Thread: pvc pipe size for ducting

Originally Posted by doug3030

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.

The poorest performing (ie most clogged up and leaky) DC I have measured by a long way in my survey of DCs has been been one connected to a chip collector (CC), and one connected to a small home made cyclone was not much better. The reason is simple. The operator thinks the CC/cyclone will improve fine dust filtering and never or rarely clean the filters. However the filters still need to be cleaned because both let fine dust through and it is the fine dust which clogs the filters. I suspect that using CCs and cyclones means the bags should probably be cleaned more often as a small amount of only fine dust that both of these let through will clog the filters faster than a a mix of coarse and fine sawdust.

The fine dust also clogs the filters so badly that leaks are more easily forced around the standard clip rims used on most DCs. Leaks appear more likely when DCs are only connected to sanders compared to when connected to thicknessers or saws which can be explained because sanders make a lot more fine dust that the other types of machines.

Then on top of all of the above, even when filters are clean, CCs and small cyclones rob small DCs of valuable sucking power that reduces fine dust collection at source. I already demonstrated that a 200L 4" ducted CC reduces flow by ~25%. This is less of problem for vacuum cleaners initially which operator at much high pressures where the flow rate loss is around 7%. VCs have their own special problems that I won't go into here. However it does not mean that VC owners can afford to be slack in cleaning filters when using CCs.
Most users of CC and small cyclones operators focus on their visible chip handling needs and do not even realise that there has been a drop off in the air flow through their DCs cause by just using small cyclones or CC and the resulting filter clogging described above. Most operators would not be able to tell the difference in a 25% drop off in air flow and one operator thought his system was working OK even though he had a 50% drop in flow rate.

Some good points there - it is very useful to have some data from someone who has actually measured the performance of DCs under various conditions. A lot of the numbers quoted by manufacturers/suppliers (especially Chinese-sourced stuff) are either meaningless or hopelessly optimistic in my experience.

I'm glad I installed a pleated filter which can easily be kept clean....

I was interested in the point you make about leaks - the 1hp dusty we use at work has a perennial problem in this regard, as the plastic dust bags just don't seal properly against the metal with the rim clip provided. I was supplied with a bunch of the plastic bags when I bought the pleated filter for my own 2hp dusty, but had so much trouble getting a good seal with these that I actually went back to using the original cloth collection bag which seals perfectly.

I've heard that wrapping many turns of duct tape around the rim before applying the clip can give a better seal, as the surface under the clip then has a bit of give to provide a seal. Interestingly, while trolling through the H&F website, I noticed that their pleated filter cartridge appears to come supplied with a length of stickyback foam as well as the plastic bags.

W328 | FC-10 Filter Cartridge | machineryhouse.com.au

I assume this is to go around the rim under the clip to give a better seal?

Well, now you all know who failed maths

Originally Posted by Mr Brush

I'm glad I installed a pleated filter which can easily be kept clean....<img src="https://www.woodworkforums.com/images/smilies/standard/rolleyes.gif" border="0" alt="" title="Rolleyes" smilieid="654" class="inlineimg">

Yep but as I said in another post, as long as they are cleaned regularly.

I was interested in the point you make about leaks - the 1hp dusty we use at work has a perennial problem in this regard, as the plastic dust bags just don't seal properly against the metal with the rim clip provided. I was supplied with a bunch of the plastic bags when I bought the pleated filter for my own 2hp dusty, but had so much trouble getting a good seal with these that I actually went back to using the original cloth collection bag which&nbsp;<strong>seals perfectly</strong>.

Visual verification of DC sealing can be a bit misleading. Large leaks are relatively easy to see since they are constant and eventually create a shadow of dust around the leak point. Small or intermittent leaks cause by pulses (eg starting or rapid blockages or moving the DC) are less obvious although they emit much dust but over time they can add considerably to the dust load in a shed.

I've heard that wrapping many turns of duct tape around the rim before applying the clip can give a better seal, as the surface under the clip then has a bit of give to provide a seal.

This does seem to be the case, but the most common leak I see is a rucked up (folded edge) plastic bag on the DCs which utilise external bag and bag/filter clamps and no matter how much tape or foam padding or clamp pressure is used these leaks seem to persist. These external clamps do not seem to be able to clamp the filters and bags onto the rim tight enough around bag or filter folds and rucks, and fine dust comes pouring out of these leaks. This is particularly the case for plastic bags but I have also seen many bad leaks around pleated filter clamps.

In this picture the black lines represent the filter/bag rim. the blue line represents the filter/bag clamp and the red line represents the filter/bag
dustyleak.jpg

The best filter/bag clamp system I have seen seems to be the one where the clamp and bag/filter are retained on the inside the bag/filter rim. The DC pressure then forces the clamp onto bag/filter which in turn is then forced onto the inside of the rim. The more the DC pushes the tighter the clamp becomes.

dustyseal.jpg

Leaks seem to be the most serious issue for DCs and is yet another reason to vent or locate them outside the shed.

thanx for the replies guys....if anyone wants to put any pics of their ducting go ahead.....

Originally Posted by rellik

thanx for the replies guys....if anyone wants to put any pics of their ducting go ahead.....

There are plenty of pics of ducting in this forum.

Mine are in this thread
https://www.woodworkforums.com/f200/b...-setup-143350/

I thought about metal ducting when I discovered that the wide radius PVC bends were no longer available. Because I only had one 90 degree turn in my main line I made it up with six 15 degree elbows, as per pic. That way I could get the economy of PVC without the tight 90 degree elbows restricting airflow. Needs six fittings, but still way cheaper than metal ducting.
IMAG0021.jpg

Where I drop down to machines two 45 degree bends were used, one M and one F, or a wye and a 45 degree bend. Seems to work well, but every shed is different and we all have our pet likes and dislikes.

This man made his own Dust Extraction

Good job too.

His weakest link is the 2 x 4" flexy connectors to his DC.

This means his Max/TOTAL air flow will be 800 CFM.
It's a pity because if he used the full X-sectional area of his Ducting his 3HP DC would be able to pull 1250+ CFM.

OTOH he only uses 4" flexy to connect machines, so unless he was to enlarge these it's a moot point.

Another potential problem is when using only 1 x 4" duct (400 cfm) in the large X-sections of his ducting (0.23 sq ft) his air speed in these sections will be 400/0.23 = 1700 FPM. At this speed sawdust will fall out of suspension in the large cross sectional ducts. I can't believe the guys claim that he has read BPs site as this point is hammered home time and time again. Even when using 2 x 4" ports his max airspeed will be only 3400 FPM which is still below the recommended 4000 FPM.

They look bigger than 4" in the pics but yes it is a problem, why would you got to so much trouble and then cripple it. I was more interested in the workmanship that had gone into it and to show that there are alternatives to PVC & steel.

Even if you do read BP's site it can still be pretty confusing for example I took delivery of my Cleaview last week and am now going through the process of figuring the best installation. The kit is now supplied with an Australian 4hp motor rather than the original 5hp Leeson and I am wondering if this changes the pipe sizes I will need. I am going to use a 6" main pipe to the blower which Chris says is the size to use but should the Y to the saw cabinet be 6" and 4" to the blade guard or some other combination to attain the required airflow As my shed is quite small the distance between the cyclone and any machine is unlikely to be more than about 6 metres.

Originally Posted by safari

Even if you do read BP's site it can still be pretty confusing for example I took delivery of my Cleaview last week and am now going through the process of figuring the best installation. The kit is now supplied with an Australian 4hp motor rather than the original 5hp Leeson and I am wondering if this changes the pipe sizes I will need.

I seriously doubt this will make a difference.

I agree BPs site can be hard to read but this stuff is not simple to explain in just a few words.

I am going to use a 6" main pipe to the blower which Chris says is the size to use but should the Y to the saw cabinet be 6" and 4" to the blade guard or some other combination to attain the required airflow.

The 4" line to the blade guard should pull 400+ CFM which will be fine. If the Cabinet saw has only a 4" port and you connect a 6" line to it then it will only have 1700 fpm going through it which is not good. If the Cabinet saw has a 6" port then (depending on how well ventilated the cabinet is) it should pull about 800-1000 cfm ( both greater than 4000 fpm) through the 6" line and it should be OK.

As my shed is quite small the distance between the cyclone and any machine is unlikely to be more than about 6 metres.

This is fine.

Thanks for that BobL. My saw has a 4" port but but will be easy to enlarge to 6"

The easiest way and neatest way to modify the saw is use a clear out fitting, just remove the cap and use the existing holes to fix it to the cabinet. That way the pipe simply slips into the clear out fitting and it results in a neat adapter. Leave the original port to supply the make up air as that plus all the gaps around a saw will easily equal a 150mm port. You do want them on different walls to make sure the air flows across the cabinet allowing the air stream to capture the dust.