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Adding 2 dust collectors together?

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Forum topic by trevor7428 posted 06-04-2016 10:22 AM 733 views 0 times favorited 17 replies Add to Favorites Watch
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trevor7428

146 posts in 420 days


06-04-2016 10:22 AM

Topic tags/keywords: question dust collection

Is it possible to add 2 Dust Collectors to my PVC ducting I have?

Currently I have my 2 HP H.F. Dust Collector connected to PVC going to my Table Saw, Router Table, Jointer and Floor Sweep.

Well H.F. had the 1 HP Dust Collector for $100 for ITC members, (currently in ads) which I purchased today.

So I was thinking can I add both of these to my PVC duct, to double suction (CFM)? If so, what would be the difference if both D.C. are close together or if I put the 2 HP at start of duct (like it is now) and 1 HP in middle?

Of course I would use a Y connecter, so the 2 D.C. don’t fight each other.

Lol if I just don’t know what I’m talking about or if this isn’t advisable. Them ill just use the 1 HP for Miter Saw and Rigid Oscillating/ Belt Sander on seperate (smaller) duct work

Thank You
Trevor OBrion

-- Thank You Trevor OBrion


17 replies so far

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Redoak49

1933 posts in 1448 days


#1 posted 06-04-2016 11:16 AM

No….it has been tried and will not increase cfm in any meaningful amount.

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MrRon

3926 posts in 2703 days


#2 posted 06-04-2016 03:00 PM

I would suggest using the 1 hp DC for a dedicated machine, but wye it into the main PVC run with a blast gate to cut off one or the other DC; putting them in line won’t do anything.

View clin's profile

clin

510 posts in 455 days


#3 posted 06-04-2016 06:46 PM

He said he would use a Y, so he’s not putting them inline, but in parallel. If they were identical units, same pressure and flow, then as long as they are combined in the same way, it should work fine.

But with two different systems, what actually happens is going to depend on the specifics of their pressure and flow relationship of both units and the ducting. I don’t think there is any question it will increase the net flow, but it may not work out as simple as the two add together.

Think of it like using two trucks to pull something. If one is in a high-speed gear and the other a low-speed, one isn’t going to be very effective.

I’d at least give it a try, if it is easy. Maybe note the amps drawn by each to make sure something bad doesn’t happen.

-- Clin

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Bill White

4448 posts in 3420 days


#4 posted 06-04-2016 09:58 PM

Stumpy tried this. Didn’t work well.
Bill

-- bill@magraphics.us

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Rentvent

148 posts in 308 days


#5 posted 06-04-2016 10:15 PM

“For my birthday I got a humidifier and a de-humidifier…I put them in the same
room and let them fight it out.”

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firefighterontheside

13435 posts in 1316 days


#6 posted 06-04-2016 11:51 PM

I think the only way it would work would be in series. May be able to put one in in the middle of a line to relay like we do with firetrucks.

-- Bill M. "People change, walnut doesn't" by Gene.

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clin

510 posts in 455 days


#7 posted 06-05-2016 02:38 AM



I think the only way it would work would be in series. May be able to put one in in the middle of a line to relay like we do with firetrucks.

- firefighterontheside

Since these are not the same size, putting them inline (in series) will limit flow to the smallest. That smaller one won’t need to work as hard, but it almost certainly would work better to just run the single larger unit. The reason for putting pumps in series is to overcome the pressure drop from relatively long runs. Tends to work best if the pumps are spaced apart. Like a booster pump on a pipeline. that’s not the issue here.

-- Clin

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AZWoody

693 posts in 683 days


#8 posted 06-05-2016 03:05 AM

Besides the other reasons that are being said, which are all valid, if you’re using 4” ducting, you’re not going to see any difference as the 2hp HF unit pretty much maxes out the capacity of a 4” piece of pipe so adding another blower wouldn’t really make much of a difference. You can only move so much air for any given size of pipe unless you’re really going oversized on the hp and the impeller and even then, the increases are minimal.

View JeffP's profile

JeffP

573 posts in 851 days


#9 posted 06-05-2016 11:47 AM

For those who might be struggling with the apparent cognitive dissonance posed by the notion of two DC’s sucking on the same pipe not significantly increasing the airflow…this might be a case where the electrical analogy can provide some assistance.

It is common to model electrical systems with the somehow more palpable “plumbing” analogy. This is sort of turning the tables on that line of reasoning.

If we think of air flowing in a tube, we can (if we choose) model the flow of air as electrical current, and the static pressure in the tube as electrical voltage.

In an electrical system, most of us are familiar with the notion that the practical current we can have in a circuit is dependent upon the size of the wire. If we try to shove (pull?) too much current through a small wire, we get hot wires and weak voltage and all of the attendant “why can’t I run my circular saw at the end of these 3 long extension cords?” issues.

At the same time, many people are surprised to find out that the seemingly tiny wires way up there on the electrical grid towers are carrying 10 thousand volts (or in many cases, much higher voltages).

Moving a lot of air very quickly through a pipe of limited size actually has similar limitations, which are actually further exacerbated by the turbulence that develops in an air pipe. Increasing the static pressure (voltage if you will) on an air pipe to increase the amount/speed of air flowing has rapidly decreasing bang for the buck above a certain air speed.

So, in theory at least, if one DC is already having its running current/power limited by the size of the pipe, putting another DC in “parallel” with it will clearly exacerbate that issue, and there will be significantly diminishing returns for having more units all sucking on the same pipe.

Since the goal with upping the power on a DC system is to move more air (rather than particularly trying to increase the static pressure at the business end), putting multiple DC’s on typically results in disappointment.

This analysis does, however, lead me to a somewhat diametrically opposed question…what about a “central” vac setup for a shop vac? With a shop vac, the parameter we are most often interested in at the business end of the hose is the “strength of the suction”, or it’s ability to suck up heavy bits of detritus.

I put together such a system in my garage/shop, with a handy long “slinky hose” that I can use to clean up any part of my shop. It works well, but when was the last time you didn’t wish for “just a little more suction” from your shop vac?

In theory, at least, for a shop vac we should have a somewhat opposite situation. In theory, we could increase the static pressure provided by the shop vac system by putting two shop vacs “in series”. That is to say, take one that is already designed to have a hose hooked to it’s output (for blowing up air mattresses and acting as a sort of ‘leaf blower’), and feeding that output into the input hose of a second shop vac.

In theory at least, this should increase the “voltage” in our model of the system, which would be roughly equivalent to increasing the static pressure of the system, thereby creating stronger suction at the business end (not a lot more air-flow still—same physics applies). In theory, this should help suck up larger and denser chunks of stuff and provide a more satisfying hissing sound when you put your hand over the end of the hose.

I’m going to try this today and see what happens.

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

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Kazooman

623 posts in 1412 days


#10 posted 06-05-2016 12:24 PM

With two units of equal size the parallel arrangement would work, but as has been pointed out, the air flow would be limited by the size of the duct work. Parallel exhaust fan systems are very common in industrial settings. The laboratory building I helped design has two 25,000 CFM Strobic fans. Under typical conditions only one fan is operating. The system rotates the master fan to equalize the wear on the pair. If the demand for air exceeds the capacity of one fan the other comes on line and they operate in parallel drawing on the same duct system without any problems. Mind you the main duct is almost four feet in diameter. The size decreases down the line to the individual fume hoods, but the smallest ducts are 10” and some hoods have two of those.

Another important factor is providing sufficient make-up air. If you are exhausting outside the building then you have to provide an equal amount of make-up air or the system will be starved.

View MustacheMike's profile

MustacheMike

172 posts in 1548 days


#11 posted 06-05-2016 12:44 PM

Check out this video we did a while back for the show. https://www.youtube.com/watch?v=SoHKfhzuDmU

-- You can trust Mike -" because I will never pull your stash!" See my show weekly at Stumpynubs.com

View Lazyman's profile

Lazyman

686 posts in 847 days


#12 posted 06-05-2016 12:58 PM

I remember seeing somewhere that you have to be careful running vac systems in series because one could basically turbo charge (I think that was the term they used) the other. I don’t remember what the possible outcome could be or other conditions but you might want to research that before trying it for extended periods or a permanent setup.

Also, I’ve seen commercial dust collection systems that had multiple vac/blowers in parallel on a single set of duct work so my thought is that the size and configuration (resistance?) of the duct work may be the most likely thing that would limit whether adding another unit has the desired affect or not. Best way to find out may be to try it and measure with a manometer. You can make a simple manometer with some clear tubing filled with water.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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JeffP

573 posts in 851 days


#13 posted 06-05-2016 01:02 PM

@lazyman, wow, turbo-charged? COOL! :)

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

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JeffP

573 posts in 851 days


#14 posted 06-05-2016 02:04 PM

Scottie, WE NEED MORE POWER!

Ok, so I tried it. (series connected shop vacs)

The results were…..meh. Rather underwhelming.

I didn’t get any “turbo-suckage” to speak of. I could “tell” a difference, but just barely…and some of that may have been just the perceived difference due to the difference in the sound level.

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

View clin's profile

clin

510 posts in 455 days


#15 posted 06-05-2016 04:31 PM



For those who might be struggling with the apparent cognitive dissonance posed by the notion of two DC s sucking on the same pipe not significantly increasing the airflow…this might be a case where the electrical analogy can provide some assistance.

- JeffP

Keep in mind that connecting two to the same pipe may or may not increase airflow significantly. While your analogy is correct, it is correct only if the pipe, duct (wire) is in fact too small and is the limiting factor. It may or may not be. That’s not been established in this case.

This goes back to what I originally said, you need the pressure and airflow curves for both blowers, and the ducting. Then you can calculate what will happen.

The only thing we do know, is that the 1 HP DC does have much less no-load airflow than the 2 HP unit. This is a common characteristics of DC’s, and in this case HF rates these at 660 and 1550 CFM respectively.

What we do know, is most likely do not want to connect these in series unless the 2 HP unit by itself was moving well under the no-load capacity of the smaller unit. If it were already moving more air, than adding the smaller unit inline would restrict airflow and degrade the system.

But similarly, larger units tend to produce more pressure, so connecting these in parallel may have similar issues. Where, as the OP put it, they may fight each other. The potential is the larger unit actually pulls air backwards through the smaller unit.

It may be that connecting the smaller unit up stream (in parallel) could do something useful. That way the greater pressure of the larger unit would be dropped across some ducting.

Again, it really requires an analysis with numbers to say what will and won’t work in a given system. As far as I know the necessary performance data (curves) are not know for the HF units. So I think the only choice is to experiment and see what works.

-- Clin

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