A-Z of Compressed Air Systems & Maintenance

To fully appreciate how impactful a properly functioning air compressor system is to your bottom line, it is foremost important to fully understand how much your compressed air costs. Compressed air is a self generated utility within your facility that is a top 3-4 utility expense for your company. This fact is often overlooked or misunderstood, because the expense is primarily linked to the electric and or gas bill. This can be a costly oversite. You will see an example below where a single common maintenance issue causes a 4psi reduction in performance and resulted in $1265 in additional annual cost to that company. Imagine when/if there are multiple issues…

In order to calculate the compressed air cost, some companies use an educated guess of @$0.25 per 1000 cubic feet of compressed air consumed, and others are more precise. The U.S. department of Energy performed an energy saving study in 2004 and they show a precise way to calculate your compressed air cost. Here is their sample calculation:

“Compressed air is one of the most expensive sources of energy in a plant. The overall efficiency of a typical compressed air system can be as low as 10%-15%. For example, to operate a 1-horsepower (hp) air motor at 100 pounds per square inch gauge (psig), approximately 7-8 hp of electrical power is supplied to the air compressor. To calculate the cost of compressed air in your facility, use the formula shown below:

Cost ($) = (bhp) x (0.746) x (# of operating hours) x ($/kWh) x (% time) x (% full-load bhp) ÷ Motor Efficiency
Where:
bhp = Motor full-load horsepower (frequently higher than the motor nameplate horsepower—check equipment specification)
0.746 = conversion between hp and kW
Percent time = percentage of time running at this operating level
Percent full-load bhp = bhp as percentage of full-load bhp at this operating level
Motor efficiency = motor efficiency at this operating level
Example:
A typical manufacturing facility has a 200-hp compressor (which requires 215 bhp) that operates for 6800 hours annually. It is fully loaded 85% of the time (motor efficiency = .95) and unloaded the rest of the time (25% full-load bhp and motor efficiency = .90). The aggregate electric rate is 0.05/kWh.
Cost when fully loaded =
(215 bhp) x (0.746) x (6800 hrs) x ($0.05/kWh) x (0.85) x (1.0) = $48,792
.95
Cost when unloaded =
(215 bhp) x (0.746) x (6800 hrs) x ($0.05/kWh) x (0.15) x (0.25) = $2,272
.90
Annual energy cost = $48,792 + $2,272 = $51,064″

Pic courtesy of Gunjan2021 Pixaby License

I encourage you to calculate this self generated utility cost for your facility. Also keep in mind that this example is using $0.05/kWh, this example was form 2004, today the average industrial sector cost in the US is $0.0747 (see more here). This annual cost puts so many things into perspective. First and foremost the importance of Maintenance. Even more specific, the preventative maintenance costs become much lower than the impact of even one small oversite. Here is an example from the Department of Energy that discusses a specific and common maintenance issue and it’s annual impact.

“A compressed air system that is served by a 100-horsepower (hp) compressor operating continuously at a cost of $0.08/kWh has annual energy costs of $63,232. With a dirty coalescing filter (not changed at regular intervals), the pressure drop across the filter could increase to as much as 6 psi, vs. 2 psi when clean. The pressure drop of 4 psi accounts for 2% of the system’s annual compressed air energy costs. (or an increase of $1,265 per year)”

The realization of the dollars spent for compressed air certainly pushes the priority of maintenance. If we extrapolate from the above filter example, we can see that a 4 psi pressure drop in that system increased the cost by $1265 per year. We need to then ask ourselves, what other areas could be causing a pressure drop or stressing the motor? And if there is an issue upstream to this issue, will it cause even more issues, or more pressure drops?

There are many tips, tools, websites, YouTube videos and more, out there that address the recommended maintenance of your compressor and system. Many of you already have specific guidelines for your precise system, and set maintenance schedules in place. Below is a sample checklist (not all-inclusive) of maintenance items to watch for with your compressor in case you need a starting point. If left unchecked and or uncorrected, any of these (if an issue) will cost your company money – over time, lots of money.

  • Visually Inspect Air Compressor
  • Check moisture traps
  • Change Air Filters
  • Change Oil Filters
  • Change Oil/Water Separators – could (should) be many of these on the lines
  • Change Oil Separator O-Ring if necessary
  • Inspect Couplers, Hubs and Shaft Seals
  • Check Drive Belts condition if applicable
  • Check and Log Drive Motor Bearing Temps
  • Check and Log Fan Motor Bearing Temps
  • Change Oil if necessary
  • Check and Log Oil Cooler Temps
  • Check and Log After Cooler Temps
  • Blow Out Coolers

I would be amiss if I finished this blog without mentioning the perils of pressure leaks. The Compressed Air and Gas Institute stated that a single 1/4″ leak, can cost you between $2500 and $8000 per year (CAGI article). Imagine the impact of several leaks!!!

How do I find leaks? I’m glad you asked. The first step is to walk your lines and check any or all of the following areas for leaks or damage.

  • Couplings
  • Hoses
  • Tubes
  • Fittings
  • Point-Of-Use Devices
  • Pipe Joints
  • Quick Disconnects
  • Filters
  • Regulators
  • Lubricators
  • Condensate Traps
  • Valves

A great way to identify leaks is to use our Ultrasonic Leak Detector to listen for leaks. Look for and ask the technicians if there seems to be a change in productivity. Install Pressure Regulators and gauges at each point of use in your facility – monitor and log these pressures often. Once you find an issue, no matter how small, correct it. A small leak adds up $$$ over the hours, weeks, and months.

In addition to leaks, there are many times that air is wasted by being blown on empty space (i.e. the space between items on your conveyor). you, please look at our Electronic Flow Control (EFC) product, this device gives you an out of the box automation solution that can be set up in minutes and save thousands. There are so many clogged and leaking pipes, bad hoses inside many plants, this coupled with using an poor performing Air Gun, or Air Nozzle all have large dollar impacts for your company. EXAIR has products that can help in all of these areas…

In parting, please keep in mind that many Utility companies offer incentives to companies that take an initiative to reduce their energy footprint. In our current time of inflation this is a real way to reduce costs, many times significantly. We are here to help. Please contact us for assistance in dramatically reducing both your utility costs, and your environmental impact.

Pic courtesy of PIRO4D Pixaby License

Thank you for stopping by. Please reach out if you have any questions about this Blog, or any of EXAIR’s amazing products.

Brian Wages
Application Engineer
E-mail: BrianWages@EXAIR.com
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About Single-Acting Reciprocating Air Compressors

One thing that is found in virtually every industrial environment is an air compressor. Some uses for the compressed air generated are: powering pneumatic tools, packaging, automation equipment, conveyors, controls systems, and various others. Pneumatic tools are favored because they tend to be smaller and more lightweight than electric tools, offer infinitely variable speed and torque, and can be safer than the hazards associated with electrical devices. In order to power these devices, compressed air must be generated.

There are two main categories of air compressors: positive-displacement and dynamic. In a positive-displacement type, a given quantity of air is trapped in a compression chamber. The volume of which it occupies is mechanically reduced (squished), causing a corresponding rise in pressure. Of the positive-displacement variety they are broken down further into two more categories: reciprocating and rotary.

A reciprocating compressor works like a bicycle pump. A piston reduces the volume occupied by the air or gas, compressing it into a higher pressure. There are two types of reciprocating compressors, single or double-acting. Single-acting compressors are the most common and are available up to 30HP at 200 psig.

Their small size and weight allow them to be installed near the point of use and avoid lengthy piping runs. Additionally, the single-acting reciprocating compressors do not need a separate cooling system. All of this leads to much simpler maintenance procedures, making the single-acting reciprocating compressors one of the easiest to maintain.

There are some disadvantages to this style of compressor. Rings have a tendency to wear out over time, if they’re not replaced as needed this can lead to lubricant carry-over into the air supply. These styles of compressor are relatively loud and comparatively cost more to operate than many other types. Because of this, they’re not designed for applications and processes that have a heavy-duty cycle of 70-90%. The single-acting reciprocating compressor should be used in installations where it’s only going to run 50% or less of the time.

At EXAIR we’re committed to providing you with the point of use products that’ll use your compressed air as efficiently and safely as possible. Feel free to reach out to an Application Engineer to discuss how we can help you improve in your processes.

Tyler Daniel

Application Engineer

E-mail: TylerDaniel@EXAIR.com

Twitter: @EXAIR_TD

Image courtesy of Compressor1 via Creative Commons License

6 Basic Steps for Good Air Compressor Maintenance (And When to Do Them)

A production equipment mechanic with the 76th Maintenance Group, takes meter readings of the oil pressure and temperature, cooling water temperature and the output temperature on one of two 1,750 horsepower compressors. (Air Force photo by Ron Mullan)

In one of my previous jobs, I was responsible for the operation of the facility.  One of my biggest responsibilities was the air compressor because it supplied pressurized air though out the facility to feed the pneumatic systems.  Like with many industries, the compressor system is the life blood of the company.  If the compressor fails, the whole facility will stop.  In this blog, I will share some preventative maintenance items and schedules for your air compressors.

Because the cost to make compressed air is so expensive, compressed air systems are considered to be a fourth utility.  And with any important investment, you would like to keep it operating as long and efficiently as possible.  To do this, it is recommended to get your air compressor a “checkup” every so often.  I will cover some important items to check as well as a recommended schedule for checking.  Depending on the size of your air compressors, some items may or may not apply.

1. Intake filter:  The intake filter is used to clean the air that is being drawn into the air compressor.  Particles can damage the air pump mechanisms, so it is important to have the proper filtration level.  But, as the intake filter builds up with debris, the pressure drop will increase.  If they are not properly monitored and cleaned, the air flow will be restricted.  This can cause the motors to operate harder and hotter as well as reduce the efficiency of the air compressor.

2. Compressor Oil:  This would be for flooded screws and reciprocating compressors that use oil to operate the air pump.  Most systems will have an oil sight gauge to verify proper levels.  In larger systems, the oil can be checked for acidity which will tell you the level at which the oil is breaking down.  The oil, like in your car, has to be changed after so many hours of operation.  This is critical to keep the air pump running smoothly without service interruptions.

3. Belts and Couplings:  These items transmit the power from the motor to the air pump.  Check their alignment, condition, and tension (belts only) as specified by the manufacturer.  You should have spares on hand in case of any failures.

4. Air/Oil Separators:  This filter removes as much oil from the compressed air before it travels downstream.  It returns the oil back to the sump of the air compressor.  If the Air/Oil Separator builds too much pressure drop or gets damaged, excess oil will travel downstream.  Not only will the air pump lose the required oil level, but it will also affect the performance of downstream parts like your air dryer and after cooler.

5. Internal filters:  Some air compressors will come with an attached refrigerated air dryer.   With these types of air compressors, they will place coalescing filters to remove any residual oil.  These filters should be checked for pressure drop.  If the pressure drop gets too high, then it will rob your compressed air system of air pressure.  Some filters come with a pressure drop indicator which can help you to determine the life of the internal filter element.

6. Unloader valve:  When an air compressor unloads, this valve will help to remove any compressed air that is trapped in the cavity of the air pump.  So, when the air compressor restarts, it does not have to “work” against this “trapped” air pressure.  If they do not fully unload, the air compressor will have to work much harder to restart, wasting energy.

Preventative maintenance is very important, and checks need to be performed periodically.  As for a schedule, I created a rough sequence to verify, change, or clean certain items that are important to your air compressor.  You can also check with your local compressor representative for a more detailed maintenance schedule.

Daily:

  • After stopping, remove any condensate from the receiver tank.
  • Check oil level.

Monthly:

  • Inspect cooling fins on air pump. Clean if necessary
  • Inspect oil cooler. Clean if necessary

Quarterly:

  • Inspect the inlet air filter. Clean or replace if necessary.
  • Check the belt for tension and cracks. Tighten or replace.
  • Check differential pressure indicators on outlet compressed air filters.

Yearly:

  • Replace Air Inlet Filter
  • Replace the air-oil separator
  • Test safety valves and unloader valve
  • Replace compressed air filters
  • Change oil
  • Grease bearings if required

Keeping your air compressor running optimally is very important for pneumatic operations and energy savings.  I shared some important information above to assist.  Another area to check would be your pneumatic system downstream of the air compressor.  EXAIR manufactures engineered products that can reduce air consumption rates.  You can contact an Application Engineer to discuss further on how we can save you energy, money, and your air compressor.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

 

Intelligent Compressed Air: Double-Acting Reciprocating Compressor

Evaluating all of the different types of compressors and which is right for you can seem like a daunting task. Today, I’d like to take some time to talk about the Double-Acting Reciprocating type of air compressor.

double acting compressor
Cut-out of a double-acting reciprocating compressor

Double-Acting Reciprocating compressors are a subset of the larger family of positive displacement compressor types. In positive displacement compressors, air is drawn into a chamber where the volume is then mechanically reduced. The energy used to displace the air volume is converted to an increase in air pressure. Dynamic compressors operate a little differently. They utilize an increase in air velocity to create the change in pressure. Air is accelerated to a high velocity through an impeller. The kinetic energy of the air is converted to an increase in potential (pressure) energy.

The Double-Acting Reciprocating compressor is a close relative to the Single-Acting Reciprocating compressor. In these types of compressors, an “automotive-type” piston driven by a crankshaft provides the compression. In a Double-Acting Reciprocating compressor, air is compressed as the piston moves in each direction. Hence the name, “double-acting”. In a Single-Acting Reciprocating compressor, air is only compressed on each full revolution of the piston. This makes the Double-Acting Reciprocating compressor much more efficient than its brethren.

Double Acting Recip
Double Acting Reciprocating Air Compressor

Double-Acting Reciprocating compressors are also available in much larger sizes. While Single-Acting compressors can be found up to 150HP, generally they’re much less common any larger than 25HP. Whereas a Double-Acting compressor is available from 10HP-1,000HP, making it a better choice for larger plants that require a significantly greater volume of compressed air. While they’re a bit more expensive due to the added mechanisms to produce the double-action compression, this cost is quickly offset by the increase in efficiency. At a performance of 15-16 kW/100 cfm, they’re 32% more efficient than a single-acting reciprocating compressor.

If you’re in the market for a new compressor and are struggling to determine the most suitable compressor, talk with your local compressor sales representative. Once you’re up an running, EXAIR has a wide-range of products that’ll make sure you’re using your compressed air safely and efficiently!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD
Image courtesy of Best Practices for Compressed Air Systems – second edition