High speed rotary vane air pump. Does it exist?

[fastline12]

We have a requirement to move 200scfm of air and be able to achieve 20psig, and must be pos disp. Problem is it needs to be super compact. Looking at centrifugal pumps, that is no biggy at all to spin the hell out of them and get what you need.

In looking at PD pumps, you are really limited to either screw or rotary vane. Weight is another concern but primarily size. I was curious if rotary vane pumps are typically run rather slow or if they can possibly be run at say 5000-10000rpm which could make them a more compact item?

I realize life of the pump, or the vanes anyway, will be largely affected but due to the intermittent application, that would not matter much.

 

[MintJulep]

Super compact relative to.....

 

[MikeHalloran]

Rubbing friction is going to make rotary vane pumps a less than perfectly satisfactory choice above ~3500 rpm, even for intermittent duty.





Mike Halloran
Pembroke Pines, FL, USA

 

[evelrod]

Fastline12...
Last job was four years at an industrial air supplier/sales/service and installation company. I'm not an expert and I don't remember all the big screw and vane compressors but there were many, it's been over 14 years but one of the smallest and highest output that I liked was Hydrovane, made in England, I think, and the Ingersoll Rand, Atlas Copco type portables that could do 200+cfm at 100 psi or better all day long with minimal service problems.

I don't understand, or at least, cannot quite grasp your problems. Is there some underlying requirement for specifically a "vane" unit and not a "screw"?

Rod

 

[fastline12]

Have not written off screws at all, just thought they were bigger and bulkier until I shopped around a bit more. It sure seems like the super charger type pumps are what we need. I am not sure what is different in the design of a supercharger pump vs shop air compressor.

For giggles, I was trying to find out what kind of clearances are inside a twin screw SC and all I find is "really tight". Duh, is that 2 tenthou tight, 2thou tight, or 10thou tight? No real need to know but interested I guess how much loss they have since there is no contact inside.

I guess I was also considering the VE to be higher with the vane with little to no loss but high speeds just might not be practical. I seem to find them specced in the 1000-2000rpm range and that would make for a huge pump.

We are looking for a pump that could easily fit in a 1ft cube if that helps.

 

[fastline12]

Could you offer an pros/cons to each pump design?

 

[hydtools]

Screw compressors generally oil lube that seals the screws and then must have oil extraction system to remove and cool the oil from the compressed air and return it to the compressor. Adds to the physical size of the compressor package.

Ted

 

[DubMac]

Plenty of rotary vaned blowers out there for your service. Go look at GardnerDenver, Kinney. I think they are your most compact solution.

 

[fastline12]

Can a rotary vane handle much over speed if we used a VFD on the drive motor to sneak upwards just a bit or are rotary vanes typically run pretty slow?

Regarding twin screw, now that it was mentioned, I to recall in a shop that had one running a lot, there was an oil haze in the shop from the oil lube in the compressor. That would probably be an issue however, I have to wonder if, at these pressures, if there would be much loss from a twin screw. I could see it as a growing issue as the pressure delta rises in the case.

Can the twin screws be run dry or do they possibly have contact seals inside that must be lubed?

 

[MikeHalloran]

I'm pretty sure there are geared screw compressors, that don't strictly require oil.

There certainly are geared dry running Roots blowers, which is another possibility if you can stand the noise.



Mike Halloran
Pembroke Pines, FL, USA

 

[moon161]

Vacuum pumps are geared and run dry, both the roots booster and the screw pumps.

 

[evelrod]

As Mike points out, Rootes types are really noisy, I mean REALLY noisy...
The smallest rotary vane units such as the aforementioned Hydrovane can supply small models but I really doubt anything near your requirements of 200cfm in a one cubic foot dimension. I think the largest vane I can think of that small was a 7 1/2 hp model, just a guess at something like 100cfm @ 90psi...just a guess, mind you.

Can you hook up a small compressor to a large external receiver? That could give you your specified flow rate as long as it is not continuous. Also, what are your requirements for a "dryer"? Any compressor without a receiver capable of anywhere near 200cfm are going to "pump" a lot of water.

Rod

 

[MintJulep]

According to this nice calculator you'll need close to 15 HP to do the job.

http://www.engineeringtoolbox.com/horsepower-compressed-air-d_1363.html

You'll have a tough job fitting a 15 HP motor into a cubic foot, let alone a compressor and motor.

 

[btrueblood]

Getting a lobed-rotor blower to push 20 psig is the tricky part, though it can be done (just not with an off-the-shelf or single unit). Gardner-Denver has some tri-lobed blowers with a slight helical twist, that have much lower pulsation than the classic 2-lobe "Roots" blowers.

 

[fastline12]

Thanks for the replies. Compressor only needs to fit this rough size window, not motor/pump assy. pump will be run by a belt. I learned that any oil in the air stream is a no go. There is not an air moisture spec as of yet but no design considerations for a drier have been provided.

The twin screws seem to be the closest match right now. HOwever, I am finding industrial screw pumps to run slow and are huge as opposed to supercharger type pumps that seems to spin VERY fast and are smaller. We also need air requirements much like that of an SC being high volume and low pressure.

Are there design differences between these? Can anyone confirm the clearances these pumps operate at between rotor/rotor, or rotor/case? I am not sure what type of filtration is need yet.

 

[evelrod]

With oil a no go, your going to need some type of dessicant/filter system and, most likely a refrigerated 'dryer'.

Sorry, I'm still not getting the 'size requirement' thing. As I said, I'm no expert but in that last four years I was around quite a few industrial installations and I must admit I'm still confused as to your requirements/specifications.... Belt drive? Most screws, vanes, Rootes are direct drive, even some of the smaller ones. Certainly 200cfm @ 20psi is within the range of conventional compressors. Remotely mounted? No receiver specs?

Rod

 

[hydtools]

Here is a Purdue study re rotor clearances:

http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2828&context=icec&sei-redir=1&referer=http://

http://www.google.com/url?sa=t&rct=...#search="screw compressor running clearances"

Ted

 

[MintJulep]

Oil-free scroll possibly?