What To Consider When Purchasing a Rotary Air Compressor?

NxB30-B-3- FS Curtis

What do you consider when purchasing a rotary air compressor? Let’s say you buy a Volvo, arguably considered one of the safest cars on the road, and you drive it 70 mph into a brick wall (by the way, don’t do this, it ruins the paint job), is it the car’s fault that it may no longer run?

The same scenario applies to equipment. If the OEMs installation recommendations are not adhered to, there will be a high degree of probability that the compressed air equipment will not be reliable, will not experience the stated longevity, may require above average maintenance, may consume more electrical energy than required and may not consistently provide the compressed air quality required for production.

While it’s impossible to cover all of the things you need to consider when installing a rotary air compressor (and we hope it’s an FS-Curtis), this short article is intended to help avoid the equivalent of driving your car into a brick wall.


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. 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. 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. 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.


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.

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.


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

If the ambient air conditions can drop below 32°F measures should be taken to prevent the compressed air equipment from being exposed to this 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.

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.

Example:  A 10 micron particle should be able to flow through an anti friction bearing suspended in the oil film without damaging the bearing surfaces.

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.

If you have questions or would like more information or pricing, please visit our Distributor Lookup page on our website to locate a distributor in your area.

Posted on: March 30, 2017, by : Cameron Ballentine