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  1. #76
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    Mr Thumbsucker,

    thanks for that suggestion. when I bought the pump the supplier suggested if I didn't want to spend the $$ on a vacuum filter to 'just go to Supacheap and get a Ryco fuel filter, then throw it away when it gets clogged', so yours looks like a similar (but more elegant) approach. And about 1/4 the price of that filter, from Bunnies. Also, with the aluminium housing, more robust than a ryco fuel filter option.
    The only issue I would have is the tubing restriction. I'm planning on building an autocycling solution (similar to joewoodworker.com), but with digital pressure gauge (as per vacupress). Putting a filter with a 6mm outlet right at the pump, before the manifold might be a little restrictive. I guess I can check ebay for any other similar filter with larger entry/exit orifices.

    elan - that's my problem. I can see max pressure ratings, but nothing listed for minimum, and with the filter having negative pressure I'm wondering if it'd collapse, as isn't necessarily rated for that.

    my system will look a lot like this:
    http://www.joewoodworker.com/veneeri...rmbruster2.jpg

    Thinking about it further, the filter is on the pump side of the solenoid, which unloads the pump when it is switched off (so the next cycle lets the pump start under normal atmospheric pressure, as the pump isn't rated to start under vacuum). So the only time there will be negative pressure exerted on the filter will be during the cycle to re-vacuum the system till it hits the cutoff level (around 25mm Hg). So it'd be relatively short burst of negative pressure. But still, I'd hate to see it collapse when the pump runs. Hopefully if it did, it'd be the polycabonate housing, and with any luck it wouldn't enter and foul the pump.

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  3. #77
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    Quote Originally Posted by TimberNut View Post
    The only issue I would have is the tubing restriction. I'm planning on building an autocycling solution
    The size of the tubing is only important when you have significant air flow. The amount of air being moved during autocycling is actually quite small and even during the initial pulldown any restriction due to tubing will only extend the time it takes by seconds.

  4. #78
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    Quote Originally Posted by TimberNut View Post
    elan - that's my problem. I can see max pressure ratings, but nothing listed for minimum, and with the filter having negative pressure I'm wondering if it'd collapse, as isn't necessarily rated for that.
    It won't have negative pressure if you have the compressor end of the filter at the bag end of the line. The bag, being the high pressure side of the system, is just a 14PSI (and falling) compressor to the vacuum pump. Just keep the high pressure end of the filter at the high pressure end of the system

    EDIT: I should also add that negative pressure in the bag is only relative to the ambient pressure outside the bag. Absolute negative pressure isn't a thing; zero pressure is a pure vacuum and you can't have less than that.

  5. #79
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    Elan, I'm not quite following your logic here. Please see attached (bodgy ) diagram.

    In a compressor, when the tool attached is in use, high pressure air flows from the compressor tank, through the regulator, and then filter, and then to the tool. During this phase, high pressure air pushes outwards on the walls of the filter, as it it filled by the air being forced through it.

    In the 2nd diagram, which is how mine will work, the filter will be directly attached to the pump. When the pump turns on, to evacuate the system, it will pull air through the filter (rather than pushing, as per compressor). So in effect it is pulling air out of the filter, reducing the pressure in it, rather than increasing it. This the opposite of what happens with an air compressor setup.

    So, as I see it, the filter is rated to accommodate increased pressure pushing out on the glass walls, but when you are evacuating air through it, doesn't that create a lower pressure in the filter? I don't know what the filter is capable of handling when we are seeing pressures below atmospheric, so isn't there a risk of the walls collapsing if it got too low?

    diagram.jpg

  6. #80
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    Quote Originally Posted by TimberNut View Post
    In the 2nd diagram, which is how mine will work, the filter will be directly attached to the pump. When the pump turns on, to evacuate the system, it will pull air through the filter (rather than pushing, as per compressor). So in effect it is pulling air out of the filter, reducing the pressure in it, rather than increasing it. This the opposite of what happens with an air compressor setup.
    Right, time for some physics. Suction doesn't exist: air is always pushed from high pressure to low pressure. What your vacuum pump (or vacuum cleaner, or dust extractor) is doing is pushing air out of itself, creating an area of low pressure inside. The higher pressure outside the vacuum chamber will push air back in until the pressure is the same inside and out, or until the supply of higher pressure air is depleted, because physics dictates that things flow from a high-energy state to a low-energy state (this is also the reason that "cold" doesn't actually exist, it's simply the lack of heat). With a vacuum cleaner, there's no limit to the air supply, so it just keeps getting more air shoved back in, along with any particles that are in the way. Since the pump is acting on a sealed bag with a fixed amount of air, the atmospheric pressure outside the bag forces the bag to collapse as it pushes the air out of the bag and into the low-pressure area in the vacuum pump until there is no air left in the bag.

    Video here might explain it better than me https://www.youtube.com/watch?v=dkkDiTsEnec

    So, as I see it, the filter is rated to accommodate increased pressure pushing out on the glass walls, but when you are evacuating air through it, doesn't that create a lower pressure in the filter? I don't know what the filter is capable of handling when we are seeing pressures below atmospheric, so isn't there a risk of the walls collapsing if it got too low?
    In a word, no. The air will still move through the filter in the same direction as it would with a compressor, as there will still be a higher pressure on the inlet than the outlet until all the air is out of the bag and both sides of the filter are at equal pressure. Every pressure vessel is capable of handling vacuum. The absolute greatest pressure possible on the outside of a vacuum chamber is 1 atmosphere, or 14.7psi, because it's the difference between the inside and the outside. If it can handle 150psi pushing one way, it can handle 10% of that pushing the other way.

  7. #81
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    excellent! That makes perfect sense. The biggest force applied will be 1 atmosphere or 14.7 PSI. Sweet! now I don't have to worry about it possibly breaking and being ingested into my shiny new vacuum pump. Thanks for the info.

  8. #82
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    Most filters have a designated inlet and outlet port. On pleated paper filters this is critical as there is generally a paper trap built into the outlet end so if the paper filter breaks down, paper particles will get trapped in the filter and not pass into whatever is attached to the outlet end.
    On some filters, it’s to do with surface areas - the inlet is connected to the filters largest surface area.

    So, if I was connecting an air compressor filter to a vacuum pump to prevent glue etc entering the pump from the bag, I would connect the filter inlet to the vacuum bag and the filter outlet to the vacuum pump.
    We use filters connected this way on the air conditioning gas recovery units in case someone’s put sealer in the vehicle AC system. Simply put, it’s in the direction the air or liquid is flowing.

  9. #83
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    Quote Originally Posted by Lappa View Post
    On some filters, it’s to do with surface areas - the inlet is connected to the filters largest surface area.
    Huh? How can a filter have one side larger than the other?

  10. #84
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    Coned and some cylindrical sintered filters generally have a larger outside surface area. Also multilayer paper filters with the inside diameter therefore surface area much smaller than the outside layer and surface area. Carbon block water filters to name a few.

  11. #85
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    If we use an ordinary purifier equipment with normal filter bags, we might simply be "rearranging the dust and dirt". The cleaner would trap some of the dust inside the bag or cyclone filter. The rest is passed straight into the room. If the exhausting air is not properly filtered, the dirt and dust could end up in the human lungs. For a HEPA (High-Efficiency Particulate Air) filter in a vacuum cleaner to be effective, the vacuum cleaner must be drafted so that all the air drawn into the machine is ejected through the filter, with none of the particles leaking around it. Air purifiers equipped with HEPA filters offer numerous benefits including the removal of bacteria and microorganisms. The HEPA filtration for heavy industrial vacuums is 99.99% efficient, down to and including 0.3 microns.

  12. #86
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    I've finally finished building my setup. for those interested I've started my own thread, outlining all the learnings along the way, and will include pics of the setup

    Auto-cycling vacuum pump for vaccum bagging veneers and vacuum clamping.

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