A Screw Compressor is an air compressor that uses two rotors (screws) to draw fresh air from outside and compress it to produce higher volumes of air compared to a reciprocating type air compressor.  The two screws sit inside of a housing called the air end of the machine and they are powered by an electric motor.  As the motor turns the screw the air is pulled in and trapped between the screws and pushed out.  A rotary screw compressor runs quieter and more efficiently than a typical reciprocating pump style compressor.  A rotary screw compressor is like an Indy race car meant to go fast and run for hours on end.  Buying a good used rotary screw compressor is a great investment for any shop or manufacturing company.  You can save thousands of dollars by buying a good used screw compressor.

Give us a call 972-487-1939 for questions regarding sizing and pricing on a used rotary screw compressor!  Thanks for checking out industrialaircompresors.com!

First, why buy a Rotary Screw Compressor at all?

• Rotary screw air compressors are the kings of air compressors. The design of the rotary screw air end is the highest technological advance in compressed air on the market today. Screw compressors run more efficiently, cleaner, and quieter than other types of compressors. Rotary screws also last many years, a well maintained screw compressor can run 80,000-100,000 hours before major repairs are necessary to the motor and the pump.

Why buy a Used Rotary Screw Compressor?

• Undeniably you will save thousands of dollars buying a used compressor. Depending on what size you need a new compressor can cost anywhere from $12,000 up to $100,000 or more.
• Secondly, you will save time buying a used compressor that has been tested and is ready to be shipped immediately. It can take up to 6 weeks for a new screw compressor to be ready for installation if ordered direct from the manufacturer.
• Lastly, a used compressor has passed the break in test, any possible manufacturing defects have been overcome and the compressor is ready to be put into service and keep your business up and running without major down time.

Quincy 30 HP QGD-30 in Stock. This machine is in excellent condition with only 14K run hours on it. It is a 2012 year model. When it comes to used screw compressors this is what you are looking for. This compressor would cost around $15,000.00 new, not including shipping, and taxes. At $9500 including shipping this is a true bargain. Call 972-533-4783 for more info.

Reciprocating/Piston Type

The recip, or piston style of compressor has been around for ages.  It's that big huge looking compressor you find in barns, shops, and plants all around the world.  They are used for many different applications in which a continuous flow of air is NOT needed.  Piston compressors are like a work horse they work best when they can run then stop, run then stop and if not overworked by continuously running can last for many years. 

Rotary Screw Type

The screw, or rotary style of compressor is a more recent design in the history of compressed air.  Rotary screw compressors are like a race horse compared to a piston type compressor.  They are designed to run and run continuously for hours at a time without.  In other words, they are built to run and if maintained can give you over 100,000 hours of service before major repairs are needed.

Which kind do I need?

To determine which compressor would be best for you, ask yourself, do I need a continuous fast flow of air, or do I need bursts of air for shorter periods of time?  If during the work shift your tools and machines run more than 60% of the time you will most likely be in the market for a Rotary Screw compressor.  But, if you just need air at certain intervals during the day and not continuously then a Reciprocating compressor is the likely choice for you. 

If your still not certain, give us a call and we can help.  972-487-1939

Well, in the world of industrial air compressors the same could be said for rotation or the spin direction of the motor.

Very often when a rotary screw compressor is installed and the wiring is hooked up and the compressor is started the first time the motor may spin backward.  This is due to one of your wire leg's being in the wrong position.  

If the motor continues to spin backward major problems can occur, not least of which may be damage to the air end of the compressor resulting in a very costly repair, sometimes upward of $5000.00 or more depending on the age and type of compressor.

A good rule of thumb during start up is to do a rotation test.  Look at the motor, usually you will find an arrow or directional symbol that will tell you which way the motor should turn.  Hook up your wires and give the machine a "bump" and immediately stop, or technically speaking a stop/start procedure.  Check the rotation, make sure the motor is turning in the proper direction.  If so, then you are ready to start up and get to work.  If not then you need to swap a leg on your lug connector or contact.  This should cause the motor to spin in the proper direction.

Just remember, for rotary screw compressors, "Rotation, Rotation, Rotation!"

During the process of compressing air, atmospheric air along with water vapor and atmospheric contaminants (hydrocarbon or chemical vapors), are drawn into the compressor intake. Additionally, the compression chambers of most compressors require oil for lubrication, sealing and cooling. Once compressed, the air flows into an aftercooler to remove the heat of compression. As the air cools in the aftercooler, water and hydrocarbon vapors will condense. Additional condensation takes place as the air is further cooled in the piping and air dryers. This condensed moisture must be removed from the compressed air system to prevent damage to downstream components and processes. Drain valves are installed on moisture separators, , , and drip legs to remove this condensate from the compressed air system. The condensate should be piped from automatic drain valves to oil/water separators to remove the oil from the condensate prior to discharge to a drain.

Environmental regulations strictly prohibit the discharge of oily wastes and chemicals, including the condensate drained from a compressed air system. Because of these requirements, municipalities regulate the discharge of compressor condensate to surface water, wastewater treatment facilities, and sanitary sewers.

Compressor condensate must therefore be either collected or treated prior to disposal. An oil/water can be used here to remove the oil from the condensate.

Collection involves the drainage of the condensate into drums or storage tanks. The drums or tanks are then hauled away to an approved disposal facility.

Transportation, storage, and disposal costs (TSD) can exceed $500 for a single 55-gallon (208 liter) drum. A typical 25 hp (18 kW) compressed air system will generate approximately 20 gallons (76 liters) of condensate in one (1) day. Eleven 55-gallon (208 liter) drums are required to dispose the condensate produced in only one (1) month of operation resulting in a cost of $5,500. This is a significant disposal cost.

Since the condensate is approximately 95% water and 5% oil, oil/water separators have been developed to reduce or eliminate the amount of oil in the condensate.

An oil/water separator system, installed on the 25 hp (18 kW) compressed air system example above, can reduce the number of 55-gallon (208 liter) drums from eleven (11) to less than one (1). Condensate disposal costs will therefore be reduced by $5,000 per month. Payback on an oil water separator is typically much less than one year.

Types of Oil Water Seperators

Oil/water separators are available in four basic technologies:
chemical adsorption
gravitational separation
mechanical separation
vaporization separators

Chemical Absorption Oil/Water Separators

Chemical absorption oil/water separators (fig. OWS1-1) are filled with a chemical media developed to attract the oil while repelling water molecules. Depressurized oily condensate drains into the chemical absorption separator were the oil is bonded to the media. Clean water then flows to drain.

The life of the chemical separator depends on the quantity of oil in the condensate. The oil concentration in the condensate may vary from 40 ppm to more than 600 ppm. Actual oil concentration is dependant on the type and condition of the compressor, the type of oil and ambient relative humidity.

Chemical Adsorption Oil/Water Separator

Since absorption capacity is approximately 50% of the media bed weight, a 15 gallon (57 liter) absorption separator will capture 7 - 8 gallons (26 - 30 liters) of contaminants.

Gravitational Separation Oil Water Separator
Gravity separation is accomplished by flowing the condensate into a settling tank. Oil is skimmed off the top and water is pumped off the bottom of the oil/water separator tank. The water removed from the bottom of the tank still contains oil. The percent depends on the demulsibility of the oil. Gravitational separation devices are simple and will separate free oils that have migrated to the top of the settling tank. Gravitational oil water separators are not effective on oils that have emulsified in the water since the oil does not naturally separate from the water.

Mechanical Separation Oil/Water Separator
Beko Qwik-Pure-Group-Overview A coalescer performs mechanical separation through pressure drop, torturous path, and oleophobic attraction. The pressure drop across the coalescer causes some of the oil to drop out of phase and separate. Pores create a torturous path through the coalescer and oil droplets adhere to the coalescer and combine coalescing. To enhance the oil's collecting and forming droplets and draining off the coalescer element an oleophobic (oil resistant) filter media is used. The combination of these factors make coalescers more than 99% effective oil separators. The actual efficiency of the coalescer will depend on the type of oil being separated. Some synthetic lubricants will not be removed by a coalescing element. Coalescer element's foul over time and require replacement based on pressure drop.

Activated charcoal adsorbs oil and most synthetic lubricants. The condensate is passed through a charcoal chamber. The activated charcoal adsorbs the oil reducing the amount of oil in the condensate. Activated charcoal chambers foul over time and require scheduled replacement.

Mechanical oil/water separators are usually a combination of a gravitational settling tank with a coalescer element. Charcoal is also typically used as a polishing bed to remove oils not separated by the coalescer.

(Note: Since the condensate will contain a mixture of water and lubricating oil, be sure to drain all condensate in a manner approved by all federal, state and local regulatory agencies. Oil/water separators are available to assist in this function.)

Vaporization Oil Water Separators
Vaporization oil water separators utilize an external heat source, such as electric or steam heaters, to boil-off the water. The remaining oil is then drained into a container for proper disposal. Vaporization separators will efficiently separate almost all oils, however attention must be given to the materials of construction of the oil/water separator since the oily waste may be corrosive.

Installation and Maintenance
Installation of the oil/water is typically quite simple. The oily condensate from drain valves is piped to a depressurization chamber/vessel to reduce the pressure to atmospheric pressure. The oily condensate then flows into the oil/water separator.Oil water separators are normally installed indoors to prevent freeze-up of the water during wintertime operation. If outdoor installation cannot be avoided, contact the manufacturer for approval and installation requirements.
Drain collected oil as necessary. Properly dispose all collected oil as required by law.
Clean the settling tank or boiling tank with water to remove particulate build-up once a year or as necessary. Dispose of water properly.
Change the activated carbon adsorber before it is fully saturated with oil.
Replace the coalescer element based on Delta P.

Follow the manufacturer's maintenance requirements.

Proper Disposal of Condensate
Since the condensate will contain a mixture of water and lubricating oil, be sure to drain all condensate in a manner approved by all federal, state and local regulatory agencies. Oil/water separators are available to assist in this function.

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