Thread: pvc pipe size for ducting

doug3030 - can I ask what length of 4" pipe you have at the end of your 6" run from the dusty, or do you have just a 6" to 4" adapter on the end??

Cheers

Originally Posted by Mr Brush

I'm in the process of throwing out a convoluted network of 4" flex duct and blast gates, to be replaced with a single 5"/6" flex hose (~2m). This will be reduced down to 4" for the last section to allow plugging onto machine dustports. I've already rearranged the shed so that the dusty is at the centre of the machines it needs to be used with. Dusty is a Carbatec 2hp unit, and I've already replaced the standard needlefelt filter with a pleated filter cartridge.

Using 5 or 6" ducting and then reducing that down to a single 4" connections will reduce a 2HP DC flow from ~1000 cfm to ~400 cfm.
The best thing to do is modify machine ports to 6", but if for whatever reason this is not possible it is only worth using larger ducting to connect to machines (like a TS) where two connections are normally used, then 2 x 4" will at least give ~800 cfm.
Remember the target CFM to collect fine dust at source is 1000 cfm @ 400 fpm.

(1) Does it make much difference going with 5" flex hose attached to the dusty, or 6" via an adaptor?

The most a standard 2HP DC can pull through a 2" pipe is ~120 cfm, through 4" its ~400 cfm, through 6" its 1000 cfm. I have not measured 5" ducting flow rates but it will around 700 cfm - I reckon the extra 300 cfm that can be obtained with 6" ducting is well worth setting up for especially for machines with double or triple inlets.

This thread seems to indicate 6" is better - does anyone have any pics of their adaptor to connect this to the dusty?

If you have a lathe adapters can be turned up using a block (sandwich) of MDF.
I used a tapered flower pot.
If you are handy at sheet metal work a cone is easy to make.

Also, apart from Felder, can anyone suggest good sources of flexible 5" or 6" ducting?

Chris Parks and Carbatech have 6" flexy.

(2) Does it make much difference what length of 4" flex hose is attached at the end of the 5"/6" hose? I was going to use about 1m of the ultra flexible translucent 4" hose that I already have, but is there any benefit in making this section REALLY short (as in 30cm or so)?

It will make little difference because merely by using 4" hose this throttles the flow down so much. The 4" smooth walled flexy itself is pretty good stuff and @400 cfm, only looses about 20 cfm per meter when it is straight and 30 cfm/m when used in a wide 90º bend. Whatever is used keep it as short as possible.

What size flex do you have between the impeller and the DC filter/collection bag?

Bob - thanks for the detailed response, much appreciated.

It sounds as if you may have saved me some $$$.......I hadn't considered that the Carbatec dusty has a short 4" connection between impeller and filter. Can't see any easy way to change this?

Of all the machines I use, the TS is about the only one that can easily have the port modified to 6". The jointer/thicknesser (JET JPT-310) has a metal hood arrangement with 4" inlet, which would need a lot of hacking to convert to 6". Bandsaw has a practically useless 4" port to the main cabinet, but I have experimented with a splitter to give 2 x 4" ports. One went to the cabinet, the other was attached under the table very close to the blade. This seemed to prevent a lot of the dust buildup inside the cabinet. Drum sander (JET 16/32) has a 4" port in the plastic lid which couldn't easily be modified.

So.....two machines (TS and bandsaw) could be modified to take advantage of the higher cfm from 6" pipe, two probably can't. Hmmmm.

Of course, even a single 2m 4" pipe off the 5" port on the dusty would be preferable to the 2 x 4" splitter, long lengths of pipe, tight bends and multiple blast gates I have at the moment - that was my original plan until I saw the thread about 6" pipe.

Given the restriction between impeller and filter, is there any point in using other than 4" elsewhere?? Since a lot of people have the Carbatec/H&F 2hp class dusty, is there any way around this? I think it would need major metalwork/butchery to alter the 4" impeller/filter connection.

Thanks again for all the information - makes a lot of sense when I think about it

I thought the 2HP CT DC had a 5" connection between the impeller and filter/bag housing?
If so, it is still better to use 6" rathe than 4" ducting and connect what machines you can with 6".

I have 6" (table) and 4" (overhead guard) to my TS
6" to my WW lathe
3 x 4" to my BS
2 x 4" to my router.
and currently only a single 4" to my thicknesser/planer until I modify it to 6"

Originally Posted by Mr Brush

doug3030 - can I ask what length of 4" pipe you have at the end of your 6" run from the dusty, or do you have just a 6" to 4" adapter on the end?

Hi Mr Brush,

If you reread my post, my 6" pipe is currently theoretical.

The plan, however, is to do a remake of my whole system. I started out with a 1hp sherwood dusty impeller sitting on a homemade cyclone made out of two 44 gallon drums then venting straight out through the window, no bags, no filters. It ran a 4" pipe system. No way at all to expand that so everything currently has 4' ports and 4" pipes.

I then got a H&F 2hp dusty which I am going to make a new intake for to allow it to attach to a 6" pipe. I can then modify the cyclone to a 6" intake and a 6" outlet. I will then mount the impeller on top of the cyclone and vent it straight out the window, once again, no bags or filters. This also eliminates the choking point of the 5" flexible hose currently between the impeller and the filter. The rectangular outlet from the impeller has a minimally larger cross section than a 6" round pipe.

This also has the advantage of the inlet to the cyclone being above head-height so the main 6' pipe will run at that height to the work area in the middle of the shed. All my machines are on mobile bases so I put the one/s I will be using in place and attach the dusty hose to it just using a friction fit using the flange off the end of a pipe. It takes 2 seconds to move it from one machine to another.

I am planning to have two alternative flexible hose arrangements to fit onto the end of the main 6" line. A 6' flexible hose to use with the machines that can be adapted to a 6" port, and another with two 4" flexible hoses for the ones that are impractical/impossible to modify.

As an aside, when I changed from the 1hp impeller to the 2hp impeller, there was really no perceptible increase in airflow through the system using the 4" pipe. I don't have any flow meters to give exact figures but there does not seem to be any improvement in flow. This pretty much substantiates what BobL has been saying about 4" ducting and 400 cfm instead of the potentially possible 1000 from the machine running larger pipe.

To take it a step further, If you want to run 4" pipe you might as well save some more money and just get a 1hp dusty.

Anyway that is what will be happening in the shed soon.

Doug

Thanks Bob and Doug for the detailed advice. I just popped out to the shed to check my CT 2hp dusty, and it does indeed have a 5" connection between impeller and filter.

Soooo.....without getting into massive metal bending and fabrication, I think the most cost-effective solution right now is to go with a short 5" flexihose directly off the dusty, i.e. remove the built-in 2 x 4" splitter. That way the system is 5" right through, which is as good as I'll get without major mods to the dusty itself.

I can easily mod the TS to have a 5" port, have a single 5" port to the underside of the bandsaw, and may even be able to modify the other machines to have 5" ports. With all hoses kept short, and the increased flow through the pleated filter (compared to clogged up needlefelt....), hopefully I can get closer to 700cfm than 400 cfm.

Doug - your approach seems like the way to go, but at this stage I'm not up to all the mods required to get the benefit of 6" pipe !! Not entirely sure about the 1hp to 2hp comparison, but I do use a CT 1hp dusty at work (with the standard needlefelt bag) and it is totally gutless even used on a single machine. This could be just the nature of the dust it is up against; fine sawdust from a double-blade mitre saw bungs up needlefelt really quickly. I can't help wondering how many people out there are getting stuff-all cfm out of their dusty because the needlefelt bag is hopelessly clogged up !

Thanks again for your help - I'll post findings when I've performed the upgrade.

Originally Posted by doug3030

As an aside, when I changed from the 1hp impeller to the 2hp impeller, there was really no perceptible increase in airflow through the system using the 4" pipe. I don't have any flow meters to give exact figures but there does not seem to be any improvement in flow. This pretty much substantiates what BobL has been saying about 4" ducting and 400 cfm instead of the potentially possible 1000 from the machine running larger pipe.

A 1HP DC with clean filter/bags will only pull 400 cfm thru a short length of straight 4" ducting.
When the filters/bags become loaded and/or ducting gets longer the flow will drop of more rapidly than a 2HP DC so there is some advantage in using a 2HP DC.
The big advantage of using a 2HP DC is that it can utilise a 6" duct from which several 4" ducts can be run at the same time.

The lowest air volume rate I have measure on a 4" - 1HP DC setup was 120 cfm - this system had about 6m of ducting and 2m of flex, and very dirty bags.
The lowest I have measured for a 2HP with 3 m of 4" flex a chip collector and dirty bags was 180 cfm.
Keep the bags clean or as doug has done getting rid of them completely is a major CFM saver.

Using 6" ducting on a 1HP DC will pull about 600 cfm but long term may damage the motor.
In addition 600 cfm in a 6" duct is about 1000 fpm below the 4000 fpm spec needed to hold sawdust in suspension ie more likely to get blocked if/when the air supply stalls.

Bob - that probably explains what I've been seeing with the 1hp dusty at work. The connection to the machine is about 4m of flexihose, as there is nowhere else the dusty can live closer to the saw. With the very fine dust being generated, the needlefelt bag seems to clog up really fast.

It gets removed, turned inside out, and beaten to within an inch of its life every couple of weeks, but any improvement in air flow is very short-lived. When I'm up at Carbatec I might see if they have the pleated filter for this 1hp dusty, as this might make it easier to maintain acceptable performance. I also plan to relocate the position of the dust port on the mitre saw in the hope of catching more dust as it comes off the blade.

Doesn't make much sense to have a fantastic dust extraction system in my home shed, then go to work every day to use a crappy system that isn't doing the job properly.....

Cheers

Originally Posted by Mr Brush

I can't help wondering how many people out there are getting stuff-all cfm out of their dusty because the needlefelt bag is hopelessly clogged up !

Probably lots of people! I bought my 2hp H&F dusty secondhand from the forum marketplace. It was still half-full of sawdust when I collected it The seller started it up to prove it worked before we dismantled it and put it in the back of the ute. The needlefelt filter was so clogged that when the machine was running the bag was as hard as a punching bag and almost impossible to push in at all. I got it home and emptied the collection bag into the front garden and cleaned out the needlefelt bag using the compressor (wearing a dust mask and outdoors on a windy afternoon). After reassembly there was definitely an increase in suction and the sides of the bag were very easy to push in.

Just having had to empty this bag and clean the needlefelt bag JUST THE ONCE was enough to confirm to me that I am on the right track. The cyclone is much easier and cleaner to deal with. It seems crazy to catch all that fine dust in a way that you eventually have to deal with a large volume of it all at once.

Mr Brush, the main reason I am going with 6" rather than 5" is that you cant get 5" pipe, so I would have to run all flexy, and that uses up more cfm.

Doug

Doug - cleaning the needlefelt filter is indeed a crappy job.......the first time I took apart the 1hp dusty at work there was a solid layer of compacted dust about 15mm thick over the inside of the bag. It had been there so long it actually cracked and came off in big chunks !

I never let my own dusty get that bad, but finally got fed up with the huge cloud of dust that was created when it was switched on and the top filter bag goes up with a "whump". The pleated filter fixed the problem for good and was well worth the money. Spin the paddle handle on top, and its amazing how much fine dust drops down into the bag. Makes it easy to maintain optimum performance.

I do use a cyclone dust bucket for my shop vac (mainly to save $$$$ on those expensive Festool bags), but haven't gone that way for my 2hp dusty yet. We'll see how it goes without first.

I only plan on using about 2m of 5" flexihose, as I have cunningly rearranged my machines in a circle around the dusty. I'll only have to wheel the dusty <1m in any direction to connect to any machine. I agree that you wouldn't want to run flexihose any further than you have to though, so the 6" pipe option sounds better for you.

Cheers

2 observations:

1: 5 vs 6 inch. Cross section of 5" pipe is pi times 25 (r2) vs. 6" which is pi times 36. So 6" should be nearly 25% more efficient.

2: clogging filters. You don't need a true cyclone, just running the hose thru a drum & letting the effective diameter increase will cause the heavier stuff to drop out before it reaches the impeller. Buy a recycled drum around 25+ lites & cut 2 ports in the lid (much stronger than the 20l 'handy pail' type sold in hardware stores), connect the hose & you are away.

Originally Posted by Mr Brush

I only plan on using about 2m of 5" flexihose, as I have cunningly rearranged my machines in a circle around the dusty. I'll only have to wheel the dusty <1m in any direction to connect to any machine. I agree that you wouldn't want to run flexihose any further than you have to though, so the 6" pipe option sounds better for you.

Yes, Mr Brush, we all work differently from each other, what works for one wont suit someone else at all. I think that is a point that is often lost sight of on this forum when people are so happy with their own setup that they cant see why everyone else wont do it their way.

The best way for me is to wheel the machines I need into the work area where I have power and dust extraction arranged and wheel them back to their storage spot when they are not in use. If I tried to arrange my equipment into a 2metre radius circle around the dusty, I would run out of circle before i ran out of machinery.

Originally Posted by bsrlee

You don't need a true cyclone, just running the hose thru a drum & letting the effective diameter increase will cause the heavier stuff to drop out before it reaches the impeller. Buy a recycled drum around 25+ lites & cut 2 ports in the lid (much stronger than the 20l 'handy pail' type sold in hardware stores), connect the hose & you are away.

Having a collector drum is going to be better than not having a collector drum, A cyclone would be better still but a collector drum would be a good start.

A 25 litre drum might work on your shopvac but I doubt it would do much on even a 4" dusty system. You might be pushing to make two 6" holes in the lid and they would not be far enough apart to allow the dust entering to fall before being sucked up the other pipe.

200 litres yes, 25 litres a definite no. I once filled up my 44 gallon drum collector below my cyclone twice in one day. And even with a 200 litre drum it will allow more of the small filter-clogging dust to pass through than an efficient cyclone will.

Doug

Originally Posted by bsrlee

2 observations:

1: 5 vs 6 inch. Cross section of 5" pipe is pi times 25 (r2) vs. 6" which is pi times 36. So 6" should be nearly 25% more efficient.

Trouble is, as I learned today, the limiting factor on airflow through my system is the short 5" connection between impeller and filter. Unless I can change that (and it wouldn't be easy without seriously hacking up the dusty), I'd get no benefit from having 6" pipe anywhere else in my system, cyclone or not.

So.....I'm happy with the likely improvement just going to a single short 5" pipe directly off the dusty vs. the current maze of 4" flexihose, splitters, blast gates, etc. A reliable 600-700 cfm will do me nicely