I am looking at replacing my old shop air compressor and have been
looking at the rotary screw type compressors because they are quiet.
They are a lot more money than a piston type compressor. The smallest
ones I have seen are 5HP which would be about the right size for what I
want.

Does anybody whether they output clean air or is there a lot of oil to
be removed?

Would I need to run a big filter and refrigerated dryer to paint or use
a plasma cutter?

Thanks,
BobH

BobH wrote in news:d2e64$47508bd4
:



Would I need to run a big filter and refrigerated dryer to paint or use
a plasma cutter?



That's what we run at work, and there is no oil in the air. Course, these
are commercial units (3x 400 HP + 1x 250HP units).
As for the dryer, any compressor needs one to get the moisture out for
painting, etc.


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

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Anthony wrote:
BobH wrote in
news:d2e64$47508bd4 :



Would I need to run a big filter and refrigerated dryer to paint or
use a plasma cutter?



That's what we run at work, and there is no oil in the air. Course,
these are commercial units (3x 400 HP + 1x 250HP units).
As for the dryer, any compressor needs one to get the moisture out for
painting, etc.

I dunno , we run a rotary screw type at the cabinet shop and I get a good
bit of oil . And water , but that's another issue entirely . OTOH , I run a
piston type at home , and have no problem at all with oil . I'm not runnin'
anywhere near the same volume though . And in fairness , the screw comp at
work was purchased used , and I kinda suspect we got took ...

--

Snag aka OSG #1
'90 Ultra , "Strider"
The road goes on forever ...
none to one to reply

BobH writes:

Would I need to run a big filter and refrigerated dryer to paint or use
a plasma cutter?

From the compressor, compressed air is saturated with water, and the only
way to get rid of it is with a refrigerated dryer. Undried air for
painting is risky at best.

You will need both oil filter as well as air dryer, for your
application. It is not a very big deal to get that.

i

Richard J Kinch wrote:



From the compressor, compressed air is saturated with water, and the only
way to get rid of it is with a refrigerated dryer. Undried air for
painting is risky at best.

Well, not the only way, but probably the most economical way on this
relativley small scale...

Paul



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-----------------------------------------
It's a Linux world....well, it oughta be.
-----------------------------------------

"BobH" wrote in message
.. .
I am looking at replacing my old shop air compressor and have been
looking at the rotary screw type compressors because they are quiet.
They are a lot more money than a piston type compressor. The smallest
ones I have seen are 5HP which would be about the right size for what I
want.

Does anybody whether they output clean air or is there a lot of oil to
be removed?

Would I need to run a big filter and refrigerated dryer to paint or use
a plasma cutter?

Thanks,
BobH



Unless your going to turn it on and run it for hours straight you will not
be happy with one. They are made to run, most are 7X24 type machines. I
was going to get one before I looked into one. For a plant or high volume
user they are GREAT. For a home shop they are not the ideal setup. They
don't normally cycle on an off they run and unload so they stay running the
whole time you need air and then some. The GD model I was looking at was a
super nice unit but it's MIN run time was 15 min. ( so if it turned on 4
times under light use it would run for a hour) and it was really designed to
be turned on that the start of the shift and off at the end..

William....

"Snag" wrote in
:


I dunno , we run a rotary screw type at the cabinet shop and I get
a good
bit of oil . And water , but that's another issue entirely . OTOH , I
run a piston type at home , and have no problem at all with oil . I'm
not runnin' anywhere near the same volume though . And in fairness ,
the screw comp at work was purchased used , and I kinda suspect we got
took ...


The 250 runs our gauge and measuring equipment supply air, which is super-
clean air. Not sure what type of conditioning it goes through after the
compressor though. I haven't been in the compressor room very often, it's
in a separate building that I have little reason, or time to visit.


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

Paul writes:

Well, not the only way,

What other way? Dessicants aren't feasible for volume air.

Richard J Kinch wrote:
Paul writes:


Well, not the only way,


What other way? Dessicants aren't feasible for volume air.

Well, actually that's a common method for really large volumes in
industrial settings. Achieving ppm moisture levels is routine.

--
-----------------------------------------
It's a Linux world....well, it oughta be.
-----------------------------------------

Paul writes:

Well, actually that's a common method for really large volumes in
industrial settings.

After a refrigerated dryer, right?

On Nov 30, 3:16 pm, BobH
wrote:
I am looking at replacing my old shop air compressor and have been
looking at the rotary screw type compressors --

I agree with some of the previous posters. Rotary units are typically
made for continuous operation, with a loading/unloading control loop
based on the pressure settings. I don't know if your situation
involves a separate enclosed room where the compressor is located, but
if you have that situation, the air dryer should not be in an
environment where the temperature is really elevated. They don't work
very well when the ambient temp is up in the 100+ F range. As a note
to Snag -- If you are getting oil and water in the distribution lines,
there MAY be an issue with one of the control/valve components on the
compressor. I had that experience a couple of times with a 25HP
Quincy, where the valve assembly got stuck, and proceeded to allow
significant oil into the air lines. Not pretty, especially in a
cleanroom environment.... Otherwise, they work very well, and the air
is pretty clean. There is no substitute for point-of-use coalescing
filtration, though, and in-line adsorbers that change color when they
start getting contaminated.

Richard J Kinch wrote:
Paul writes:


Well, actually that's a common method for really large volumes in
industrial settings.


After a refrigerated dryer, right?

No refrigeration at all. This method employes dryer beds in parrallel,
one in service and one regenerating, connected via three way valves.
After some time interval, less than the time of moisture breakthrough
for the bed, the three way valves switch, lining up the in service bed
to regen and the newly regened bed to in service. The regening bed is
then vented to atmosphere and a relatively smaller flow of dried air is
purged through the bed. The reduced pressure releases the trapped
moisture in the dessicant and to vent (PSA or pressure swing
absorption). This is all done with timers or PLC's, with moisture
measurement instruments to monitor the air dew points.

The primary driers (one on each compressor) give plant air with -40 to
-60 degree F or better dew points. For instrument air some of the dried
air goes to another set of drier beds giving dew points of -150 deg F or
lower. If I remember correctly -164 deg F is no moisture and its not
uncommon to see dew points just about that low. I've got a table at
work relating ppm H2O to dew points that would be more precise.

Now these are pretty big compressors, 1000 to 1500 HP, and corresponding
large volumes of air, but I'll bet that this process would scale down
with no problems.

Just where the economics curves for refrigeration vs desiccant dryers
cross is unknown to me.

Regards
Paul


--
-----------------------------------------
It's a Linux world....well, it oughta be.
-----------------------------------------

BobH wrote:
I am looking at replacing my old shop air compressor and have been
looking at the rotary screw type compressors because they are quiet.
They are a lot more money than a piston type compressor. The smallest
ones I have seen are 5HP which would be about the right size for what I
want.

Does anybody know whether they output clean air or is there a lot of oil to
be removed?

Would I need to run a big filter and refrigerated dryer to paint or use
a plasma cutter?

Thanks,
BobH


Thanks for the information Everybody!

The main reason I was looking at the screw type compressor was for the
quiet operation. The compressor lives in the shop with me and I want
something as quiet as reasonably possible. Putting it outside or in a
separate room are not really options for me. Currently, I use an old
Speedair that is so noisy that I almost never use it. The oil-less ones
are worse. I need something to keep up with a small bead blast cabinet,
but if I had a compressor that did not chase me out of the shop, I would
use compressed air a lot more.

Are low RPM compressors available as small as 5 HP?

Thanks,
BobH

For quiet operation, get a better, slower compressor. The 10 HP Quincy
that I resold recently, was unbelievably quiet.

i

"BobH" wrote in message
.. .
I am looking at replacing my old shop air compressor and have been looking
at the rotary screw type compressors because they are quiet. They are a lot
more money than a piston type compressor. The smallest ones I have seen are
5HP which would be about the right size for what I want.

Does anybody whether they output clean air or is there a lot of oil to be
removed?

Would I need to run a big filter and refrigerated dryer to paint or use a
plasma cutter?

Thanks,
BobH


I wonder if a screw compressor is a good choice? My understanding is a screw
compressor runs constantly, and "unloads" when the air is not needed. Unless
you use allot of air continually is a screw compressor a good choice?
I think Iggy may have a better choice, a good quality, 5-10 HP slow turning,
cast iron, two stage compressor may be a better choice.
Greg

BobH wrote:
Thanks for the information Everybody!

The main reason I was looking at the screw type compressor was for the
quiet operation. The compressor lives in the shop with me and I want
something as quiet as reasonably possible. Putting it outside or in a
separate room are not really options for me. Currently, I use an old
Speedair that is so noisy that I almost never use it. The oil-less ones
are worse. I need something to keep up with a small bead blast cabinet,
but if I had a compressor that did not chase me out of the shop, I would
use compressed air a lot more.

Are low RPM compressors available as small as 5 HP?
I've never heard a rotary screw that was truly "quiet". They
make a totally different sound, more like a hum than a
chug-chug, but it really isn't that quiet. They do put
sound-absorbing huts around them to reduce the hum. I have a
small Quincy, and it was pretty quiet with a 1 Hp motor on it at
450 RPM, but when I upped the motor to the design rating of 2
Hp, and changed the pulley for 915 RPM, it got surprisingly
QUIETER! I think the intake valves were rattling at the lower
speed. This is right in the shop with me, and with no acoustic
cover or intake muffler. I think you could cut the noise quite
a bit with a very simple muffler on the intake, just like a
coffee can with some holes in it or something, but I haven't
bothered.

I do wear an ear protector when I will be in the shop with it,
but I usually wear that anyway when working with the machines.
If I put a sound damping "house" over it and an intake muffler,
I think it would so quiet I wouldn't need the protectors.

Jon

On 2007-12-02, Greg O wrote:

"BobH" wrote in message
.. .
I am looking at replacing my old shop air compressor and have been looking
at the rotary screw type compressors because they are quiet. They are a lot
more money than a piston type compressor. The smallest ones I have seen are
5HP which would be about the right size for what I want.

Does anybody whether they output clean air or is there a lot of oil to be
removed?

Would I need to run a big filter and refrigerated dryer to paint or use a
plasma cutter?

Thanks,
BobH


I wonder if a screw compressor is a good choice? My understanding is a screw
compressor runs constantly, and "unloads" when the air is not needed. Unless
you use allot of air continually is a screw compressor a good choice?
I think Iggy may have a better choice, a good quality, 5-10 HP slow turning,
cast iron, two stage compressor may be a better choice.
Greg


I do not have anything currently, but that's what I would buy. A slow
reciprocal compressor. The Quincy that I had, was so quiet that it
felt a little unreal.

i

Remoting the inlet filters will also help dampen the noise. We did
that with a 25Hp Quincy and
it really helped reduce the noise level, even when the unloaders
kicked in. At that point it was
easy to hold a conversation standing right next to it.


Craig C.