Thread: PCV pipe and flexible duct size

Originally Posted by petemacsydney

i have a little bit of drool in the right hand corner of my mouth right now, lol.
i'm just starting out (after 25 years of pretty much next to no wood working) so i have no budget nor room for a dust system right now, BUT! its great to see these systems available and I've now added this to my wish list!
Until then... the broom rules the shop...

At least get yourself a mask and open any doors and windows?

As I said earlier, full modification, if required, will occur at a later date when I have time. In the meantime I will be setting up two full runs in parallel as a bit of an experiment. One will be the 6" system and the other will be a 4" system. The 4" system bits won't go to waste as I have to run some drainage for a new carport and the bits are cheap. A couple of the experiments are with the suction sizing vs impellor design and suction size vs discharge size.

absolutely. i have a 3m 7258 welders half face mask that i use for welding fumes. i just switch out the filters as the welding filters are pretty darn expensive! its a great mask - very big fan of it.

Originally Posted by petemacsydney

absolutely. i have a 3m 7258 welders half face mask that i use for welding fumes. i just switch out the filters as the welding filters are pretty darn expensive! its a great mask - very big fan of it.

I've had to wear 1/2 face masks at work a few times .
Besides being uncomfortable having a beard meant they not very effective so we ended up going with full air masks - also hot, sweaty and uncomfortable

Before I retired I spent some of time setting up my shed to be as comfortable as possible for both wood and metal work so for welding I installed vented welding booth.

Here is my setup.

The bi-folding doors can wrap full around the hood so that grinding grit is constrained and you can see it also doubles as a small spray booth.
That small wooden tower thing on the bench is a Lazy Susan table for easily turning things on when painting.
The 1600 cfm squirrel cage blower fair whips away any welding fumes - even ZnO if I get slack.
At full speed the blower does pull away too much shielding gasses so I have to slow it down when I'm using TIG.

Fan.jpg

This booth suits the size of stuff I usually work with but if the welding work pieces are bigger than the booth it's no drama because I have 2 other ways of venting fumes and gasses.

One is the wood working DC system which can pull 1200 CFM and I have another 1200 CFM ventilation fan.
I prefer to not use the DC system for welding fumes as they can gum up the filter bags.

With all 3 fans running I'm venting ~4000 CFM and my shed volume is less than 4000 cubic ft in total.

Hope you can keep the drool to a minimum.

nice. drool contained for now, but only just! i don't have much room so i've just made a big bench on wheels and move it to the edge of the garage door when using it for turning, but most of my welding jobs i do on the concrete floor. unfortunate, but i just don't have the room for a better set up (without permanently moving the cars out - which cant happen). might need to move some kids out of the house to create more space!

BobL

I was was reading through the Generic 2hp mods and near the beginning, this was stated.

"I also noticed the inner diameter of the area where there are no impeller blades is only 125 mm. This would then be the maximum optimum inlet size for this impeller. Using an inlet bigger than this may not generate the expected flow. While I have it open I might knock up a 6" inlet and see what happens"

Other articles I've read seem to agree that opening wider can in fact be detrimental.

Your tests further on seem to indicate that opening up to 150mm actually improved the flow. Is that correct?

Other papers also mention that the suction side should be one size? larger that the outlet. What's you views on that?

I'm in the process of building a dusty shed and I'm looking at running the pipes this week.
Thanks.

Originally Posted by Lappa

BobL
I was was reading through the Generic 2hp mods and near the beginning, this was stated.

"I also noticed the inner diameter of the area where there are no impeller blades is only 125 mm. This would then be the maximum optimum inlet size for this impeller. Using an inlet bigger than this may not generate the expected flow. While I have it open I might knock up a 6" inlet and see what happens"

Other articles I've read seem to agree that opening wider can in fact be detrimental.

Your tests further on seem to indicate that opening up to 150mm actually improved the flow. Is that correct?

Yes there was greater flow, but don't forget that all my measurements were for minimal resistance air flow.

I'm pretty confident that opening this impeller up to 150 mm will effect (reduce) the performance under resistance.
By resistance I mean dirty filters, long ducting, Many junctions and choked machinery.
This probably why the 2HP is not released with a 6" inlet option as the manufacturer has no control over these resistive aspects of duct extraction and doesn't want people coming back saying the 2HP is a dog.

This effect is best described by what is known as the fan curve.
So even though a generic 2HP can move a lot of air (hence catch a lot of dust) it is limited at doing this only when it as unrestricted as possible.
Once again;
Short ducting runs - no more than ~3m
Minimal auctions, minimal flexy
Ducting ends should be Bell Mouth Hooded.
Machine has to be opened up big time so it can breathe
Keep filters clean religiously
Don't not used a chip catcher.

2HP should work OK on unthrottled situations like lathes and some big belt sanders but will be less effective on machines with built in restriction table saw cabinets and router tables.

Other papers also mention that the suction side should be one size? larger that the outlet. What's you views on that?

I haven't done many experiments on this and all the ones I have done have shown the opposite effect. There may be cases where this is correct but I have never seen one.

So, if the inlet to the impellor is 5" (as shown in your example in the sticky), it may be better to leave it at 5" and run 5" piping?

Most of the papers I spoke about related to fluid pumps. These papers were from system and pump designers so I would hope they are correct. This larger inlet to outlet ratio is also true on most turbocharger compressors I have examined.

So basically, what you are saying in your summary re 2hp Machines, is they unsuitable for a multiple connected ducting system as I can't see one keeping under the 3 metres ie. manifold plus even one flexible connection.
Cheers

Originally Posted by Lappa

So, if the inlet to the impellor is 5" (as shown in your example in the sticky), it may be better to leave it at 5" and run 5" piping?

Firstly, good luck in finding 5" ducting.

5" ducting under performs for wood dust extraction because the most flow you can get through a 5" duct is ~700cfm (for 4" ducting its ~425 CFM while for 6" its 1250 CFM) whereas ~1000 CFM is recommended for most intense wood dust activities
Remember those flow figures for various size ducting are a max, adding filters longer ducting and junctions and throttled machinery and its downhill quickly from there.

6" ducting on modified 2HP system will get you 850 CFM with needle felt filters and ~925 CFM with pleased filters, Once again its downhill from there which is why a modified 2HP DC fails to really satisfy but is often the best that can be achieved given the limited electrical power available in many DIY Sheds.

Most of the papers I spoke about related to fluid pumps. These papers were from system and pump designers so I would hope they are correct. This larger inlet to outlet ratio is also true on most turbocharger compressors I have examined.

This is related to the fan curve requirements of Turbo chargers. My understanding is that the they are more about pressure (e.g. up to 10 PSI) than flow. It is essential they build up pressure to be able to force air into an engine. While a certain amount of pressure is needed at the outlet to drive cyclones and through filters it's not the main game, Dust extractors only operate up to about 1/2 PSI and it's more about flow.

So basically, what you are saying in your summary re 2hp Machines, is they unsuitable for a multiple connected ducting system as I can't see one keeping under the 3 metres ie. manifold plus even one flexible connection.

Stock 2HP DCs are indeed sub par for almost all DIY operations.

A modified DC could be sufficient for some situations, e.g. a small shed where an occasional wood turner with a Bandsaw and a lathe, provided the two machines are on one side of a wall and the DC on the other.
It usually limits all machines be able to be placed up against a wall

When I say 3m I don't mean 3.00m - if its 3.5m or 4m or even 6m the performance does not fall off the edge of a cliff after the 3.00 m but degrades slowly.
The 3m duct length figure is just a nominal figure or guide - e.g. if one of the ducting arms was a straight 5m them that will have more flow than a 3m duct with a right angle bend in it.
Clever installation can do a lot with 3m, the 3m could be the radius of a circle with the DC in the middle, so in effect the DC system could cover 3m one way and 3m the other.
However, it won't cover placement of large machinery like a table saw in the middle of a large shed - that simply won't work even with a modified 2HP DC.

The same applied to all systems wherethey all have a nominal length guide. For stock 3HP DCs running 6" ducting in I reckon that's about 6m which is still very limiting. My 3HP system connects to my table saw guard via 4m of 6" overhead ducting and then 1m of 4" flexy, while the TS cabinet uses 8m of 6" ducting with 5 right angle bends - It's not ideal at all but its all I can really do. Given I used my TS mainly for cutting Al its not a big dust maker AND I have an additional 2800 CFM of quiet, low power, ventilation I can use to extract fine dust. 1200CFM of this extraction is located immediately above the TS.

Bigger, efficient, systems with more flow can enable much larger trunk lines to be installed that reach much further into a large sheds.
For example, at the mens shed I attend (wood working area is 14 x 7m) we have a 4HP 16"impeller ClearVue. The trunk line is ~14m long and 240 mm in diameter and the branches are up to 4 m long and 6" in diameter. This system works because it is efficient.
OTOH some pro setups just use brute strength e.g. 20" impellers and 20HP Motors, since they are not worried at about the paltry $3.75 per hour that it costs to run such a system.

Most of the risk from wood dust is related to exposure.
If you have a shed and machinery with no dust extraction and only use it and a mask for an hour a month you probably have the same risk as some one with good dust extraction that works in the shed for 40 hours a week.

Hi Harry

I have the same thicknesser as yours. I see you moulded the pvc over the existing shroud. How did this work out. Does it get in the way at all.

Legin

Originally Posted by harry wall

I also use pipeonline here in Perth. They are helpful and their prices are sensible. I don't bother trying anywhere else these days.
As for ducting..... I use 150mm PVC (either stormwater or DWV fittings) and purchased the 6 inch grey flexi duct from Timbecon. I just poke the ducting into the female 150mm PVC fitting and seal it with gaffa tape or packaging tape. I've made each piece of equipment duct inlet to be a male fitting so I just move the female flexi duct end to wherever I need it.
My thanks to BobL and others on this forum who have provided great information on the issue of dust extraction.
Here's a couple of photos of my setup....Attachment 401484Attachment 401485Attachment 401486

Gee, sorry legin. I have only just seen your post. Yes the dust extraction for the thicknesser works really well and no there is no interference from my moulded additions.

5 years 11 months classic

Well you would have to rub in my embarrassment by calculating exact timing. Must have been the mods I reckon..... they must have hidden the thread from me .

Originally Posted by harry wall

Well you would have to rub in my embarrassment by calculating exact timing. Must have been the mods I reckon..... they must have hidden the thread from me .

I was about to comment that you can sometimes get a quicker response at Bunnings, Harry, but on reflection, I will stay stum.