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

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

Basics of the Compressor Room

EXAIR Corporation has staked our reputation on a keen ability to help you get the most out of your compressed air system since 1983.  Now, the bulk of our expertise lies in the implementation and proper use of engineered products on the demand side, but we fully recognize that there are critical elements for optimization on the supply side too.  And that, quite literally, starts in the compressor room.  This is not an exhaustive, specifically detailed list, but here are some you might consider to get the most from the (again, quite literally) beginning:

  • Location.  If you’re building a new facility, or doing a major rehab of your existing one, having the compressor room as close as practical to the point(s) of use is best, IF all other things are equal.  You’ll use less pipe if you don’t have to run it so far.  You’ll also be able to use smaller diameter lines because you won’t have to worry about line loss (pressure drop due to friction as the air flows through the total length) as much.
  • Location part 2.  If all other things are NOT equal, having the compressor room close to the point of use may not be best for you.
    • Your air compressor pulls in air from the immediate environment.  It’s better to go with longer and bigger pipe in your distribution system than it is to put your compressor in a location where it’ll pull in dust & particulate from grinding operations, humidity from a boiler plant, fumes from chemical production, etc.
    • There are some pretty darn quiet air compressors out there, but there are some pretty loud ones too.  Especially in small to mid size facilities, putting the compressor in an area that upsizes the required piping is still likely a better idea, due to the downsizing of the noise levels that personnel will be exposed to.
  • Environment.  No matter where your compressor is located, the machine itself should be protected from heat and other harsh environmental elements.  That means if it’s inside the plant, the compressor room should be adequately ventilated.  In some situations, the compressor may be best installed outside the plant, in its own building or protective structure.  This should be designed to protect against solar load…in addition to the high temperature associated with a hot summer day, the sun’s rays beating down on your air compressor will radiate a tremendous amount of heat into it.
  • Filtration.  Whatever is in the air in your compressor room is going to get into your compressed air.  This is doubly problematic: particulate debris can damage the air compressor’s moving parts, and it can likewise damage your pneumatic cylinders, actuators, tools, motors, etc. as well.  Make sure the intake of your compressor is adequately filtered.
  • Maintenance.  Air compressors, like any machinery with moving parts, require periodic preventive maintenance, and corrective maintenance when something inevitably breaks down.  There should be adequate space factored in to your compressor room’s layout for this.  The only thing worse than having to fix something is not having the room to fix it without taking other stuff apart.

Patrick Duff, 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. Each compressor is capable of producing 4,500 cubic feet of air at 300 psi. The shop also has a 3,000 horsepower compressor that produces 9,000 cubic feet of air at 300 psi. By matching output to the load required, the shop is able to shut down compressors as needed, resulting in energy savings to the base. (Air Force photo by Ron Mullan)

These are a few things to consider on the supply end.  If you’d like to talk about how to get the most out of your compressed air system, EXAIR is keen on that.  Give us a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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About Air Compressors: Air Intake Best Practices

Take a second and think about where the air compressor is located within your facility.  It is more than likely not a major focal point displayed prominently in the floor layout. There is a better chance it is tucked away in a corner of the facility where operators seldom travel.  No matter the type of air compressor, it still has an intake where it pulls in the ambient air from around the compressor then sends it through some process and on the demand side of your compressed air system.  These intakes can easily be placed out of sight and out of mind especially in older facilities that were designed when compressors were loud and the piping layout kept them away from operators due to sound level restrictions.

Air Compressor
Antique Air Compressor (Not safe for use!)

That’s why your compressor manufacturer supplies a specific grade of air inlet/intake filter, and this is your first line of defense. If it’s dirty, your compressor is running harder, and costs you more to operate it.  If it’s damaged, you’re not only letting dirt into your system; you’re letting it foul & damage your compressor. It’s just like changing the air filter on your car, your car needs clean air to run correctly, so does your compressor and the entire demand side of your compressed air system.

According to the Compressed Air Challenge, as a compressor inlet filter becomes dirty, the pressure drop across the inlet increases, this is very similar to the point of use compressed air filters.  The inlet filter on the compressor is the only path the compressor has to pull in the air, when restricted the compressor can begin to starve for air very similar to if you only had a small straw to breath through and told to run a marathon.  A clogged inlet filter can give false symptoms to compressor technicians as well.

The effects can mimic inlet valve modulation which result in increased compression ratios. If we were to form an example based on a compressor with a positive displacement, if the filter pressure drop increases by 20″ H2O, a 5% reduction of the mass flow of air will be present without a reduction in the power being drawn by the compressor. This all leads to inefficiency which easily amounts to more than the cost to replace the depleted inlet air filter.

compressor
Compressed Air System

Where you place the filter is just as important as how often you replace it.  There are some tips to be used when mounting the inlet filter.

  1. The filter can be placed on the compressor, but the inlet pipe should be coming from an external area to the compressor room or even the building if possible. The inlet should be free from any contaminants as well.  Some examples that are easy to overlook are nearby condensate discharges, other system exhausts and precipitation.
  2. Depending on the type of compressor being used, a lower intake air temperature can increase the mass flow of air due to the air density.  A compressor that is lubricant injected is not susceptible to this due to the air mixing with the warmer lubricant before being compressed.

If you would like to discuss improving your compressed air efficiency or any of EXAIR’s engineered solutions, I would enjoy hearing from you…give me a call.

Jordan Shouse
Application Engineer
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Images Courtesy of  the Compressed Air Challenge and thomasjackson1345 Creative Commons.