Dust collection ducting advice?

[Pete Costa]

Hello all, I’m looking for advice on sizing my fixed dust collector ducting. I recently picked up a used PSI Tempest 142CX to replace my older portable, non-HEPA filter unit. Although the owner’s manual says it has a 6” inlet, it actually has a 5”. Additional specs below:

• 2 HP
  
• 14” impeller
  
• Max CFM (free air) 1900 CFM
  
• Max static pressure 10.6”

I ran a jury-rigged test using lots of 5” flex hose and unsealed fittings to connect it to my machines (over their actual final distances). I’m happy with the performance and expect it can only improve when I get it properly set up.

So here’s the question - what are the implications of using 6” or even 7” piping for the system? I’d put a reducer right at the inlet to bring it down to the required 5”. My reason for asking is that there’s a good likelihood that we’ll be downsizing our home in the next few years (but not the shop!), at which point I may upgrade to a 3HP unit with a 7” inlet. Piping and fittings are expensive, and I’d like to be able to reuse whatever I can.

This is a hobby shop, so I will only run one major machine at a time. These include a 3HP cabinet saw, 6” jointer, 13” lunchbox planer, and a 14” bandsaw. All have 4 inch ports and the TS has an additional 2.5 on the saw guard. Longest runs are 12’ to the planer and TS and 16’ to the jointer.

Thanks,
Pete

[Jim Becker]

You do not want to make your main trunk larger than the inlet of the cyclone...it will drop the velocity of air movement which will hurt collection. Dust collectors work by moving air. That moving air is what moves the chips and dust. It's not about "suction" like with a shop vac that has high negative pressure. If the unit only has a 5" inlet and it cannot be changed to 6", then put in 5" duct for your main trunk. You "might" be able to get away with 6", but again, it could affect performance in a negative manner.

[Malcolm McLeod]

With a future upgrade 'planned', ducting selection could get a little complicated. Flow in the main trunk, irrespective of size, need only be fast enough to keep the dust load moving. But the critical aspect of a cyclone's ability to separate lies in the (average) linear velocity of the dust at the cyclone inlet. The worst thing you can do to a cyclone IMHO, is install 90*Els on the inlet as this creates turbulence and so degrades the average linear velocity of dust particles - critical for good separation.

You could run a 8" trunk (just as example), then drop to a 5" inlet - - IF - - the 5" section is long enough and straight enough to reestablish laminar flow. (Perhaps this makes the 5" section the trunk in most minds - - YMMV.)

For the OP's application, perhaps a larger 'trunk', sized for a future DC, could be paired with a final short section of inlet duct sized for the current DC. If so, then only this inlet section needs replacement down the road..?? A good rule of thumb is that a run equal to 10 pipe diameters is generally enough to restore laminar flow :: so 50" of 5" duct.

[Ryan Yeaglin]

Here is my outlook on this, your current collector is plenty for all that you do, why invest is a larger collector and then up-size your duct? I would let well enough alone and just stick with the tempest and 5" duct. Also the type of duct will play a large role as well. Do you plan on metal duct either spiral or something like norfab style?

[michael dilday]

If you are a single man shop running one (or maybe two) machines at a time a 5" main will be just fine. Verticals should be no larger than the machine port typically 4".

[Bill Dufour]

Good luck finding 5" pvc duct. They do make it for electrical conduit. I think that is very similar setup to mine that I run 6" duct from. I added a simple neutral pipe (vane) inside the inlet that increased the vacuum by a good 20% with very little flow loss. I think it went in about 4-5 inches. I just had a gauge in the middle of the intake pipe and moved it in and out until it maxed the gauge. One sheet metal screw holds it in place. Just a roll of sheet metal with no joint.
I made an adapter cone by cutting a wedge lengthwise in a piece of 6" pvc then bending it into a funnel. It is about 18" long.
Bil lD
Bill D

[Pete Costa]

Thanks all, i am always amazed by how quickly you get thoughtful and well-informed answers from this community. I neglected to mention that the DC came with a decent number of 5" spiral metal ducting and fittings, so I will stick with that material. Based on the above advice, I'm going to use 5" for the main lines. As for the drops, Michael's advice to use 4" makes sense as a way to get higher velocity in those areas where it has to lift the dust/chips, but I've read elsewhere that you should keep the duct as large as possible right up to the machine and neck down there. Highest lift will be 7" for the jointer and TS. Other thoughts? Pete

[Ole Anderson]

Not sure why PennState would put a 5" inlet on a 2 hp machine with a free flow of 1900 cfm. I would have no problem running 7" duct for your main with a temporary long 7"-5" reducer. As long as you can pull 800 cfm with open gates you are good with 7" pipe (obviously metal as you will not find PVC in odd sizes). 7" will work fine for a future 3 hp collector. Do your duct design for you future machine, you don't want to do that twice. Not like you are using a 1 hp collector initially. Even if your velocity is a bit low, your ducts will not fill up, if there is a restriction, the velocity at that point will be increased enough to keep probably a 5" or 6" airway open. I run 7" duct with my 2 hp Oneida Dust Gorilla with zero problems. I run 5" drops to 4" hose for my BS, 6" belt sander, lunchbox planer and my 6" jointer as well as my router station and TS bottom which is 5" hose to a bell mouth into the saw. I do run a 6" all the way to my MS.

[Jim Becker]

Ole, 1900 CFM would be "dreaming under the influence" for a machine of this size and type, even in free air. I also don't see the benefit of the OP putting in a larger duct for future use given downsizing would mean moving anyway. A 5" duct system would still be very usable in the new space for the drops while he upsizes the main trunk to whatever that future DC system is optimal for. He also says he has a bunch of 5" duct already so that's a start on "now". My opinion, of course, but it was cheap to obtain.

[Robert Engel]

A basic principle the same as making panels - "keep them as big as you can as long as you can" LOL.

[Ryan Yeaglin]

I just bought a Jet VX1200, it's also 5'' out of the impeller to the filter housing. The inlet is 6".. dumb right? I built a cyclone at work, but now don't know if I feel like going through all the hassle of re-configuring everything to run the cyclone. Also my basement shop is pretty small so rather than a duct run I can just use a flex and swap from machines. There might be a pretty sexy stainless cyclone with 6" ports for sale in the future..