On Sat, 04 Feb 2006 20:38:30 GMT, Ignoramus28190
wrote:

Can a typical "125 PSI air tank" be used as a "buffer" of vacuum?

Yes, but not desperately well.

You can't "compress" vacuum. So for a 90psi outlet on a 135psi tank you
have nearly twice the energy stored on there, compared to a tank at
90psi. With vacuum you can only store the same (negative) pressure as
you're using. Also -15psi of vacuum isn't much energy either (although
you probably don't need much).

As you're also working on a pressure difference of a mere 15psi, you
need short fat hoses too. Typical airlines will carry vacuum without
collapsing, but the flow rate is terrible.

There's also the question of how clean your suction air is, and how you
get the crud out of the tank afterwards.

Generally "stored" vacuum is done by storing compressed air and
distributing it round the shop, then converting it to vacuum with a
venturi device at each bench, where it's needed.

"Andy Dingley" wrote in message
...
On Sat, 04 Feb 2006 20:38:30 GMT, Ignoramus28190
wrote:

Can a typical "125 PSI air tank" be used as a "buffer" of vacuum?

Yes, but not desperately well.

You can't "compress" vacuum. So for a 90psi outlet on a 135psi tank you
have nearly twice the energy stored on there, compared to a tank at
90psi. With vacuum you can only store the same (negative) pressure as
you're using. Also -15psi of vacuum isn't much energy either (although
you probably don't need much).

As you're also working on a pressure difference of a mere 15psi, you
need short fat hoses too. Typical airlines will carry vacuum without
collapsing, but the flow rate is terrible.

There's also the question of how clean your suction air is, and how you
get the crud out of the tank afterwards.

Generally "stored" vacuum is done by storing compressed air and
distributing it round the shop, then converting it to vacuum with a
venturi device at each bench, where it's needed.

Someone here has some nice vacuum venturi plans on their site. I found them
a month or two back. Very simple to make - I was interested in one for
desoldering also.
I could probably dig them out if anyone wants them and cant find them. IIRC
they were based on a Harbour Freight product.
rob

"Rob" wrote in message
...

"Andy Dingley" wrote in message
...
On Sat, 04 Feb 2006 20:38:30 GMT, Ignoramus28190
wrote:

Can a typical "125 PSI air tank" be used as a "buffer" of vacuum?

Yes, but not desperately well.

You can't "compress" vacuum. So for a 90psi outlet on a 135psi tank you
have nearly twice the energy stored on there, compared to a tank at
90psi. With vacuum you can only store the same (negative) pressure as
you're using. Also -15psi of vacuum isn't much energy either (although
you probably don't need much).

As you're also working on a pressure difference of a mere 15psi, you
need short fat hoses too. Typical airlines will carry vacuum without
collapsing, but the flow rate is terrible.

There's also the question of how clean your suction air is, and how you
get the crud out of the tank afterwards.

Generally "stored" vacuum is done by storing compressed air and
distributing it round the shop, then converting it to vacuum with a
venturi device at each bench, where it's needed.

Someone here has some nice vacuum venturi plans on their site. I found
them
a month or two back. Very simple to make - I was interested in one for
desoldering also.
I could probably dig them out if anyone wants them and cant find them.
IIRC
they were based on a Harbour Freight product.
rob


Here it is courtesy of Nick Muller:
http://www.motor-manufaktur.de/werks.../en_index.html

How about this? Drill holes in the sides of the tank, and slip steel rods
through the holes, so each one follows a diameter. Weld them in. Now the
tank is braced from the inside, so it can't collapse.

For future safety, label the tank as "Not a pressure vessel."

On Sun, 5 Feb 2006 22:17:50 +0800, "Rob" wrote:


"Rob" wrote in message
...

"Andy Dingley" wrote in message
...
On Sat, 04 Feb 2006 20:38:30 GMT, Ignoramus28190
wrote:

Can a typical "125 PSI air tank" be used as a "buffer" of vacuum?

Yes, but not desperately well.

You can't "compress" vacuum. So for a 90psi outlet on a 135psi tank you
have nearly twice the energy stored on there, compared to a tank at
90psi. With vacuum you can only store the same (negative) pressure as
you're using. Also -15psi of vacuum isn't much energy either (although
you probably don't need much).

As you're also working on a pressure difference of a mere 15psi, you
need short fat hoses too. Typical airlines will carry vacuum without
collapsing, but the flow rate is terrible.

There's also the question of how clean your suction air is, and how you
get the crud out of the tank afterwards.

Generally "stored" vacuum is done by storing compressed air and
distributing it round the shop, then converting it to vacuum with a
venturi device at each bench, where it's needed.

Someone here has some nice vacuum venturi plans on their site. I found
them
a month or two back. Very simple to make - I was interested in one for
desoldering also.
I could probably dig them out if anyone wants them and cant find them.
IIRC
they were based on a Harbour Freight product.
rob


Here it is courtesy of Nick Muller:
http://www.motor-manufaktur.de/werks.../en_index.html

These venturis are very noisy and they take a lot of air. For
soldersucking, you don't need high sustained volume. What you need is
a pulse, like the trigger-actuated hand-held single-shot piston pump
"Soldapullt", though perhaps a bit longer in duration. I think a
small reservoir like a 16.4 oz propane bottle very near the point of
use would do the job. It could also accumulate the crud because it's
easily and cheaply replaced, and a 16.4 oz reservoir would hold years
worth of sucked solder. You might want a larger reservoir mounted
out of the way somewhere. Some restriction between that and your
pulse reservoir (a point-of-use vacuum capacitor, if you will) might
actually be beneficial. You get your shot, then it takes a second or
two to suck back down from the larger remote reservoir which is
cyclically maintained by the pump.

Teflon tube (drilled rod) works well as a sucker nozzle. You'll want
a poke rod to clean it out periodically.

Braid works better for surfacemount, but a sucker really does work
well for clearing out holes in thru-hole boards.

In article ,
says...

These venturis are very noisy and they take a lot of air. For
soldersucking, you don't need high sustained volume. What you need is
a pulse, like the trigger-actuated hand-held single-shot piston pump
"Soldapullt", though perhaps a bit longer in duration.

The usual setup when using venturi vacuum generators (Piab is on of the
large mfrs - http://www.piab.com ) for parts handling in automated
machinery is to switch the air supply in order to turn the vacuum on and
off. This minimizes the problems of high air consumption and noise and
may make a venturi acceptable for desoldering.

It's been several years since I've had occasion to use a Piab unit, but
I believe some models provide for an external surge tank that kicks in
when the air supply is turned on. Details might be on Piab's site.

Ned Simmons

Ignoramus2963 wrote:
I will also try to find a vacuum relay of some sort, so that the pump
is not running needlessly -- only when the pressure inside is higher
than a set limit. Have not found one yet.

SWITCH I will assume you mean't, of course you can or may need to use a
contactor or relay as well.

Good ol' Mcmaster has switches for vacuum situations, but they are
listed under "Pressure" switches.

The most reliable are the Bourdon Tube type with a mercury bulb, but
they are not cheap.

The "Snap Switch" type are best installed on something that rattles or
shakes as sometimes they will stick. Nothing a good kick doesn't take
care of, but if you leave the shop for a week and forget to unplug the
pump, you might find it melted down when you get back (don't ask how I
know).

EBAY often has bourdon tube units for around $25.

Grummy

On Sun, 5 Feb 2006 15:08:59 -0500, Ned Simmons
wrote:
The usual setup when using venturi vacuum generators (Piab is on of the
large mfrs - http://www.piab.com ) for parts handling in automated
machinery is to switch the air supply in order to turn the vacuum on and
off. This minimizes the problems of high air consumption and noise and
may make a venturi acceptable for desoldering.

It's been several years since I've had occasion to use a Piab unit, but
I believe some models provide for an external surge tank that kicks in
when the air supply is turned on. Details might be on Piab's site.

Ned Simmons

A few projects ago I was looking to cast some clear resin, and was
looking for a vacuum chamber. I found an old 1 gal. paint pot at an
auction. I changed some fittings so as to be able to use my
automotive A/C gauges and vacuum pump with it. The pot turned out to
be an acceptable vacuum chamber for my project.

John Normile

On Mon, 06 Feb 2006 22:19:18 GMT, (John Normile)
wrote:

The pot turned out to be an acceptable vacuum chamber for my project.

I use a Vac-u-vin coffee jar with a hand pump made from a rubber cork.

Works just fine for degassing PU and epoxy resins!

Ignoramus19736 wrote:
On Mon, 06 Feb 2006 22:19:18 GMT, John Normile wrote:

On Sun, 5 Feb 2006 15:08:59 -0500, Ned Simmons
wrote:

The usual setup when using venturi vacuum generators (Piab is on of the
large mfrs - http://www.piab.com ) for parts handling in automated
machinery is to switch the air supply in order to turn the vacuum on and
off. This minimizes the problems of high air consumption and noise and
may make a venturi acceptable for desoldering.

It's been several years since I've had occasion to use a Piab unit, but
I believe some models provide for an external surge tank that kicks in
when the air supply is turned on. Details might be on Piab's site.

Ned Simmons

A few projects ago I was looking to cast some clear resin, and was
looking for a vacuum chamber. I found an old 1 gal. paint pot at an
auction. I changed some fittings so as to be able to use my
automotive A/C gauges and vacuum pump with it. The pot turned out to
be an acceptable vacuum chamber for my project.


I would try to use a small glass jar as a vacuum chamber. (and a steel
plate with a gasket as the cover)

i

Well wrapped with tape to control the fragments if it implodes I hope,
or better enclosed in a shield as well :-)
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.

On Sun, 05 Feb 2006 19:02:54 GMT, Ignoramus2963
wrote:



I will also try to find a vacuum relay of some sort, so that the pump
is not running needlessly -- only when the pressure inside is higher
than a set limit. Have not found one yet.

I appreciate your comments.

i

You'll probably find a pressure switch on EBay. Failing that, you
can get a 0 to 100 kPa (0 to 14.7 PSIA) sensor from DigiKey for $7.88.
MPXM2102AS-ND This is an absolute pressure sensor, measuring against
an internal vacuum reference so you would turn on the pump when
pressure in your reservoir rises above x PSIA (0 PSIA being a total
vacuum) and turn it off when it goes below x - hysteresis. You
could set these pressure trip points to anything you like with fixed
resistors or trimpots.

Other elements needed would be an instrumentation opamp (INA126,
$2.25), a 12VDC supply, a solid-state relay or a transistor and
relay, maybe an LM393 comparator (42 cents) and some resistors.
Maybe a 3-terminal voltage regulator for 72 cents. The whole works
shouldn't cost $15 plus the relay which you probably already have.

I would try to use a small glass jar as a vacuum chamber. (and a steel
plate with a gasket as the cover)

Please don't. Imploding glass containers are very dangerous.
If you must, put it inside a wooden box or something to contain
the fragments if it explodes. If you want a cheap bell jar, fisher
scientific sells some small ones for under 50 dollars.

chuck

On Tue, 07 Feb 2006 03:58:08 GMT, Ignoramus19736
wrote:

On Mon, 06 Feb 2006 21:41:51 -0600, Don Foreman wrote:
You'll probably find a pressure switch on EBay. Failing that, you
can get a 0 to 100 kPa (0 to 14.7 PSIA) sensor from DigiKey for $7.88.
MPXM2102AS-ND This is an absolute pressure sensor, measuring against
an internal vacuum reference so you would turn on the pump when
pressure in your reservoir rises above x PSIA (0 PSIA being a total
vacuum) and turn it off when it goes below x - hysteresis. You
could set these pressure trip points to anything you like with fixed
resistors or trimpots.

Other elements needed would be an instrumentation opamp (INA126,
$2.25), a 12VDC supply, a solid-state relay or a transistor and
relay, maybe an LM393 comparator (42 cents) and some resistors.
Maybe a 3-terminal voltage regulator for 72 cents. The whole works
shouldn't cost $15 plus the relay which you probably already have.

Thanks Don. I have some parts already, such as comparator chips and an
SSR and 12 vdc supplies.

I won something on ebay that is called Barksdale Pressure Switch,
D1H-H18SS, 1/4 inch SS NPT, .40 - 18.00 PSI range, 1 setting, you can
see it and the datasheet at

http://www.anderson-bolds.com/Mercha...gory_Code=PSME

http://www.anderson-bolds.com/Mercha...fs/D1H_D2H.pdf

I appreciate the suggestion though, I will save your post for the
future.

i
That should work. With that small differential your pump will
probably cycle with each hit of the soldersucker valve.

A half-vacuum (7 PSIA) is plenty to suck solder.