Testing a CT collector for efficiency?

[PeterK]

I have both a CT33 and a Midi.
Is there any easy or low cost way to check a collector for function? I am questioning my CT33 as it seems not to be sucking as well as it should. Using new bag, filter appears clean, never used without a bag. Still sounds the same when run at full speed. I am using the 50mm hose to my Dewalt saw and don’t seem to be getting much air flow.

Thanks for any ideas!
Pete

 

[Bob D.]

Peter came up with a nice test rig when he reviewed the Ultimate Dust Deputy.
Here's a link to the YT video cued up to where he talks about the test rig he built.
=540

 

[yangwoodworking]

I used a cheap wind detector ($15) bought from Amazon to do the comparison. I assume you can hold it at the air inlet of each DC to see how strong the wind is.

 

[Alanbach]

I don’t mean to be the master of the obvious here but have you checked the hose for obstructions? Also the saw,  right behind the blade just before the debris hits the hose?

 

[peter halle]

Might want to switch to a smaller diameter hose.  If you have the 50 mm I suspect you might also have a 36. 

Peter

 

[Michael Kellough]

Adding to Peter’s post, volume of a circle quadruples when diameter is doubled. Apparent air velocity at the end of a 50mm hose will be about a quarter that of a 26mm hose.

 

[PeterK]

Thanks all!
Yes the hose is clear as is the port on the saw.
Suppose it is possible there is some plugging on the HEPA filter that I can’t see.
Peter and Michael - I thought about using the 36 mm hose but haven’t tried it yet. Going to rig up a short 36 mm hose and give that a try later today hopefully.
Getting into the physics of airflow and that is what I guess I am interested in. Was starting to question what hose diameter is best for a CT collector.
Pete

 

[Gregor]

Suppose it is possible there is some plugging on the HEPA filter that I can’t see.

Take the HEPA-Filter out (out of the VAC and outside the room/house) to gently blow it out using compressed air.

I thought about using the 36 mm hose but haven’t tried it yet. Going to rig up a short 36 mm hose and give that a try later today hopefully.

Getting into the physics of airflow and that is what I guess I am interested in.
Was starting to question what hose diameter is best for a CT collector.

Simply said: Bigger is better (as long as we're talking diameter), straight and smooth is better than bend and rough (laminar vs. turbulent flow), shorter is better than longer (friction losses increase with length).

All up to a point, as you want enough airspeed (which is a function of the CFM vs. the diameter they go through) to take the whatever-sized particles with it so the hose won't clog.

In Peter's video he's testing more the static pressure (which though is somewhat meaningless for a vacuum) instead of the airflow (which is what does the extraction work), with the differences likely more being caused by leakage (like the bad reading on the white cyclone stemming from bad seals of the container) rather than stemming from increased friction losses.

 

[xedos]

Get yourself an anemometer if you want to study the physics of your setup.