Duct sizes for dual ports off 6" main

[Craig Behnke]

I recently acquired a used DC, a PSI Tempest, 3.5HP, 15" impeller. The distance from the DC to my TS and Router is about 10-12 feet (see attached PDF for a schematic). I would like to have two ports for DC on my TS (cabinet port and a blade guard/overhead port) and Router (cabinet and fence ports).

I have a 6" main duct. For the Router I have a 6x6x6 wye that I'm proposing to use to drop off the main and connect to a 6x6x4 wye. That gives me two potential ports, a 6" and a 4" to the Router. The TS is at the end of the main line, so I'll use an elbow to drop the main line and then use a 6x6x4 wye to establish two ports.

What is an effective duct size combination for good chip and dust collection on the tools (keeping enough velocity and CFM etc to do a good job)? Should I keep the 6" and 4" and run them to tools? Or should I reduce the 6" to a 5" and use a 5" and 4" combo on them?... or reduce the 6" to a 4" and use dual 4" ports on them?

I'll only run 1 tool at a time.

Thanks for the input.

[David Kumm]

Craig, It depends on how much velocity you have coming out of the 6" main at each machine. Generally you can get two 4" from a 6" but due the the short runs you might be running 5000 fpm from the 6 or 1000 cfm. The gates and flex will cause some loss but two 4" will probably go 4500 fpm if that is the case. The blade hood may work fine with a 3" port and the saw port may only be 4" anyway. I would opt for keeping more velocity going into the saw and use a 5" flex into the saw port even if the opening is restricted to 4. I'm assuming the 1000 cfm is available here. If you can borrow an anemometer from and HVAC guy you will know for sure what the machine is pulling at all openings and that will really help you with the piping. Anything else is an educated guess at best. Dave

[Craig Behnke]

Velocity off the main? Sheeeeeet, I dunno.

The marketing materials state the unit has 2500 cfm "free air" (i've not heard that measure before) and the the airflow curve (i've seen those before) is about 1500 cfm at 4 inches of SP and 1300 at 8 inches of SP. All of that info + $1 will get me a Venti, sugar-free, non-fat, vanilla soy, decaf, no foam, extra hot, Peppermint Chocolate Mocha with a light whip at Starbucks.

I don't know how to accurately measure the SP but here is what I do know: The duct is spiral steel, the DC is about 12 ft away from the tools, and there are two 90 degree turns from the DC to the tool. All the ductwork is the "premium" level from Penn State Industries.

I can pick all the port sizes except for one...the fence on the router. It's not something i'm going to modify. So i can go with 5" into the TS and Router cabinets if that is desirable.

[Rod Sheridan]

Craig, my saw has a 5" cabinet connection and a 2" overhead guard connection, fed from 6" mains.

It works great..................Rod.

[David Kumm]

Craig, the cfm numbers seem a little optimistic but even so you have enough to run 5" into the saw and probably three into the blade. When you get below 3" on a blade guard you almost need to use a shop vac as you can't get enough air through the smaller port to really control the dust- at least with my saw. Dave

[ian maybury]

There seems to be a fair bit of flexibility - you see 5+2in, 4+4in and 5+4in diameters mentioned, depending on the system and who is writing.

The basic starting point is probably that the combined cross sectional area of the two ducts should be similar to that of the 6in (or whatever size) duct so that the same velocity/air speed is maintained before and after the split - less a little area in the case of the split to take account of the fact that the resistance to flow in the two ducts combined will be more. (maybe less 15 - 20% if the combined surface area is the deciding factor?)

It's fairly approximate, in that in the end we're basically tied into stock duct sizes anyway.

Other factors are probably which extraction point do you feel is most important (would benefit from having the best airflow), and as the guys say are the related machine ports likely to cause more or less restriction.

Another consideration is that of how strong a flow your system is generating in the 6in duct. If you have lots of velocity/fpm then it's probably possible to go to say the 5+4in. The risk if you overdo it is that in a negative situation (e.g. dirty filters, restrictive machine hoods) the velocity in one of the vertical legs could get a little lower than is ideal for effective transportation....

ian

[Craig Behnke]

the cfm numbers seem a little optimistic

I agree, but it's all I have to go on right now as the system was never run by the previous owner, I don't have the system up and running yet, and even if I did, I don't have tools to measure the cfm/velocity/everything else. I figured that since I bought the system used, the company that made it may not opine on the layout, but I may just give them a call to see what they say...ya never know, they may do it gratis or for a reduced rate.

It's actually a strange/sad story of this DC system. The cyclone and ductwork was purchased in September 2009 as a complete system from PSI (penn state industries), brand new, with the ductwork designed by PSI. The gentleman who purchased it passed away three months later in December 2009 before it was ever even installed or even taken out of the boxes. It was in the original boxes until this weekend when I purchased it from a friend of the deceased.

[Paul Wunder]

Craig,

There is the "ideal" and then there is the "practical". Let's start with the practical: For a 10" typical table saw, the lower dust port is 4", and a typical blade guard port will run from 2 1/2" TO 4". You are running a decently powered cyclone with only a 12' main run. I would keep the mains at 6" and split to a 6X4X4 for the table saw. You may need reducers to get you to the actual size of the port on the blade guard collector (Bigger is better and you can certainly use a 4" above and 4" below that is fed from a single 6" main) For the router table, I would use a 4" port to the bottom of the table and a 2 1/2" to the fence (typical fences use 2 1/2". That too can be fed from a single 6" main.

Congrats on the "new" cyclone. If you do not have an overarm blade guard with dust pickup you may want to look at the Sharkguard. It has excellent dust pickup. I use the one with the 4" port and I have a 4" lower port for my 10" cabinet saw. Excellent dust control. I am running a ClearVue with a single 6" main. The table saw is about 25' feet from the cyclone

Bill Pentz will want bigger ports at each machine, but he will agree that in a single man shop with short runs that 6" mains should not be reduced until you get close to the machine port.

Paul

[David Kumm]

Craig, though the talk gets more technical you bought the correct system for your application so you got the hardest part of dust collecting right. Undersized is fatal and everything else can be adjusted so you are golden. I looked at the system curve and if it were mine I would run 7" mains and take all the risk out of the deal. Even if you just go around the first elbow you will improve cfm. While probably not necessary, the 7" mains would allow for any combination of gates you might need with your current machines or what you might upgrade to in the future. Dave