CT-VA 20 - Swapping out right angle connectors for straight better?

[bwehman]

I've had the CT-VA since it came out and can't even compute the number of bags I haven't had to buy as a result, maybe 50+? Works great. Just wondering though - anybody think there could be more suction improvement by swapping out the 90-degree connectors for  straight connectors? The suction isn't shabby by any means, just always looking for that last big of extra performance.

 

[squall_line]

The newer models come with a straight connector and a 90-degree elbow, along with a second 90-degree elbow.  This allows the unit to work with the older MINI/MIDI as well as the newer MINI-I/MIDI-I.

I haven't done any comparisons between the straight and elbow to see which works better, other than requiring one or the other to be able to connect under the hose garage on the smaller models.

 

[mino]

Firstly, the cyclone unit itself is the narrow point. That is where 90%+ of the pressure loss happens and what then limits the air volume you get. Even if you had a straight D50 hose after that, it would have almost no effect on the air volume you get.

Secondly, the CT-VA is a mid-to-low air volume unit. Meaning, its separation efficiency is optimal at about middle vac power setting and goes down when the air volume gets too high - like when the inlet does not have a hose attached. When the airflow inside the CT-VA bin gets too fast it becomes turbulent and starts (slowly) sucking its previously separated dust. Even at default configuration and full vac power (CT 26) the air volume is slightly higher than optimal. The diameters of the cyclone piping are tuned to achieve sufficient air speed in the cyclone even at very low air volumes typical of sanding (without bleed air fitting). The price of this configuration is a lower maximum air volume one can drive through it.

In total, do not mess with the input hose unless there is some other reason - it is too short, too long, etc. for your placement of the unit.

If you need a high-volume cyclone, get the Oneida DD 2.5 set for those tasks and use the CT-VA for sanding and mid-volume tasks where it works well as is.

ADD:
I remember someone was testing it a couple years back, there is a thread around. With the bare CT26 and a D27/32 at 100% air flow and the D36 gives about 140% and with a 2.5M D50 it went up to about 170% of the default hose equivalent.

The CT-VA affected the max airflow with the D27/32 hose to about 90% and with the D36 it came back to about 100%, thus showing the bottleneck was the CT-VA as the hose pressure/flow loss effect was minimal.

If a 3.5 meter D27/32 hose had such a small effect, the 3' D32 hose connecting the cyclone to the vac must have even a smaller one, in the single percentage points. All that at the max vac power, at lower vac power levels or with a tool attached the differences would be even less.

 

[WillettBarrel]

There's two previous threads about the CT VA suction where folks have done various tests to identify areas for improvement. The 90-degree bend doesn't really have an impact; as others have mentioned, the cyclone itself is the choke point.

However, it has been tested and shown that a layer of plumbers tape around the internal components, sealing all the air gaps, does improve suction a small, but not insignificant, amount.

I wound up selling mine. Though it did save CT bags, I was still buying VA liner bags. Ultimately, the suction loss was more critical to me.

 

[bwehman]

All good input, make sense!

 

[mino]

There's two previous threads about the CT VA suction where folks have done various tests to identify areas for improvement. The 90-degree bend doesn't really have an impact; as others have mentioned, the cyclone itself is the choke point.

Alhough it does not hurt, there is no real need to mess with any plumber's tape. The cyclone parts are precise and will "attach" themselves by the air suction when in operation. This of course presumes the parts put in place correctly.
What does help is not using the bin liner - the seal around the bin is almost perfect without a liner but with it it can leak signifficantly on the bends - a non-issue for drywall work but a problem for ... say .. sawing ...

Allow me a couple points for posterity to add to that:

There is pretty much no reason to use the "liner" bags *unless* you are on a professional drywall crew etc. and there are good reasons not to even besides the cost.

Drywall dust tends to stick to the plastic and creates huge ammounts of dust when emptying => liner bags help.

Wood (or paint) dust has no such properties and can be very easily (and cleany) emptied. In that case using the liner bags is actually detrimental as the uneven internal surface in the cyclone reduces the separation efficiency even further.

@ OP
Do not let the acrylic bin fill completely. It should be emptied after about 1/3 full, at the absolute worst when 1/2 full. When too full, the cyclone will start "sucking" its own separated dust.

 

[ChuckM]

To be emptied whenever it's 1/3 full? I'm not familiar with this product, but if that's true, the unit needs to be redesigned. I never need to empty my dust deputy bucket until it's 4/5 (?) full or more.

 

[WillettBarrel]

There's two previous threads about the CT VA suction where folks have done various tests to identify areas for improvement. The 90-degree bend doesn't really have an impact; as others have mentioned, the cyclone itself is the choke point.

Alhough it does not hurt, there is no real need to mess with any plumber's tape. The cyclone parts are precise and will "attach" themselves by the air suction when in operation. This of course presumes the parts put in place correctly.
What does help is not using the bin liner - the seal around the bin is almost perfect without a liner but with it it can leak signifficantly on the bends - a non-issue for drywall work but a problem for ... say .. sawing ...

I'm not sure if you're speaking from an experiential or theoretical basis. But if you search the forum for "suction loss" you'll see two different users (I was one of them) have measured air speed and gathered empirical evidence that sealing the internal components improves suction.

Many variables could go into it, so your mileage may vary.

 

[Coen]

[...]
@ OP
Do not let the acrylic bin fill completely. It should be emptied after about 1/3 full, at the absolute worst when 1/2 full. When too full, the cyclone will start "sucking" its own separated dust.

That too probably highly depends on the type of dust it catches. The last time I used a CT-VA it was sucking up moist-brick "dust" (from 55mm hammer drill). I don't think that goes airborne again that early...

 

[mino]

To be emptied whenever it's 1/3 full? I'm not familiar with this product, but if that's true, the unit needs to be redesigned. I never need to empty my dust deputy bucket until it's 4/5 (?) full or more.

Nope, works as designed, it is just misunderstood at times.

The bin in the CT-VA acts both as a waste bin and as the "air cyclone" space where the air rotates and the separation happens. That is why (and the only way) the unit can be so compact on height. When used for the heavy drywall dust one can probably go up to 2/3 (as in the Festool images), but not with wood which is very easy to disturb even after it settles.

The bucket is like 40 liters total, so emptying at about 1/3 full means about 10-15 liters of dust.

Were one to "compress" the DD, for example, into the same height, the same effects will be seen - one cannot compress the cyclone for particle separation reasons so would have to make a very shallow bucket in the DD case. Would still end up with a higher unit, getting a same-capacity bin ...

If someone has such a huge dust generation this is a problem, one can just get the CT-VA cyclone unit and attach it to a bigger bin, but then the ability to see the bin fullness is lost ... so not sure that would make much sense ... probably DD is a better option then.

That too probably highly depends on the type of dust it catches. The last time I used a CT-VA it was sucking up moist-brick "dust" (from 55mm hammer drill). I don't think that goes airborne again that early...

Absolutely, I was assuming dry wood dust ... which is the worst case.

There's two previous threads about the CT VA suction where folks have done various tests to identify areas for improvement. The 90-degree bend doesn't really have an impact; as others have mentioned, the cyclone itself is the choke point.

Alhough it does not hurt, there is no real need to mess with any plumber's tape. The cyclone parts are precise and will "attach" themselves by the air suction when in operation. This of course presumes the parts put in place correctly.
What does help is not using the bin liner - the seal around the bin is almost perfect without a liner but with it it can leak signifficantly on the bends - a non-issue for drywall work but a problem for ... say .. sawing ...

I'm not sure if you're speaking from an experiential or theoretical basis.

Experience supported by theory.

It is very easy to mis-align the parts when one takes the cyclone apart, one needs to be gentle and take care of the details. No force (at all) is needed when the parts are properly aligned.

Also this is supported by the theory how airflows at various pressures works - any "bleed" air introduced has verry little effect when this is between the air-restrictive place and the vacuum source which is not capacity constrained - this is the case of a CT 26 and to a lesser extent CT Mini/Midi when used with the CT-VA.

Secondly, any such "bleed air" could have signifficant effect on maximum air pressure (when flow is blocked at the tool) but will not have such an effect once the restriction is released as.

E.g. if one is using the vac with Maffel air holding system => can face an issue. If one is using it with sanding => non-issue. Etc.

I am not sure what is your use case, so can imagine it could be a problem. But for (most) woodworking jobs we do not rely on the air pressu anywhere as much so I find it a non-issue.

Thinking about it a bit more, you do have a point that the CT-VA is not suitable for maximum-pressure-required use cases and in those cases one may consider to tape/glue it. Though I would argue for those use cases one should not be using a cyclone in the first place.

YMMV indeed

 

[WillettBarrel]

There's two previous threads about the CT VA suction where folks have done various tests to identify areas for improvement. The 90-degree bend doesn't really have an impact; as others have mentioned, the cyclone itself is the choke point.

Alhough it does not hurt, there is no real need to mess with any plumber's tape. The cyclone parts are precise and will "attach" themselves by the air suction when in operation. This of course presumes the parts put in place correctly.
What does help is not using the bin liner - the seal around the bin is almost perfect without a liner but with it it can leak signifficantly on the bends - a non-issue for drywall work but a problem for ... say .. sawing ...

I'm not sure if you're speaking from an experiential or theoretical basis.

Experience supported by theory.

[/quote]

quote author=mino link=topic=72627.msg702612#msg702612 date=1698423376]

I am not sure what is your use case, so can imagine it could be a problem. But for (most) woodworking jobs we do not rely on the air pressu anywhere as much so I find it a non-issue.

Thinking about it a bit more, you do have a point that the CT-VA is not suitable for maximum-pressure-required use cases and in those cases one may consider to tape/glue it. Though I would argue for those use cases one should not be using a cyclone in the first place.

YMMV indeed

Yep! You're nail on head.

If you're in a production space or stand alone shop, your concern is more likely to be cost efficiency. You want to save money on consumables, and you're less concerned about dust collection efficiency. If dust escapes during extraction, who cares? It's a shop.

If you're in a space where dust collection efficiency is the priority, like a client's home or a hobbyist working in a garage next to vehicles, you want max air flow. As you said, the CT VA 20 (or any Cylcone) really isn't you're friend. They're effectively giant diffusers and inherently have lower suction. Hence why I sold mine. It didn't fit my use case.

Where the OP is coming from is a use case where he loves the CT VA 20, but wants to improve suction. I agree with your theory; it's quite sound. Empirically measured, independently confirmed data says sealing the internals is the only way to produce a meaningful increase in suction with the CT VA 20 in the system.