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Thread: Plumbed in DX - minimum ft3/m ?

  1. #1

    Plumbed in DX - minimum ft3/m ?

    Hi

    I have a 4" dust extractor as well as my Festool Mini vac. It's not, I don't suppose, designed for a plumbed in system...but I would like to make it work for me in this way and am asking if you guys can tell me what the minimum air flow is for a plumbed in system? I would only ever have one tool running at any one time (the electricity wouldn't take it for one thing and for another there's only me at work!).

    The DX I have boasts 50L/s or 106ft3/m or 180m3/h.

    Is that going to be powerful enough? I would use blast gates.

    Thanks!!

  2. #2
    Have I asked a silly question?

  3. #3
    Join Date
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    Hi Hector. Not a silly question, but perhaps one that could draw answers from a number of different perspectives.

    106 cfm (cubic feet/minute) sounds more like the sort of airflow a vacuum might deliver. That's not going to be enough to do a proper job of collecting dust from a floor machine like say a jointer, never mind if it loses some more by extending the hose. It wouldn't create a fast enough air flow in a 4in duct to transport chips properly either - that takes something like 4,000ft/min to get up a vertical, or at least 3,500. Say 400cfm for that duct size - although by some standards that's enough to collect chips, but not enough to do a great job on pulling in fine dust thrown from the cutter.

    What sort of tools/machines do you want to collect from?

    Vacuums are normally used on hand tools with tight dust shrouds that don't need a lot of air flow. They generate quite a lot more suction than a typical low pressure dust system though, and so can function with a smaller hose.

    There may be scope to do something with the 4in extractor - depending on what cfm at what pressure (usually measured in inches of water gauge) it can deliver. Some of these 4in units claim numbers that are not very achievable in reality though, while others like the Record Power units sold in the UK move quite a lot of air because they go to higher pressures than a typical low pressure unit.

    The lower cfm and pressure 4in units will struggle to run any sort of ducted system - even one floor machine at a time. It's probably better with that sort of unit and requirement to do what you can to improve the dust and chip collection by maximising the suction and cfm you get - by keeping them mobile and located close beside whichever machine you want to use, and running the shortest hose possible. (as much less than 10ft as you can manage)

    The issue with installing a ducted system is that it normally requires that you collect dust and chips through a longer run of pipe than is the case with a mobile unit with a short flexible hose. This means that the pressure drop or suction the blower has to deliver increases relative to a shorter hose/duct set up to maintain the same flow. (bearing in my though that flexible hose causes about 3 times the pressure drop per distance run than ducting. Remember too that bends and restrictions greatly increase the pressure drop too - one 90 deg bend alone is equivalent to maybe 8 - 12 ft of straight duct depending on the flows)

    This means that any blower has to be able to generate enough pressure drop/suction to overcome this resistance if it's to deliver enough airflow. Meaning that if a 4in unit is already at the lower end in terms of cfm and pressure capability then it's probably going to struggle to do even a very basic chip collection job through ducting.

    Can you provide a bit more information on the dust extractor? Make, model and type? The full load amps number listed on the motor plate is a good indication of capability, but maybe the maker specifies cfm and pressure drop numbers too???

    ian
    Last edited by ian maybury; 01-06-2012 at 7:43 PM.

  4. #4
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    Are you talking about making a fixed plumbing system for the vacuum that you will use with hand or benchtop power tools? If so it certainly can work as many have done it. Some of the much cheaper large shop vacs actually have higher CFM and can be a better basis for this type of system and you can enclose it so you don't hear it screaming.
    Of all the laws Brandolini's may be the most universally true.

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  5. #5
    Thanks for the fantastic reply. I was also amazed that the extractor is rated for so low an airflow. It is designed to be a chip extractor. It is rated at 50L/S and I made the conversion to 106ft3/m myself. Perhaps I have made an error because it clears chips from my bandsaw, router table, planer/thicknesser and table saw with ease. On an individual basis, of course.

    It's this one.
    Last edited by Hector M Torvisque; 01-09-2012 at 7:42 AM.

  6. #6
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    The 106 cfm number seems to tie with their specification, but it's hard to know as there's a typo in the manual, and minimal information anyway. There's no pressure capability listed, and no proper description of what sort of applications it's intended for. The 50L is maybe the capacity of the bucket. The 1.1kW is the usual 'input power' that gets quoted to maximise the number, but may be well removed from the actual power produced.

    I don't know the unit Hector, but it seems similar to some of the smaller ones in the Record Power line that I've seen discussed on one of the UK forums. They trade a bit more suction for a bit less CFM/volume - but judging by comments of owners i seem to remember are pretty marginal. (they had a more powerful twin motor model that did better)

    They seem to just about move enough air to do a minimal chip collection job through a short hose on a small machine close by. Filter life is likely to be short too if it's getting much use. The paperwork (as is typical of these sorts of products) is meanwhile very carefully massaged to avoid making any commitment to the unit doing anything much in particular.

    Sorry not to be more encouraging, but it doesn't seem very likely to be able to handle ducting or anything else that would reduce its performance. You could try adding some extra hose length to test what happens..

    ian
    Last edited by ian maybury; 01-09-2012 at 10:06 AM.

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