Pentz cyclone questions

[JoshD]

New workshop is currently under construction, and I have now spent some months with wet towel round my head trying to absorb the mass of information on dust collection on Bill Pentz's site. My conclusion is that I would like to source a Pentz cyclone, install it in an enclosure outside, venting outside, and try it without filters.

One possibility is to buy ready built from ClearVue Cyclones in the US ... but shipping costs are huge: $1400 when I last checked; and VAT, duty, etc always come to much more than you think they should, not least because they are calculated on the gross cost including shipping.

So am I now exploring having a fabrication shop build a cyclone to Pentz's design (yes, I daresay theoretically I could do it myself, but I like woodwork, and metalwork never ends up working for me the way it does for the youtube guy). First question: how thick? Pentz talks about eg, 24 gauge (0.6mm) or thinner, but I saw something somewhere from a guy who talked about 2mm thickness (BTW this will probably end up being stainless steel: although galvanised is theoretically cheaper, one-off galvanising always seems to end up the same price as stainless ...).

And then there's the centrifugal fan: in the ClearVue product it sits directly on top of the cyclone; but none of the suppliers I've spoken to would approve of their fans being mounted with the shaft vertical like this. Nor have I found any fans with open backward curved impellers the way Pentz talks about: research so far shows plenty of closed backward curved impellers, suitable for light dust (which would be fine until I forget to empty the bin, then would probably be not happy at all) and open impellers either straight radial or forward curved. Forward-curved open impellers would seem to make a lot of sense in the Pentzian world: they're capable of working at relatively high pressure, so seem eminently suited to the task of trying to get a 6" duct to do the work of a 7" one. I'm looking at 3kW/4hp: at this level the closed backward-curved impeller based fans seem to stop working around 9" or 10" pressure (2250-2500Pa); but I'm looking at a forward-curved one that could deliver me 1000cfm even at 10" (2500Pa), and carries on working all the way to 14" (3500Pa). But they don't even get a mention on the Pentz site .... Preliminary calculations suggest I'll be looking at around 8-10" (2000-2500Pa) if I want to get 1000 cfm at the machine.

I'm planning 150mm ducting to the machines, with blast gates at the junction with the main artery. Main artery could be 150mm or 175mm---if 175mm I'm thinking about having a permanently open 75-100mm port at the end of the run; and I'm also wondering whether to switch the fan off when not actually in use---apparently air-starved fans are quite happy and sit there whirring away without drawing much current, so maybe I should just leave it running.

Advice welcome ....

Josh

 

[Inspector]

Your basic plan is fine with having the cyclone outside without filters. The Aussies do that almost always but they don't have a heating problem. You could if wanting to conserve the heat use filters when cold and divert to the outside when it is warmer. The dust in the air exiting the DC is invisible and just dissipates in the wind. You do have to consider the noise though if you have any neighbours within sight. For that enclose the DC in a shed and make a tortured path/labyrinth exhaust box/muffler to absorb the noise. Aussies have set them up like that and the next door neighbour only hears the same sound levels that a bathroom or kitchen stove hood makes and there is no coating of dust on their swimming pools either. Just don't forget to empty the barrel often but there are a number of bin sensors that sound/flash an alarm for the sort of thing.

Lots of people have made them with thin metals primarily because they can be bent and formed without rollers etc at home. A fab shop doesn't have that constraint so can easily work with thicker but there is no need to go to 2mm unless you or the fabricator has lots around. 1mm or 1.5mm is plenty and is more easily welded than thinner material. Most welders don't like galvanized as it is toxic when welded and Stainless is expensive. Plain steel is fine and you can paint it or have it sent out to a powder coater. If you have a flange welded to the joint between the cone and body that you bolt together with a gasket, has to be good though as you don't want any leaks, the inside can easily be painted too. When facing the impeller housing it can be made and welded traditionally rather than of plywood/MDF Bill designed for home fabrication. There have been some people make their cyclones of wood (plywood rings, staved solid, bending plywood) polycarbonate plastic sheet, not Perspex, fibreglass over a sacrificial styrofoam molds . You name it it has been tried but metal is generally easiest.

The ClearVue impellers use a taper lock shaft mounting system that locks the impeller tight to the motor shaft. They don't slip like cheap import impellers that rely on a key and setscrews or a centre bolt. The only times I have heard of any slipping were when they were not properly tightened and those are rare. I did have a 3hp 4bag DC's impeller loosen and it was horizontal, using a centre bolt to secure it. Here is a picture of the ClearVue 16" impeller with the backward inclined blades. You can see the welded on portion of the taper lock on the hub. The flanged conical portion when bolted to the three threaded holes grabs the shaft.

ClearVue used to publish a fan curve for their machines. You can see what kind of flows you will get with any given duct size. Unfortunately I can't seem to get the pdf to load into the thread. I will if somebody can tell me how.

If you use a 15" impeller and 4hp motor then you might as well run 6"/150mm all the way as expanding the main to 7" causes the airstream to slow down a little, with the possibility of some dust dropping out of the flow, not likely in this case but still possible. You will also need to reduce the pipe to 6"/150mm when you get to the cyclone anyway so staying with the smaller duct is better and a touch cheaper. You also simplify the ducts and fittings. Blast gates along the main line are more efficient than the more convenient position at the machine. The Aussie forum has an number of pictures and drawings of rotating blast gates mounted along the main duct, opened and closed with a loop of rope. They can have actuators attached if you want to activate them by switch manually or automatically when a machine is turned on. The motor will draw minimal power when all the blast gates are closed as the impeller is just spinning the air in a circle. You can reduce the startup current that way too. Leaving a full size gate open will help scrub the air but not a small one all the time. It would take away from the flow of the machine you need. I don't know what the motor you plan on using is rated for but ClearVue recommends no more than about six starts an hour or the motor builds up heat that doesn't dissipate fast enough, shortening the life of the motor. Leave it running between a lot of quick uses and turn it off if there will be lots of time between needs.

If you went to a 220V delta wound three phase inverter rated motor with a VFD powering it you don't get the heat build up and high amperage starts because it can be set to ramp up to speed over several seconds. You can slow it down between uses while getting some scrubbing benefits and you can overspeed the motor some to get a little more flow as long as you have the extra power from your mains. There is an Aussie running his at 70hertz. Running at 60 hertz will match the performance of our single phase power, 20% improvement over yours.

Soak your towel a little and ponder things.

Pete

 

[TheTiddles]

2mm stainless… holy cow, it’s going to be a thing of beauty, please post about it.

I’m presuming money is no object here or you could just buy an industrial unit for less than it sounds like you’re going to spend

 

[JoshD]

2mm stainless… holy cow, it’s going to be a thing of beauty, please post about it.

I’m presuming money is no object here or you could just buy an industrial unit for less than it sounds like you’re going to spend

I'm hoping to get away with 1 or 1.2 mm .... but let's see what the fabricators say!

 

[Sachakins]

Have you looked at this all in one solution
https://grovewoodmachines.co.uk/product/laguna-cflux3-cyclone-dust-collector/

 

[JoshD]

Your basic plan is fine with having the cyclone outside without filters. The Aussies do that almost always but they don't have a heating problem. You could if wanting to conserve the heat use filters when cold and divert to the outside when it is warmer. The dust in the air exiting the DC is invisible and just dissipates in the wind. You do have to consider the noise though if you have any neighbours within sight. For that enclose the DC in a shed and make a tortured path/labyrinth exhaust box/muffler to absorb the noise. Aussies have set them up like that and the next door neighbour only hears the same sound levels that a bathroom or kitchen stove hood makes and there is no coating of dust on their swimming pools either. Just don't forget to empty the barrel often but there are a number of bin sensors that sound/flash an alarm for the sort of thing.

Lots of people have made them with thin metals primarily because they can be bent and formed without rollers etc at home. A fab shop doesn't have that constraint so can easily work with thicker but there is no need to go to 2mm unless you or the fabricator has lots around. 1mm or 1.5mm is plenty and is more easily welded than thinner material. Most welders don't like galvanized as it is toxic when welded and Stainless is expensive. Plain steel is fine and you can paint it or have it sent out to a powder coater. If you have a flange welded to the joint between the cone and body that you bolt together with a gasket, has to be good though as you don't want any leaks, the inside can easily be painted too. When facing the impeller housing it can be made and welded traditionally rather than of plywood/MDF Bill designed for home fabrication. There have been some people make their cyclones of wood (plywood rings, staved solid, bending plywood) polycarbonate plastic sheet, not Perspex, fibreglass over a sacrificial styrofoam molds . You name it it has been tried but metal is generally easiest.

The ClearVue impellers use a taper lock shaft mounting system that locks the impeller tight to the motor shaft. They don't slip like cheap import impellers that rely on a key and setscrews or a centre bolt. The only times I have heard of any slipping were when they were not properly tightened and those are rare. I did have a 3hp 4bag DC's impeller loosen and it was horizontal, using a centre bolt to secure it. Here is a picture of the ClearVue 16" impeller with the backward inclined blades. You can see the welded on portion of the taper lock on the hub. The flanged conical portion when bolted to the three threaded holes grabs the shaft.

View attachment 126725

ClearVue used to publish a fan curve for their machines. You can see what kind of flows you will get with any given duct size. Unfortunately I can't seem to get the pdf to load into the thread. I will if somebody can tell me how.

If you use a 15" impeller and 4hp motor then you might as well run 6"/150mm all the way as expanding the main to 7" causes the airstream to slow down a little, with the possibility of some dust dropping out of the flow, not likely in this case but still possible. You will also need to reduce the pipe to 6"/150mm when you get to the cyclone anyway so staying with the smaller duct is better and a touch cheaper. You also simplify the ducts and fittings. Blast gates along the main line are more efficient than the more convenient position at the machine. The Aussie forum has an number of pictures and drawings of rotating blast gates mounted along the main duct, opened and closed with a loop of rope. They can have actuators attached if you want to activate them by switch manually or automatically when a machine is turned on. The motor will draw minimal power when all the blast gates are closed as the impeller is just spinning the air in a circle. You can reduce the startup current that way too. Leaving a full size gate open will help scrub the air but not a small one all the time. It would take away from the flow of the machine you need. I don't know what the motor you plan on using is rated for but ClearVue recommends no more than about six starts an hour or the motor builds up heat that doesn't dissipate fast enough, shortening the life of the motor. Leave it running between a lot of quick uses and turn it off if there will be lots of time between needs.

If you went to a 220V delta wound three phase inverter rated motor with a VFD powering it you don't get the heat build up and high amperage starts because it can be set to ramp up to speed over several seconds. You can slow it down between uses while getting some scrubbing benefits and you can overspeed the motor some to get a little more flow as long as you have the extra power from your mains. There is an Aussie running his at 70hertz. Running at 60 hertz will match the performance of our single phase power, 20% improvement over yours.

Soak your towel a little and ponder things.

Pete

Pete,

AS I've come to expect from you, an information-packed and superbly helpful reply! Agreed the ClearVue impellers look quality ... but I'm searching around for what I can buy here! I thought this (from a well known auction site) looked like a contender (I'd be buying 3kW/4hp version, 16" impeller, forward curving)

It seems that the thing with forward-curved impeller blades is that they carry on working at higher pressures then radial or backward-curved can cope with---which makes them on paper appealing for someone trying to get a 6" duct to carry what you'd usually use 7" for; you can see this in the graph

The backwards-curved impellers for the same 3kW/4hp seem to give up around 250 mm H2O pressure ....

Incidentally none of the fans I am looking at permit mounting like the ClearVue one, with shaft vertical, so I will have to duct from the cyclone outlet to the fan.

Josh

 

[JoshD]

Have you looked at this all in one solution
https://grovewoodmachines.co.uk/product/laguna-cflux3-cyclone-dust-collector/

Yes ... I don't want to say negative things specifically about Laguna, they have a fine reputation; but talking about this sort of product in general I think Bill Pentz would say that at 3hp power is inadequate, that you need 5hp to run a cyclone, that the cyclone shapes are non-optimal, and that after short while either the filters will be so clogged that the cfm plummets, or that they will be leaking the most toxic particles back into the shop. For my part I am not qualified to judge ...but knowledgeable people I respect have pointed me to Bill Pentz and it does seem to make sense ....

 

[Sachakins]

I agree whole heartedly with Bill Pentz design logic and processes, and have read a lot but not his entire site.

But also designs and types have progressed, the newer Gyro type turbine extractors have emerged at more competitive prices.

I wasn't advocating the brand, just the type, as they do have overhead motors and impellers.
Also, after reading further research, there is also an impact on efficiencies dependent on your particles mix, more chippings and less dust requires different cyclonic ratios than more dust and and less chippings, since I don't see that there is a one cyclone fits all solution.

Example from https://powderprocess.net/Equipments html/Cyclone_Design.html
...
"The approach is valid for standard cyclones with squared tangential inlets and with a small dust load in the order of max 10 g/m3. For different types of inlet or higher dust loads, some corrections are necessary.

 

[Inspector]

I'll have to admit the metric graphing has me struggling. I think it will work for you if you think the static pressure is enough to get the flows. Separating the blower and cyclone is not a problem as long as you use large radii elbows. I haven't seen any Pent cyclones made with one like that so I can't say with certainty. You might try asking Bill through hid site to see what he thinks of it. Not sure how long he might take to reply though. Posing the question on the Australian Woodworking site in their dust forum will get you a quick response from Bob the moderator of that section. DUST EXTRACTION
I figured how to get the CV fan curves to post. Had to take a screen shot and that .png file seems to work in Preview mode.

For the most part a 6"/150mm duct will max out at 1250cfm/2120M3h and will not appreciably increase until you start reaching shop vacuum static pressures. An 8"/200mm duct will flow twice as much as a 6"/150mm which is why the ClearVue max (now called CV1950) with its 16" impeller can run a couple machines at the same time.

Pete

 

[MikeK]

When I spoke with one of the Bernardo technicians about my 2.2kW/3HP blower, I asked about the orientation of the impeller since I intended on mounting the blower to the top of the cyclone. The technician told me they buy general purpose motors to be used interchangeably in vertical or horizontal installations. I have the RV 350 blower assembly, which is used in several Bernardo products in both vertical and horizontal applications, such as the RLA 1500 (vertical) and the DC 500E (horizontal).

I respect Bill Pentz's work and would have loved to find a 5HP motor with a 15-inch impeller; however, unicorn tears are easier to find in my area. I am satisfied with the 3HP blower and monitor the dust in my shop with a Dylos DC1700 air quality meter. The measured dust rarely exceeded the ambient background readings at the start of the day until I used the DeWalt miter saw. Then I had to take breaks and let the AC400 run for 15 minutes to scrub the air. I can use the table saw, band saw, router table, and belt/disc sander without seeing any concerning rises in the particle count.

I will make changes to my system to correct faults I introduced, but I would have no problems using it as is for my projects. For example, my cyclone with a 5-inch inlet and 6-inch outlet is sized for up to 3HP. I will replace it with a larger cyclone with a 6-inch inlet and outlet and sized for 3-5HP. At the same time, I'll replace my 120mm main ducting with 150mm or 160mm ducting and remove the two 90-degree bends I foolishly put in the duct at the cyclone inlet.

 

[Inspector]

Thanks for the link Sachakins. It is going to take a while to read through all of it.

Pete

 

[JoshD]

I agree whole heartedly with Bill Pentz design logic and processes, and have read a lot but not his entire site.

But also designs and types have progressed, the newer Gyro type turbine extractors have emerged at more competitive prices.

I wasn't advocating the brand, just the type, as they do have overhead motors and impellers.
Also, after reading further research, there is also an impact on efficiencies dependent on your particles mix, more chippings and less dust requires different cyclonic ratios than more dust and and less chippings, since I don't see that there is a one cyclone fits all solution.

Example from https://powderprocess.net/Equipments html/Cyclone_Design.htmla
...
"The approach is valid for standard cyclones with squared tangential inlets and with a small dust load in the order of max 10 g/m3. For different types of inlet or higher dust loads, some corrections are necessary.

View attachment 126782

I hope I didn't come across as dismissive, I'm new to this whole subject and trying to piece my way through; but my conclusion so far is that this is a massively technical area with numerous pitfalls. Big picture I think I'll end up with a system with 8-10" back pressure at 1000cfm .... but the Laguna (and also Axminster) top of the range cyclones stop working at 11", and are struggling at 10. Hard to have confidence that all will be well when sweet spot is so narrow ....

 

[JoshD]

When I spoke with one of the Bernardo technicians about my 2.2kW/3HP blower, I asked about the orientation of the impeller since I intended on mounting the blower to the top of the cyclone. The technician told me they buy general purpose motors to be used interchangeably in vertical or horizontal installations. I have the RV 350 blower assembly, which is used in several Bernardo products in both vertical and horizontal applications, such as the RLA 1500 (vertical) and the DC 500E (horizontal).

I respect Bill Pentz's work and would have loved to find a 5HP motor with a 15-inch impeller; however, unicorn tears are easier to find in my area. I am satisfied with the 3HP blower and monitor the dust in my shop with a Dylos DC1700 air quality meter. The measured dust rarely exceeded the ambient background readings at the start of the day until I used the DeWalt miter saw. Then I had to take breaks and let the AC400 run for 15 minutes to scrub the air. I can use the table saw, band saw, router table, and belt/disc sander without seeing any concerning rises in the particle count.

I will make changes to my system to correct faults I introduced, but I would have no problems using it as is for my projects. For example, my cyclone with a 5-inch inlet and 6-inch outlet is sized for up to 3HP. I will replace it with a larger cyclone with a 6-inch inlet and outlet and sized for 3-5HP. At the same time, I'll replace my 120mm main ducting with 150mm or 160mm ducting and remove the two 90-degree bends I foolishly put in the duct at the cyclone inlet.

Thanks Mike. I looked at Bernardo fans: specification says 400V, not 230/400; I'm not ruling them out because I may get 3phase; but for the moment it probably looks more economical to have 1ph supply and use VFD after rewiring 230/400V motor from star to delta ....

 

[MikeK]

Thanks Mike. I looked at Bernardo fans: specification says 400V, not 230/400; I'm not ruling them out because I may get 3phase; but for the moment it probably looks more economical to have 1ph supply and use VFD after rewiring 230/400V motor from star to delta ....

Most industrial tools with motors rated at or above 1.5kW here are normally 3-phase 400V delta. Since residential wiring in Germany is three phase, I usually buy 400V equipment if I have a choice.

 

[JoshD]

I'll have to admit the metric graphing has me struggling. I think it will work for you if you think the static pressure is enough to get the flows. Separating the blower and cyclone is not a problem as long as you use large radii elbows. I haven't seen any Pent cyclones made with one like that so I can't say with certainty. You might try asking Bill through hid site to see what he thinks of it. Not sure how long he might take to reply though. Posing the question on the Australian Woodworking site in their dust forum will get you a quick response from Bob the moderator of that section. DUST EXTRACTION
I figured how to get the CV fan curves to post. Had to take a screen shot and that .png file seems to work in Preview mode.

View attachment 126785

For the most part a 6"/150mm duct will max out at 1250cfm/2120M3h and will not appreciably increase until you start reaching shop vacuum static pressures. An 8"/200mm duct will flow twice as much as a 6"/150mm which is why the ClearVue max (now called CV1950) with its 16" impeller can run a couple machines at the same time.

Pete

Metric graphing: ~1800 m3/h is 1000cfm; on graph I sent that is rate just below 250mm H20 pressure aka 2500 Pa aka 10". Looks like Pentz fans do rather better, able to deliver 1000cfm at 10-12" and keep on going right up to 16": fantastic! But seems to be the exception rather than the rule. For example Geovent backward-curved closed impeller 14" fan, 3kW/4hp, gives up aorund 10" pressure ...

 

[Sachakins]

I hope I didn't come across as dismissive, I'm new to this whole subject and trying to piece my way through; but my conclusion so far is that this is a massively technical area with numerous pitfalls. Big picture I think I'll end up with a system with 8-10" back pressure at 1000cfm .... but the Laguna (and also Axminster) top of the range cyclones stop working at 11", and are struggling at 10. Hard to have confidence that all will be well when sweet spot is so narrow ....

No at all, have looked in the business/industrial sectors for the larger scale impellers etc, its unlikely you'll find anything in the hobby and retail outlets that will near to Bill's ideals.
Impeller fans in example Industrial Fan | Fan Impellers | Centrifugal Blower

 

[JoshD]

No at all, have looked in the business/industrial sectors for the larger scale impellers etc, its unlikely you'll find anything in the hobby and retail outlets that will near to Bill's ideals.
Impeller fans in example Industrial Fan | Fan Impellers | Centrifugal Blower

yes, i hadn't been to that specific site, but I'm working my way through ....

 

[JoshD]

No at all, have looked in the business/industrial sectors for the larger scale impellers etc, its unlikely you'll find anything in the hobby and retail outlets that will near to Bill's ideals.
Impeller fans in example Industrial Fan | Fan Impellers | Centrifugal Blower

@Sachakins the site you linked to will make any impeller to order; but so far I haven't found any off-the-shelf fans with open backwards-curved impellers (a la Pentz): lots of backwards-curved closed, and lots of radial (and a few forwards curved) open/paddle-blade impellers

 

[Inspector]

Don't write off a straight blade impeller completely. They are designed to handle the dirtier airstreams, including the odd chunk, at only a slight loss of airflow compared to the backward inclined ones. They are somewhat noisier though. One thing to keep in mind is the 16" static pressure of a CV impeller is at almost no flow. As are the claims of many DC sellers that say for example 2,000cfm and 8" of static pressure, they just are not at the same time. The 10" or 12" of static pressure at 1,000 CFM is at the impeller. You then have to subtract the static pressure losses of the ducts, hoses, elbows and drag through the machine from that 10" or 12" and as long as there is a reasonable amount of static pressure left you have the airflow you need. That is why a 1 1/2hp or 2hp DC runs out of suction with long ducts or hoses and people have fine dust settled throughout their shop. So the loss of 3" or 4" from the ducting isn't a factor with the bigger system you are wanting to make.

Pete

 

[JoshD]

@Sachakins mentioned Gyro type dust collectors/separators, which prompted me to go back and take a look at the Harvey/Axminster G700. I was quite impressed when I saw the capacity as 1110cfm with 6" ducting ... but this is then contradicted when you scroll down to graph slightly further on, which shows machine maxes out at ~750cfm, rough guess will deliver perhaps up to 600cfm with the sort of set up I expect to have ... which isn't really enough for 6" duct. The bigger Gyro collectors don't have graphs ... but if there's a single message I've taken from the Pentz site it's not to buy an extractor without studying the graph.

Back in the cyclone world, overnight I sent out a few requests to industrial suppliers to quote for material moving fan able to deliver 2000 m3/h at 2500Pa (1150cfm at 10" pressure): this looks like the best route, I am getting helpful replies.