I have a rotary oil vacuum pump in the laboratory.

Everybody says all connections to & from this pump
must in tubing of large diameter.

But I get results from 6mm OD thick-walled
silicone medical tubing, which is easier to
handle.

There seems no differentiation in the literature
between static & dynamic vacuum systems, and
understandably the dynamic case would need
wide-dia tubing, but for the static system (such
as vacuum distillation) the small tubing seems OK.

Am I wrong?

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Dear Peter Jason:

On Tuesday, November 27, 2018 at 1:54:42 PM UTC-7, Peter Jason wrote:

I have a rotary oil vacuum pump in the laboratory.

Everybody says all connections to & from this pump
must in tubing of large diameter.

But I get results from 6mm OD thick-walled
silicone medical tubing, which is easier to
handle.

There seems no differentiation in the literature
between static & dynamic vacuum systems, and
understandably the dynamic case would need
wide-dia tubing, but for the static system (such
as vacuum distillation) the small tubing seems OK.

Am I wrong?

What kind of vacuum are you trying to hit? Vacuum distillation can be done to remove zinc from brass, and you can imagine this is VERY low pressure.

The ID of the piping limits how fast you hit the lowest possible pressure, including "eternity", as compared to connecting the vacuum pump directly to the vessel. These tubes do not "direct" atoms / molecules towards the pump, they simply contain them,
bouncing them in essentially random directions. Larger diameter (essentially) lets them bounce fewer times before encountering the vacuum pump inlet.

Also, with high vaporization rates, smaller diameter tubing will limit getting / sustaining a high vaporization rate, since the tubing will throttle mass flow rate. But you indicate THIS is not the issue, and this also serves to control / limit
vaporization rate, someone one might control with a valve or controlling the vacuum pump speed.

David A. Smith

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On Tue, 27 Nov 2018 13:53:54 -0800 (PST), dlzc
<dlzc1@cox.net> wrote:

Dear Peter Jason:

On Tuesday, November 27, 2018 at 1:54:42 PM UTC-7, Peter Jason wrote:

I have a rotary oil vacuum pump in the laboratory.

Everybody says all connections to & from this pump
must in tubing of large diameter.

But I get results from 6mm OD thick-walled
silicone medical tubing, which is easier to
handle.

There seems no differentiation in the literature
between static & dynamic vacuum systems, and
understandably the dynamic case would need
wide-dia tubing, but for the static system (such
as vacuum distillation) the small tubing seems OK.

Am I wrong?

What kind of vacuum are you trying to hit? Vacuum distillation can be done to remove zinc from brass, and you can imagine this is VERY low pressure.

The ID of the piping limits how fast you hit the lowest possible pressure, including "eternity", as compared to connecting the vacuum pump directly to the vessel. These tubes do not "direct" atoms / molecules towards the pump, they simply contain them,

bouncing them in essentially random directions. Larger diameter (essentially) lets them bounce fewer times before encountering the vacuum pump inlet.

Also, with high vaporization rates, smaller diameter tubing will limit getting / sustaining a high vaporization rate, since the tubing will throttle mass flow rate. But you indicate THIS is not the issue, and this also serves to control / limit

vaporization rate, someone one might control with a valve or controlling the vacuum pump speed.

David A. Smith

Thanks, this is the setup...
https://postimg.cc/v1CXHBZ1
The vacuum gets down to about 1mm Hg and the
distillate comes over at about 200cc/hr. It does
work because I've tested it with known liquids.
The silicone tubing is very convenient because it
is very flexible. Would wider-bore tubing make
any difference in this case?
P

By the way, could a super vacuum remove plastic
insulation from copper wiring, at an elevated
temperature?

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Dear Peter Jason:

On Tuesday, November 27, 2018 at 4:17:01 PM UTC-7, Peter Jason wrote:
...

Thanks, this is the setup...
https://postimg.cc/v1CXHBZ1
The vacuum gets down to about 1mm Hg and the
distillate comes over at about 200cc/hr. It does
work because I've tested it with known liquids.

It isn't a matter of working, it is how fast is it working? If "fast enough", then you need do nothing more.

The silicone tubing is very convenient because it
is very flexible. Would wider-bore tubing make
any difference in this case?

Might allow you to double or triple the cc/hr flow rate, if the pump can handle it. This might spray whatever solids are left behind all over the inside of your containment, or it might just save you power and time.

...

By the way, could a super vacuum remove plastic
insulation from copper wiring, at an elevated
temperature?

Depends on the "plastic". Many have no particular liquid or vapor state, without chemical breakdown (probably leaving carbon on the copper). Many have been highly crosslinked using electron beams, for high abrasion applications, and then they too will
leave carbon fines behind. Get some teflon insulation in there, and your vacuum pump may go away (or may not).

I have to say, I have done none of this, so proceed with a white cane with a red tip (so carefully, to reduce damage to you and equipment. Remember, if you succeed in vaporizing the insulation, this stuff will congeal in the outlet stream from your
vacuum pump, if not in the pump itself. So maybe you want an intermediate chamber, with a large cold body, onto which the "plastic" can plate itself off, and not on the interior of your vacuum pump (or your lungs).

David A. Smith

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