DC System which way to go?
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what size Jet DC?
I have the 1 1/2 HP model which I think has 1100 CFM of air flow.
The newer models have the Vortex cone:
Is this what you are referring to? Or do you mean a cyclone system?
I don't think it matters whether you use the metal or the PVC because from what I know that model doesn't flow enough air to be highly efficient. It will work OK, just not top notch performance. Check out this site and you'll see what I mean:
http://billpentz.com/woodworking/cyclone/index.cfm
http://billpentz.com/woodworking/cyclone/blower.cfm
here's an excerpt from the Blower description:
Finally knowing our airflow and pressures we can look up our needed information from a good fan table. Also that table lets us pick the blower opening which matches our ducting size. Unlike again some of the nonsense advertizing, with small shops we should have a consistent size duct going right from our blower to each of our tools. Smaller duct sizes kill the airflows needed to keep larger mains from plugging or building up ducting dust piles that pose a serious fire risk. Going to the steel pressure blower fan table shared by Cincinnati Fan we see by looking down the 12” pressure column the first blower with a 6” inlet that will move at least our needed 1000 CFM is a 15.5” diameter impeller with 3.5” tall blades. The blower table shows this impeller will move a real 1022 CFM at 12” and draws a real 3.44 hp. To size our blower motor we simply look at this same impeller at our minimum resistance level. This 15.5” diameter impeller at 4” of resistance moves a real 1957 CFM and draws a real 4.88 hp which is why I have long recommended use of a 5 hp blower motor with at least a 15” diameter impeller and 5” diameter ducting.
Almost all small shop vendors now supply even their larger cyclones with only 14” diameter impellers. We can use the same blower table and see that at 9” of resistance a 14” diameter impeller with 6” ducting only moves 767 CFM and pulls 2.05 hp. That is close enough that a 2 hp motor would work just fine, but look at what kind of airflow we get at 12". At 12" resistance this 14" impeller moves so little air with such an unsteady flow that it does not even have a value in this table. In short, at normal maximum expected resistance a 14" diameter impeller does not even move enough air to provide the needed 350 CFM needed for good "chip collection". Next look at that same table and see what happens to the horsepower demand when the resistance is only 4” with that 14” diameter impeller. At 4” of resistance that impeller moves 1543 CFM while pulling 3.09 hp. Now look at that same table at what happens during the vendor supplied tests that instead use an 8” opening with 1” of total resistance. The airflow climbs to 1893 CFM while the horsepower climbs to 3.68 hp. Because the normal fixed speed 3450 RPM induction motors we use to power our dust collectors are made to pull starting loads six or more times their running loads, our vendors can get by with quick tests at these kind of horsepower loads. Unfortunately, if these loads go on for a few minutes the motors will quickly overheat and burn up.
I have the 1 1/2 HP model which I think has 1100 CFM of air flow.
The newer models have the Vortex cone:
I don't think it matters whether you use the metal or the PVC because from what I know that model doesn't flow enough air to be highly efficient. It will work OK, just not top notch performance. Check out this site and you'll see what I mean:
http://billpentz.com/woodworking/cyclone/index.cfm
http://billpentz.com/woodworking/cyclone/blower.cfm
here's an excerpt from the Blower description:
Finally knowing our airflow and pressures we can look up our needed information from a good fan table. Also that table lets us pick the blower opening which matches our ducting size. Unlike again some of the nonsense advertizing, with small shops we should have a consistent size duct going right from our blower to each of our tools. Smaller duct sizes kill the airflows needed to keep larger mains from plugging or building up ducting dust piles that pose a serious fire risk. Going to the steel pressure blower fan table shared by Cincinnati Fan we see by looking down the 12” pressure column the first blower with a 6” inlet that will move at least our needed 1000 CFM is a 15.5” diameter impeller with 3.5” tall blades. The blower table shows this impeller will move a real 1022 CFM at 12” and draws a real 3.44 hp. To size our blower motor we simply look at this same impeller at our minimum resistance level. This 15.5” diameter impeller at 4” of resistance moves a real 1957 CFM and draws a real 4.88 hp which is why I have long recommended use of a 5 hp blower motor with at least a 15” diameter impeller and 5” diameter ducting.
Almost all small shop vendors now supply even their larger cyclones with only 14” diameter impellers. We can use the same blower table and see that at 9” of resistance a 14” diameter impeller with 6” ducting only moves 767 CFM and pulls 2.05 hp. That is close enough that a 2 hp motor would work just fine, but look at what kind of airflow we get at 12". At 12" resistance this 14" impeller moves so little air with such an unsteady flow that it does not even have a value in this table. In short, at normal maximum expected resistance a 14" diameter impeller does not even move enough air to provide the needed 350 CFM needed for good "chip collection". Next look at that same table and see what happens to the horsepower demand when the resistance is only 4” with that 14” diameter impeller. At 4” of resistance that impeller moves 1543 CFM while pulling 3.09 hp. Now look at that same table at what happens during the vendor supplied tests that instead use an 8” opening with 1” of total resistance. The airflow climbs to 1893 CFM while the horsepower climbs to 3.68 hp. Because the normal fixed speed 3450 RPM induction motors we use to power our dust collectors are made to pull starting loads six or more times their running loads, our vendors can get by with quick tests at these kind of horsepower loads. Unfortunately, if these loads go on for a few minutes the motors will quickly overheat and burn up.
Not sure where my mind was when I said vortex, I meant cyclone. I plan on purchasing a 2 HP or larger machine. I was going to last year but bought a powermatic wood lathe instead. Not sure the cost different between HVAC and PVC. I have priced PVC but not the metal HVAC. If there is not big difference in price and ease of installation I will go with the least expensive.
Tom
Tom
Metal vs plastic:If you're asking this question,then go with plastic.And not being the least bit disrespective.
You'll be able to source your parts easier.Metal is a factor when you are a commercial shop and/or,you have waaaaay too many machines.Metal also shines(ha) when you have to have custom parts fabricated.Plastic is always just a "make do" situation.....but,if thats all you need?
Imagine a 5-12 inch transition...that's 3' or so long.In this we have several "wyes" coming in from below.These wyes are coming into that transition.In metal this is maybe a 2 hour fitting(labor to make).In plastic it would be a mess.
In general....the more complicated the "system"...the more it rewards metal.Keep it simple,1/2 dz or so machines,and plastic works O.K.
You'll be able to source your parts easier.Metal is a factor when you are a commercial shop and/or,you have waaaaay too many machines.Metal also shines(ha) when you have to have custom parts fabricated.Plastic is always just a "make do" situation.....but,if thats all you need?
Imagine a 5-12 inch transition...that's 3' or so long.In this we have several "wyes" coming in from below.These wyes are coming into that transition.In metal this is maybe a 2 hour fitting(labor to make).In plastic it would be a mess.
In general....the more complicated the "system"...the more it rewards metal.Keep it simple,1/2 dz or so machines,and plastic works O.K.
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When you do your pricing on the duct work, consider the fittings cost first, that's where most of the dollars go. If you wind up with PVC, be sure to get the right stuff.....since it's called by so many names (and Skippy Stockboy usually doesn't know any of them) look for the proper markings on the side: you want ASTM D2729, that's the thinnest, least costly pipe. You can get by with 3034, but it's heavier, costs more, and is beyitch to try and hang from the ceiling by yourself (DAHIKT).
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