I was always interested in messing around with vacuum, but I know
better, I have way too much stuff going on as it is. Hope you guys have
fun with it.

A crude light bulb is pretty simple to make. Use a piece of iron wire (a
single strand from picture frame wire works nicely) between two nails
in a cork. Wire the filament up to a transformer. Drop a light match
into a baby food jar and immediately put the cork in place. When the
match goes out, turn on the voltage.

What you need to do is get rid of the oxygen, not pull a good vacuum.

I saw this demonstrated in 5th grade, and had to try it when I got home.
My dad helped and thought we should turn off the lights, since it would
be pretty dim. I just missed one piece of the setup--the transformer. We
plugged it directly into 110VAC. Really nice flash.

Steve

Chuck Sherwood wrote:

My 11 year daughter is showing a strong interest in science.
We received a Edmunds catalog with lots of cool stuff in it.

I have always wanted to play with vacuum stuff when I was a kid
and I didn't get much of a chance so I figure now is my chance.

I figure it would be cool try to make a crude light bulb inside
a bell jar and things like that.

I looked at ebay and there are many vacuum pumps FA.

Do I need a two stage pump and how big of a pump do I need?
The killer is these things are heavy and shipping is expensive.

chuck

Don Foreman wrote:
On 13 May 2005 10:45:09 -0700, jim rozen
wrote:


In article , Chuck Sherwood says...


Will a two stage pump work faster or slower ?

Two stage pumps will go down to a lower pressure.

Typcially five or ten microns (1 micron = 1 millitor)

A single stage pump might do 40 or 50 microns ultimate
pressure.


Related question: what does "gas ballast" mean in the context of
vacuum pumps, and what is it for?

When a vacuum pump reduces the pressure in a vessel, this reduces the
boiling point of any liquids (usually water) within the vessel.
Eventually the pressure in the vessel will become so low that water will
boil at room temperature. At this stage all the water will evaporate and
consequently the water vapour is sucked into the vacuum pump. As gases
pass through the pump they are compressed, which raises the boiling
point of water again, and some water condenses inside the pump. This is
not desirable because it can reduce pump performance and cause
corrosion, so the water needs to be expelled from the pump. The gas
ballast valve allows dry air (well, hopefully dry) from the atmosphere
to enter the pump chamber just before the air is expelled through the
exhaust valve. Because this air isn't saturated (i.e., it isn't at 100%
humidity) it can absorb extra water vapour and carry moisture out of the
pump. So the gas ballast valve helps to purge the pump of water or other
contaminants. Opening the gas ballast valve does however reduce the
ultimate vacuum attainable.

Hope this helps,

Chris

Chuck Sherwood wrote:

how about a piece of tungsten??



well I have some tungsten rod for tig welding, but its much to
big. Can you buy tungsten wire or do I have to break a light bulb
to get some?



Break a "new" light bulb for the metal. The new tungsten is still
flexible and can be formed
but an old one will be brittle. Also you may want the metal to glass
seal that is hard to
make your self (I think).

Bill K7NOM

In article , Don Foreman says...

Related question: what does "gas ballast" mean in the context of
vacuum pumps, and what is it for?

The answer given by Christopher is completely correct.

I could add the following though:

The idea is that pumps have a hard time pumping any 'condensible'
vapor (which includes water, but also some solvents) so aside
from contaminating the oil, the pressure the pump will reach
is limited when pumping these vapors.

There is another port on the pump stator that communicates with
the gas volume as it is being compressed and swept around by
the vanes in the rotor - and this is connected to a small
fixed orifice which can be opened up to room air. Because
the pressure in the swept volume is still below atmosphere
it will pull air in and this dilutes the condensible vapor
and prevents it from condensing to liquid, and allows the
vanes to sweep it around. The extra air charge in the
swept volume will open the exhaust reed valve and will be
expelled.

Without the gas ballast charge the pressure in the swept
volume will drop very low as the rotor comes around (vapor
has gone to liquid as the pressure comes up) and the exhaust
reed valve will not burp.

As the rotor continues around to the intake port the pressure
will rise and the vapor will still be there, along with the
next slug of air/vapor. So without the gas ballast
valve the pump becomes a machine that sucks only the condensible
vapor from the chamber and dumps it into the oil.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

Christopher Tidy wrote:
Chuck Sherwood wrote:
All the broken pumps I've seen were neglected and ruined on the pump side,


What are the important clues to look for when buying a used pump?

Here are a few things to look for. Some of these you can only check if
you can see the pump in person, but that's always a good idea if it's
nearby.

* Check out the general physical condition: does the pump appear to have
been looked after well or is it knocked around and covered with grime
and rust?

* Ask the seller what is has been used for. If it has been used in
industry for neon sign manufacture or air conditioning servicing it will
probably have seen much heavier use that if it was used in a school
science laboratory.

And probably in better condition as it was used recently and when it was used it probably worked. Unuse is worse for a pump than use. Every pump I got from a school was is poor condition because they never use them enough or change the oil.

I've never seen a HVAC pump at the pawn shop that had dirty looking oil in it. They were all working just fine before getting lifted. Stuff at schools sits around and rots forever.


* If the seller has a vacuum gauge available, ask them to measure the
pump's ultimate vacuum.

* Inspect the oil. Is it dirty? Metallic particles in the oil may
indicate heavy pump wear. Vacuum pump oil is usually colourless and
doesn't smell. If it smells it's the wrong kind of oil.

* Unscrew the oil drain and let a few drops run out. Is the oil
contaminated with water?

* Listen to the pump running. These pumps are usually pretty quiet.
Clacking noises may indicate sticking vanes.

Getting an oily smoke/mist out of the exhaust when it's pumping down with a covered up inlet is a good sign it's sort of working.


It seems from what Harry says that you should be fine with a mechanical
pump for making neon signs, although you will need to be able to
manufacture and seal the glassware. Perhaps Harry could confirm if a
single stage pump is adequate or if a two stage pump is required?

Hope this helps

Chris

Cydrome Leader wrote:
Christopher Tidy wrote:

Chuck Sherwood wrote:

All the broken pumps I've seen were neglected and ruined on the pump side,


What are the important clues to look for when buying a used pump?

Here are a few things to look for. Some of these you can only check if
you can see the pump in person, but that's always a good idea if it's
nearby.

* Check out the general physical condition: does the pump appear to have
been looked after well or is it knocked around and covered with grime
and rust?

* Ask the seller what is has been used for. If it has been used in
industry for neon sign manufacture or air conditioning servicing it will
probably have seen much heavier use that if it was used in a school
science laboratory.


And probably in better condition as it was used recently and when it was used it probably worked. Unuse is worse for a pump than use. Every pump I got from a school was is poor condition because they never use them enough or change the oil.

I've never seen a HVAC pump at the pawn shop that had dirty looking oil in it. They were all working just fine before getting lifted. Stuff at schools sits around and rots forever.

Obviously there's a difference of opinion here. I personally don't see
that there's much harm that can come to a pump if it's left unused,
provided that it doesn't contain water and that it isn't left with the
inlet open so that it can fill with dirt. It's just like leaving an
engine filled with oil for years; I don't think it will do any
irreparable damage. One pump I had from a laboratory which had been
standing for a year or two (and DID have some water in it) was a bit
stiff at first but after an oil change and a few rotations it was fine.
When I dismantled it there wasn't any appreciable corrosion either, just
a very slight discoloration where the rotor had stopped. I think
abrasive dirt is probably the biggest cause of pump damage. But in
general these belt-driven pumps are very rugged and reliable.

Chris

My son and I did just the same experiment 4 years ago with great results we
used different inert gasses like argon, helium
"Chuck Sherwood" wrote in message
...
My 11 year daughter is showing a strong interest in science.
We received a Edmunds catalog with lots of cool stuff in it.

I have always wanted to play with vacuum stuff when I was a kid
and I didn't get much of a chance so I figure now is my chance.

I figure it would be cool try to make a crude light bulb inside
a bell jar and things like that.

I looked at ebay and there are many vacuum pumps FA.

Do I need a two stage pump and how big of a pump do I need?
The killer is these things are heavy and shipping is expensive.

chuck

In article , Christopher Tidy says...

* Ask the seller what is has been used for. If it has been used in
industry for neon sign manufacture or air conditioning servicing it will
probably have seen much heavier use that if it was used in a school
science laboratory.

* If the seller has a vacuum gauge available, ask them to measure the
pump's ultimate vacuum.

* Inspect the oil. Is it dirty? Metallic particles in the oil may
indicate heavy pump wear. Vacuum pump oil is usually colourless and
doesn't smell. If it smells it's the wrong kind of oil.

* Unscrew the oil drain and let a few drops run out. Is the oil
contaminated with water?

* Listen to the pump running. These pumps are usually pretty quiet.
Clacking noises may indicate sticking vanes.

You missed the most important one: attempt to determine if the
pump has been used with any toxic substances in its former life.
This is hard to do, but some common tip-offs include:

Off-board oil filtration devices

Inert gas feed for purge or ballast

Residue around the intake or exhaust ports

Former owners include medical, or laser users

By all means, *ask* what the pump was used for, and ask
who owned it before the present owner, if that information
is available. Any fishy answers would be grounds for
me to pass on the item.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

"Chuck Sherwood" wrote in message
...
Or salvage a small AC compressor from an old window unit or water
cooler. You will need the run capacitor. Mount it on some type of base and
insulate everything so it is safe.

But don't they need oil which is usually lost when you cut the lines?

There is enough oil left in the sump for lots of operation, and I suppose
you could add some once in a while if you really wanted. I have had mine for
about 6 or 8 years of occasional operation without a problem. If it ever goes
bad on me, I will simply scrounge another.

Vaughn

jim rozen wrote:
In article , Christopher Tidy says...


* Ask the seller what is has been used for. If it has been used in
industry for neon sign manufacture or air conditioning servicing it will
probably have seen much heavier use that if it was used in a school
science laboratory.

* If the seller has a vacuum gauge available, ask them to measure the
pump's ultimate vacuum.

* Inspect the oil. Is it dirty? Metallic particles in the oil may
indicate heavy pump wear. Vacuum pump oil is usually colourless and
doesn't smell. If it smells it's the wrong kind of oil.

* Unscrew the oil drain and let a few drops run out. Is the oil
contaminated with water?

* Listen to the pump running. These pumps are usually pretty quiet.
Clacking noises may indicate sticking vanes.


You missed the most important one: attempt to determine if the
pump has been used with any toxic substances in its former life.
This is hard to do, but some common tip-offs include:

Off-board oil filtration devices

Inert gas feed for purge or ballast

Residue around the intake or exhaust ports

Former owners include medical, or laser users

By all means, *ask* what the pump was used for, and ask
who owned it before the present owner, if that information
is available. Any fishy answers would be grounds for
me to pass on the item.

Good point Jim. I should have remembered that one!

Chris

On Sat, 14 May 2005 16:22:30 GMT, "Vaughn"
wrote:
"Chuck Sherwood" wrote in message
...

Or salvage a small AC compressor from an old window unit or water
cooler. You will need the run capacitor. Mount it on some type of base and
insulate everything so it is safe.

But don't they need oil which is usually lost when you cut the lines?

There is enough oil left in the sump for lots of operation, and I suppose
you could add some once in a while if you really wanted. I have had mine for
about 6 or 8 years of occasional operation without a problem. If it ever goes
bad on me, I will simply scrounge another.

If you know which soldered off tubes go into the sump and the ullage
space, you can install a simple vinyl-tubing sight glass gauge to
monitor the oil level in the hermetic can - the problem being to
determine the proper oil level to begin with.

I suppose if you call the manufacturer with the compressor model
number from the data plate, they can tell you how many fluid ounces of
oil, and what weight and type - mineral, POE or PAG synthetic. Do NOT
mix or change the oil, the oil seals inside are different to be
compatible with the oil. And you can drain and fill it to make the
initial 'full' level mark.

Oh, and put an oil separation filter on the compressed air output to
trap the excess oil - in refrigeration they don't care about a little
bit of oil entrainment in the output, because it's a sealed system and
the oil will be back soon...

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

On 13 May 2005 17:13:11 -0700, jim rozen
wrote:

In article , Don Foreman says...

Related question: what does "gas ballast" mean in the context of
vacuum pumps, and what is it for?

The answer given by Christopher is completely correct.

I could add the following though:

The idea is that pumps have a hard time pumping any 'condensible'
vapor (which includes water, but also some solvents) so aside
from contaminating the oil, the pressure the pump will reach
is limited when pumping these vapors.

There is another port on the pump stator that communicates with
the gas volume as it is being compressed and swept around by
the vanes in the rotor - and this is connected to a small
fixed orifice which can be opened up to room air. Because
the pressure in the swept volume is still below atmosphere
it will pull air in and this dilutes the condensible vapor
and prevents it from condensing to liquid, and allows the
vanes to sweep it around. The extra air charge in the
swept volume will open the exhaust reed valve and will be
expelled.

Without the gas ballast charge the pressure in the swept
volume will drop very low as the rotor comes around (vapor
has gone to liquid as the pressure comes up) and the exhaust
reed valve will not burp.

As the rotor continues around to the intake port the pressure
will rise and the vapor will still be there, along with the
next slug of air/vapor. So without the gas ballast
valve the pump becomes a machine that sucks only the condensible
vapor from the chamber and dumps it into the oil.

Jim

Thanks!

I managed to get the welch 1400 pump off ebay for $130. I picked it
up last night and it looks good. The seller stated that his father
owned it for AC work but stated he never saw him use it. The inlet
had AC fittings on it (and was capped) so it appears it was used
for AC work.

I have no way to test it, other than putting my finger over the intake
and observing that it does suck. The noise changes considerably as
the vacuum is built up. Opening the gas ballast also increases the
noise a lot when the input is capped.

This pump should work much better than a converted AC compressor
and was a turn-key operation for 130. can't beat that!

I will probably pick up a cheap automotive vacuum gauge to get a
rough idea if its working well.

thanks for all the help
chuck

oil, and what weight and type - mineral, POE or PAG synthetic. Do NOT
mix or change the oil, the oil seals inside are different to be
compatible with the oil. And you can drain and fill it to make the
initial 'full' level mark.

The ultimate pressure you can achieve is very much affected by
the oil in the vacuum pump and I'm not convinced that AC oil is good
vacuum pump oil.

I think the primary factor with AC oil is that it has to be compatable
with the Freon (as well as the seals). In the AC, I doubt very much
that they care about the vapor pressure of the oil which is critical
in vacuum operations.

Supporting data from one of the laser web sites indicate that they
change the oil when they use an AC compressor as a vacuum pump.

Its a moot point for me, because I just bought a welch 1400 two
stage pump for 127 off ebay. While that is more than an AC compressor,
its a turn key operation and I believe this vacuum pump will perform
way better than a converted AC compressor.

chuck

In article , Chuck Sherwood says...

I will probably pick up a cheap automotive vacuum gauge to get a
rough idea if its working well.


A bourdon tube gage won't really tell you what's going on, see
if you can hunt up a thermocouple gage. These read down to about
one micron and will tell you if the pump is working up to what
it should be doing.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

A bourdon tube gage won't really tell you what's going on, see
if you can hunt up a thermocouple gage. These read down to about
one micron and will tell you if the pump is working up to what
it should be doing.

I have read a little about these on one of the laser web sites.
Any recomendations where to get a good one ?
chuck

Chuck Sherwood wrote:
I managed to get the welch 1400 pump off ebay for $130. I picked it
up last night and it looks good. The seller stated that his father
owned it for AC work but stated he never saw him use it. The inlet
had AC fittings on it (and was capped) so it appears it was used
for AC work.

I have no way to test it, other than putting my finger over the intake
and observing that it does suck. The noise changes considerably as
the vacuum is built up. Opening the gas ballast also increases the
noise a lot when the input is capped.

This pump should work much better than a converted AC compressor
and was a turn-key operation for 130. can't beat that!

I will probably pick up a cheap automotive vacuum gauge to get a
rough idea if its working well.

thanks for all the help
chuck

Good luck with the experiments. I'd be interested to see some pictures
sometime!

Chris