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  1. #16
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    Quote Originally Posted by doug3030 View Post
    I hope the "smily" means you don't accept her point of view on this. I enjoy the time I spend with my girlfriend, kids and grandkids, but the time I have for myself is very valuable.
    SWMBO only says that because I'm retired and she is still working.

    In the model in my mind, as the impeller spins it forces the air outwards, but it only exits the impeller housing where the exit port is. The air that cant exit because there is no opening for most of the travel of the impeller would be building up some pressure towards the outside of the impeller housing.This would create a pressure that may impact on air entering through the inlet. The closer the impeller blades are to the housing walls the less air or pressure can come back to slow air entering the inlet. I reasoned that by rounding the inside of the inlet that increased the space between the impeller blades and the housing wall. leaving it square means the gap is as narrow as possible for as long as possible.
    Optimum flow will be trade off between the pressure loss you describe and feeding the impeller enough air so it does not create spaces internally that are too negative pressured. Ideally the impeller should perform all its work on creating a significantly greater pressure that the atmosphere as it is this what ultimately drives the air through the system. Typically the volume in the middle of the impeller is not pressurised but under the same pressure as the incoming air.

    Have a look at this typical pressure diagram for these types of impellers.
    See Ventilatorenfabrik Oelde GmbH: Computational Fluid Dynamics for fans and plants
    The Generic 2HP DC-impeller-jpg

    The pressure at the start of the blades have tinges of blue indicating that they are under a greater vacuum than the middle volume. So easing the inlet of the air so it can negate this pressure is worth doing. Advanced turbo designs and impellers all use this curved intake idea. Ideally the impeller blades are much taller in the middle to close up the gap between the intake housing and the blades which improves things even more. There are some nice diagrams in this article http://www.netl.doe.gov/technologies...dial_inlet.pdf

    I was even considering letting the end of the 6" PVC pipe protrude maybe 1/4" past the mounting plate to form a lip to further restrict the effect of this back pressure and get the incoming air a bit closer to the low pressure area created in the centre of the impeller.
    This would create a negative volume behind the ring which would add drag to the incoming air.

    I was a bit hesitant about doing that because I do not have a means of measuring the current, (but I might have to get one if the cost is not prohibitive for the small amount of use I would have for it) and if it was too efficient it might have overloaded the motor. Having seen the results of more air being used with less power drawn above, I am not so certain of that now anyway .
    Do you mean electrical current?

    [QUOTE]Absolutely identical to the specs on your motor Bob, 240v 7.7a 2hp.[QUOTE]
    thanks - all of the ones I saw used the same motor. I have seen this design on some older models that used 1.5 HP (well that is what it said on the motor name plate)

    One difference between your impeller housing and mine is the spacing between the impeller and the outside of the housing wall. they both start out narrow just past the exit port and get wider and wider as it goes round to the other side of the exit port, but yours seems to start out a lot closer to the wall than mine. Probably just different versions of the same thing, or someone copied one from the other at some time and did not have precise measurements. I doubt anyone made several and tested the difference.
    Yeah I don't imagine the naufacturing tolerances on these would be that reproducible.
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  3. #17
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    Bob, that's why the "solved" was in in comma's. I still have free floating dust thru the shed, especially when sanding on the lathe, big gulp as close to the work piece as possible, aiming the rotary sander towards the big gulp and with fans at my back, air cleaner on and extraction fan in the roof.

    So yes I am interested in improving capture at the source and improving air flow, thus looking at this and other related threads of yours. Keep going, I am trying to decide on a solid dust collection and after this last thread leaning towards a total remake of my DC system to 6", especially my separator.
    Pat
    Work is a necessary evil to be avoided. Mark Twain

  4. #18
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    OK I did the tests, and broke my more sensitive anemometer in the middle of doing the first one ! DANG !
    My own fault, I precariously balanced the test duct on a stack of timber but the duct rolled bending and breaking the telescopic arm with the air flow meter sensor or it.
    The sensor appeared OK and testing it against another anemometer showed it to be the case. I will test it the sensor against the pitot tube which is a calibrated dooberry.

    Here are the results

    With 6" take and 5" outlets and bags all connected
    Quick and dirty measurement was 680 cfm, full test was 669 cfm

    With 6" intake and all outlets and bags removed
    Q&D measurement was 1060 cfm, full test was 1008 cfm

    Here are the air speed profiles.
    Using a single air speed measurement in the middle of the pipe will give 1400 CFM but that is not right most of the CFM is carried at the lower speeds at the sides of the pipe. The non-smoothness of the data is almost certainly due to not collecting sufficient data but there is more than enough data to get a reliable answer to better than +/- 10%
    The Generic 2HP DC-airspeedprofilefor2hp6in-jpg
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  5. #19
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    Quote Originally Posted by BobL View Post
    Have a look at this typical pressure diagram for these types of impellers.
    See Ventilatorenfabrik Oelde GmbH: Computational Fluid Dynamics for fans and plants
    Great article a lot of which is too deep for my needs but there are two videos near the end of the article:

    - Video: Flow line diagram of the fan

    - Video: Pressure distribution inside the fan

    I highly recommend everyone access that article and if nothing else, watch those two very short videos.

    These videos show that the maximum flow and pressure AFTER the exiting the impeller occurs some distance down the exit ducting. This is where these dusties are choked down into a 5" flexy on a 90 degree curve. It would probably make more sense to widen the ducting at that point rather than narrow it. I might make my short piece of rectangular ducting

    Quote Originally Posted by BobL View Post
    Do you mean electrical current?
    Yes
    I got sick of sitting around doing nothing - so I took up meditation.

  6. #20
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    Quote Originally Posted by doug3030 View Post
    Great article a lot of which is too deep for my needs but there are two videos near the end of the article:

    - Video: Flow line diagram of the fan

    - Video: Pressure distribution inside the fan

    I highly recommend everyone access that article and if nothing else, watch those two very short videos.

    These videos show that the maximum flow and pressure AFTER the exiting the impeller occurs some distance down the exit ducting. This is where these dusties are choked down into a 5" flexy on a 90 degree curve. It would probably make more sense to widen the ducting at that point rather than narrow it. I might make my short piece of rectangular ducting
    I agree the vids are very good - I have seen similar ones where I used to work.

    This is a minor point but In a woodworking DC the pressure changes are so low that there is no significant change in the density of the air inside a flowing system, so the flow is pretty much the same everywhere in any pressurised flowing part of single duct. In a system with a 6" inlet pipe, a large blue or orange box, and a 5" pipe in series it doesn't matter what the pressures are in any single component they will all still have the same CFM- they have to otherwise there would be violation of the conservation of mass. The fact that an impeller generates a higher pressure point some way down the ducting inside a small pipe is not that significant. If the 6" and 5" pipes were swapped around the 5" would still act as the bottle neck.

    OTOH the 5" is definitely the second major bottleneck after the 4.5" intake on these systems and is worth getting replacing with something bigger. As I have posted before, for those that still want to use bags it would be better if the impeller was connected direct to the bag housing. I will explore a way to do this if the impeller generates a decent pressure/flow curve.

    BTW the 1000 cfm going down that big (225 mm) test pipe was a little disconcerting. I had the air speed probe poking through the side of the test dust and to continually check the probe was oriented correctly into the air flow so I had to continually look down the pipe with a torch. Of course I left the DC running and at one point I left the torch a little too close to the test pipe inlet and the torch started to roll towards the inlet but I managed to grab it before it went down the pipe. Everyone should note that these tests are being done WITHOUT an impeller guard and should bear the consequences there of if they have any problems with this.


    RE: Current measurement.
    Yes
    For $8 delivered on ebay I use these because I want to know what is going on in my 15A circuits, but for not much more you can get a power meter (eg they were $15 on special at Aldi and Zazz does one for $20) which display current etc.

    They are usually only good to a reading of the nearest 100 mA but that will get you quite far.

  7. #21
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    Default 2HP DC upgrade

    During last week I made an adapter/flange that looks like this.

    The Generic 2HP DC-flangeadapter-jpg


    and a motor/impeller stand that looks like this

    The Generic 2HP DC-stand-jpg



    These items, together with the modification to the impeller entrance to accept 6" ducting shown in post # 9 in this thread makes a generic 2HP DC looks like this.
    The Generic 2HP DC-combo2-jpg



    The black metal stand is made of 6 mm thick scrap steel plates, and the upright post is a piece of scrap 50 x 50 x 3 mm SHS, all welded together.
    The holes in the base of the stand are drilled such that it uses the existing holes in base of the DC.


    The adaptor flange bolts straight onto the existing holes of the impeller outlet and attaches to the bag/filter housing via a 300 mm long arc.
    A rectangular hole needs to be cut into the filter/bag housing which take minutes with an angle grinder and a thin kerf cutting wheel.
    The Generic 2HP DC-hole-jpg


    I made the adaptor out of 2 mm thick steel plate because I had some laying around
    The plate was copper and then chromium plated and even though I ground away the plating it was a right PITA to weld giving off lots of fumes so lucky I have a fume hood to weld under.

    A couple of more shots of the combo

    The Generic 2HP DC-joinedup-jpg
    The Generic 2HP DC-joinedup2-jpg
    The Generic 2HP DC-joinedup3-jpg



    In terms of motor impeller orientation I chose the option of having the motor below the impeller as opposed to the motor being above the impeller.
    I did this mainly because when I mocked it all up with the motor above the impeller it required a more complex stand to connect to the motor and it also seemed like it would be really easy to tip the whole DC over.
    The orientation I used also leaves the original 5" duct inlet on the filter/bag housing untouched (although it still has to be blocked off) so that if for whatever any reason the DC could be more easily restored to its original state.
    I have no idea why anyone would want to return it to it's original state but I guess it always remains a possibility.

    I blocked off the 5" duct ope inlet using some galvanised steel sheet and a half dozen rivets and added sealant to the sheet before riveting it on.
    The Generic 2HP DC-holepatch-jpg



    Installing the Impeller above the motor makes the whole DC a bit more stable but then the ducting then has to be connected to the impeller at the top.
    This requires a 180º ducting turn to bring the ducting back down to floor level - if a wide enough radius is used this is not a big deal but it will remain awkward to do things this way

    The orientation I chose suits a DC being used in a fixed ducting format and ducting needs to go upwards to an overhead trunk line.
    However, if the DC is being used next to a machine it would be better if the motor was on top, so the ducting would come out underneath and could the connect directly to that machine.
    Also if the DC is up against a wall then stability would be less of an issue so having the motor on top is probably better
    If the DC has to be moved around a shed an stability is important the motor on the bottom is safer.

    I also explored the possibility of the motor horizontal but this requires a more complex flange/transition as well as placing the motor higher up than the way I installed it..

    So - how does it work?

    Well you will have to wait until tomorrow to find out.

    Back to TOC

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    Last edited by BobL; 5th March 2020 at 01:50 PM.

  8. #22
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    I like it Bob.

    The intake is now "bored out" to the full 6" and the outlet is as big as it can be with the choke point being the manufactured impeller outlet. Your interface that you made widens out into the collector straight away, minimising any choke effect of the outlet being marginally smaller than the intake.

    I am looking forward to tomorrow to see what results you get, particularly how much air it can move now and what amps it is pulling to make sure the motor is not overloaded with the (hopefully) increased air flow.

    Cheers

    Doug
    I got sick of sitting around doing nothing - so I took up meditation.

  9. #23
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    Quote Originally Posted by doug3030 View Post
    I like it Bob.

    The intake is now "bored out" to the full 6" and the outlet is as big as it can be with the choke point being the manufactured impeller outlet. Your interface that you made widens out into the collector straight away, minimising any choke effect of the outlet being marginally smaller than the intake.

    I am looking forward to tomorrow to see what results you get, particularly how much air it can move now and what amps it is pulling to make sure the motor is not overloaded with the (hopefully) increased air flow.

    Cheers

    Doug
    Yep - it is now as bored out as it can be.
    I don't reckon the choke point is the impeller inlet, I reckon it's the impeller itself.
    There are two choices - bigger impeller (will need a bigger motor) or spin impeller faster ie 3 phase with VSD.

  10. #24
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    Quote Originally Posted by BobL View Post
    I don't reckon the choke point is the impeller inlet, I reckon it's the impeller itself.
    There are two choices - bigger impeller (will need a bigger motor) or spin impeller faster ie 3 phase with VSD.
    Thanks Bob,

    I actually said "outlet" not "inlet" since if the dimensions on your machine are the same as mine, your outlet is now about 3 square inches smaller than you inlet. But it is better shaped to take the output than a 6" round outlet so it probably isn't really a choke point in practice.

    As to the impeller and motor being the limiting factors at this point, there are many of us whose circumstances do not permit use of a 3hp motor, which therefore prevents use of a larger impeller, are hanging out for an answer on what the performance figures are now. We cant change these factors anyway but I for one am keen to see just what improvement you can make by widening out the intake and outlet.

    I will still be mounting my 2hp impeller on top of my home-made cyclone, which is a project I managed to restart after a long hiatus, having recovered some shed-space. I will be back at work tomorrow after a week and a half on holiday but I hope to continue on with the cyclone modification through the week on the evenings and hopefully will have some photos to post in a week or so. I keep forgetting to take progress pictures. Too keen to do what I can when I can to stop occasionally and record the milestones.

    Cheers

    Doug
    I got sick of sitting around doing nothing - so I took up meditation.

  11. #25
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    Quote Originally Posted by doug3030 View Post
    I actually said "outlet" not "inlet" since if the dimensions on your machine are the same as mine, your outlet is now about 3 square inches smaller than you inlet.
    But it is better shaped to take the output than a 6" round outlet so it probably isn't really a choke point in practice.[/QUOTE]Good point and I agree.

    As to the impeller and motor being the limiting factors at this point, there are many of us whose circumstances do not permit use of a 3hp motor, which therefore prevents use of a larger impeller, are hanging out for an answer on what the performance figures are now. We cant change these factors anyway but I for one am keen to see just what improvement you can make by widening out the intake and outlet.
    Maybe not for the faint hearted but more for an entrepreneurial manufacturer, a 2HP 3Phase motor with a VSD should be able to at least spin the impeller a bit faster and still stay within the 10A limit of a standard GPO.

    I keep forgetting to take progress pictures. Too keen to do what I can when I can to stop occasionally and record the milestones.
    Yeah I'm the same. It's only fortuitous that I was interrupted so often during this project that I had time to take pics. I had to stop fabbing several times last week to deal with a HWS debacle, then last friday I went to a blacksmithing course over the weekend, then when I came back on Sunday arvo I was too shagged to keep working on it. Most of yesterday was taken up by taking 87 year old MIL and friend to the cruise ship in Freo - this involves a 60 km drive to pick up, lunch and non-stop gossiping till we had them on board - took all bloody day...... I only got back onto it at 3pm yesterday. Anyway at least i remembered to take some pics.

  12. #26
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    OK , lots f distractions,
    - breakfast with SWMBO,
    - a much needed walk for the dogs
    - tried to fix broken dishwasher (failed - call the serviceman)
    - then SWMBO new lapidary gear arrived and we had to set that up
    - finally got around to start testing and Washing machine dies (ignore and leave it)
    ARRRGGH!!!! @%#$^!

    OK now to cut to the chase.

    Firstly I discovered a leak in the 6" inlet I made a couple of weeks back. The inlet was made with lighter gauge steel plate than the original so it did not clamp down firmly enough on the impeller housing. I fixed the leas with a bit of Silastic and lo-and-behold the static pressure increased from 7.5 to to 8.1" which is what these are nominally rated for. That is of course effectively for the impeller alone.

    The current being drawn has increased to 5.7A or 1.82 HP and one thing I noticed is it takes more than 5 seconds for the current being drawn to settle to less than 10A. This is more than enough to trip a 10A expander board circuit breaker so the modified unit MUST be connected directly to a GPO.

    In terms of air flow the result is 1112 CFM! which is almost exactly what it should be theoretically for an unrestricted 6" pipe at 8.1" of WC.

    I am very happy with this improvement. I reckon this is about the best this impeller motor combo can do.

    Adding the bags (one plastic and one new needle felt) kills the flow somewhat with the flow rate dropping to 839 cfm.
    Working backwards this means the needlefelt bag used on the Timbecon verson sucks up 3.5" of WC which is indicative of a cheap bag.

    Still, the ~50% improvement from 567 CFM for the 4.5" constricted inlet stock item, is well worth it.
    According to BP replacing these bags with a basic cyclone or chip collector will drop 4.5" so it will probably fair no better than this bag and maybe even worse.
    A BP designed cyclone will drop 2.25" and so should be able to pull over 950 cfm.

    The best thing to do would be to use a large surface area pleasted filter which would only drop 0.5" of WC - of course these figures for bag only applies until they get clogged which is where a quality cyclone will be able to maintain flows.

    Back to TOC
    Last edited by BobL; 5th March 2020 at 01:52 PM.

  13. #27
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    Quote Originally Posted by BobL View Post
    OK , lots f distractions,
    - breakfast with SWMBO,
    - a much needed walk for the dogs
    - tried to fix broken dishwasher (failed - call the serviceman)
    - then SWMBO new lapidary gear arrived and we had to set that up
    - finally got around to start testing and Washing machine dies (ignore and leave it)
    ARRRGGH!!!! @%#$^!
    Jeez Bob, and I thought my day started badly. A hot water pipe burst in our vanity unit while I was in the shower this morning - hot water spraying all round the bathroom, me in the shower with one foot bandaged up standing on one leg trying to keep the bandage dry and having to hop out through the hot spray and wet floor without slipping over.

    Quote Originally Posted by BobL View Post
    The current being drawn has increased to 5.7A or 1.82 HP and one thing I noticed is it takes more than 5 seconds for the current being drawn to settle to less than 10A. This is more than enough to trip a 10A expander board circuit breaker so the modified unit MUST be connected directly to a GPO.

    In terms of air flow the result is 1112 CFM! which is almost exactly what it should be theoretically for an unrestricted 6" pipe at 8.1" of WC.
    It sounds like you have got that little sucker working at peak performance!

    So it runs at 5.7 amps but startup current is over 10 amps for a bit of a while. Did the startup current requirements drop significantly when the bags were added? I would imagine that in actual use with a few metres of ducting and some restricted airflow through a machine in addition to the restriction of the bags (or in my case, the cyclone) that it would not be able to move sufficient air on startup to draw more than 10 amps.

    I think I am going to be very happy with my unit when I get it modified and connected to the cyclone.

    Thanks for doing that experiment, Bob. The results are a big help to me and reassuring that I am on the right track. I am sure that many other forumites will benefit too.

    Cheers!

    Doug
    I got sick of sitting around doing nothing - so I took up meditation.

  14. #28
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    Quote Originally Posted by doug3030 View Post
    Jeez Bob, and I thought my day started badly. A hot water pipe burst in our vanity unit while I was in the shower this morning - hot water spraying all round the bathroom, me in the shower with one foot bandaged up standing on one leg trying to keep the bandage dry and having to hop out through the hot spray and wet floor without slipping over.



    So it runs at 5.7 amps but startup current is over 10 amps for a bit of a while. Did the startup current requirements drop significantly when the bags were added? I would imagine that in actual use with a few metres of ducting and some restricted airflow through a machine in addition to the restriction of the bags (or in my case, the cyclone) that it would not be able to move sufficient air on startup to draw more than 10 amps.
    Same start up current and at least 5 seconds to go below 10A with the bags, but ends up drawing 5.3A

    A standard 10A GPO will handle this (well mine is) but less so depending on what is already on that line (mine just had 2 fluoro tubes on it was well).

  15. #29
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    I'm following the number of "views" on this thread and there have been 119 since yesterday - given this number of views I'm surprised there are not more questions.
    So to anyone out there just lurking and maybe cautious about asking a question please feel free to ask anything about this.

  16. #30
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    Quote Originally Posted by BobL View Post
    Same start up current and at least 5 seconds to go below 10A with the bags, but ends up drawing 5.3A.
    Bob, did you happen to note the startup current used before the modifications? I am just thinking that if the startup current was below 10 amps when the inlet was restricted then maybe those who need to could possibly close a blast gate, start teh machine then open the blast gate or something just to avoid power problems?

    Doug
    I got sick of sitting around doing nothing - so I took up meditation.

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