Tag Archives: Compressed Air Systems

Safety Concerns Associated With Compressed Air Blow-Off

Compressed Air GunIn factories and other industrial settings, it’s not uncommon to see workers remove dust and debris from their clothing and skin using compressed air guns. While this might seem like an innocuous and practical method of cleaning off after a long day of work, compressed air can actually cause severe injuries and even death when not used properly. In fact, the Occupational Safety and Health Administration (OSHA) heavily regulates the use of compressed air for cleaning purposes to prevent workplace injuries.

So what types of injuries are associated with compressed air blow-off? Today we’ll address three main concerns:

Air Embolism

When high-pressure compressed air is used to clean skin and clothing, it can penetrate the skin and enter the bloodstream. This, in turn, can cause blood vessels to become blocked by air bubbles, triggering stroke-like symptoms. If left untreated, an air embolism can lead to coma, paralysis and death. Air embolisms are commonly associated with decompression sickness in divers, but they can just as easily be caused by compressed air accidents as well.

Oil Injection Injury

Similar to an air embolism, this type of injury occurs when a high-pressure fluid creates a small puncture wound in the skin, injecting the fluid into the body and causing extensive soft tissue damage. The injury may seem minor at first, but become far more serious in the hours following the incident. You don’t have to look far to find some pretty gruesome examples of injection injuries on the Internet. These injuries often occur when paints, solvents or fuel oils are injected into the skin, but they can also be caused by the injection of high-pressure air alone. In severe cases, an injection injury may result in the loss of a limb.

Flying Shavings and Debris

When compressed air is used to blow off debris, it can also cause “chip fly-back,” where small pieces of flying debris cause bodily harm to the operator or other nearby workers. In these incidents, flying debris—even very small particles of dust – can cause debilitating eye injuries. As such, it’s essential for operators to employ effective chip guard barriers that block flying debris to prevent injuries.

OSHA prescribes a few other methods to prevent compressed air blow-off injuries as well.

To begin with, OSHA requires that compressed air “shall not be used for cleaning purposes except where reduced to less than 30 PSI.” Factory air lines typically run between 80 and 120 PSI, which is far too high to be used for personal cleaning purposes. Furthermore, OSHA requires that when air lines are dead-ended (blocked), the static pressure at the point of the blockage may not exceed 30 PSI. Some air gun nozzles also include dead-ending safety features which allow airflow to exit through side ports when the nozzle tip is blocked.

In addition to standard chip guards, protective cone air nozzles can also be used to prevent chip fly-back. In these nozzles, some of the airflow is diverted to slots around periphery of the nozzle to form a protective cone of air that prevents debris from flying back towards the operator. It’s important to note, however, that these nozzles may not prevent debris from being propelled towards other nearby workers. Therefore, they should always be used in conjunction with physical chip barriers.

Finally, OSHA suggests that pneumatic vacuums should be used as an alternative to compressed air systems for self-cleaning purposes. These vacuums can effectively remove most dust and debris without posing a threat of air embolism, injection injury or chip fly-back.

Interested in learning more about compressed air systems and their operation? Stay tuned for the latest updates from our blog, or give us a call today at (812) 422-2422 to speak with a representative at Case Controls!

What Is a PID Loop for AirLogix?

AirLogixThe term PID is short for proportional, integral and derivative. The AirLogix® controller uses a total of four PID loops to optimize the performance of a centrifugal air compressor. A PID loop is a complex method of controlling a process (in this case air pressure) using feedback. Simply put, the PID is constantly looking at a process variable (air pressure, motor current, etc.) and comparing the process variable (PV) to the process set point (SP). If the PID sees a mathematical difference between the two (%error), it will adjust the control variable (CV) or the inlet or bypass valve, to try and meet the process set point.

Each element of the PID controller refers to a particular action taken on the error.

Proportional

With the Allen-Bradley CompactLogix and many other controllers, this term is referred to as ‘gain.’ This element is the amplifier of the control loop and increases rise time. It takes the %error multiplied by the gain constant and directly applies it to the CV. Gain affects the amount of valve movement each time the PID updates. A gain too large will cause overshoot and PV oscillation, and a gain too small will cause a slow, sluggish response—possibly not allowing the controller to ever stabilize.

Integral

This element is referred to as ‘reset.’ It takes the responsibility of reducing overshoot and attempts to allow the gain to affect the PV before any other action is taken. Reset is a time constant measured in seconds. Simply put, when %error is calculated and the CV is adjusted accordingly, the reset determines the time span before another CV change is made (time elapsed per repeat). With the AirLogix® controller, the lower the integral value, the more frequently the CV will be updated. A value too low will result in overshoot because the controller did not allow for the CV to affect the PV. A value too high will make the process sluggish because too much time was allowed to pass before making another change.

Derivative

This element—referred to as ‘rate’—attempts to reduce any lag that occurs in the process variable. It is also a time constant like the integral element, but this one looks to predict what is going to happen next by looking at the rate at which the PV is changing in time due to a change in the CV. It sounds very useful but can cause much grief and is commonly referred to as the villain of PID loop control. You can think of rate as a weather forecaster, with respect to the fact that it isn’t always correct. Rate works fairly well when the fluctuations in demand amount are always the same (very rare), and when process variable lag times are relatively long. Good candidates might be temperature and level control. With compressed air, demand amounts are usually changing, and lag times are short. This reduces the need for any derivative action. In most situations, if not all, a properly-set gain and reset will produce adequate results.

Interested in learning more about AirLogix® controllers or any of the other compressed air system solutions we offer at Case Controls? Feel free to give us a call or contact us online today to speak with a representative!

Upgrading the Compressed Air System at ArcelorMittal Indiana Harbor

In 2016, Case Controls was recruited to help upgrade a compressed air system at the AcelorMittal Indiana Harbor steel mill. The plant had recently revamped its No. 2 continuous caster machine, and the compressed air upgrade was necessary to support the machine’s air mist system for secondary cooling.

In addition to installing new compressors, the plant wanted to implement a new compressed air automation system as well. Two years later, this system has significantly improved both the reliability and efficiency of the plant’s compressed air infrastructure. While reliability and efficiency are sometimes regarded as mutually-exclusive performance requirements, this is simply not the case in modern, well-designed compressed air systems.

In fact, many of the improvements we made to improve system reliability also benefit its efficiency, and vice versa.

The steel plant’s compressed air system required additional capacity to meet the demands for two separate headers—a “wet” air mist header (AMH) for casting operations, and a “dry” instrument air header (IAH) to supply air for control valves, etc. The plant also wanted to implement its existing Allen Bradley programmable logic controllers (PLCs) into the new automation system.

In the upgraded compressed air system, the IAH is supplied by two of the plant’s existing Sullair fixed-speed 400-hp rotary screw compressors. These compressors were outfitted with Case Controls’ own AirStar™ PD PLC-based local controls.

The AMH, meanwhile, was upgraded with three new 1250-hp Sullair IHI centrifugal air compressors with AirLogix® PLC-based control systems. These centrifugal compressors were chosen based on their mechanical longevity and their ability to regulate as variable displacement machines. An inlet air temperature measurement was also added to the centrifugal compressors to provide air density compensation and offer efficiency gains.

The two headers are tied together and connected via a modulating crossover valve.

The addition of this crossover valve ultimately benefited both the reliability and efficiency of the system, but its installation posed a few unique challenges. To begin with, the valve had to be large enough to allow the AMH to supply air at the capacity of the compressors on the IAH, plus a 20 percent buffer. Because the air from the AMH compressors was not dried, the crossover valve also required an additional small dryer to supply dry control air to the IAH.

The position of the crossover valve is governed by a master PLC, which facilitates load sharing between the two headers and provides connectivity to caster networks for alarming and data collection of system variables. The primary goal of the load-sharing system is to stabilize the IAH and prevent rotary screw short-cycling. Of the two headers, the IAH is most critical to the plant, so it takes priority when there are not enough compressors to keep both headers at their pressure setpoints.

The crossover valve also prioritizes providing air from the AMH to the IAH, because the two rotary screw compressors that feed the IAH are older, less efficient and less reliable. As such, air is only shared from the IAH to the AMH if the header pressure setpoint can be maintained on the IAH.

The new automation system operates on a two-level failover philosophy that’s loosely based on IT networking applications.

A failover exists within each of the two headers, as well as another between the two headers thanks to the crossover valve. In the event that one compressor on either header fails, a backup is automatically brought online and the plant personnel are alerted to the problem. The automation system also saves energy by keeping only the required amount of compressor horsepower online at any given time.

As it turns out, it didn’t take long for the new compressed air system to demonstrate its improved reliability.

Soon after the installation was completed in December 2016, a block valve on the exit of one of the centrifugal compressors was closed, causing it to surge and shut down. The system automatically started and loaded another compressor into the header, and the system pressure never fell low enough to stop the casting process during the incident. It has also become standard operating procedure at the plant to share air from the AMH to the IAH and not run the older rotary screw compressors on that header whenever possible.  

Interested in learning more about how the team at Case Controls can make your compressed air system more efficient and reliable? Feel free to give us a call at (812) 422-2422 or contact us online today!

Compressor Check Valves: What They Do and Why They Fail

Compressor MaintenanceA compressor’s check valves perform an essential function that’s vital to the operation of a compressed air system. Located between the compressor and the air receiver tank or main header, a check valve is designed to prevent air from bleeding out of the tank or header and back into the inlet line when a compressor shuts down. Unloader valves, meanwhile, allow air to bleed out of the compressor line to reduce load on startup.

A check valve typically consists of a valve mechanism that keeps the header sealed when there is higher pressure in the header than on the compressor side. As a result of this design, a faulty check valve may sometimes leak at lower pressures but not at higher pressures. In fact, leaks can often be traced back to a faulty check valve.

So what happens to compressors when their check valves fail?

In addition to causing leaks, a check valve failure can damage the compressor itself. If a check valve fails in its open position, it can allow air to leak back from the header into the compressor when it’s not running. This, in turn, can cause the compressor to spin backwards, thereby damaging it in the process. More often than not, however, we see check valves fail when they’re closed. When this happens, the stuck valve can cause pressure to increase uncontrollably, ultimately leading to a compressor surge.

The good news is, there are steps you can take to reduce the likelihood of check valve failures in your compressed air system.

To begin with, it’s important to select an appropriately-sized check valve based on the valve’s orientation (vertical or horizontal), your compressor’s flow conditions and type of media (air or another gas). Your compressed air system should also be outfitted with filters to keep compressor lines and check valves free of debris. Finally, be sure to conduct routine maintenance on the system’s valve and compressor lines. This includes flushing the system, disassembling valves to inspect for corrosion and replacing damaged valves if necessary.

At Case Controls, we can help you maintain your compressed air system to prevent check valve failures and other common performance issues. To learn more about the onsite and remote support services we offer, feel free to give us a call at (812) 422-2422 or contact us online today.

Compressor KPIs: What Are They and How Can They Be Used?

If you own or operate an industrial operation that relies on compressed air systems, then you know exactly how important it is for these systems to run as efficiently as possible. Inefficient compressed air systems can cost companies thousands of dollars every year and take a toll on equipment over time. Therefore, it’s important for companies in the industrial sector to take a look at all of the Key Performance Indicators, or KPIs, associated with their compressed air systems. KPIs can be used to evaluate the performance of systems and to improve the overall compressed air efficiency in your facility.

There are a handful of KPIs that can be measured during routine inspections of compressed air systems.

For efficiency, power consumption is a KPI. There are many companies that don’t monitor their power consumption closely enough over time to see if they could reduce it, and again, it ends up costing them money. The basic measure could be CFM/HP or CFM/KW (the inverses KW/CFM is often used). It would be good to compare the CFM to standard SCFM conditions to adjust for temperature and other atmospheric conditions. It is important to measure the actual CFM going to the plant. If done properly this KPI will provide valuable information as to how well the supply of compressors online is matched to the demand.

One KPI that represents demand is to compare CFM to production measures. Examples of this are CFM/parts produced per week or month. It could also be CFM/tons produced. This KPI will provide a good indication of compressed air wasted at the process or an increase in leakage or artificial demand.

One other important KPI is system pressure. As the pressure increases in your system, so will the power consumption, which could end up costing you additional money. By keeping your system pressure within an acceptable range, you can cut costs and make your system more efficient. The KPI can be measured as an average pressure as well as a standard deviation around that average.

There are other KPIs that can also be monitored to evaluate how efficiently a compressed air system is running as well. Air flow, temperature and carbon footprint are all KPIs that you should be keeping an eye on. By keeping track of KPI data and crunching numbers based on your findings, you can make your operation running more efficiently in the future. As it is often stated, you cannot control what you do not measure.

At Case Engineering Inc., we’ve been designing, maintaining and servicing compressed air control systems for more than 30 years. Contact us at 812-422-2422 to learn more about how we can make your company’s compressed air system better and more efficient today.