Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.


Rotary Screw Versus Vane Compressors- which one is a good choice?

Rotary Screw Versus Vane Compressors- which one is a good choice?

Hi Folks,

Just a basic question about rotary compressors:

what are the advantages or distadvantages of a rotaty screw compressor over a rotary vane compressor or vice versa? we are using it for plant instrument air  application and need to decide on one type? Apparently, a vane unit is quite economical than a screw unit.

I would like to get feed back on performacne, machine life, maintenance issues, noise and ability to handle solid particles(although the application is air however would like to know if the service was for natural gas VRU applications)

Thanks for your time.


RE: Rotary Screw Versus Vane Compressors- which one is a good choice?

You are probably going to need to provide more details to get much value from the response.  The terminology is not always consistent between different industries and in different countries.  So, please be specific.  

•    If this is an air machine, what capacity range are you looking for?  Some machines are more economic when they are large. What discharge pressure do you require?  Some machines work very, very well, but are limited to relatively low pressures.
•    Are you asking specifically about dry screw or flooded screw technology?  Perhaps you don't care. I have never heard of anyone using a dry screw compressor for air. But, if you had a great need for oil-free air, someone might consider it.
•    Are you talking about sliding vane or some other vane technology?  We only have one sliding vane unit in air service, but it is a very specialized non-lubricated model.

In plant air (instrument air) service, we use all of the following:

•    Oil lubricated reciprocating piston compressors.
•    Oil flooded screw compressors
•    High speed centrifugal compressors (multi-stage)
•    One non-lubricated sliding vane compressor

We have dry screw machines in off-gas service.  We have liquid ring machines in vacuum service.  We have oil lubricated sliding vane machines in flare gas recovery service.  We have many multi-stage centrifugal compressors in variety of services.  

Johnny Pellin

RE: Rotary Screw Versus Vane Compressors- which one is a good choice?

Here are specific details on the unit:

capacity: 50 scfm.
Discharge pressure: 125 psig

I am refering to an oil-injected compressor and the compressor is a sliding vane unit.



RE: Rotary Screw Versus Vane Compressors- which one is a good choice?

The only place I've ever seen dry screws is in air service, it is funny to me that you've never seen them in that service.  I guess "normal" really is a function of the path you've taken.

50 SCFM for an air compressor is less than 15 hp, or about $10/day in electric cost.  I wouldn't spend a lot of time chasing much effeciency improvement.

VRU's are the single hottest topic in my world right now.  It is an amazingly complex subject and probably should be its own thread.


RE: Rotary Screw Versus Vane Compressors- which one is a good choice?

We have a number of oil flooded screw machines in plant air service running at about 125 psig.  In general, they all run very well and have been trouble free.  They are package units that came in complete, so installation was relatively simple.  There is a certain about of routine maintenance required for the filters, coolers and coalescers.  However, it seems to me to be a small price to pay.  The oldest of these machines has probably been running for about 15 years with no major repairs.  

We do not have any oil lubricated sliding vane machines in air service. But the ones we have in other services are much more trouble.  We tend to see wear on the vanes which requires a rather intensive PM program.  We have to remove and measure the vanes for wear and replace them frequently. This has improved since we changed to Kevlar vanes.  We tend to see wear in the bores of the cases (wash-boarding) that cannot be fully repaired.  After some number of years, the vibration and vane wear caused by the worn cases requires us to completely replace the case.  Our sliding vanes machines were not purchased as package units, so the installation was quite complex.  We have a circulating glycol system for cooling, an oil injection system for lubrication of the compressors and bearings.  We have gearboxes to achieve the needed speed which required another circulating oil system for the gearbox and motor.  

The flooded screw machines are much quieter than the vane machines.  The building that houses our largest pair of sliding vane compressors is one of only two areas in the plant that requires double hearing protection (plugs plus muffs).  The noise level is too high for ear plugs alone.

Given my experience, I would much prefer the flooded screw option for air service rather than the sliding vane machine.  I am not sure I know what you refer to as VRU, so I can't comment on that service.  

Johnny Pellin

RE: Rotary Screw Versus Vane Compressors- which one is a good choice?

VRU is "Vapor Recovery Unit".  As state and federal governments are tightening the restrictions on outgassing from tanks, people are starting to get serious about stabalizing liquid hydrocarbons in a place where the vapors can be recovered.

I get questions about VRU's every day.  The solutions range from amazingly ineffectual, to ok.


RE: Rotary Screw Versus Vane Compressors- which one is a good choice?

For longevity at 125 psi the oil flooded screw would be my choice. In a low volume and low discharge pressure I.e. less than 50 psi the rotary vane is ok but efficiency over time is not one of its best atributes  

RE: Rotary Screw Versus Vane Compressors- which one is a good choice?

Sliding vane compressors are noisy.

RE: Rotary Screw Versus Vane Compressors- which one is a good choice?

My experience with rotary vane are that the vanes break and the unit is down all the time.  That was in nat gas service. The large differential pressures cause lots of problems with the vanes too.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


eBook: Product Innovation Platform Assessment
Over the past few years, there has been growing interest among industrial companies and solutions providers with regards to Product Innovation Platforms, where design, manufacturing and IoT tools are bundled into a single software package. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close