What To Consider When Purchasing a
Rotary Air Compressor?
214-428-2868
What do you consider when purchasing a rotary air compressor?
Let’s say you buy a Mercedes, BMW or a new Tesla (considered three of the best
brands on the market today) and you drive it 95 mph and get a speeding
ticket. You pull over to the side of the
road and scrape the passenger side door against the side rail. You now have an expensive car with side
damage and an expensive speeding ticket…What do you do? Blame the police officer for pulling you over
and ruining your expensive auto? Why not
blame the car? Or, better yet, why not
blame Elon Musk for inventing the electric Tesla that can go from zero to sixty
miles per hour in less than five seconds.
I mean, let’s face it, the odometer says that the car can go 190 miles
per hour and you just wanted to make sure that the car could actually obtain
this speed! You were simply fact checking
the odometer. Heck, you should be given a metal, not a ticket!
Well, that same sort of logic applies to the equipment that you
buy for your facility. The OEM has
certain specifications and recommendations and believe it or not, you should
adhere to those guidelines like the posted speed limits on every roadway in
America. If you chose not to adhere to
those OEM guidelines, your compressed air equipment will not be reliable and
not experience the stated longevity that you thought it would. In a nutshell, it may consume more electrical
energy and may not produce the compressed air quality required for your daily
production.
It’s also important to have the right size for your
manufacturing needs. Having an oversized
compressor is just as bad as having too small of a compressor. You don’t need to impresses your competitors
or neighbors here. Maybe you don’t need
a Mercedes Benz or a Tesla for your business.
Perhaps a Honda Pilot or a Ford F150 would be a better fit. The important thing to consider before buying
a rotary screw compressor is the CFM (cubic feet per minute). How much air do you really need to run all
the machines at once. This is also true
when you are considering what size refrigerated air dryer best compliments your
rotary screw compressor. Same is true
here. Having too big of a dryer is just
as bad as having too little of a dryer!!
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THE AIR DRYER CFM AND THE COMPRESSOR CFM ARE ALMOST THE SAME.
FOR INSTANCE: THE NXB06 SERIES IS A 7.5HP ROTARY SCREW COMPRESSOR
THE 7.5HP ROTARY SCREW PRODUCES AROUND 28CFM
THE DRYER (BLUE MACHINE ON TOP OF THE TANK CAN HANDLE AROUND 30-35CFM)
We could talk about rotary screw horsepower and size all day
long, but it really comes down to the CFM.
Here are some important things you will need to consider when installing
your brand new Curtis NXB rotary screw air compressor:
Electrical
1) Have your system
voltage measured. The most common electrical utility voltages in the United
States are 200 volt, 208 volt, 230 volt, 460 volt.
2) Electrical
utilities guarantee a voltage supply tolerance of + 10%. For example, if the voltage stated supply is 230 volts it could
measure at any given time from 207 up to 243 volts.
3) Most electrical
utilities attempt to hold the supply voltage to + 5%. Operating electrical motors off
design or away from their nameplate voltage will generate additional heat
leading to reduced motor life expectancy.
4) The majority of
induction motors, 5 hp through 600 hp supplied to the U.S. market, are 230 & 460 volts; however, 200
& 208 volt systems are becoming more popular. If a 230 volt name plated
motor is operated on a 200 to 208 volt system it will operate in an elevated
heated condition leading to extremely reduced motor life. This is not a
recommended practice. There are motors specifically designed for 200 & 208
volt operation. For these applications, motors name plated as such should
be used.
2) Many air compressors operate into the motor service factor.
As such, request the package full load operating amp draw from the manufacturer
to properly size the electrical utility supply equipment (i.e., wire,
electrical quick disconnect, overloads, transformers). Seek out a qualified
electrical contractor in your area to assist in proper electrical utility
modeling and sizing. I reiterate, find
a GOOD electrician in your area to properly diagnose and install the correct
equipment for your facility.
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Placement
1) Proper placement and mounting is vital. Request a
General Arrangement (GA) drawing from the OEM for each piece of
compressed air equipment purchased. The GA drawing should illustrate the weight
and recommended clearances to be maintained around the equipment. The floor
will need to support the static weight of each piece of equipment. The
equipment should be secured to the floor to prevent it from shifting around
imparting stress on connected utilities such as piping, electrical and ducting.
In addition, many states have adopted seismic codes mandating equipment be
structurally secured to the floor. Many floors appear flat to the eye but are not flat
enough to meet accepted equipment mounting practices. Many floors can be
crowned (bowed) or have undulations. When securing equipment to a floor it is
important to identify floor imperfections filling the air gaps with shims. When
properly shimmed, the tightening of the mounting bolts will not bend or distort
the equipment frame. Frame distortion will lead to excessive equipment
vibration. Excessive vibration causes premature component failure which reduces
machine reliability, increases the cost of ownership and could potentially
create an unsafe situation and void your warranty.
Proper clearances should be adhered to. These recommended
clearances provide boundary area around the machine for safe, effective
operation and servicing of the machine. This boundary area also allows adequate
cooling airflow around the machine.
Piping
All piping should be properly supported as to not impart stress
on the equipment. When connecting piping to the equipment pipe connector, it
should be supported with proper tooling to prevent the equipment connector from
turning during the piping tightening process. If the equipment receiving
connector is allowed to rotate it very well could damage internal components to
the equipment. Air piping should be properly sized and configured to prevent
short cycling of the air compressor controls. A rule of thumb is to always use
piping at least the size of the supply connection. If the dryer connections are
larger don’t worry, the reason could be that the dryer is over sized due to
rerating or simply the fittings are larger to slow down the compressed air
velocity through the dryer. The piping exiting the dryer can be the same size
as the air compressor connection or the outlet of the dryer, which can be used
to establish the piping downstream of the dryer.
Ambient Air
Ambient air temperature plays a crucial role in not only human and
animal performance, but on the life of your equipment. If it’s too hot or too cold, your equipment
may not function properly.
If the ambient air condition drops below 32°F, measures should be
taken to prevent the compressed air equipment from being exposed as it will
freeze. During air compressor operation the most effective way to condition the
room temperature is to use the heat generated by the operating air compressor(s).
Excessive heat can be discharged from the room by way of a properly sized wall
fan. The wall fan can be thermostatically controlled to keep the room at a
constant temperature. If there are times when all of the compressed air
equipment is not operating, an auxiliary heating system should be considered.
Air-cooled rotary screw air compressors give off 2545 BTUs/hr
per horsepower.
Example: A 50 horsepower air-cooled rotary screw air compressor
discharges 127,250 btus/hr into its surrounding environment.
That is enough heat to keep a 1500 square foot home comfortable
in the dead of winter with outdoor temperatures below 32°F. Many of these
air compressors are installed with little thought of eliminating heat build-up
around the air compressor. The heat discharged into the ambient air surrounding
the air compressor is continuously cycled through the heat exchangers elevating
the temperature. Unchecked, the temperature will rise to an unacceptable level,
eventually overheating the air compressor & shutting it down. Ducting can
be attached to the air compressor to directly route the cooling air discharge
outdoors or away from the rotary air compressor. Wall or ceiling fans can also
be strategically placed in the room to exhaust the hot cooling air outside.
Either way, an adequate amount of replacement cooling air must be brought into
the room.
All installations have contaminants in the ambient air.
Contaminants can negatively impact an air compressor in many ways, two of which
are indigestion into the air compressor itself and or fouling of the air-cooled
heat exchangers. The best way to determine if the air compressor is digesting
an abnormally high amount of contaminants is to frequently perform oil
analysis. The oil analysis should find components not normally part of the oil
make-up. Important to note: religiously
blow out the radiator and clean the filters once a day or at least once a
week!!
In the case of a lubricated rotary air compressor, all of the
ambient air drawn into the machine for compression flows right past or through
the airend bearings. Too much ingestion of particulate will damage the
bearings. The oil not only cools the air during compression, but it also washes
the contaminants out of the air. Over time these contaminants will build up
continuing to be cycled through the bearings.
This doesn’t account for multiple particles clumping together,
which will damage the bearing surfaces. Two solutions for reducing digestion of
contaminants are to install an air filter with a lower micron rating and higher
efficiency rating. The ratings should be adjusted until the oil analysis
indicates the level of contaminants is satisfactory. Remember, as the rating of
the inlet air filter is increased the surface area should also be increased or
the air filter may have to be changed out too frequently from excessive
fouling. The second solution is to relocate the inlet air filter to a remote
environment, which is cleaner than the immediate area around the air
compressor. The piping used to remotely mount the air filter should be
non-ferrous. PVC works great as it is light, easy to assemble and inexpensive.
Connect it to the air compressor airend with an easily removable joint in case
machine repairs or troubleshooting is required. The piping i.d. should be
no smaller than the i.d. opening in the OEM supplied inlet filter mounting
assembly. For every 10 feet of inlet pipe run, the pipe diameter should
increase one size or 1″. If the inlet air filter is relocated outdoors it
should be protected from digestion of rain or snow.
Relocation of the inlet air filter is a recommended solution
when the surrounding area around the air compressor contains hazardous vapors
or fumes. There are air filters, which can remove hazardous fumes or
vapors; however, they are costly to purchase and maintain.
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