Subject: [Shop-talk] compressor/sandblast guru question

From: "John Niolon" <[email-masked]>
Date: Fri, 20 Apr 2012 10:42:33 -0500

Ibve got a Quincy 310 compressor sitting on a 80 gallon tank... using a 5 hp
motor.  Itbs turning about 800 rpm

the rating is 3.9 to 9.6 ACFM @ 175psig   with a 2-3 hp motor...

Ibm wondering if it will handle a small (bench top) or small upright sand
blast cabinet without laboring it to death

Harbor Freight rates their 40# upright model at  9.5 cfm at 90 psi..

A NESCO about the same size says 12 cfm at 80 psi...

An ATLAS says 15 cfm at 100 psi

sounds like blast cabinets are rated like lawn mower engine horsepower ratings
!!!!!

any ideas if I have enough compressor ??

thanks
John
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From: Bob Spidell <[email-masked]>
Date: Fri, 20 Apr 2012 16:37:03 +0000 (UTC)

Probably not. My dad has a large IR 2-stage; probably a 'real' 7HP or greater on I believe (at least) a 60-gal tank (maybe 80). It struggles to keep up with his blast cabinet--the compressor is off for the first 5min or so of blasting, then has to run almost continuously thereafter. 

>From what I know of fluid dynamics--not much--I've always wondered what a large tank offers. Yes, the tank will put out more air before it reaches min pressure and the compressor fires, but then the compressor has to run longer to replace the volume of air lost. 

Seems to me you need the most powerful compressor you can get, regardless of tank size, so the compressor can replenish the tank quickly then get a rest cycle. I think the 'HP' and 'gallons' numbers aren't particularly relevant; what you need to know is what volume of air at what pressure the compressor can put out (maybe that's the second set of numbers you mentioned; it's not clear to me). The tank just 'buffers' the air flow. 

Maybe a guru can enlighten us. 

Bob 

-------------------------------- 
Bob Spidell - San Jose, CA 

----- Original Message -----
From: "John Niolon" <[email-masked]> 
To: "shop-talk" <[email-masked]> 
Sent: Friday, April 20, 2012 8:42:33 AM 
Subject: [Shop-talk] compressor/sandblast guru question 

thanks 
John 

[email-masked]

---

From: "Randall" <[email-masked]>
Date: Fri, 20 Apr 2012 12:05:26 -0700

> Maybe a guru can enlighten us.

I am certainly no guru; but my opinion is that as long as the compressor can
keep up with the load, you don't need a large tank or a larger compressor.
It won't hurt the compressor to run continuously, in fact it is probably
worse (in terms of overall wear, power consumption etc) to keep starting and
stopping it.

The large tank is primarily an advantage in two ways: it lets you work
longer with tools that take more air than the compressor can produce, and it
allows for longer on/off cycles.  In other words, it is actually an
advantage to have the compressor off for longer, followed by being on for
longer.  (Among other things, every time the compressor stops, a certain
amount of compressed air is vented to the atmosphere, so it doesn't have to
start under full load next time.)

Compressor "hp" ratings are indeed like lawnmower "hp", except maybe worse.
CFM ratings seem to be a little more consistent to me, but you have to be
very careful about what kind of CFM they are talking about.  Air tools (like
blast cabinets) seem to typically be rated in ACFM at their inlet; while
compressors are generally rated in ACFM or SCFM (by which they really mean
ACFM) at their inlet.  The problem is that the ACFM at the outlet of a
compressor (where the air tool is attached) is many times lower than the
ACFM at the inlet!

> Ibve got a Quincy 310 compressor sitting on a 80 gallon tank... using a
> 5 hp motor.

This probably falls into the fake hp department.  According to Quincy, their
310 compressor is not suitable for more than 3 hp.

> Itbs turning about 800 rpm

According to Quincy's data sheet, that should be about 8 ACFM @ 175 psi;
about 11 ACFM free air.  For the sake of argument, let's assume 10 ACFM @ 90
psi.  ACFM at the outlet is roughly the ACFM at the inlet times the ratio of
absolute pressures.  90 psi is roughly 6 atmospheres "gauge" or 7
atmospheres absolute, so the pressure and CFM ratio is roughly 1:7.  So the
actual output is roughly 10/7 or 1.4 cfm.

My small, bench top blast cabinet draws about 4 ACFM @ 90 psi.

So no, I don't think you have enough compressor for continuous operation of
the blast cabinet, unless your nozzle is a lot smaller than mine is (which
is certainly possible).

A cubic foot is about 7.5 US liquid gallons, so your 80 gallon tank holds
about 10.6 cubic feet.  If it is at 175 psi and you regulate the output down
to 90 psi, that will expand to roughly 19cf @ 90 psi.  If the gun is drawing
4 cfm and the compressor supplying 1.4 cfm, then you'll get about 19/2.6 or
7 minutes of blast cabinet operation before you'll have to stop and wait for
the compressor to catch up.

Depending on what you want to do, 7 minutes may be enough.  I rarely spend
that long on a single part; and the compressor could catch up while you are
preparing the next part for blasting (removing all the loose scale, dirt,
grease, etc).

PS Feel free to "beat up" on my numbers.  I've used only rough
approximations to a lot of things, including using 15 psi for atmospheric
pressure (it's closer to 14.7) and ignoring the effects of temperature
changes and humidity.  But I think the result is good enough to answer your
question.

-- Randall 

[email-masked]

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From: "John T. Blair" <[email-masked]>
Date: Fri, 20 Apr 2012 18:16:42 -0400

At 11:42 AM 4/20/2012, John Niolon wrote:

 >motor.  Itbs turning about 800 rpm the rating is 3.9 to 9.6 ACFM @ 
175psig
 >with a 2-3 hp motor...

 >blast cabinet without laboring it to death

John,

For starters compressors are a lot like computer memory, disk size, and money;
you never have enough.

That said, I run a blast cabinet and a pressure blaster (not at the same time)
with my craftsman 30 gal, 5 hp 110psi compressor.  I can blow more air than my
compressor can make, so every 5 to 15 minuites I have to take a break and let
the compressor catch up.

But one thing no one has mentioned, is the size of the nozzle.  For a 
hobbiest,
use the smallest (dia.) you can get.  Then as it wears, and opens, 
you will use
more and more air.  You blasting will get slower and slower.

John

John T. Blair  WA4OHZ     email:  [email-masked]
Va. Beach, Va                  Phone:  (757) 495-8229

           48 TR1800    48 #4 Midget    65 Morgan 4/4 Series V (B1106)
      75 Bricklin SV1 (#0887)    77 Spitfire    71 Saab Sonett III
                        65 Rambler Classic

Morgan:    www.team.net/www/morgan
Bricklin:  www.bricklin.org

If you can read this             - Thank a teacher!
If you are reading it in English - Thank a Vet!!

 From Dennis Prager - The American Trilogy:
      e pluribus Unum, "from many, one."
      In God We Trust
      Liberty - the  power  of  choosing,  thinking,  and  acting  for
                   oneself; freedom  from  control  or  restriction
_______________________________________________

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From: Doug Braun <[email-masked]>
Date: Fri, 20 Apr 2012 18:37:58 -0400

A permanent blast cabinet setup is so handy that it is worth putting up
with a somewhat undersized compressor.  You will have to stop and wait
occasionally, but that will take less time than:

1: earning the money to buy a bigger compressor
2: Actually buying it.
3: Getting it delivered and hooked up.

I have a 169.CFM, 6.5HP compressor, and it has no trouble at all running my
cabinet, with
a TP Tools medium-size nozzle.

Doug

On Fri, Apr 20, 2012 at 11:42 AM, John Niolon <[email-masked]> wrote:

> Ib ve got a Quincy 310 compressor sitting on a 80 gallon tank... using a 5
> hp
> motor.  Itb s turning about 800 rpm
>
> Ib m wondering if it will handle a small (bench top) or small upright sand

[email-masked]

---

From: Bob Hare <[email-masked]>
Date: Fri, 20 Apr 2012 15:48:26 -0700 (PDT)

You have more than enough pressure & more importantly, volume to run a small
blast cabinet.  I've run a 6.5 HP / 60 gallon rated at 9.4 SCFM for years on a
small blast cabinet.  I finally stepped up & added a second 60 gallon air
receiver, and piped my entire shop with 3/4 galvanized pipe.  Now my
compressor runs alot less.  So I'd say that the increased volume really
stopped my compressor from running all the time.  Oh yea, John Blair has my
old bench top blast cabinet, and I'm glad to see he is still using it!

Bob
Hare (eBay id: rhare34)
Virginia Beach, Va.
1934 Ford Streetrod Pickup
2005
Ford Five Hundred Limited

If you can read this, thank a teacher.... If you
are reading this in 
English, thank a Veteran.......
________________________________
From: John T. Blair <[email-masked]>
To:
shop-talk <[email-masked]> 
Sent: Friday, April 20, 2012 6:16 PM
Subject: Re: [Shop-talk] compressor/sandblast guru question

At 11:42 AM
4/20/2012, John Niolon wrote:

>motor.  Itbs turning about 800 rpm the rating
is 3.9 to 9.6 ACFM @ 175psig

>Ibm wondering if it
will handle a small (bench top) or small upright sand

John,

For starters compressors are a lot like computer
memory, disk size, and money;
you never have enough.

That said, I run a blast
cabinet and a pressure blaster (not at the same time)
with my craftsman 30
gal, 5 hp 110psi compressor.  I can blow more air than my
compressor can make,
so every 5 to 15 minuites I have to take a break and let
the compressor catch
up.

Va. Beach, Va       
          Phone:  (757) 495-8229

          48 TR1800    48 #4 Midget    65
Morgan 4/4 Series V (B1106)
    75 Bricklin SV1 (#0887)    77 Spitfire    71
Saab Sonett III
                      65 Rambler Classic

Morgan:   
www.team.net/www/morgan

If you can read this     
      - Thank a teacher!
>From Dennis Prager - The American Trilogy:
    e pluribus Unum, "from many,
one."
    In God We Trust
    Liberty - the  power  of  choosing,  thinking, 
and  acting  for
                  oneself; freedom  from  control  or 
restriction
_______________________________________________
[email-masked]
Donate: http://www.team.net/donate.html
Suggested
annual donation  $12.96
Archive: http://www.team.net/archive
Forums:
http://www.team.net/forums
Unsubscribe/Manage:
http://autox.team.net/mailman/options/shop-talk/[email-masked]
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From: Bob Hare <[email-masked]>
Date: Fri, 20 Apr 2012 15:51:37 -0700 (PDT)

BTW, I'm running a Tip Tools medium nozzle on a home built blast cabinet. 
www.tptools.com

Bob Hare (eBay id: rhare34)
Virginia Beach, Va.
1934 Ford
Streetrod Pickup
2005 Ford Five Hundred Limited

If you can read this,
thank a teacher.... If you are reading this in 
English, thank a
Veteran.......

________________________________
From: Doug Braun
<[email-masked]>
To: John Niolon <[email-masked]> 
Cc: shop-talk
<[email-masked]> 
Sent: Friday, April 20, 2012 6:37 PM
Subject: Re:
[Shop-talk] compressor/sandblast guru question

A permanent blast cabinet
setup is so handy that it is worth putting up
with a somewhat undersized
compressor.  You will have to stop and wait
occasionally, but that will take
less time than:

2: Actually
buying it.

I have a 169.CFM, 6.5HP
compressor, and it has no trouble at all running my
cabinet, with
a TP Tools
medium-size nozzle.

Doug

On Fri, Apr 20, 2012 at 11:42 AM, John Niolon
<[email-masked]> wrote:

> the
rating is 3.9 to 9.6 ACFM @ 175psig  with a 2-3 hp motor...
> Ib m wondering
if it will handle a small (bench top) or small upright sand
> sounds like blast cabinets are
rated like lawn mower engine horsepower
> ratings

[email-masked]

---

From: "Karl Vacek" <[email-masked]>
Date: Sun, 22 Apr 2012 09:08:15 -0500

John,

Blasting quickly takes a huge amount of air - as someone else said, it's
like computer RAM - you could always use more.

I have that exact cabinet - certainly one of the nicest things Harbor
Freight has ever offered.  My compressor is a 2-stage, "real" 2-HP motor (a
little over 12 amps at 220V single-phase) and puts out about 7 SCFM.
Handles my old-style paint guns just fine - the ones that take 7 SCFM - I
can paint all day without any problem.

But for blasting, I use the smallest nozzle of the several that come with
the cabinet, and I can only blast for a few minutes at decent pressure and
then it gets to the less-effective pressure range. If I just keep blasting
the compressor will be able to keep it a little above 60 PSI,.  It works,
especially on very light rust or thin paint, but that's just not enough to
blast most things off very quickly.

Soon I hope to get a new pump for my 5-HP, 80-gallon upright compressor, and
I anticipate that will be just about enough for average blasting.  Even with
that though, I'll probably have to do the toughest jobs in spurts, while the
tank is at or near max pressure, and then wait for it to build back up
again.

Karl

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]] On Behalf Of John Niolon
Sent: Friday, April 20, 2012 10:43
To: shop-talk
Subject: [Shop-talk] compressor/sandblast guru question

Ibve got a Quincy 310 compressor sitting on a 80 gallon tank... using a 5
hp motor.  Itbs turning about 800 rpm

sounds like blast cabinets are rated like lawn mower engine horsepower
ratings !!!!!

thanks
John

[email-masked]
http://autox.team.net/mailman/options/shop-talk/[email-masked]

[email-masked]

---

From: David Scheidt <[email-masked]>
Date: Sun, 22 Apr 2012 11:15:31 -0500

On Apr 20, 2012, at 11:37 AM, Bob Spidell <[email-masked]> wrote:

>
>
> From what I know of fluid dynamics--not much--I've always wondered what a
large tank offers. Yes, the tank will put out more air before it reaches min
pressure and the compressor fires, but then the compressor has to run longer
to replace the volume of air lost.
_______________________________________________

[email-masked]

---

From: Bob Spidell <[email-masked]>
Date: Sun, 22 Apr 2012 18:34:18 +0000 (UTC)

Also good to run an extended line--25 ft or more--from the compressor to the water trap. That way the air cools and water condenses before it hits the trap. 

Bob 

----- Original Message -----
From: "David Scheidt" <[email-masked]> 
To: "Bob Spidell" <[email-masked]> 
Cc: "John Niolon" <[email-masked]>, "shop-talk" <[email-masked]> 
Sent: Sunday, April 22, 2012 9:15:31 AM 
Subject: Re: [Shop-talk] compressor/sandblast guru question 

> From what I know of fluid dynamics--not much--I've always wondered what a large tank offers. Yes, the tank will put out more air before it reaches min pressure and the compressor fires, but then th…

One thing a big tank can give you is cooler drier air. Air straight out of the compressor is hot and wet. As it cools, the water condenses. A tank big enough to ensure the air being drawn off is room temp means the driers have to work less hard. I've worked with some industrial set ups that had oodles of compressor capacity to meet their peak load, but used large tanks to buffer the temperature and moisture. 
_______________________________________________

[email-masked]

---

From: "John Niolon" <[email-masked]>
Date: Sun, 22 Apr 2012 18:44:20 -0500

thanks guys for all the info...  I guess my quest begins to find/build a blast
cabinet...  the shop is plumbed per tip tools diagram using 1/2" galvanized
pipe (yes, I know black is better but galvanized was free.)

The main run is about 25' long with 4 drops that come off the top of the
pipe... down to a fitting in a tee and a ball valve/drain at the end of each
drop...  water filter at head end about 5' from compressor and another at the
end.  Compressor makes about a cup of water a week with occasional use with
air tools and a da sander... I've never gotten the first drop of water out of
the system when opening the drains... but I did blow a lizzard across the yard
once.

can anyone recommend tip sizes ... if I build, I'll just buy the kit from TIP
I guess... but all info and recommendations are appreciated..

thanks
John

[email-masked]

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From: Doug Braun <[email-masked]>
Date: Sun, 22 Apr 2012 21:37:24 -0400

Here are some photos of the cabinet I built from their kit:

http://www.dougbraun.com/model_a_gallery/main.php?g2_itemId=1244

Doug

[email-masked]