllers

Intelligent devices are used to monitor and adjust the power output of a motor. They are capable of automatically varying the torque and speed variables to match the load on the motor. This results in greater efficiency, lower noise, lower vibrations, and less radiant heat.

They will typically use PLC (programmable logic controllers) to help with their automation. The driver determines how much power goes into the compressor and how fast the compressor components spin, offering the possibility to vary it. Varying the speed of the driver will vary the output of the compressor, which is particularly useful in applications where the output of the compressor needs to change often.

Variable Drive and Speed Controllers

Variable drive and speed controllers enable the adjustment of the drive and its speed. The controller is comprised of a series of speed controllers, power converters, and regulators. Typically known as VSDs (variable speed drives), many industrial motors also use VFDs (variable frequency drives) to control speed.

A VFD varies the frequency of the AC input voltage supplied to a three-phase motor to increase or decrease the speed and torque of the motor – because a motor is controlled by the frequency of the supply voltage.

Miniature Circuit Breakers

Circuit breakers offer electrical protection to people and equipment from sudden surges, overloads, and short circuits. MCB’s (miniature circuit breakers) are typically used as part of a control system, automated process, or control panel to provide information on condition and control monitoring of different types of processes, machinery, and equipment.

Stable Operation

With air compressors, to have a stable operation you need to be running at optimum RPMs, optimum gas input, and steady output. Compressor controls have to deal with two common undesirable conditions:

  • Choke
  • Surge

Choke Condtions

Choke is caused by a very high flow rate at the input of an air compressor operating at low discharge pressure. Choking drastically reduces the compressor’s performance making it unable to deliver optimum pressure and flow.

Choke controls constrict the inlet system automatically by closing the inlet valve partially. Gas coming into the inlet can already be under pressure or accelerated, and in such a case, the controls will opt to dump the excess gas into low-pressure buffer storage to diver the gas from the inlet.

Surge Conditions

Surge is the opposite of choke. When a surge happens, the input gas supply falls below the optimum capacity and sends the drive motor into overload because the compressor is trying to draw in more gas and push the output out at the same time.

The result of the surge is fluctuations in output, irregular power usage by the motor, increased vibration and noise. Most air compressors will be configured to automatically offload if inlet capacity drops below 40%. Most compressors have a surge control system to stabilize the compressor.

To solve the surge problem, controlled flow reversal is needed. Once a drop in gas supply is noted, the valve linking the outlet pipe to the inlet pipe is opened to feed some of the output gas into the input to increase the volume. The valve remains open until the gas source restores its regular supply.

Modulating Controls

The compressor control system is responsible for maintaining the requirements of the compressor. It’s only a matter of flipping switches or interacting with an HMI on the control panel. It is very important that the compressor produces the expected output, and so, it is the controller’s job to ensure that this is the case.

Besides adjusting drive speed to control the flow rate and displacement of a compressor, the control system can also modulate the inlet valve to throttle the gas intake to keep the pressure at a designated level.

Reducing the capacity of the incoming gas will reduce the pressure and the amount of gas at the output. However, cutting off the inlet supply at full speed causes the compressor to draw a vacuum at the inlet which may cause the motor to overload, and therefore, overheat.

The modulating controls prevent this from happening by adjusting the motor controls. This matches the inlet reduction. Most air compressors are capable of operating with a partial load, meaning that displacement can be adjusted without engaging the driver controls.

Alerts and Alarms

All compressor controls come equipped with alarm systems to alert and warn users when something goes wrong. These alarms include alerts for leaks, overheating, oil pressure, and failure of vital components. The alarms may be visual lights on the control panel as well as beeping sounds.

These alerts are particularly helpful when the gas being compressed has dangerous physical or chemical properties such as being corrosive, flammable, or toxic and allow the operators to take immediate action.

Automatic Shutdown in Unsafe Conditions

Most components inside compressors have very low fault tolerances and sensors can monitor the status of these critical components. They can take drastic preemptive measures to prevent damage if something was to go wrong.

Compressor control systems can initiate an automatic shut down after a catastrophic failure of vital components or if the compressor is in unsafe working conditions. Hazardous conditions include uncontrollable surge and choke, or overload of the electrical systems.

FAQs (Frequently Asked Questions)

What is compressor control system?

A compressor control system is a system that allows you to monitor and change your air compressor. The sort of controls includes adjusting the speed of the compressor motor as well as setting automatic load and unload depending on a pre-set pressure.

How are air compressors controlled?

Air compressors are typically controlled by control systems. These control systems are composed of a collection of sensors and electrical components that monitor the compressor’s operation to ensure everything is working accordingly. All controls can typically be commanded from a central terminal.

How do you control the pressure on a compressor?

To control the pressure on an air compressor you use the air compressor pressure regulator. This component is essentially a control valve that allows you to regulate the pressure by increasing or decreasing it. To learn more, visit our How To Adjust Air Compressor Pressure Regulator guide!


If you have any questions regarding air compressor control systems, please leave a comment below, with a photo if applicable, so that someone can help you!