Guide to choosing a rotary screw air compressor
Occupied with shopping for a rotary screw air compressor? Learn this primary to learn the way a rotary screw air compressor works, what they’re used for, and the way they’re maintained. Plus, 5 vital inquiries to ask when figuring out whether or not a rotary screw air compressor is best for you.

What’s a Rotary Screw Air Compressor?

A rotary screw air compressor (typically known as a “twin-screw compressor”) is a sort of air compressor that makes use of a pair of enmeshed helical screws to compress air. Because the screws flip, the air is frequently compressed. Rotary screw air compressors are broadly used for functions that require excessive CFM (Cubic Toes of air per Minute) and steady use. That is probably the most generally used air compression expertise for heavy industrial functions comparable to powering pneumatic manufacturing traces and conveyor methods.

They are often contrasted with a reciprocating air compressor, which makes use of pistons pushed by a crankshaft to compress air. Learn extra: Reciprocating vs. Rotary Screw Air Compressors: What’s the Difference?

How Does a Rotary Screw Air Compressor Work?

A rotary screw air compressor works by forcing air by a pair of rotating helical screws (or rotors). The 2 rotors interlock as they flip, making a sequence of chambers. As air is pressured by the rotors, it’s squeezed right into a smaller quantity. This discount in quantity compresses air because it strikes the chambers. A rotary screw air compressor is a type of optimistic displacement compressor.

  1. The 2 enmeshed helical screws or rotors flip quickly, powered by the air compressor motor.
  2. The revolution of the screws forces air by the chambers. This creates a vacuum, which pulls extra air into the chamber by the air compressor air consumption.
  3. As air moved by the successive chambers of the paired rotors, it’s squeezed right into a smaller quantity, leading to air compression.
  4. Compressed air exits the screw unit, the place it may be captured, dried, filtered, and used or saved.

Kinds of Rotary Screw Air Compressors: Oil-Injected vs. Oil-Free

There are two primary sorts of rotary screw air compressors: oil-injected and oil-free.

  • An oil-injected (or oil-flooded) rotary screw air compressor makes use of oil to lubricate the screw unit and guarantee its easy operation. The oil additionally helps to chill the compressed air and stop overheating of the unit. After the air is compressed, the oil is eliminated utilizing an oil separator. A small quantity of oil could also be left within the compressed air (oil carryover), which will be additional diminished utilizing inline filtration. Oil-injected compressors are the commonest sort of rotary screw air compressor and work properly for many functions.
  • An oil-free (or oil-less) rotary screw air compressor makes use of a two-stage compression course of. Air passes by an intercooler between compression levels to carry temperatures down and stop overheating. Oil-free rotary screw air compressors get rid of any oil carryover, producing very clear air. Nevertheless, they are usually dearer, extra sophisticated to take care of, and noisier than their oil-injected cousins.

Rotary Screw Air Compressor Parts

These are the essential elements of a rotary screw air compressor.

Air-Finish (Pump)

The air-end is the place the work of air compression occurs contained in the rotary screw air compressor. The air-end consists of a number of part elements.

Air Inlet Valve

The place atmospheric air comes into the air-end for compression.

Rotors/Screws/Rollers

A pair of interlocking helical screws that rotate quickly to compress air.

Compression Cylinder

The housing that accommodates the rotors. A rotary screw air compressor could have a single compression cylinder or a number of cylinders for multi-stage compression. Cylinders are sometimes fabricated from forged iron or metal. Oil-free compressors can even have an intercooler between compression cylinders.

Discharge Valve

The place compressed air exits the air-end. Air could go from the discharge valve to an air receiver tank or on to air-using processes.

Bearings

Bearings on each rotor ends assist the rotors to remain in place and switch easily and quickly. Bearings are sometimes anti-friction and corrosion-resistant.

Different Core Compressor Parts

A rotary screw air compressor will need to have a number of different elements along with the air-end.

Air Compressor Motor

The compressor motor powers the rotation of the rotors. The motor could also be fixed-speed or variable-speed.

Air Compressor Management System

The air compressor management system controls the motor, screens system operation and output, and offers a technique for human operators to watch and management the system.

Air Compressor Filters

Filters maintain contaminants out of the air provide. Filters for a rotary screw air compressor could embody:

  • Consumption filters to take away contaminants from atmospheric air earlier than it enters the air-end.
  • Inline filters to take away particulate and oil from compressed air.
  • Oil filters to take away particulate from liquid oil in oil-lubricated rotary screw air compressors.

Read more: What Type of Filtration Does Your Air Compressor Need?

Air Compressor Cooling System

Rotary screw air compressors generate a whole lot of warmth throughout compression. This warmth should be dissipated by a cooling system to stop overheating. Cooling system choices embody:

  • Closed-loop dry cooling, which circulates a cooling liquid by a sequence of coils that carry warmth away from the air compressor.
  • Open-loop evaporative cooling, which makes use of a mix of contemporary water and transferring air to chill the compressor.

Gaskets & Seals

Your entire system should stay air-tight to take care of strain. Gaskets and seals stop air from escaping and keep the strain within the system.

Oil-Injection System for Rotary Screw Air Compressor

An oil-injected (or oil-flooded) rotary screw air compressor could have further elements as a part of the oil injection system.

Oil Sump

The reservoir the place oil is saved to be used within the compression system.

Oil Filter

The oil filter removes particulate from the liquid oil whereas it circulates.

Oil/Water Separator

The oil/water separator separates liquid water (created throughout air compression) from the oil provide. Learn extra: Oil/Water Separators for Compressed Air Systems—Complete Guidelines

Oil Cooler

The oil cooler permits sizzling lubricant (heated by the compression course of) to chill down earlier than it’s recirculated. A thermostatic bypass valve screens oil temperature and sends too-hot oil to the oil cooler.

Rotary Screw Air Compressor Equipment

An entire compressed air system will embody a variety of different elements along with the air compressor itself.

Compressed Air Dryers

Scorching, compressed air popping out of the air compressor will comprise extra moisture. For many functions, it’s fascinating to take away moisture from compressed air to make sure a provide of unpolluted, dry air for industrial processes. There are two primary forms of compressed air dryers.

  • Refrigerated air dryers work by cooling compressed air to permit extra moisture to condense into liquid water, which is drained away. A refrigerated compressed air dryer can decrease the dew point of compressed air to ~38°F, which is satisfactory for many functions. That is the commonest sort of air dryer used with rotary screw air compressors.
  • Desiccant air dryers take away water vapor from the air utilizing an adsorptive materials. Desiccant air dryers are dearer than refrigerated dryers, however they will get air a lot dryer—right down to a dew level of -40°F to -100°F. They’re used for functions requiring ultra-dry air.

Learn extra: Refrigerated vs. Desiccant Air Dryers—How to Choose a Compressed Air Dryer

Air Receiver Tank

The air receiver tank (or compressed air storage tank) shops compressed air after it leaves the air compressor. The air receiver tank could also be positioned both earlier than or after the air drying system. Learn extra: Air Receiver Tank Full Guidelines

Drain Valves

Drain valves are used to take away extra liquid water from the compressed air system. When compressed air comes out of the rotary screw air compressor, it is extremely sizzling—and sizzling air can maintain extra moisture than chilly air. Because the air cools again right down to atmospheric temperatures, extra liquid will fall out of the air as condensation. Drain valves are used to empty extra liquid out of the air compressor, air receiver tanks, air dryers, compressed air piping, and different elements of the system the place liquid could accumulate.

Benefits and Disadvantages of Rotary Screw Air Compressors

Rotary screw air compressors are the preferred sort of air compressor for industrial functions—and for good cause. These air compressors are the workhorses of the business: dependable, quiet, energy-efficient, and highly effective. They’re a wonderful alternative for high-volume functions requiring a steady provide of air.

Benefits of Rotary Screw Air Compressors

Larger CFM per Horsepower

In comparison with reciprocating or piston-type air compressors, rotary screw air compressors can produce extra compressed air (measured in Cubic Toes per Minute, or CFM) per horsepower. A rotary screw air compressor delivers 4-5 CFM per HP, whereas a reciprocating air compressor delivers 3-4 CFM per HP. In different phrases, in case you examine a 20HP reciprocating compressor to a 20HP rotary screw air compressor, the rotary screw will produce 20-25% extra air. Which means they use much less power for producing the identical quantity of compressed air.

Steady Use and Constant Airflow

Rotary screw air compressors can crank out a whole lot of compressed air repeatedly—the truth is, that’s what they’re designed to do. A rotary screw air compressor operates finest at 100% responsibility cycle. Since they will produce air at excessive CFM on a steady foundation, they’re a fantastic alternative for twenty-four/7 manufacturing operations. Relying in your utility, you could possibly skip the receiver tank and simply energy operations instantly from the air compressor. You may as well depend on a rotary screw air compressor for extremely constant airflow, so you possibly can measurement your air compressor very near your most use state of affairs.

Decrease Whole Value of Possession

A rotary screw air compressor prices extra upfront however will lower your expenses in the long term. Along with decrease power prices on account of their increased CFM output, a rotary screw air compressor simply lasts longer than a reciprocating or piston-type air compressor. A rotary screw compressor can final between 60,000 – 80,000 hours earlier than a rebuild is critical—about 6-8 occasions so long as a reciprocating air compressor.

Cleaner Air

Rotary screw air compressors ship very clear air with low oil carryover. An oil-injected rotary screw compressor could have an oil carryover of ~3 ppm. Oil-free compressors, after all, haven’t any oil carryover.

Quiet Operation

Are rotary screw air compressors quiet? In comparison with the choice, sure. The motion of the rotary screws is quieter than the motion of transferring pistons. A rotary screw air compressor may have a sound-dampening enclosing. A typical rotary screw air compressor will function at 65-75 dBA, or someplace between the noise stage of a automobile engine and a vacuum cleaner. A rotary screw air compressor can even generate much less vibration.

Cooler Temperatures

Typical inner working temperatures for a rotary screw air compressor are ~ 80-99°F. For comparability, a piston-type or reciprocating air compressor operates at inner temperatures of ~150-200°F. Decrease temperatures translate to much less work for coolers and air dryers, additional saving power prices.

House Financial savings

A rotary screw air compressor will take up much less ground house than a reciprocating air compressor with comparable CFM output. In manufacturing services the place ground house is at a premium, this is usually a large benefit.

Disadvantages of Rotary Screw Air Compressors

Larger Preliminary Capital Funding

A rotary screw air compressor requires a better preliminary capital funding than a piston-type air compressor of comparable CFM output. Nevertheless, a rotary screw compressor could have decrease complete lifetime prices on account of its power effectivity and longevity.

Requires Expert Upkeep

Rotary screw air compressors are extra sophisticated to take care of, requiring expert and educated upkeep employees.

Requires a Clear Working Atmosphere

Air coming into the rotary screw air compressor ought to be as clear as doable. In case you are working in a really soiled setting or finding the air compressor exterior, a reciprocating air compressor could also be one other alternative. Consumption filters will help to scale back the quantity of particulate coming into the compressor in case you are utilizing your rotary screw open air or in a dusty facility.

Ought to Not Be Used for Intermittent Functions

A rotary screw air compressor is designed for steady operation and a 100% responsibility cycle. It isn’t the only option in case your compressed air wants are intermittent and require frequent biking of the compressor on and off. In case your air demand is variable however doesn’t drop to zero, a variable velocity drive motor will assist the compressor ramp air manufacturing up and down relying in your wants.

What Is a Rotary Screw Air Compressor Used For?

Rotary screw air compressors are finest for functions that require steady use (100% responsibility cycle) and excessive CFM. They’re additionally a sensible choice for functions requiring very clear air. Typical functions embody:

  • Robotic manufacturing
  • Pneumatic conveyor methods
  • Paint traces
  • Meals processing
  • Packaging traces

5 Inquiries to Ask Earlier than Selecting a Rotary Screw Air Compressor

Earlier than deciding on a rotary screw air compressor, be certain that it’s the proper alternative in your utility. Listed here are 5 vital inquiries to ask when making your resolution.

1. How giant is your demand?

Rotary screw air compressors are particularly sturdy and are capable of deal with giant quantities of demand for prolonged intervals of time. They’re nonetheless extra environment friendly and sturdy than piston compressors even at smaller sizes, however the effectivity advantages are most noticeable when entering into bigger calls for (i.e., 15 HP and extra). Rotary screw air compressors are designed to run at 100% responsibility cycle, day in and day trip.

2. Is lifetime value vital to you?

Whereas a rotary screw compressor could have increased air compressor maintenance prices and/or preliminary capital value, its life expectancy is way higher than a piston-type air compressor. Piston-type (reciprocating) compressors sometimes final about 10,000 hours earlier than a rebuild is critical. However, a rotary screw compressor will final between 60,000 – 80,000 hours. Rotary screw compressors are identified for his or her reliability and longevity.

3. Does your machine function close to your manufacturing employees?

Rotary screw air compressors are identified for his or her quiet operation. Being that the majority rotary screw air compressors come customary with sound dampening enclosures, they often function between 65 – 75 dBA, which is way decrease compared to different forms of compressors. For comparability, a reciprocating or piston-type air compressor can function at round 80 – 85 dBA.

4. How clear does your compressed air should be?

Rotary screw air compressors are designed to have not more than 3 PPM of oil carryover, whereas piston compressors can have 10 PPM or extra as they age. Much less oil carryover signifies that it’s a must to change your filter components much less typically, subsequently lowering upkeep prices.

5. Do you utilize your compressed air repeatedly all through the day? Or does your demand range all through the day?

  • Rotary compressors have turn into an increasing number of fashionable due to their effectivity and their potential to maintain up with fixed excessive demand. Many rotary screw compressors are used 24/7.
  • Even in case you don’t have a relentless demand, rotary screw reliability and sturdiness are available in a variable velocity drive model. This may velocity up and decelerate in relation to your demand at that given level. This feature ought to undoubtedly be thought-about in case your demand varies, as a result of yesterday’s controls together with on-line/off-line, modulation, and even flip valves have confirmed pricey when in comparison with the advantages of the VSD.

Upkeep Necessities for Rotary Screw Air Compressors

What sort of upkeep is required for a rotary screw air compressor? Rotary screw air compressors require common inspection and upkeep to function at peak efficiency and defend the system from extreme put on and tear. Test your proprietor’s guide for particular pointers in your make and mannequin of rotary screw air compressor. Upkeep duties could embody:

  • Draining extra water through the drain valves
  • Checking oil
  • Altering and flushing oil
  • Changing oil filters
  • Changing air consumption and inline filters
  • Altering the oil/water separator
  • Inspecting and changing belts or drive practice elements
  • Lubricating motor bearings
  • Inspecting and adjusting controls
  • Cleansing and sustaining air compressor coolers and warmth exchangers

How typically is oil modified for a rotary screw air compressor?

Checking and altering the oil is among the most vital upkeep duties for an oil-injected rotary screw air compressor. Relying in your compressor mannequin and the kind of oil used, you possibly can count on to alter the oil each 4,000 – 8,000 hours. Nevertheless, in case your rotary screw air compressor is working in a grimy setting, the oil could should be modified extra typically. Test oil ranges and examine the oil for contaminants not less than weekly. No less than annually, oil ought to be utterly drained and flushed. At all times substitute your oil filter after flushing.

How typically are filters modified for a rotary screw air compressor?

Air compressor filters (together with air consumption filters and inline filters) ought to be modified at a minimal each 2,000 hours for a rotary screw air compressor. In case your setting could be very soiled, you might want to alter filters extra typically.

How typically does water should be drained for a rotary screw air compressor?

Water ought to be drained for a rotary screw air compressor not less than every day, if no more typically. To scale back upkeep time, search for automated drain valves. Electric drain valves will be set to open on a timer to empty condensate often. A zero-loss drain valve makes use of a float mechanism to activate the drain, so it solely opens when wanted. This may scale back compressed air loss.

Different Often Requested Questions for Rotary Screw Air Compressors

Do you want a tank for a rotary screw air compressor?

It’s doable to make use of a rotary screw air compressor and not using a tank. Tankless operation for a rotary screw air compressor works finest for big operations utilizing air repeatedly. In giant operations, the piping system acts as residual storage as properly. In case your air use is extra variable or liable to sudden spikes in demand, it’s nonetheless advisable to make use of an air receiver tank.

How quiet are rotary screw air compressors?

Rotary screw air compressors are identified for his or her quiet operation in comparison with piston-style (reciprocating) air compressors. A rotary screw compressor operates at about 65-75 dBA, or someplace between a automobile engine and a vacuum cleaner.

How do you measurement a rotary screw air compressor?

One of many benefits of a rotary screw air compressor is that it may be safely sized at only a bit over your most demand. Not like reciprocating air compressors, they don’t require a big overcapacity. It’s because the rotary screws can produce air at a really quick, dependable, and constant price to maintain up together with your demand.

Are you able to get a variable velocity drive motor for a rotary screw air compressor?

Sure, it’s doable to get a variable velocity drive motor for a rotary screw air compressor. A VSD motor will permit the compressor to ramp air manufacturing up and down in response to precise want. That is advisable in case your compressed air wants range over the course of a day or shift. A VSD motor is a significantly better answer than turning the compressor on and off, as frequent on/off cycles can injury the rotary screw compressor. Learn extra: Why Choose or Upgrade to a Variable Speed Drive Air Compressor?

Do it’s a must to use an air dryer with a rotary valve air compressor?

Generally, sure. All air compression strategies will lead to condensation as compressed air cools. Extra moisture within the compressed air piping system or within the air provide can create issues for each manufacturing processes and the compressed air system itself. Learn extra: Getting Rid of Moisture in Your Compressed Air System

How you can Select the Proper Rotary Screw Air Compressor

Selecting a rotary screw air compressor is dependent upon your airflow necessities, manufacturing processes, and price range. The specialists at Fluid-Aire Dynamics will help you choose one of the best rotary screw air compressor in your utility.

Need assistance selecting a rotary screw air compressor? Contact us for assist.

Chicago (847) 678-8788 – Minneapolis (612) 246-3432 – Milwaukee (414) 273-1994

All in all, rotary screw compressors at this time have turn into fashionable due to their effectivity, noise stage, and the truth that the fee for this kind of compressor has dropped considerably within the final 10 years. They’ve low oil carryover and are sturdy and dependable. They arrive in VSD for functions with various calls for all through the day. Rotary screw compressors are a worthwhile funding for any producer on the lookout for high quality, general cost-effective unit.





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