Two dust extractors in parallel

[Midnight Man]

Hi folks, I have done a bit of a search here, but with not much luck, and wondered if I was onto a good or bad idea...

To achieve good extraction, we all read much about the fact that most of the published statistics on the 2hp (and 3hp, and 1hp) units are somewhat... optimistic. And given the level of expertise on the part of posters here, I absolutely believe it.

What I am wondering is simply this... if we want to achieve more airflow at the extraction end of our equipment, why could we not purchase (say) 2 x 2hp dust extractors, and hook these up to run together. So, the first dust extractor is plugged into the very end of the PVC pipe leading into the shed. Next to this, on the shed side, of the first extractor, we join a second extractor using a Y type joint to minimise air turbulence. Would this not significantly increase the rate of air flow through the system? I won't say "double", because I am sure there is the potential for diminishing returns here, but wouldn't we maybe see 1.5 times the extraction of a single unit?

Will be most interested in hearing thoughts on this one, with many thanks!

[BobL]

This has been discussed before, in fact several times.

If you are going to use two DC on the same ducting network you have to run the the DCs in SERIES

However, for a variety of reasons you can only get ~400 CFM through a 100 mm duct and you won't get much more than this (maybe 450 - 500 CFM), even using two DCs. Underthese conditions the ducting will also start to make significant noise.

To be assured of moving twice as much air you need to use two completely separate sets of ducting and a DCs on each set of ducting - this is true Parallel extraction.
However, this is expensive and takes up space

Running 2 DCs in parallel using a single larger ducting (e.g. 150 mm) is fraught with problems as the pumps can end up just fighting each other for the same air/water and this leads to inefficiencies

Then you will also need twice as big a external enclosure to house the DC.

A significant reason many DIY use 2HP DCs is because of power restriction problems but now with 2 of them you need a constant 15A JUST FOR THE DC.

It makes much more sense for smaller DIY situations to use a 3HP DC and a 150 mm ducting and to open up machinery to fully utilise the 150 mm ducting, which requires around 9.3A.

To give you an example of how efficient the BP Cyclone is, it uses a 4HP motor and once running it only needs about the same current as a conventional 3HP DC.

[ian]

hi Bob

as you mention the current draw of 2 x 2hp DCs might easily exceed the current capacity of the shed power supply.
So in a sense I see where you are coming from BUT may I draw some comparisons with fighter jets?
some have a single engine, dual air inlet
and some have a single air inlet and two engines

based on those examples, it should be possible to connect two DCs to one inlet pipe -- the critical element would be the design of the inlet "manifold", and having a large enough pipe supplying air to the DCs.

taking a rough stab at the impact of boundary effects, 2 x 150 mm tubes have approximately the same cross-sectional area and flow rate as one 200 mm tube.

which then leaves the issue of designing a suitable manifold.
the first stab at a manifold design might be a box with 2 x 150 mm bell mouth hoods -- connected independently to each DC -- on the outlet side, with a 200mm BMH on the inlet side. Minimising turbulence within the box might be a challenge though. In this regard, I don't need convincing that a Y-junction would be unsuitable.

so a parallel DC design might look like = Main duct 1 x 200 mm -- manifold -- 2 x 150 mm outlets each connected to the 150 mm inlet of a 2hp DC.

comments?

[Midnight Man]

I am reading with avid interest, thank you to those who have given input!

Very interesting thought you have Ian. A manifold, if large enough, might not actually present a big problem airflow wise... sure, it will need to be large, but I am thinking in terms of an air compressor in reverse here - on an air compressor, we have a pressurised tank to feed the nozzle when we fire the nail gun/trigger/whatever. A large manifold could represent a pool of air ready for the DC's to evacuate, which would simply be replenished by air coming in from the pipes leading to the workshop.

At the end of the day, the point of electricity consumption is a good one, as is the space required. For sure, many have limitations in this regard, but luckily, for other reasons above a workshop, I had tor eplace the power run to my shed, so I planned in advance and with a big of jiggling and patching, I can push 192 amps in there... space out the back (within sanity boundaries) is also not much of an issue, hence me asking :) I had considered a 3Hp dusty, and was looking at the Timbecon unit (https://www.timbecon.com.au/extraction-safety/dust-extractors-filters/3hp-industrial-dust-extractor) - but I have heard it has some... shortcomings. Plus I now also already own a nice 2Hp dusty, and was considering how the system could be expanded without replacing existing equipment.

[tonzeyd]

I've also read somewhere that doing this can fry your motor as you'll be drawing significantly higher currents than what its designed for.

[Lappa]

I'd be interested to know how you are going to get 192 Amps into your shed.
thanks

[BobL]

Comparisons with high pressure systems like compressors and jet engines are unlikely to be useful.
Remember the pressure regime of Dust collectors is only about 1/3rd that of a vacuum cleaner.

It's not wise to go for too big a duct or any sort of reservoir in the line. A reservoir will act like a chip collector and generate added turbulence and stymie flow. Using a 10" duct requires a flow rate of about 2200 CFM to maintain the recommended 4000 FPM linear airspeed to keep sawdust suspended in the air. If you use a 6" feeder ducting the most you will get through that is about half that. If 4" ducting is used it will be around 3X worse.

[BobL]

I had considered a 3Hp dusty, and was looking at the Timbecon unit (https://www.timbecon.com.au/extraction-safety/dust-extractors-filters/3hp-industrial-dust-extractor) - but I have heard it has some... shortcomings. Plus I now also already own a nice 2Hp dusty, and was considering how the system could be expanded without replacing existing equipment.

The 3HP Timbecon unit would be a much better all round bet than any combination of 2 x 2HP DCs.
The 2HP in stock form is not a "nice" machine and has to be modified to let it breathe and even then it's nothing special.. By the time you do the mods to 2 x 2HP machines and tackle the raft of other problems of using 2DCs you'd wish you got the 3HP Timbecon unit.

[BobL]

I've also read somewhere that doing this can fry your motor as you'll be drawing significantly higher currents than what its designed for.
I didn't mean to clock on the "needs pictures" link.

I agree any mod to a DC that is likely to increase the flow should be accompanied by some motor current measurements.

[Midnight Man]

I'd be interested to know how you are going to get 192 Amps into your shed.
thanks

2 x 80 amp circuits plus a backup 32 amp that can be connected if required... or am I missing something?

[ian]

2 x 80 amp circuits plus a backup 32 amp that can be connected if required... or am I missing something?
what you are missing is the current coming into the property from the street.

As far as I know, unless specially upgraded, your supply from the street is limited to something like 60-70 Amps per phase.

so 2 x 80 amp would imply a 2 phase circuit -- but would also assume no current draw anywhere else in the property.

a more likely explanation is that the distance between the house switch board and the shed required that your sparky run a wire with an 80 amp capacity in order for you to have 240 volts in the shed.
The phenomena is known as voltage drop. The following table (based on US 110 volt) gives an indication of how wire size needs to increase (the gauge number gets smaller) to maintain the required voltage as the current draw and length of cable increases. Note how a 12 gauge cable can supply 16-20 amps (at 110 Volts) over a distance of 25 feet (8 metres), but if the distance is increased to 200 feet (60 metres), the same cable can only supply 5-7 amps (at 110 volts).


Extension Cord Length/Amperage/Size Chart for US 110 Volt supply



Extension
cord
length

Amperage Required














25 feet
0-2
amps

16 gauge
2-5
amps

16 gauge
5-7
amps

16 gauge
7-10
amps

16 gauge
10-12
amps

14 gauge
12-15
amps

14 gauge
16-20
amps

12 gauge


50 feet
16 gauge
16 gauge
16 gauge
14 gauge
14 gauge
12 gauge
12 gauge


100 feet
16 gauge
16 gauge
14 gauge
12 gauge
12 gauge
10 gauge
8 gauge


150 feet
16 gauge
14 gauge
12 gauge
12 gauge
10 gauge
8 gauge
–


200 feet
14 gauge
14 gauge
12 gauge
10 gauge
8 gauge
–
–


300 feet
14 gauge
10 gauge
8 gauge
–
–
–
–


400 feet
12 gauge
8 gauge
–
–
–
–
–


500 feet
12 gauge
8 gauge
–
–
–
–
–

[tonzeyd]

The timbecon 3hp unit is around $1k, assuming you're purchasing new 2, 2hp units will cost you $658, plus whatever materials to modify the smaller DC's to maximise their performance. Plus the 3hp dust collector has 2 very large filter bags which would further improve flow. You may be financially better off by at most a couple of hundred at most.

If you had sufficient space and keen on going down your route ie with the two dusties. I'd probably be inclined to run two separate systems rather than trying to run them in series/parallel. This way it'll allow you to reduce your runs, potentially minimise amount of ductwork required.

Having said that I'd still prefer to have the one system. I originally went down the 2hp dusty and after a while ended up upgrading to a 3hp dusty. Having a spare 2hp dusty is actually quite handy, particularly for times when you're setting up a workshop and not everything is plumbed to the main DC or have been working outside. I know its not its intended usage but its also very good at sucking up/mulching dried leaves.

[Dibbers]

I know nothing about modifying DCs or airflow rates etc, and this may be overly simplistic, but it you don't want to shell out for a 3hp unit, why not buy a 2nd 2hp unit and run them both separately...

So run the ducts of one dusty into machines A,B & C, and the other dusty is ducted into machines X, Y & Z?

I understand the level of curiosity in frankensteining (i love doing that myself), but i think in this instance it's probably over complicating things. Unless multiple machines are being run at the same time, you'd only ever need to have one DC running at a time so negates the power supply issue too...

Thats just a perspective from someone still starting out though... so feel free to ignore. I won't be offended :U

[BobL]

I originally started with a 1HP, then a 2HP, and finally I realised I knew stuff about dust and air flows from my day job that I could apply to wood dust, and only then did I go for a 3HP DC and 6" ducting

I agree with Tonzeyd, if you have 2 x 2HP DCs use them as two separate systems especially in a large shed to reduce ducting runs. Having a spare 2HP DC is very useful at the mens shed for machines that are used outside.

[Midnight Man]

Many thanks for all the good ideas and advice - it's truly appreciated (and by all means, the discussion should continue if needed), but it sounds like my idea - putting it simple - wasn't a good one, and I'm glad to know this, as it'll save a lot of mucking about!

Essentially, then, I will use what I have now, in a mobile fashion (this is actually what I had planned to do in the first place), and then see what the requirements are once everything is set up and in it's place :)

Cheers all, and many thanks!

[pjt]

Fans/pumps in series and parallel are both a done thing, at the textile factory we made the air conditioning units with 3 fans in parallel, this is not an uncommon thing to do if you want to increase output flow, in a large (industrial) chook shed it's not too unusual to see the end wall completely filled with fans, this is multiple fans in parallel, the shed itself forms a plenum chamber, the important thing to consider is allowing airflow into the plenum, any restriction will impact on the potential total flow, for e.g. a 100mm main which fed into a 100mm y that connected to each of the 100mm inlets of the 2hp DCs, that exercise would be a complete waste of time if the aim was to 2x the flow, your main has to be large enough to allow max flow into each 100mm legs of the y, further good design would be a low angle between each leg, 15 is better than 30 is better than 45 etc. and symmetry.
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1st pic fans in para, we put 3 fans in a plenum as depicted at the textile factory, note that above the dashed line (high restriction) not a lot of flow increase, could even be less flow than one fan! but keep the restriction low and potential for good flow,
3rd pic gives an indication of what happens with flow restriction,
4th is the inside view of my thicknesser outlet, this is a twin outlet and this will flow much more than a single of same size, note the symetry and a smooth transition from square to round, if (in operation) I remove a hose off one leg, air will flow into the now open outlet, this is an indication that airflow thru the machine offers more restriction than flow reversal and a sharp 180° bend, (fans fighting for air that Bob alludes to) however with both hoses in place my fan is able to produce enough pressure to overcome restriction thru the machine and the net result (of the twin hose setup) is more flow thru the machine,
4th is a 200mm main (to the left unseen) 118mm on the top side, 125 btm side, ok not symetrical but re-made for a modification for this application, 15° between each leg.

Pete