Air compressor question

(Craig) wrote in message . com...
"Frederick Wilson" wrote in message news:FmC9b.365132$Oz4.142857@rwcrnsc54...
What size and compressor (one or two cylinder) should I look at?

Any name brand preference?

Assuming that you will end up using it more than you think, shop
around for a two stage, 220VAC unit with at least a 60 gallon tank.
Stay away from the oilless units for noise reasons. The lower the rpm
of the compressor, the lower noise factor it will have. Keep an eye
out for Champion, IR, and any other big name vendor. Be aware that the
ratings on Crapsman units are very inflated. When you compare units,
use cfm @ pressure to make the comparisons meaningful.

Lots of people have built a/c using the litle hotdog tanked units and
the small household units, but if you have to spend much time waiting
on them to return to the required pressure to do the job, then they
are way too small if you have minimal time to devote to the projects.
For average usage, if the compressor has to cycle one more than once
every minute and a half or less, you need either a bigger unit or more
tankage.

What ever you do, DO NOT...I repeat DO NOT use PVC or CPVC for
pressure piping on your system. Many people use it, but do not
understand that it is not rated for or intended for use with
pressurized air. When it fails, and it will, it will almost always
fail explosively and send shrapnel all over the place. If you don't
belive me, I will show you the pressure rating for PVC with all the
derating factors applied....it's very scary.

More questions? ask away....

Craig C.


Always wondered why people use PVC/CPVC when copper is marginally more
expensive. Some places have large diameter plastic pipes to increase
their air storage "capacity". Kind of like sleeping with a rattle
snake-sooner or later.....

"Bryan Martin" wrote in message
...
in article , Tim Ward at

wrote on 9/17/03 11:08 PM:

I dunno beans about air compressors, so maybe someone else can
explain it to
me:
The usual wall circuit is 15 Amperes, times 120 volts peak is 1800
watts.
746 watts in a horsepower, so how do you get 4.5 HP out of a wall
socket?

Tim Ward


You would run a 30 Amp, 120 Volt circuit with a 30 Amp receptacle.
Most
likely this compressor can be wired for 240V by moving some jumpers in
the
motor then you could run it on a 15A, 240V circuit. By the way, the
nominal
voltage for an AC system is given in RMS voltage not peak.


If it's 4 CFM and 30 Amps at 120 Volts, then the crankcase must be
filled with used oil and wood chips. ;-)

If you check some of HF's other ads, you'll see that they have similar
compressors with similar output that are rated at 2 hp (only inflated a
little). The 4.5 hp thing is just something some ad weenie thought he'd
try to see if Sears would notice and call with a better job offer.

I like HF, but some of their ad writers are goofy. My favorite was the
caption for the little combo lathe/milling machine which for years read
"every plumber needs one". For what? Making all those short pieces of
pipe with straight threads? For his night job as a master machinist?

For yuks I just picked up the topmost HF catalog from my stack of 17 (I
threw out the ones from last week). I knew there'd be something
brainless on the cover. Sure enough, a $70, 600W inverter featuring the
"latest sine-wave technology" that can run "compressors" and "toasters"
among other things. Certainly you need the latest sine waves for
toasters. :-)

Wayne

(Fitzair4) wrote in message ...
We have PVC in our full time shop for 23 years. Never a problem. Just clean
and seal all the joints right. Have 120 psi.

Larry

Been in lots of places that used it and seen lots of failures. You do
know that Sch 40 and 80 both have an ultimate tensile strength of
only 7400psi at 73 deg. F.,( black iron is about 10-15 times that )
and that by the time you get to around 90deg F., that is reduced by
almost 50%? By the time you run the numbers for the data given in ASTM
D1784, the code that your pvc pipe is rated by, when you do all the
required derates and apply all the safety factors required for sound
engineering practices, 1" PVC is rated to handle about 4psi working
pressure. It also might interest you, in that the code specifically
states that the rating is good for incompressible liquids only and
that pvc and cpvc are to never be used in a compressible gas system
without revising the pressure ratings to those found under ASME B31.3.

BTW...if you are a commerical shop, the use of pvc like this will get
you some nice little code violations if the inspectors ever look
notices it, or OSHA visits.

Craig C.

!doctype html public "-//w3c//dtd html 4.0 transitional//en"
html
I'm no engineer and don't have a lots of formal smarts but common sense
tells me  if the following is true, then PVC is useless as tits on
a boar hog for any use. 4 psi???
p"when you do all the required derates and apply all the safety factors
required for sound engineering practices, 1" PVC is rated to handle about
4psi working pressure."
pL.D.
pCraig wrote:
blockquote (Fitzair4) wrote in message ...
br We have PVC in our full time shop for 23  years. Never a problem.
Just clean
br and seal all the joints right. Have 120 psi.
br
br Larry
pBeen in lots of places that used it and seen lots of failures. You do
brknow that  Sch 40 and 80 both have an ultimate tensile strength
of
bronly 7400psi at 73 deg. F.,( black iron is about 10-15 times that )
brand that by the time you get to around 90deg F., that is reduced by
bralmost 50%? By the time you run the numbers for the data given in ASTM
brD1784, the code that your pvc pipe is  rated by, when you do all
the
brrequired derates and apply all the safety factors required for sound
brengineering practices, 1" PVC is rated to handle about 4psi working
brpressure. It also might interest you, in that the code specifically
brstates that the rating is good for incompressible liquids only and
brthat pvc and cpvc are to never be used in a compressible gas system
brwithout revising the pressure ratings to those found under ASME B31.3.
pBTW...if you are a commerical shop, the use of pvc like this will get
bryou some nice little code violations if the inspectors ever look
brnotices it, or OSHA visits.
pCraig C.
/blockquote
/html

"L.D." wrote in message
...
I'm no engineer and don't have a lots of formal smarts but common sense
tells me if the following is true, then PVC is useless as tits on a boar
hog for any use. 4 psi???
"when you do all the required derates and apply all the safety factors
required for sound engineering practices, 1" PVC is rated to handle about
4psi working pressure."

L.D.

Craig wrote:

It works great at what it is intended for, when installed correctly, and
that is cold water supply. The temperature is the big issue, when dealing
with pressure. Any building inspector has a piece of pvc blown up from 3/4"
up to about 3", found after someone incorrectly installed it hooking up a
hot water heater.
--
Jim in NC

On 22 Sep 2003 08:40 PM, Roger Halstead posted the following:

As for my air system I run 175 psi and plastic is "to me" out of the
question. I have 1/2 galvanized installed. I gotta figure how to get
that monster out into a leanto on the back of the shop...even if it's
insulated with a little heat...It has to stay warm enough to keep the
condensate from freezing. It's not terribly noisy, but noisy enough
to startle you when it starts and you don't want to be doing some fine
work when it does. :-))

Get one of those orange 110v heating pads that you stick to the oil pan
of your car or airplane, and stick it to the bottom of your compressor
tank. I've got a similar sized compressor (used) sitting out in my shed,
and if/when I get around to hooking it up, that is what I am going to do.
No way am I going to put that sucker inside my workspace.

----------------------------------------------------
Del Rawlins-
Remove _kills_spammers_ to reply via email.
Unofficial Bearhawk FAQ website:
http://www.rawlinsbrothers.org/bhfaq/

"Craig" wrote
Been in lots of places that used it and seen lots of failures. You do
know that Sch 40 and 80 both have an ultimate tensile strength of
only 7400psi at 73 deg. F.,( black iron is about 10-15 times that )
and that by the time you get to around 90deg F., that is reduced by
almost 50%? By the time you run the numbers for the data given in ASTM
D1784, the code that your pvc pipe is rated by, when you do all the
required derates and apply all the safety factors required for sound
engineering practices, 1" PVC is rated to handle about 4psi working
pressure. It also might interest you, in that the code specifically
states that the rating is good for incompressible liquids only and
that pvc and cpvc are to never be used in a compressible gas system
without revising the pressure ratings to those found under ASME B31.3.

OK, I can accept at face value that PVC isn't meant to handle compressed air
Compressible vs incompressible fluids, no problem.

But out of curiosity, how do you get from a 7400 psi under ANY conditions to
a safe working pressure of 4 psi?
That requires dividing 7400 by 2 almost TWELVE times!!!
Are there twelve (or more) separate conditions that each compromise the
tensile strength by 50% (or more)??!?!?

Just wondering, Eric

"Roger Halstead" wrote As for my air system
I run 175 psi and plastic is "to me" out of the
question. I have 1/2 galvanized installed. I gotta figure how to get
that monster out into a leanto on the back of the shop...even if it's
insulated with a little heat...It has to stay warm enough to keep the
condensate from freezing. It's not terribly noisy, but noisy enough
to startle you when it starts and you don't want to be doing some fine
work when it does. :-))

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)




Put sides on that lean-to and insulate the crap out of it. Wrap a couple
lengths of pipe heat tape around it near the bottom, then some more
insulation around the tank. If the shop has heat on it all the time, a
couple muffin fans blowing hot air into the lean-to will keep it warm, too.
--
Jim in NC

"Richard Lamb" wrote in message
...


wmbjk wrote:


For yuks I just picked up the topmost HF catalog from my stack of 17
(I
threw out the ones from last week). I knew there'd be something
brainless on the cover. Sure enough, a $70, 600W inverter featuring
the
"latest sine-wave technology" that can run "compressors" and
"toasters"
among other things. Certainly you need the latest sine waves for
toasters. :-)

Wayne

Actually, isn't a toaster something of a challenge for an inverter?

Mine basically said not to use for any kind of heating device.

(Nearly pure resistive load?)

Not sure about others, but our Trace SWs work just fine with toasters.
They have trouble with some clocks though, including the clock in one
bread maker. The clock ran double quick, which caused the loaf to mix
and bake in a much shorter time. But sometimes shorter isn't better.
;-)

Wayne

On 22 Sep 2003 02:31:48 GMT, Del Rawlins
wrote:

On 21 Sep 2003 04:31 PM, butch burton posted the following:
(Craig) wrote in message news:3ca216ab.
more tankage. What ever you do, DO NOT...I repeat DO NOT use PVC or
CPVC for pressure piping on your system. Many people use it, but do
not understand that it is not rated for or intended for use with
pressurized air. When it fails, and it will, it will almost always
fail explosively and send shrapnel all over the place. If you don't
belive me, I will show you the pressure rating for PVC with all the
derating factors applied....it's very scary. More questions? ask
away.... Craig C.

Always wondered why people use PVC/CPVC when copper is marginally more
expensive. Some places have large diameter plastic pipes to increase
their air storage "capacity". Kind of like sleeping with a rattle
snake-sooner or later.....

My two cents in; I have used pvc (white plastic) for TEMPORARY
compressed air lines @ 120 psi + and 90 cfm and also Victaulic
grooved in the 2" size. As has been alluded to, but not nailed down,
it is mostly the temperature and time constraints that make pvc an
iffy solution. I do agree that a permanent solution involves STEEL
pipe or IRON pipe (not copper) or properly welded SDR 17 or better
HDPE pipe (use the proper mechanical couplers!) because of the
thermodynamics thing -- rapid expansion results in extreme cooling, or
solid connections near the source will experience extreme heat. This
is what kills pvc -- temperature extreme. This is an engineered
approach for 120 psi (8.3 bar) with sch 40 pvc as a TEMPORARY solution
far from source (thousands of feet/meters) with Victaulic couplers or
equivalent based on a FOS (Factor of Safety) of near 1. Kids, don't
try this at home.