I have noticed that lately my Sears 115VAC compressor is having more
trouble than I remember keeping up with my 1/4 inch die grinder. I
started taking some measurements and doing some calculations. I have a
few questions:

Why would a 1/4 inch die grinder use more air than a 6 inch dual action
sander? This makes no sense to me at all.

Are my calculations below roughly correct?

How big a compressor do I really need? I would like to be able to run
my die grinder at almost 100% duty cycle.

Richard



Air compressor calculations:

Tank Size: 25 gallons equals 3.3 cubic feet.

Experimental data:
The compressor took 1 minute 45 seconds to increase the tank pressure
from 90 to 120 psi.

The IR 1/4 inch die grinder, operating at 90 psi with no load, took the
tank pressure from 120 to 90 psi in 25 seconds, with the compressor off.
(For comparison, a couple of inexpensive die grinders from Taiwan drew
down the tank in around 19 seconds, so used even more air).

The IR 6 inch dual action sander, operating at 90 psi with no load, took
the tank pressure from 120 to 90 psi in 37 seconds, with the compressor off.

Calculations:

Ignoring the change in temperature as the pressure is changed, a 30 psi
pressure change on a 3.3 cubic foot tank is equal to 6.6 standard cubic
feet of air.

If the compressor takes 1.75 minutes to deliver 6.6 standard cubic feet
of air, that would be 3.77 SCFM.

If a die grinder takes 25 seconds to use 6.6 standard cubic feet of air,
that would be 15.8 SCFM.

If the dual action sander takes 37 seconds to use 6.6 standard cubic
feet of air, that would be 10 SCFM.

From the Ingersoll-Rand site, the SS3L3 compressor is rated at 11.3
ACFM at 40 psi.
11.3 ACFM at 40 psi would be 30.7 SCFM, as I understand it, again
discounting temperature effects. The SS3L3 is a single stage 220VAC
single phase compressor rated at 3 HP, (a more honest rating than most).

Altitude:

Since I live at about 5400 ft (1700m) elevation, any compressor in my
shop loses efficiency due to lower air density. I understand that the
air density here is 15-20% less than at sea level, so I would expect the
altitude to reduce compressor output by the same factor.

Richard Ferguson wrote in
:

I have noticed that lately my Sears 115VAC compressor is having more
trouble than I remember keeping up with my 1/4 inch die grinder. I
started taking some measurements and doing some calculations. I have
a few questions:

At a glance, calcs look ok. With the altitude, you will probably be
looking for a dual cylinder compressor rated at 20 CFM (this due to the
fact that 'rated' CFM is at sea level under absolutely IDEAL conditions,
and then exaggerated by the marketing dept by probably 20% or more.
I have found that using "Blaster" air tool conditioner/oil regularly will
not only reduce wear on air tools, it will cause a noteable drop in CFM
usage of the tools. It cleans out the sludge and gunk that causes the
blades to not seat properly against the bore allowing a better seal.





--
Anthony

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

Remove sp to reply via email

"Anthony" wrote in message
. ..
Richard Ferguson wrote in
:

I have noticed that lately my Sears 115VAC compressor is having more
trouble than I remember keeping up with my 1/4 inch die grinder. I
started taking some measurements and doing some calculations. I have
a few questions:

At a glance, calcs look ok. With the altitude, you will probably be
looking for a dual cylinder compressor rated at 20 CFM (this due to the
fact that 'rated' CFM is at sea level under absolutely IDEAL conditions,
and then exaggerated by the marketing dept by probably 20% or more.
I have found that using "Blaster" air tool conditioner/oil regularly will
not only reduce wear on air tools, it will cause a noteable drop in CFM
usage of the tools. It cleans out the sludge and gunk that causes the
blades to not seat properly against the bore allowing a better seal.

What Anthony said.
Except I don't know if the calcs are correct, but that is not even relevant
here. Pressure-volume calcs are subtly bitchy...
What is useful is the *relative* measurements you took, as reference points.
It proly is a good idea for everyone to measure times between reference
pressures, as an operating performance baseline. Proly best w/ the tank
valved off, for accuracy (no leaks, etc.)
Why one tool uses more air than another maybe can't really be answered. But
poss. solutions are below.

Probably the other problem is Sears. When I was looking for a compressor,
the advice I most often got was, Don't get Sears!

You can "effectively" increase your capacity by increasing the pressure
setting of your tank, and then getting a second tank regulated down to what
your real operating pressures will be. This gives you more reserve--poss a
*lot* more. Same thing w/ hot water heaters and temp.
So you might not strictly have a 100% duty cycle capacity, in that your
compressor itself don't have the cfm capacity you are actually operating at,
but your reserve/higher pressure can fudge this.

I have a 26 gal husky sort of arranged like this, and altho the cycle times
are longer, this is not nec'ly a bad thing. Works good. The Husky seems to
have a very good compressor. I actually have 4 tanks in tandem, tucked away
whereever one will fit!
----------------------------
Mr. P.V.'d
formerly Droll Troll







--
Anthony

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

Remove sp to reply via email

I have an industrial Quincy 5hp 2-stage compressor and it can just about
run a 1/4" die grinder at 100% duty cycle while still keeping the air
pump below 50% duty cycle (the desired goal). - GWE

Richard Ferguson wrote:

I have noticed that lately my Sears 115VAC compressor is having more
trouble than I remember keeping up with my 1/4 inch die grinder. I
started taking some measurements and doing some calculations. I have a
few questions:

Why would a 1/4 inch die grinder use more air than a 6 inch dual action
sander? This makes no sense to me at all.

Are my calculations below roughly correct?

How big a compressor do I really need? I would like to be able to run
my die grinder at almost 100% duty cycle.

Richard



Air compressor calculations:

Tank Size: 25 gallons equals 3.3 cubic feet.

Experimental data:
The compressor took 1 minute 45 seconds to increase the tank pressure
from 90 to 120 psi.

The IR 1/4 inch die grinder, operating at 90 psi with no load, took the
tank pressure from 120 to 90 psi in 25 seconds, with the compressor off.
(For comparison, a couple of inexpensive die grinders from Taiwan drew
down the tank in around 19 seconds, so used even more air).

The IR 6 inch dual action sander, operating at 90 psi with no load, took
the tank pressure from 120 to 90 psi in 37 seconds, with the compressor
off.

Calculations:

Ignoring the change in temperature as the pressure is changed, a 30 psi
pressure change on a 3.3 cubic foot tank is equal to 6.6 standard cubic
feet of air.

If the compressor takes 1.75 minutes to deliver 6.6 standard cubic feet
of air, that would be 3.77 SCFM.

If a die grinder takes 25 seconds to use 6.6 standard cubic feet of air,
that would be 15.8 SCFM.

If the dual action sander takes 37 seconds to use 6.6 standard cubic
feet of air, that would be 10 SCFM.

From the Ingersoll-Rand site, the SS3L3 compressor is rated at 11.3
ACFM at 40 psi.
11.3 ACFM at 40 psi would be 30.7 SCFM, as I understand it, again
discounting temperature effects. The SS3L3 is a single stage 220VAC
single phase compressor rated at 3 HP, (a more honest rating than most).

Altitude:

Since I live at about 5400 ft (1700m) elevation, any compressor in my
shop loses efficiency due to lower air density. I understand that the
air density here is 15-20% less than at sea level, so I would expect the
altitude to reduce compressor output by the same factor.

"Grant Erwin" wrote in message
...
I have an industrial Quincy 5hp 2-stage compressor and it can just about
run a 1/4" die grinder at 100% duty cycle while still keeping the air
pump below 50% duty cycle (the desired goal). - GWE


You have what is likely one of the finest compressors that were available at
the time of its manufacture.

Harold

Your calcs and conclusions are about what I'd expect. The die grinders
are nothing but turbines that suck down a lot of air. Use a bigger hole
to get more power. Tighter tolerances on the more expensive units make
them more efficient. Your dual action sander does not need to run at
such high speed, it can use a smaller orifice to get the necessary power.

To run a die grinder at 100% duty cycle will require something like an
honest 15 cfm at 90 psi. Derate 20% for your altitude.

For some examples take a look at the "Speedair" units at www.grainger.com
They aren't cheap.


Richard Ferguson wrote:

I have noticed that lately my Sears 115VAC compressor is having more
trouble than I remember keeping up with my 1/4 inch die grinder. I
started taking some measurements and doing some calculations. I have a
few questions:

Why would a 1/4 inch die grinder use more air than a 6 inch dual action
sander? This makes no sense to me at all.

Are my calculations below roughly correct?

How big a compressor do I really need? I would like to be able to run
my die grinder at almost 100% duty cycle.

Richard



Air compressor calculations:

Tank Size: 25 gallons equals 3.3 cubic feet.

Experimental data:
The compressor took 1 minute 45 seconds to increase the tank pressure
from 90 to 120 psi.

The IR 1/4 inch die grinder, operating at 90 psi with no load, took the
tank pressure from 120 to 90 psi in 25 seconds, with the compressor off.
(For comparison, a couple of inexpensive die grinders from Taiwan drew
down the tank in around 19 seconds, so used even more air).

The IR 6 inch dual action sander, operating at 90 psi with no load, took
the tank pressure from 120 to 90 psi in 37 seconds, with the compressor
off.

Calculations:

Ignoring the change in temperature as the pressure is changed, a 30 psi
pressure change on a 3.3 cubic foot tank is equal to 6.6 standard cubic
feet of air.

If the compressor takes 1.75 minutes to deliver 6.6 standard cubic feet
of air, that would be 3.77 SCFM.

If a die grinder takes 25 seconds to use 6.6 standard cubic feet of air,
that would be 15.8 SCFM.

If the dual action sander takes 37 seconds to use 6.6 standard cubic
feet of air, that would be 10 SCFM.

From the Ingersoll-Rand site, the SS3L3 compressor is rated at 11.3
ACFM at 40 psi.
11.3 ACFM at 40 psi would be 30.7 SCFM, as I understand it, again
discounting temperature effects. The SS3L3 is a single stage 220VAC
single phase compressor rated at 3 HP, (a more honest rating than most).

Altitude:

Since I live at about 5400 ft (1700m) elevation, any compressor in my
shop loses efficiency due to lower air density. I understand that the
air density here is 15-20% less than at sea level, so I would expect the
altitude to reduce compressor output by the same factor.

On Sat, 16 Apr 2005 02:57:10 -0700, Harold and Susan Vordos
wrote:


"Grant Erwin" wrote in message
...
I have an industrial Quincy 5hp 2-stage compressor and it can just about
run a 1/4" die grinder at 100% duty cycle while still keeping the air
pump below 50% duty cycle (the desired goal). - GWE


You have what is likely one of the finest compressors that were
available at
the time of its manufacture.

Harold



Harold,

Based on one of your previous posts, I've been working on getting a
Quincy. I'll get a quote on Monday. My old home made one got a
pin hole in the tank. Had it for 27 years. Time to give it up.

Wayne D.

"Wayne" wrote in message
news
On Sat, 16 Apr 2005 02:57:10 -0700, Harold and Susan Vordos
wrote:


"Grant Erwin" wrote in message
...
I have an industrial Quincy 5hp 2-stage compressor and it can just
about
run a 1/4" die grinder at 100% duty cycle while still keeping the air
pump below 50% duty cycle (the desired goal). - GWE


You have what is likely one of the finest compressors that were
available at
the time of its manufacture.

Harold



Harold,

Based on one of your previous posts, I've been working on getting a
Quincy. I'll get a quote on Monday. My old home made one got a
pin hole in the tank. Had it for 27 years. Time to give it up.

Wayne D.

Hi Wayne,
As I recall, Quincy introduced a line that is not up to the standard of
which I speak, although I can't imagine it isn't of good quality. I paid
just under $1,000 for my 5 horse 80 gallon horizontal unit when it was
purchased. About 12 years ago, while I was still in Utah, I went back to
the dealership from which it was purchased to buy the gasket that was
leaking. Out of curiosity, I inquired as to the cost of the same unit at
the time, and was shocked to find it had gone up to something like $3,000,
but they had a line that was less expensive. Unfortunately, I didn't
manage to learn what the differences were.

Here in logging country (the greater NW region, where we grow Douglas Fir
250' tall), skidders, the large four wheeled devices used for dragging the
logs in, are all equipped with Quincy 10 horse compressors, identical in
every way with the head on my 5 horse, but larger. I've yet to discover
what the purpose is. One thing for sure is they use the best quality
available so they're not shut down unnecessarily.

Good luck buying the new one. I can't imagine you'd be unhappy with it,
even if it's one of the later models. Sure would appreciate reading a
report should you get it.

Harold