Dust collection design questions

[Brent Romero]

I am beginning to think about my dust colllection system. I seem to have settled on the HF 2hp 1550cfm system. My question what size pipe do I need to run my system and how far can I run my lines? I will most likely be using no more than one tool at a time. My current thoughts are to:

-Run pipe 6ft upward and make a 90deg turn
-Run a run of pipe across the ceiling 24ft
-Make a 90deg downward turn and come down ~6ft

I can will install a few blastgates in the line.

Am I trying to get too much out of the HF unit? Will it be able to support the run I described?

Thanks

[Thom Porterfield]

The HF unit isn't really 2hp, and it's questionable whether it actually can push air at 1550 cfm. That said, it's one hell of a good deal at $150. In designing my stystem, I discovered that 4" pipe is too small, except for one-machine-at-a-time use, and 6" is too large. Unfortunately, cheap piping (PVC) only comes in 4" or 6" diameters. The best solution (for my system, based on calculations) is to use 5" diameter, 26-ga metal. I suspect that for short runs 30-ga would work with this blower, but having already collapsed a 30-gallon garbage can with my shop vac, I'm leery of the thinner gauges.

My system has about the same length of run yours does, and my calculations indicate it should work with one gate open at a time. (It's still under construction). As for 90s, try to avoid them, but that's not always possible. I discovered that by using two 5" adjustable elbows together, it's possible to create a nice large radius 90-degree bend.

The HF unit pulling air through a 5" pipe should work well. (The inlet to the impeller is 5", and from impeller to filter also.) If you intend to add a separator in-line before the impeller, performance will suffer, but by how much, I can't say.

[Brent Romero]

Thanks for the info. So if I only use one machine at a time it sounds like 4" should work. I was questioning the validity of the HF specs...

Where is a good outlet to purchase 5" metal piping?

[Brent Romero]

Another option, not necessarily my first option, would be to position the collector and make one single horizontal run ~20ft and have my machines positioned along the 20ft run. What size pipe would work in that scenario?

Thanks

[David Kumm]

Brent, you are asking a lot to run 4" pipe 24' with two ells. You can barely on the best day get 1500 working cfm from a 5 hp unit. The pipe restrictions on 4" will kill the cfm, 5" will be adequate for smaller machines but I would probably err on the side of a 6" main. It will bring the velocity down but overall I think you have better shot at success. I've seen pictures of some of the HF collectors with the blades in a forward curved rotation rather than backward. That gives the high CFM number you were quoted under low pressure but drops really fast under SP. You can't use too small of pipe and get acceptable results. Dave

[Ole Anderson]

I would go with 6" to keep the losses down, but design it so you can clean out the bottom of the verticals. And using 26 ga snaplock from the borg at $1.50 per foot isn't going to break the bank. Do not use 30 gauge pipe.

[Michael W. Clark]

Try to run at least 5", and preferrably 6". If you use S&D pipe, don't glue it so you can take it apart if you get a plug. Same with metal duct, just teck screws to put it together so you can get it apart if something plugs. Plugs are not necessarily that common, but you want a way of clearing them should one occur.

If you have to put a 90 at the inlet of your fan, consider reworking the mounting of the fan or the duct routing to give you more straight at the fan inlet. An elbow at the fan inlet hurts performance and has the same effect as additional system resistance.

Mike

[Brent Romero]

The HF unit isn't really 2hp, and it's questionable whether it actually can push air at 1550 cfm. That said, it's one hell of a good deal at $150. In designing my stystem, I discovered that 4" pipe is too small, except for one-machine-at-a-time use, and 6" is too large. Unfortunately, cheap piping (PVC) only comes in 4" or 6" diameters. The best solution (for my system, based on calculations) is to use 5" diameter, 26-ga metal. I suspect that for short runs 30-ga would work with this blower, but having already collapsed a 30-gallon garbage can with my shop vac, I'm leery of the thinner gauges.

My system has about the same length of run yours does, and my calculations indicate it should work with one gate open at a time. (It's still under construction). As for 90s, try to avoid them, but that's not always possible. I discovered that by using two 5" adjustable elbows together, it's possible to create a nice large radius 90-degree bend.

The HF unit pulling air through a 5" pipe should work well. (The inlet to the impeller is 5", and from impeller to filter also.) If you intend to add a separator in-line before the impeller, performance will suffer, but by how much, I can't say.

Still kicking around what I will do...probably use the unit as a mobile unit. But I wanted to add that I just spoke to a buddy of mine who happens to have the exact HF unit. He measured the CFM levels with a meter and told me that the unit moves every bit of 1550 CFM...he was a bit surprised as well. Sounds like a good deal at $200.

[Dave Goodyear]

Just noticed this post and read through the comments. I have to agree with most of the comments. Most specs on these collectors are hype. The manufactures do not provide any fan curves that indicate performance. THey give you CFM at the inlet without any duct attached and the static pressure under vacuum without any air moving. I would like to know how your friend did those measurements. They need to be done with at least 10 x the duct diameter attached to the inlet with a pitot tube just upstream of the inlet in order to get any realistic measurements. That being said, the 5" pipe will give less static pressure than the 4". 4" will kill the air flow necessary to collect all the fine dust that tries to get away from your machines.

[Jim Finn]

http://billpentz.com/woodworking/cyc...DuctingDiamter .......... read this.

[Brent Romero]

Hi Dave,

Thanks for the info. I am absolutely positive he did not build the test setup properly based on your description. That being said, I am sure he measured the flow right at the machine...which is sounds is not the proper way to do so. I am really looking at using the unit as a portable and hooking it up directly to a single piece of equipment at a time. Sawdust sure makes a man sneeze a lot!!!

[Michael W. Clark]

Hi Dave,

Thanks for the info. I am absolutely positive he did not build the test setup properly based on your description. That being said, I am sure he measured the flow right at the machine...which is sounds is not the proper way to do so. I am really looking at using the unit as a portable and hooking it up directly to a single piece of equipment at a time. Sawdust sure makes a man sneeze a lot!!!

If you get the unit, connect the hose to it that you will be using then have your buddy over to measure the airflow. Assuming he is using a pitot tube, put a slit in the hose for the tube about 2-3 diameters away from the fan inlet. Measure the VP (VP converts to velocity, then you get the CFM based on duct size) and SP (disconnect the TP port on the tube) with the hose straight and with bends in it. It will give you a good idea of the performance curve and show you how the flow varies with bends in the hose.

Mike

[Jim Andrew]

What size impeller does the hf unit have? My 2hp cyclone has a 14" impeller, and consider it minimum to do a decent job. Sure glad I read Bill Pentz website before I set up my system, in 7 years have not had a plug. Used no 90 degree bends, all Y's and 45's.

[Rod Sheridan]

Thanks for the info. So if I only use one machine at a time it sounds like 4" should work. I was questioning the validity of the HF specs...

Where is a good outlet to purchase 5" metal piping?

Brent, 4" is too small for almost any stationary machine, I would use 6" for main runs, then 5" to machine cabinets.

If you look up airflow requirements for machines you'll find that the old 400CFM for table saws is now is 500 to 600 for the cabinet, and 100 to 200 for the overblade collection.

I have an Oneida cyclone with BORG HVAC ducting, which isn't a problem for collapse as long as you make pipe hangers out of wood with the correct hole size.

2 pipe hangers on a 5 foot long piece of straight pipe, space to divide the pipe into 3 equall sections will prevent the pipe from deforming. Fittings have built in ridges to strengthen them and don't require any additional support.

Use foil tape to seal all the seams on your system...................Regards, Rod.

[Ole Anderson]

HD in my area stocks up to 7" snap lock at a reasonable price, just make sure it is 26 gauge and not 30 gauge. For me, the J hangers worked out fine. If you use 26 gauge, you won't need to provide circular support as Ron suggests. 30 gauge, yes.

Check out this thread for a steel duct install with tips: http://www.sawmillcreek.org/showthre...tall&highlight
And here are the pics: http://www.sawmillcreek.org/showthre...31#post1973931