Maintenance for your Air Compressor

In one of my previous jobs, I was responsible for the operation of the facility, and one of my biggest jobs was the operation of our air compressor.  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 maintenance items and schedules for air compressors. 

Because the cost to make compressed air is expensive, the compressed air system is considered to be a fourth utility.  With such an 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.  Depending on the size and type of air compressor, some items may or may not apply.  It is always best to check with the manufacturer. 

Intake filter:  The intake filter is used to clean the air that is being drawn into the air compressor.  The better the filtration, the less debris that will get into your system.  Particles can damage the air pump mechanisms over time as well as plug filters and heat exchangers downstream.  If they are not properly monitored and cleaned, the air flow can be restricted.  This will cause the motor to operate harder and hotter. 

Compressor Oil:  This would be for flooded screws and reciprocating compressor that use oil to lubricate the bearings and sleeves in the air pump.  Most systems have an oil sight gage to verify levels.  The oil can also be checked for acidity which will tell the degree at which the oil is breaking down.  Just like the motor oil in your car, you will have to replace it out after so many hours of operation. 

Belts & 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.

Electric Motors:  A mechanical device that turns electric energy into rotational energy.  It is the main component that uses much energy to make compressed air.  So, some checks are required to foresee any potential issues and major shutdowns.  For the windings inside, the resistance should be measured with a multimeter, and it should fall within the motor’s specifications.  Another check should be on the start capacitor.  The start capacitor stores energy to give the motor a powerful boost to get it turning.  One other item is the centrifugal switch.  Just like the name states, it will disconnect the start capacitor when the motor starts spinning.  One other item for large electric motors is the phase convertor.  These are typically capacitors, and they are designed to keep the direction of a three-phase motors going in the correct rotation.  Both types of capacitors can be checked with a multimeter. 

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, excess oil can travel downstream.  Not only will the air pump loose the required oil level, but it will affect the performance of downstream parts like your air dryer and after cooler.  Also, the pressure drop is a waste and can rob your air system of workable energy.  

Internal filters:  Many air compressors will come with an attached refrigerated air dryer.   With this type of air compressor, 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 pressure, and you will not get the required performance.  Some filters come with a pressure drop indicator which can help you to determine the time to change the element.    

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

Preventative maintenance is very important.  As for a schedule, I created a rough sequence to check, change, or clean certain items that are important to your air compressor.  You should 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.
  • Ohm check on the electric motor

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 optimal is very important for pneumatic operations and energy savings.  To help your air compressor, you should also check your pneumatic system for optimization.  EXAIR manufactures engineered products that can blow, coat, clean, and cool at reduced air consumption rates; saving you money.  As an example, the model 1102 Mini Super Air Nozzle can save your company $1,872.00 per year for one blow-off device by replacing a 1/8” NPT open pipe.  You can contact an Application Engineer to determine how much EXAIR products can save your company and your air compressor.   

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

Image courtesy of Compressor1Creative commons license

Save Your Compressed Air Today with These Simple Methods

When discussing ROI, return on investment, for an industrial compressed air system it is necessary to  understand what it costs to produce compressed air.  Generally we calculate that it costs .25 cents to produce 1,000 SCF (Standard Cubic Feet) of compressed air here in the Midwest of the United States. For our example let’s consider a typical 250 HP industrial compressor running 24 hours per day/5 days per week for 52 weeks.  This compressor can generate 374,400,000 SCF per year, using the industry standard utility cost for the Midwest of .25 cents per 1,000 SCF it will cost $93,600 to produce that volume of compressed air.

To avoid wasting money on compressed air generation it is extremely important to eliminate unintended or wasteful compressed air use in your plant. The two main offenders are leaks and open tube blow-offs.  While soapy water is a good method for discovering leaks, EXAIR offers the Ultrasonic Leak Detector.  This handy device allows leaks to be detected at distances of up to 20′ away! Also consider how safe and convenient it is to find leaks in overhead pipes while standing on the ground instead of on a ladder. Using a tool like this to do an entire system leak audit can easily result in many small leaks being identified and when fixed result in a large savings.

open tubes
Thirteen Open Tube Blow-Offs

Now let’s look at what an open pipe or tube may consume. A single 1/4″ OD copper tube can use 33 SCFM @ 80 PSIG inlet pressure.  Using the manifold pictured above as our example with 13 open tubes, each tube can consume 33 SCFM @ 80 PSI inlet pressure. With 13 open tubes running 24 hours a day, 5 days a week, 52 weeks per year equates to a total consumption of  160,617,600 SCF annually.  If we installed the EXAIR model 1100 Super Air Nozzle  using a simple compression fitting we would reduce the air consumption dramatically.  The EXAIR 1100 Super Air Nozzle consumes 14 SCFM @ 80 PSIG inlet pressure, running 24 hours a day, 5 days a week, 52 weeks per year equates to a total consumption of 68,140,800 SCF annually.  That change will save you 92,476,800 SCF annually which is equal to $23,119.20 and 24.7% of air compressor capacity!  These calculations are all based on continuous running applications, if intermittent operation is possible consider the EXAIR Electronic Flow Control for even greater savings.  The EXAIR Electronic Flow Control combines a photoelectric sensor with timing control that limits compressed air use by turning it off when no part is present

Open pipe blow offs also violate OSHA standard 29 CFR 1910.242(b) requirement for using compressed air for cleaning when pressurized above 30 PSIG. Not to mention they generally are louder than 90 dBA, which is the maximum allowable noise exposure without hearing protection under OSHA standard 29 CFR – 1910.95 (a). The EXAIR engineered Super Air Nozzle is a great way to avoid a OSHA fine.

A great product that will help you keep your fingers on the pulse of compressed air consumption and demand is by incorporating the EXAIR Digital Flow Meter.  This handy item mounts directly to the pipe.  The digital display shows the amount of compressed air being used in any leg of your distribution system.  The Digital Flow Meter is offered in sizes for 1/2″ – 4″ Schedule 40 Iron Pipe and 3/4″ – 4″ Copper Pipe.  It also is available with the Summing Remote Display that is prewired with a 50′ cable, it is powered by the Digital Flow Meter and with a push of the button will display either the current compressed air consumption, consumption for the previous 24 hours or the total cumulative usage.

The Digital Flowmeters are also available with wireless capability using the ZigBee mesh network protocol, data can be passed from meter to meter to extend the distance over which the wireless system can operate.  Each meter has a range of up to 100′ (30 meters). Or you can opt for the USB Data Logger option.  The USB Data Logger can store approximately 9 hours of readings if set to sample once every second or up to 2 years if sampled every 12 hours.

If you would like to talk about any of the quiet EXAIR Intelligent Compressed Air® products or our line of Optimization Products, feel free to contact me or any EXAIR  Application Engineer.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Air Compressors: Air Intake and Altitude

Flow rate is the quantity of material that is moved per unit of time.  Generally, the quantity of material can be expressed as a mass or a volume.  For example, mass flow rates are in units of pounds per minute or kilograms per hour.  Volumetric flow rates are stated in cubic feet per minute or liters per hour.  The trick begins when volumetric flow rates are used for a compressible gas in different altitudes.

From the history of air compressors, they could calculate the volume of air being drawn into the air compressor by the size of the cylinder.  With the volume of the compression chamber and the rotations per minute of the motor, RPM, they could calculate the volumetric air flows.  As conditions change like air density, temperatures, and relative humidity; the values of the volumetric flowrate changes.

Since we are looking at the intake flow rates of an air compressor, what happens when they run at different altitudes?  I remember that when I was in Denver, I got easily winded.  Now, this could be that I was out of shape, but it was also because the air is less dense.  That means for a volume of air, the mass of air was less.  This is called the specific volume.  Air compressors work the same way.  So, let’s look at the Ideal Gas Law; Equation 1.

Equation 1:

P * v = R * T

v – Specific Volume

R – Universal Gas Constant

T – Absolute Temperature

P – Absolute Pressure

In a comparative relationship, we can show the changes that can occur with an air compressor at different altitudes.  Since we are looking at altitude, the air density and pressure will change at different elevations above sea level.  If we keep the temperature the same, we can derive a formula from Equation 1.

Equation 2:

P1 * v1 = P2 * v2

P1 – Absolute Pressure at Sea Level

P2 – Absolute Pressure at elevation

v1 – Specific Volume of air at P1

v2 – Specific Volume of air at P2

Specific volume is the inverse of density, so it has the units of ft3/lb or M3/Kg.  If we use an example of a 40 CFM air compressor at sea level, it will produce 40 cubic feet per minute.  We can calculate the flow rate of air that it can produce at 5,000 feet of elevation.  The absolute air pressure at sea level is 14.7 PSIA, and at 5,000 feet, the air pressure is at 12.2 PSIA.  So, if we look at Equation 2, we can rearrange the values to find the change in specific volume from sea level (position 1) to 5,000 feet (position 2):

v2 / v1 = P2 / P1 = 12.2 PSIA / 14.7 PSIA = 0.83

With the 40 CFM air compressor, it will now only produce 40 * 0.83 = 33.2 CFM of compressed air at 5,000 feet.

When sizing an air compressor, it is important to know the conditions.  In this blog, I discussed the effects of altitude as it applies to the intake of an air compressor.  But, no matter the size, elevation, or type of air compressor, EXAIR blow-off products like Super Air Knives, Super Air Nozzles, and Safety Air Guns will help you to save energy and increase safety.  You can speak to an Application Engineer to see how.

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

ICFM, SCFM, ACFM, CFM What does it all mean!

A common question we get asked is “What does SCFM mean?” Most people are aware of CFM but the “S” in front seems to be less known about! Well strap on your seat belt, we are about to go into a compressed air worm hole all about volumetric flow rates!

Here at EXAIR we rate all of our products air consumption in SCFM at a given supply pressure. CFM stands for Cubic Feet per Minute, but one definition will not satisfy the conditions that will be experienced in many applications by a number of variables  (altitude, temperature, pressure, etc.). Air by nature is a compressible fluid. The properties of this fluid are constantly changing due to the ambient conditions of the surrounding environment.

This makes it difficult to describe the volumetric flow rate of the compressed air. Imagine you have a cubic foot of air, at standard conditions (14.696 psia, 60°F, 0% Relative Humidity), right in front of you. Then, you take that same cubic foot, pressurize it to 100 psig and place it inside of a pipe. You still have one cubic foot, but it is taking up significantly less volume. You have probably heard the terms SCFMACFM, and ICFM when used to define the total capacity of a compressor system. Understanding these terms, and using them correctly, will allow you to properly size your system and understand your total compressed air consumption.

SCFM is used as a reference to the standard conditions for flow rate. This term is used to create an “apples to apples” comparison when discussing compressed air volume as the conditions will change. EXAIR publishes the consumption of all products in SCFM for this reason. You will always notice that an inlet pressure is specified as well. This allows us to say that, at standard conditions and at a given inlet pressure, the product will consume a given amount of compressed air. It would be nearly impossible, not to mention impractical, to publish the ACFM of any product due to the wide range of environmental conditions possible.

ACFM stands for Actual Cubic Feet per Minute. If the conditions in the environment are “standard”, then the ACFM and SCFM will be the same. In most cases, however, that is not the case. The formula for converting SCFM to ACFM is as follows:

ACFM = SCFM [Pstd / (Pact – Psat Φ)](Tact / Tstd)

Where:

ACFM = Actual Cubic Feet per Minute
SCFM = Standard Cubic Feet per Minute
Pstd = standard absolute air pressure (psia)
Pact = absolute pressure at the actual level (psia)
Psat = saturation pressure at the actual temperature (psi)
Φ = Actual relative humidity
Tact = Actual ambient air temperature (oR)
Tstd = Standard temperature (oR)

The last term that you’ll see floating around to describe compressed air flow is ICFM (Inlet Cubic Feet per Minute). This term describes the conditions at the inlet of the compressor, in front of the filter, dryer, blower, etc. Because several definitions for Standard Air exist, some compressor manufacturers have adopted this simpler unit of measure when sizing a compressor system. This volume is used to determine the impeller design, nozzle diameter, and casing size for the most efficient compressor system to be used. Because the ICFM is measured before the air has passed through the filter and other components, you must account for a pressure drop.

The inlet pressure is determined by taking the barometric pressure and subtracting a reasonable loss for the inlet air filter and piping. According to the Compressed Air Handbook by the Compressed Air and Gas Institute, a typical value for filter and piping loss is 0.3 psig. The need to determine inlet pressure becomes especially critical when considering applications in high-altitudes. A change in altitude of more than a few hundred feet can greatly reduce the overall capacity of the compressor. Because of this pressure loss, it is important to assess the consumption of your compressor system in ACFM. To convert ICFM to ACFM use the following formula:

ICFM = ACFM (Pact / Pf) (Tf / Tact)

Where:

ICFM = Inlet Cubic Feet Per Minute

P = Pressure after filter or inlet equipment (psia)

Tf = Temperature after filter or inlet equipment (°R)

If you’re looking into a new project utilizing EXAIR equipment and need help determining how much compressed air you’ll need, give us a call. An Application Engineer will be able to assess the application, determine the overall consumption, and help recommend a suitably sized air compressor.

Jordan Shouse
Application Engineer

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