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  • Vacuum pump connections.

    From Peter Jason@21:1/5 to All on Wed Nov 28 07:54:37 2018
    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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  • From dlzc@21:1/5 to Peter Jason on Tue Nov 27 13:53:54 2018
    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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  • From Peter Jason@21:1/5 to [email protected] on Wed Nov 28 10:16:56 2018
    On Tue, 27 Nov 2018 13:53:54 -0800 (PST), dlzc
    <[email protected]> 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?

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From dlzc@21:1/5 to Peter Jason on Wed Nov 28 06:05:18 2018
    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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