How do I minimize losses with a flexible pipe based dust collection system?

[James W Glenn]

I have approximately 200 sq-ft of open floor space in my shop and have the majority of my tools on mobile bases. The plan is to have a dust collection system that will allow me to set up the machines in various configurations to preform different processes. For example: breaking down sheet goods, cutting small furniture components, or working on small boats IN the shop. All the machines will be stowed when not use, so I can have some open floor space when desired.

I recently purchased the bones of a 2hp Delta 50-851 dust collector. I am going to ad an internal Thien baffle and a Wynn filter. This machine is rated at 1500cfm, and as it is at least 20% physically larger than the other units I have seen, I have some hope for sufficient power. The machine has an 8" port, and originally had a factory manifold attached with 3 x 4" ports.

I would like to run a 10' leangth of 6 or 8" flex hose to a valved manifold with at least 4 branches of flexible hose approximately 5' long to the machines. The hope is that if the manifold is convenient enough to reach and operate, I will use it for "just one cut"s.



In general, what can I do to minimize losses with this type of system?

I thought running of pipe, but I would end up with 30+ feet of pipe for the main and 10 to 12' for flexible pipe drops from the ceiling. I don't think I would gain much, while loosing flexibility in my tool placement. The other option I can see is to shorten the main line to the manifold, which I will do if it works with tool placement, and or replace more or less of the main line with a rigid boom which would still need flexible pipe on each end and only remove 6 feet of flexible pipe, while limiting placement of the dust collector.

I do have a couple other questions:

Will machine will move enough air to clear an 8" hose?

Would it be possible to run a chip separator right next to the planer as a coarse first stage?

What kind of fittings should I use to minimize additional losses to the flow?

Dose anyone have a good manifold design? Maybe I can build one into a cart that will act as a out-feed and downdraft table?

As always, any guidance or suggestions would be greatly appreciated. Woody

[ian maybury]

I hate to say it, but i think you are probably asking too much of a 2HP system James - and there's little worse than struggling with marginal dust collection.

The baffle/separator, the filter (especially if only a single one), the valves and their associated leakage, bends/the manifold, the use of flex hose and the likelihood that the machines may have restrictive ports (what are they?) further ups the ante. Reading through this by now very well proven set of pages by Bill Pentz might help with some calibration before deciding anything: http://billpentz.com/woodworking/cyclone/dc_basics.cfm

Put simply you need to maintain an airspeed of something like 4,000ft/min in a duct for reliable transportation of heavier chips - this in a 6in duct (i.e so that you get 800CFM plus) if you also want decent clearance of dust from the volume around the work area. Or at least (depending on how lucky you feel) something not too far off.

I'm not familiar with the dust collector, but 2HP is realistically going to run only an 11 or possibly 12in dia impeller. Flex hose is regarded as causing x3 or more times the pressure drop of a smooth duct, and when the effects of everything else are considered it's even possible that you could struggle to get enough airflow to do a decent job of picking up chips. This requires a real world roughly 400CFM +/- a little depending on the machine, and if this is the case then it's unlikely to deliver reliable heavy chip transportation in a duct much larger than 4 - 5in dia.

Lots of especially older dust collectors claimed greatly inflated airflow numbers - which often were achieved by spot testing in highly favourable but not very realistic circumstances. It's not either as though it's possible to magic up more flow by increasing the ducting size beyond a certain point - because if there are restrictions anywhere in the line then the CFM will still be greatly reduced, and the air speed in the big sections likely too slow for reliable transportation. (dust and chips may drop out to cause problems) If the bore is simply very large right through (including machine ports, valves etc) so that the fan is pulling against a lower than normal pressure drop then (apart from delivering relatively low airspeeds) it quite likely could end up drawing more amps than it can handle steady state and burning out the motor.

Methods of estimating this stuff rely on rules of thumb and are a little approximate, but i'd want to at least arrange a realistic trial before proceeding.

I guess the direct way to reduce hose runs and pressure drops to the absolute minimum is to go with a mobile dust collector. (build the fan/separator/bin/filters etc into an assembly on wheels) This would allow you to run with the absolute minimum length of flex hose, and if very short and the rest of the installation very free flowing it might even permit use of a 6in hose. The requirement to hook it up to each machine when needed might not be wildly more inconvenient than what you would have with a manifold either.

It'd need enough space around the machines for access though. Either way stepping up to a fan with a 13x3.25in impeller or thereabouts and a 3HP motor would bump the whole deal to a situation where you were sailing much less close to the wind….

[Art Mann]

There are lots of different kinds of flexible hoses. The ones that are really flexible and compressible like an accordion are much worse for air flow than the stiffer, smoother surface hoses. You only have 2 hp and that is the limiting factor. That much horsepower will not maintain adequate velocity in an 8 inch pipe and you may have sawdust settling in the low places. By the way, the 1500 cfm is just an advertising number which is measured at the input with no hose and no filter connected. By the time you route the air through all that pipe and the filter, you will do well to achieve 750 cfm.

[Robert Engel]

You'll lose alot of air flow with flex pipe.

I would bite the bullet and use 6" ducts and as little flex as possible.

Or just move hose from machine to machine if its not too aggravating.

Art is right about the advertised cfm vs. reality.

[Prashun Patel]

I have a flexible system with a Thein baffle. I messed around with manifolds and blast gates.

In the end, I find the following to be the biggest keys to success with such a system:

Minimize or eliminate the branches and don't use blast gates. I use a single pipe from the separator inlet. I connect it to each tool in turn. Focus on good quick-disconnect fittings. Make your tool ports easy to get at.

Keep the filter clean. Find a way to blow out the filter or gently bang it clean as often as you can. I've never had a separator (and I use 3 on different systems) that fully protected the filter.

Keep the bin less than half full. If you have way to monitor it the fill, you'll be less likely to go over this.

As far as chips from the jointer or planer, I'm with you. I'm planning on building a simpler pre-preseparator for the chips from these. The chips are so big an dust relatively minimal compared to my saws. Anecdotally, I don't notice that they don't generate a lot of finer dust. Conversely, they throw so many chips that they fill up the separator too quickly. Having a quick access one for these will be a boon.

[James W Glenn]

I just checked the blower and it has a 12" fan and the motor is rated at 3450 RPM. The original collection bag was 24" in diameter an maybe 6' tall. I am assuming that this 2 hp is not the same as a Harbor Freight 2hp. Hopefully the electrician will get my 220 circuits in next week and the tinkering can move ahead. I am trying to budget for the good smooth flex hose, and may need to do an intermediate set up with a single 5" hose to get a performance base line to work from. If the machine can handle a 6" trunk line and manifold, I can cut the 5" hose for branches to the machines.

[James Gunning]

James,

Here is my DC, built to be portable and used with one machine at a time. http://www.sawmillcreek.org/showthre...able-SDD-build. I use the short length of 6" flex hose (from Wynn Environmental) that shows in the photos, in combination with the ports on my machines being upsized to 6". The current blower is only 1 HP with a 10" fan and will not get to the point of meeting the 800 CFM at the tool standard. Looking at fan curves for similar blowers I estimate this one does about 550-600 CFM at 6" SP, so not terribly far away. I'm limited to 110 volts in the shop, so 1.5HP is as big as I can go currently. IMO your 2HP Delta with a 12" fan would probably get to the 800 CFM number, but only if you optimize your system. The suggestion of making yours portable and hooking up to one machine at a time is probably the best way to get there. A piping run+flex hose on each end+small machine ports would probably hobble your blower enough that it may not perform as you hope. My small blower works fine with all my machines including a Jet 22-44 sander. I never have anything settle in the hose, and very little dust escapes. I do use ventilation and wear a dust mask, as I consider it unlikely I'm capturing all the fine stuff.

At the current state of the art in dust collection, you need three things to make it work properly: 1. Two stage separation - either a cyclone or a well built Thien separator. 2. Large enough piping and tool ports - 6" minimum. The 4" ports and pipe will just not flow enough air. The cross section is too small and the internal friction and losses are too great. 3. A minimally restrictive filter (Wynn Environmental again) or outside venting.

If you want a piping system that feeds multiple machines, then your Delta will probably not be adequate. Then you need 3HP+ and a larger fan to overcome the losses in the piping system.

[ian maybury]

Hi James G - that's a nice set up. A mobile unit is the one way i know of to truly maximise what's on offer from a smaller fan by minimising hose runs, although I didn't actually know anybody who had DIY headed off down that route with a cyclone. It sounds like your numbers more or less verify the story set out by several posts above.

To James W G - the intention isn't to be pushy or dogmatic, but there's no magic and no free gifts in this stuff. 2HP is 2HP. Fan efficiencies are similar/generic in this space so that more or less dictates that its pressure and CFM capability wll be as normal. Your 12in x 3,450RPM impeller (with likely 3in high BC vanes) is exactly the impeller that would be expected on a 2HP system - nothing special. The 8in dia side opening in the fan looks to be to do with mounting the 3 x 4in dia dust collection manifold, and nothing to do with CFM capability or any implied recommendation as to duct/hose size.

A skim of a Delta manual for the unit on the web is notably silent on the matter, but (a) the fan seems set up to run short flexibles connected to the stubs, and (b) it's unlikely to power more than one at a time very effectively. (the manifold would confer the ability to leave several machines hooked up at once to be selcted one at a time via blast gates) As a mobile unit it seems it was clearly intended to pull through only a short flexible hose.

It's hard to predict CFM numbers precisely, and you have to make the call - but it's very likely you're going to end up with marginal performance if it's set up to pull through a manifold, valves and longer hoses as originally proposed.

It will move air, and it will transport fine dust - but it's not going to do a lot more (and it's not going to deliver healthy shop air conditions presuming machines of any normal size and type) unless it's set up so that the size and length of hose and other factors contributing to pressure drop are aggressively optimised...

[James W Glenn]

Ian, do have a feeling about the relative CFM gains that would be seem by upgrading James G's cyclone to 2hp?

Edited to add:

I found this related post, which gives me some more to ponder.

http://www.sawmillcreek.org/showthre...ight=Flex+hose

[ian maybury]

Thanks James W, i was concerned i might have caused offence. There's some good info in the topic you linked - especially regarding the pretty dramatic pressure drop induced by flex hose. Pardon the length of this, but it is what it is. I've taken a shot at your question at the end.

It's hard to tie rule of thumb/back of envelope exercises like this down to better than within maybe 40% or even lots more - and because seemingly inconsequential and unstated factors can have big effects. Also because with these smaller sized fans quite small differences in the guesstimates used for pressure drops also have big effects.

This doesn't even for want of information amount to going through any proper estimating procedure - totalling the system pressure drop at the required ft/min flow from proven data, and backing this number into a reliable fan curve to estimate real CFM. I'm taking huge liberties here, and it's most definitely not advice. Only an illustration of how this stuff can play, and what some of the major considerations may be. So health warnings apply, and testing a mock up is always highly advisable.

Your original proposal may (a) have seemed to hope that the 2HP fan might do better than typical. This seems unlikely, it'll probably do what 2HP fans do. (b) was that 10ft of flex hose, a manifold with valves, and a further 5ft of flex were proposed.

Given that flex typically rates at x3 (or potentially more) of the pressure drop of a smooth duct, and a manifold possibly entails 2X 90 deg tight bends (= roughly 12ft of duct run equivalent each) and a valve this is actually equivalent to a pretty long run of smooth ducting - of the order of (10x3 = 30 ft) + (12 +11+12 = 35ft) + (5x3 = 15ft) = 80ft run equivalent.

James G is hampered by having to run a small fan, but his going to a mobile unit drops him down to perhaps 6ft of flex hose = 6x3 = 18ft run equivalent.

This might not sound like it matters a lot, but 6in ducting runs 3.5 - 4.3 in WG pressure drop per 100ft run or thereabouts at the 3,500 to 4,000 ft/min airspeeds we target, so 80 ft run equivalent contributes maybe 3.2in WG, while the 18ft maybe 0.72in WG. So the 80 - 18 = 62 ft run equivalent saved could be worth a reduction of anything from 2 - 3in WG (water gauge) in pressure drop.

The combined pressure drop for the cyclone or separator and the filter has also got to be added - also for the machine ports and other losses. Presume for the moment that the machine ports are modded and 6in dia/full bore equivalent. I'm relying on fuzzy memories, but very good examples may contribute of the order of a further 3in WG pressure drop combined. (presuming a correctly sized cyclone and clean and free flowing cartridges)

This all becomes very critical because small fans have very limited pressure capability, and this falls away quickly as they get smaller in diameter. Picking very approximately from typical 3,450 RPM BC fan curves (by Cincinatti) a 13x3.25 in 3HP impeller starts to tail off sharply in CFM output by maybe 8in WG, and is essentially gone (down to airflow too low to be of any use) by 10in WG. For a 12x3in 2HP impeller this drops to tailing by 6in WG and gone by 8in WG. For a 11x3in 1HP impeller this drops away again to tailing by 4in WG and gone by 6in WG. (for reference the 5HP/16in impeller on a Clear Vue or similar Pentz recommended fan is still pulling strongly at 12in WG, and goes futher if needed)

The big variable lurking in the background is machine ports - but stuff like local other restrictions, wrongly sized cyclones/restrictive separators, leaky blast gates, small area/dirty filters and the like can also be hugely significant. It's important that pretty much everything is genuinely optimised, especially with smaller fans like these. If the machine ports are restrictive (and it's not always possible to open these right up) they have the potential to possibly head for even doubling the pressure drop, and all bets are off. The only real protection at that stage is a higher HP and larger diameter impeller - apart from delivering the higher CFM needed for effective air cleaning and chip collection (read the linked Bill Pentz pages for what he and the international H&S regulators feel is required to achieve safe air quality) the above gives a very rough feeling for just how much better a larger diameter impeller (which requires more HP) may do at higher pressure drops. Even an extra inch in diameter makes a significant difference.

James G may have of the order of 3 + 0.75 + ? for misc further losses (e.g. duct entry etc) - so his estimate of maybe 5in total pressure drop probably isn't far off. He's approaching the point where his 1HP fan will quickly tail off (it's probably quite sensitive to dirt in filters), but his estimate of 5 - 600CFM may not be far off. (this can be read off from section H 5 'Blower Fan Table' well down the Bill P page linked above)

It seems possible that your originally proposed system might have had 3 + 3.2 + ? for restrictive machine ports if they have not been opened up + ? for misc = 7.2 in WG minimum plus potentially quite a bit more. (e.g. i don't know how much pressure drop a separator may contribute in your situation) This would very probably place your 2HP fan well into tailing off territory (and left it very sensitive to any further inceased in pressure drop), and again by Bill P's table maybe doing some thing like a pretty marginal 350 - 400CFM. James G's 1 HP fan would likely be pretty much unusable in CFM terms with that hose set up.

Minimising the length of flex hose and hence the pressure drop by instead building the 2HP fan into a mobile unit would likely reduce the pressure drop by maybe 3in WG - to possibly by Bill's table above double the CFM delivered. Bumping it up to possibly around 700CFM (presuming as before no issues with machine ports, other problems etc - a truly optimised run all the way from entry to exhaust) Best of all it'd very possibly leave the fan with a little cushion in terms of pressure capability, so that the CFM wouldn't drop overly fast in response to filters starting to blind up etc...

Hope this helps to paint a picture - but again don't bank on the numbers being correct without testing a mock up. Even a fairly highly compromised system will still move enough air to transport fine dust, but as before it takes decent airflow Bill P style to deliver decent shop conditions...

[M Toupin]

James, I'm sort of in the same boat. My "shop" is a 1 car garage stuffed to the rafters with light industrial machines so everything has to be mobile. The machines get dragged out into the driveway for anything big which of course becomes a collection problem. Like many I started the bag collector with crappy bags so I "upgraded" to Wynn filter. Miserable, the filer clogged with dust constantly and it was a pain to empty. Next I added a baffle system thinking it would keep the filters cleaner. It did, but not much and it was still a pain to empty and clean the filter constantly. I finally built a Penz cyclone with a 3hp 14" impeller which is mounted on the wall. The only problem was with mobile stuff dragged all around, fixed ducting wasn't an option. So I went with two 10 feet pieces of the 4" Harbor freight dust collection pipe which used to be surprisingly good. Fairly stiff and smooth on the inside, the new version... not so much (don't waste your money). That worked but the 4" was only marginal at best. I lived with that for several years until I upgraded my planner to a Delta Rockwell 22-401 with 5hp. At that point I needed to increase the CFM to handle the chip load of the 22-401 which can hog off a 1/4 at a wack. Nice if you're trying to get to dimension quickly, but the chip load was far overwhelming the little 4" hose not to mention the fan wasn't operating at full capacity. Finally I upgraded to Flex-Tube PU 6" flex. it's a bit spendy, but it's heavy duty and smooth inside and does not collapse like less expensive flex hose. The increase in CFM from 4" to 6" was tremendous! I should have done it a long time ago! The only down side is the size, going from 4" to 6" is a big jump, it's a LOT bigger but it works soooo much better. I use PVC fittings for quick disconnects (6" DWV fits inside a 6" sch40 coupling) Ive upgrade about half my machines to 6" but even on the machines still with 4" ports I can definitely tell a difference using a 6" to 4" reducer right at the machine. I'll be the first to admit it's not the "best" solution but it works well for the constraints I'm stuck with.

Mike

[ian maybury]

I guess most of us live with compromises of one sort or another in our dust systems. Compromise is rarely ideal, but a decent sized (ideally Pentz spec/5HP/6in duct/15 or 16in dia impeller) fan makes the whole deal so much less sensitive. I run a 16in CV max based DIY version to Bill P's drawings with Hammer machines. I've still got some port restrictions (especially underneath on the saw which would require major surgery to sort out), but it's been such a pleasure to work with…

It works really well even on stuff like the Incra router table which has small ports. The big fan when restricted just winds to up to a very high level of suction pressure (maybe 12 - 15in WG) in a way that a smaller diameter one cannot, and while not ideal it certainly maximises the performance in the situation...

[James W Glenn]

I guess I will start off with a 6" hose and switch it from machine to machine. Dose any one have a source for shorter lengths of the "Flex-Tube PU 6" flex"? The listings I have found for 10' lengths + shipping are too close to the Amazon cost for 25' shipped.

[Art Mann]

I noticed that hose you linked to is very similar to what I use. It seems to be all plastic rather than having an embedded spiral wire. That provides for a much smoother interior surface. You will get better air flow with that type hose. The price seems a lot higher than what I paid. I think I ordered from either Woodcraft or Rockler.

[James Gunning]

You very likely don't need hose that is quite that stout. The stuff on Amazon is 35 mil wall thickness. The hose I got from Wynn is 25 mil with a stiff wire spiral. A 6" x 25' piece is $92 plus either $11 or $16 shipping depending on where you live.