Thread: CV - 1800 vs Max

Originally Posted by pjt

point being is that if the vel. is a bit less than 4000fpm the dust won't necessarily fall out of suspension, what might be an interesting experiment is to see what flow/vel the dust starts to settle in pipework, I would say BP has done this but not sure I have seen any info on his site.
Given that we have hard data on flow/vel in a real world DE system (John S.'s) my feeling would be that vel. in a 225mm pipe via a 1800 or max will still be ok, even if both run at 50hz.

I should add that I am not suggesting that we shouldn't aim for the 1000/4000 figures, the main figure to aim for is the 1000cfm and if the velocity is <4000fpm in a given pipe size but not blocking pipes I'd be happy at that.
Pete

Pete,

As soon as I read your post it was clear you were likely right. The 4,000 FPM is what we need to keep vertical ducts clear. According to Bill Pentz's site we need about 2,800 FPM to keep horizontal ducts clear. Bob indicated in an earlier post that this is about what Mick could expect in an 8 inch duct with one 6 inch port open. So, because this 8 inch section of duct is horizontal, Mick is likely in pretty good shape. I would still use a clear PVC panel, just in case off-cuts such as those that zip into the ductwork from my saws settle in the larger duct, and because it is both fun and comforting to watch the dust/chips zip through the ductwork and around the cyclone.

Instead of making the bigger section of duct square, why not pull the transition off the inlet of a Max and make the duct the same sized rectangle as the cyclone inlet and attach it to that rectangular inlet? That would minimise disturbance to the air (no transition at the cyclone) as it enters the cyclone.

Cheerio!

John

Originally Posted by John Samuel

BobL responded to a similar query recently and talked about creating a lance with air being provided through it by a compressor.

If the installation were mine and I decided to put in a shortish 8" duct, I likely would do what Bob suggested, make my own 8 inch square duct, but make one side (or the bottom) from 3 mm clear PVC sheet, held in place with self tapper screws and some sealant (or even better a strip of foam door seal). That way you could see if build up was occurring in the duct and the clear PVC could be pulled off in a flash if necessary to do a clean out.

John,

thanks once again. Some clear PVC sheet on the bottom and built in such a way that I can pull it apart reasonably easily seems straight forward enough.

Showing (once again) my ignorance as a handyman, why self tappers and not just drill a pilot hole and screw in?

thanks

Mick

Originally Posted by mick59wests

John,

thanks once again. Some clear PVC sheet on the bottom and built in such a way that I can pull it apart reasonably easily seems straight forward enough.

Showing (once again) my ignorance as a handyman, why self tappers and not just drill a pilot hole and screw in?

thanks

Mick

Any screw with a flat head would likely do the job ... I just happen to always have a supply of self tappers and have used them extensively and successfully on 3 mm MDF and clear PVC.

Putting the clear PVC on the side may be a better idea than on the bottom. That way if you do need to clear it the crud won't fall on top of you when you remove this panel.

Cheerio!

John

Originally Posted by John Samuel

Pete,

As soon as I read your post it was clear you were likely right. The 4,000 FPM is what we need to keep vertical ducts clear. According to Bill Pentz's site we need about 2,800 FPM to keep horizontal ducts clear. Bob indicated in an earlier post that this is about what Mick could expect in an 8 inch duct with one 6 inch port open. So, because this 8 inch section of duct is horizontal, Mick is likely in pretty good shape. I would still use a clear PVC panel, just in case off-cuts such as those that zip into the ductwork from my saws settle in the larger duct, and because it is both fun and comforting to watch the dust/chips zip through the ductwork and around the cyclone.

It is sounding better and better to me. Everything new that comes up supports getting a Max. I also like Pete's idea of seeing when the dust starts dropping out of the air (probably more for fun than anything else) but I'll be more worried about the CFM so without good measurements for this I don't think I'd want to run even a Max below 50hz

Originally Posted by John Samuel

Instead of making the bigger section of duct square, why not pull the transition off the inlet of a Max and make the duct the same sized rectangle as the cyclone inlet and attach it to that rectangular inlet? That would minimise disturbance to the air (no transition at the cyclone) as it enters the cyclone.

John - another great idea

Originally Posted by John Samuel

Putting the clear PVC on the side may be a better idea than on the bottom. That way if you do need to clear it the crud won't fall on top of you when you remove this panel.

John

That would make sense (probably why I had not thought of it ) and maybe I'll do both so I can see it move as well .

I'm certainly going to be busy in my retirement as I am moving out of Sydney next week and am in the process of getting a quote from shedman

Originally Posted by John Samuel

As soon as I read your post it was clear you were likely right. The 4,000 FPM is what we need to keep vertical ducts clear. According to Bill Pentz's site we need about 2,800 FPM to keep horizontal ducts clear. Bob indicated in an earlier post that this is about what Mick could expect in an 8 inch duct with one 6 inch port open. So, because this 8 inch section of duct is horizontal, Mick is likely in pretty good shape. I would still use a clear PVC panel, just in case off-cuts such as those that zip into the ductwork from my saws settle in the larger duct, and because it is both fun and comforting to watch the dust/chips zip through the ductwork and around the cyclone.

I agree the 4000 fpm is a nominal value. The air inside the pipe does not all travel at the same speed anyway, with the air flow at the walls of the duct flowing around 30% slower than stuff in the middle.

One thing I did not take into account in my calculations yesterday was that by the time ducting and machinery is attached, as you measured, the flow rates in a 150 mm duct are more like 850 cfm. In a 225 mm pipe that will generate air speed of 1924 fpm which is now well below even the 2800 fpm supposed needed for horizontal pipe.

The only hard number evidence for sawdust drop out was for my old 1HP 4" ducted system where the sawdust was dropping out of vertical ducting at around 3400 fpm.
For horizontal ducting I had a lot of problems below about 1500 fpm

Instead of making the bigger section of duct square, why not pull the transition off the inlet of a Max and make the duct the same sized rectangle as the cyclone inlet and attach it to that rectangular inlet? That would minimise disturbance to the air (no transition at the cyclone) as it enters the cyclone.

Good idea.

Originally Posted by BobL

I agree the 4000 fpm is a nominal value. The air inside the pipe does not all travel at the same speed anyway, with the air flow at the walls of the duct flowing around 30% slower than stuff in the middle.

One thing I did not take into account in my calculations yesterday was that by the time ducting and machinery is attached, as you measured, the flow rates in a 150 mm duct are more like 850 cfm. In a 225 mm pipe that will generate air speed of 1924 fpm which is now well below even the 2800 fpm supposed needed for horizontal pipe.

The only hard number evidence for sawdust drop out was for my old 1HP 4" ducted system where the sawdust was dropping out of vertical ducting at around 3400 fpm.
For horizontal ducting I had a lot of problems below about 1500 fpm

Bob,

Your figures are in pretty good agreement with mine.

If we use an average of 900 CFM @ 4,581 FPM (for my system) through a 6 inch duct, that equates to 2,046 FPM through a 9 inch duct. I reckon Mick is likely OK if he proceeds with a rectangular duct 4 feet long attached to the rectangular cyclone inlet with one side made of clear PVC that is removable.

I ran some trials with my system at 50 Hz, or about a 20% drop in flow. There was still enough airflow to pull cedar off-cuts up the riser for the table saw, through the ducts and into the cyclone. A 20% drop in flow means I was getting around 720 CFM at 3665 FPM (6 inch pipe). A couple of these off cuts got stuck in the corrugated 4 inch flexy. A shake of the flexy soon had them on their way, but anything that hit the 6 inch line zoomed off to the cyclone (to be expected ... lots more air arriving from the saw cabinet).

Cheerio!

John

On the subject of dust extraction, I am purely an armchair "expert", and that expertise is at a low enough level, so please feel free to ignore my comments.

It seems that the cost of the ducting is at least as much of an issue as the cost of the CV. Based on what I've read here (pricing and spec wise), I'd go for the Max, run it straight off 50hz mains, and save money on the ducting by using 6" and no VFD. That leaves a few hundred $ to making the Max affordable and leaves you a staged upgrade path. By upgrading some of the ducting later you will be able increase your airflow, and when that is no longer enough, you install a VFD and run it at 60hz.

Originally Posted by Colin62

On the subject of dust extraction, I am purely an armchair "expert", and that expertise is at a low enough level, so please feel free to ignore my comments.

It seems that the cost of the ducting is at least as much of an issue as the cost of the CV. Based on what I've read here (pricing and spec wise), I'd go for the Max, run it straight off 50hz mains, and save money on the ducting by using 6" and no VFD. That leaves a few hundred $ to making the Max affordable and leaves you a staged upgrade path. By upgrading some of the ducting later you will be able increase your airflow, and when that is no longer enough, you install a VFD and run it at 60hz.

Colin,

my understanding was that it was a 3-phase motor so if you only have single phase power (like me) then a VFD is essential. Having said that, my knowledge of things related to electricity is very limited (I have learnt more on this forum in the last 2 months than all previous knowledge). You are right in that going beyond 150mm ducting increases the cost significantly

cheers

Mick

Sorry. I did warn you though.

The Max is available in single phase, but that would make adding a VFD later a lot trickier, as single phase output VFDs are less common, and I think often only sold for smallish motors.

If you wanted to add variable speed to a machine with a single phase motor later, rather than purchasing a single phase variable speed setup, it may be cheaper to replace the single phase motor with a used 3 phase motor. Used 3 Phase motors are relatively cheap and because they are relatively simple in construction and built more ruggedly than many single phase motors they will last for a long time. You can also probably on-sell your single phase motor for more than double what you pay for a used 3 phase motor of a similar power rating.

However, it's still not as straightforward as it sounds because
- the motors have to be of the correct wiring configuration
- if you cannot do it yourself then calling in a sparky to do this may involve $$$ and some sparkies will not want to deal with a used motor
- there may be mechanical adaptations required to mount the replacement motor to the impeller.

Originally Posted by BobL

If you wanted to add variable speed to a machine with a single phase motor later, rather than purchasing a single phase variable speed setup, it may be cheaper to replace the single phase motor with a used 3 phase motor. Used 3 Phase motors are relatively cheap and because they are relatively simple in construction and built more ruggedly than many single phase motors they will last for a long time. You can also probably on-sell your single phase motor for more than double what you pay for a used 3 phase motor of a similar power rating.

However, it's still not as straightforward as it sounds because
- the motors have to be of the correct wiring configuration
- if you cannot do it yourself then calling in a sparky to do this may involve $$$ and some sparkies will not want to deal with a used motor
- there may be mechanical adaptations required to mount the replacement motor to the impeller.

Bob / Colin62,
I like the different ideas from Colin62 but I'll go with the 3-phase motor and VFD. One less thing to have to deal with down the track

cheers

Mick

Hi Mick/Colin 62
As far as I am aware CV's are not available with Australian single phase motors. All CV in Au are supplied with 3phase motors. Check with Stephen But I am pretty sure I am right.

If you do not have 3phase power available your only options are a VFD or other Phase Convertor. The VFD is by far the better option.
Ron

Originally Posted by ronboult

Hi Mick/Colin 62
As far as I am aware CV's are not available with Australian single phase motors. All CV in Au are supplied with 3phase motors. Check with Stephen But I am pretty sure I am right.

If you do not have 3phase power available your only options are a VFD or other Phase Convertor. The VFD is by far the better option.
Ron

yes, Stephen confirmed - it is a 3-phase motor so a VFD is required if you only have single phase power. He sources a compatible one

cheers

Mick