Are you assuming that the only way to do it is to weld the pipe to a
oversize plate with a fillet on the outside? That could certainly be
strong enough, although if it were me I think I'd cut the plate to the
pipe ID, leave the root a bit open, and fill the corner. Assuming a
flat fillet, that would make the thinnest part of the joint about .35"
I qualify.
It's 150 psi, and 8.625" OD. About 323 pounds per inch of weld. Are
you saying that there's some reason that the best welders you know
can't build up a one inch long fillet you'd trust to hold 323 pounds?
Then how come my own little quicky test tank, made from a 3" coupling
with plating barely ground off, and single-pass fillet welded to 1/4"
plate, can hold 500 psi, which is about 475 pounds per inch of weld?
Why write about soda bottles when somebody is prepared to build the
actual item, spot you 50 psi, and let you make an easy 2 grand off
your opinion? I'm sure we could run the thing through a couple hundred
cycles in less than 2 hours including setup. Where else can you make
$1000 an hour for doing nothing? Would it help if I upped the wager? I
think you're as exactly sure as I am that your money would be moving
into my wallet, but just aren't willing to admit it.
Wayne
I would have the plate oversize and bevel the pipe. Also leave a gap
at the root. That would end up with a flange which I think would help
keep the plate from flexing. From what I can deduce, a flat plate
causes concentrated stresses. A hemispheric dome can be made of much
thinner material because there is no bending force.
The formula I found for the stress in a flat plate end on a tank is:
f = d^2/ t^2 3/16 p Where f is the stress
d is id
t is thickness of plate
p is pressure
So 3^2/ .250 ^2 equals 9 / 1/16 or 9 * 16 or 144
And 8^2 / .5^2 equals 64/ 1/4 or 64 * 4 or 256 so your test
tank is about twice as robust as the bigger tank. But both tanks
ought to be fine according to what I could find.
The strength of the weld is not as significant as the thickness of the
plate from what I could find. But I would not want to use a fillet
weld on the outside of the pipe as you would then have a larger
diameter on which the pressure is acting.
Please note that I am not a mechanical engineer and don't rely on my
calculations.
Dan
On 14 May 2007 19:49:11 -0700, snipped-for-privacy@krl.org wrote:
Makes sense, and very little more prep work.
Sure, but the OP's original idea was to make the thing as simple as
possible. There's obviously a thickness that will do, and I'm looking
forward to reading what that should be.
The second half isn't clear to me. Is the source available online?
I get the idea, and the ratio makes sense. But we don't really know if
the small one had a margin or was at its limit. The existing gauge is
pegged at 500. I think I'll get a 1000 psi gauge and crank the thing
up to that or failure, whichever comes first. :-) It would be
interesting to know how much the quicky single-pass fillet can take,
as well as how much pressure a cheap pistol grip grease can produce.
One could place a round bar across the plate, shimmed off by say
.030", tack weld the ends, and then use a feeler gauge to measure the
deflection (if any) while testing.
I found this in a quick search, but couldn't determine what material
the calculator is for
http://www.epcserver.com/Structural/Analysis/plates/plate8.asp 8"
square plate, .5" thick, 150 psi.= .0023 deflection. There's other
interesting stuff at the site, and despite the $5 warning, no request
for payment appeared. This doc might interest you
http://www.powerengineering.ca/errata/PE2_%201_01_revised.pdf . Flat
plate calcs on page 31.
My thoughts as well. I can't think of any practical reason to use an
outside fillet in the application anyway. Maybe if it was Sunday and
one was out of grinding discs? :-)
Wayne
Pete, just a thought, but fatigue testing can be done with a air valve
(I think that 3 way will work), and a timer. Assuming a 10 second
cycle, after just one day you will have tested 8,640 cycles.
i
I've not seen it personally so I'm not 100% positive. As near as I can
tell from the pics and the test in the catalog PDF the lid is a disk of
1" thick plexiglass with some O ring arrangement for sealing. I'm not
clear on whether the O ring is on the perimeter of the plex. or the
steel, but it does not appear to be on the bottom pressing on any sort
of flange. This makes some sense due to the bayonet locking lugs not
appearing to have enough travel to apply any sort of downward pressure
against a seal.
This plex. is attached to the steel locking ring which looks to be about
1" square plus the reinforcing bar across the middle. The whole lid
assembly has six locking lugs that drop down in the six slots of the
pipe housing and rotate to the lock position.
Pete C.
My guess is the plastic is Lexan. I would put an O ring groove in the
plastic as a piston seal. Easier to machine, smaller part to chuck in
a lathe, and does not depend on clamping pressure to seal.
Dan
Yesterday I substituted the gauge from my Oxygen tank. Pumped it up to
1100 psi. About then a bead of water appeared on the 3/8" ball valve
shaft and I noticed that the shaft appeared to have shifted outward.
So I called that the limit. The grease gun was definitely bypassing.
Thicker oil might be better, or maybe 1100 is all that can be
expected. The gun is more effective with grease but that gets in the
fill tube and is a pain to clean before refilling for successive
tests.
I looked around and realized that I had every single thing I needed to
build a little larger and better tank, and that the turntable I'd made
for a previous project would make the job easier and nicer. I used
some scrap 1/4" pipe and plate, and a piece of truck inner tube for a
gasket. Inside dimensions are 4" diameter and 6" tall. 1/2" bolts
because that's what I had. Squared up the ends in the lathe. Used a
bendable rest for the MIG gun and supported my elbow on the drill
press while cranking the winch handle. Overdid the welding quite a
bit. Winch handle turned smoothly for the cutting, but got somewhat
draggy when welding. Probably arcing at the pivots and gear teeth.
Cleaned the tank up this morning and assembled. First I tightened the
bolts until the lid just started to deform. Gasket was evenly
compressed, but every squeeze of the grease gun after 400 psi just
seeped water past the gasket. Let it sit for a while at 400, no drop.
Relieved the pressure and tightened down the bolts some more which
caused a permanent doming of the lid. Repressurized and got the same
effect at 700 psi. Working pressure for my application is 500, so I
won't bother making a thicker lid or doubling up on the bolts. 7
hours total including testing, 6.9 of it grinding. ;-) Even though
the seal doesn't hold as well as the previous threaded one, it's
faster and nicer to use than having to dope and crank down a 3" pipe
bushing. Photos here http://www.citlink.net/~wmbjk/testtank.htm . All
equipment solar powered.
Wayne
Likely not for this one Pete -
But the group might be interested.
I have a plasma machine and it had been in and out of moisture in the lines.
Not good for plasma.
I put two dryers in-line and it cleaned up. But I noticed I keep getting
water in the tank (80-90$ RH here most of the time ) and I figured a little
money was worth a rusted out tank and lots of bad cuts.
I would empty the tank when I could think of it - then one day I didn't get
the valve as tight as I should. A slight (no sound) leak drives out of the
bottom. It keeps the bottom dry or at least nothing comes out when opened up!
I noticed the tank turns on once in a while and I get the tank running to fill
before I use it on the machine. There are two sets low and high - I like to
start with the tank full to allow less pump on time. I pump faster than
use anyway.
Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com /
Pete C. wrote:
I've not been paying attention the last few days. Where is this
"eng-tips"?
The HF paint pot looks like it will work ok, within it's 80 PSI
limitations with just the requisite plumbing changes.
Pete C.
This link will take you to a sample thread
http://www.eng-tips.com/viewthread.cfm?qid 5280&pageg. I searched
the forum but didn't see any directly applicable info. If you have the
time perhaps you'll have better luck. Failing that, this pdf
http://www.powerengineering.ca/errata/PE2_%201_01_revised.pdf (pg 29)
appears to have the appropriate formula but I couldn't find any online
copies of the referenced tables. By doing some substituting I
estimated that my 4.5" tank with a 1/4" head and an 8" version with a
1/2" head might both be rated at about 250 psi using material with an
allowable stress of 13000 psi, which should represent a substantial
safety margin for a low use item. Note that if you break down the
equation, using a thicker than needed cylinder wall reduces the cap
thickness. Presumably making the cap oversize as I did is worth
something as well, perhaps someone can put a number on that.
This site http://www.risacher.org/rocket/testing.html has a more basic
formula for minimum wall thickness - that it should equal pressure in
psi (1.5X recommended) times tank OD in inches, divided by two times
the allowable stress in psi. That's about .075" for 8.625" diameter,
150 psi operating pressure and 13,000 psi allowable stress (they used
20k for seamless), which jives with the estimated .105" of a cheap,
larger diameter portable air tank. The writer used a cap about 6X the
minimum wall thickness for his 4.5" diameter project, and the other
link noted 5X in their 30" diameter example.
Meanwhile I cranked my own tank up to 1200
http://www.citlink.net/~wmbjk/testtank.htm . I might drill for more,
smaller bolts and a hole circle with a shorter arm, to see how much
pressure a simple gasket can seal.
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