Oversize Dust Collector? Oneida V System 3HP vs. 5HP

[Michael W. Clark]

One thing has always puzzled me about the 5hp smart oneida. If it increases RPMs to get better suction at higher SP, that means it must have some RPMs to add....

meaning either their motors are running less then 3450 rpms by default (probably), or they somehow get them to spin faster than that at full speed?

I agree, it has to be something like that. You are going to get the max SP at full speed (100%+ maybe some small amount of overspeed). When you slow the fan down, the fan curve (relationship of CFM and SP) is also going to shift down, giving you a lower max SP.

The other thing I noticed is the flow and SP they quote for 10' of hose. I have a spreadsheet I have used for DC system design and the only way I can get that SP in their chart is to assume a bellmouth inlet on the hose (yes I'm a dork). Suspiciously, the calcs for the 6" and 2.5" hoses work out perfectly, but that's the only two I tried. I would venture to say that none of our tools have hood losses as low as a bellmouth inlet in free air. What I am trying to say is that, one would likely not be able to obtain flows this high in an actual setting. They also mention that its "patent pending", how can you patent a VFD on a fan or HP control? VFDs on industrial fans are typical and HP control is also common place.

I've tried to be an Oneida fan, and I want to like them, but they seem to have so many "gimmicks" that are unnecessary and it makes me loose confidence.

Edit: Not trying to single out Oneida, this is true with me for a large number of the hobby DC suppliers. Whether they are talking about gadgets or quircky performance numbers, it makes it hard for an average person to know what they are getting. I do this stuff for a living, and still wouldn't be 100% sure of what I'm getting if I were evaluating. Until information is more clear and consistent between suppliers, evaulation of equipment from two suppliers will be difficult IMHO.

Mike

[Chris Parks]

What I meant was that, almost all motors in this size class are meant to run at 3450rpm.

either the motor goes up beyond 3450 or its operating under that most of the time.

I think that the designed motor rpm is not in fact true but is an assumption we make due to motors running at that speed by default at 60hz. In Australia those exact same motors run at 2850 and everyone assumes the same thing. I have run the old Leeson that Clearvue supplied at anything from 2850 to 4000 and it appeared to take it all in its stride as did the impeller. Of course the higher rpm must shorten the life of the bearings but no one knows by how much until they do it.

[David Kumm]

If you are going to get the best bang for the buck when running a vfd on a DC a straight blade radial is the way to go. Speeding up the motor won't lead to problems but every fan has an rpm limit and aluminum fans generally won't run at as high a speed as steel. In addition, a BI fan is designed so it won't draw more than a certain amperage regardless of available cfm. It maxxes out at fairly low pressure so additional speed isn't as effective as with a straight blade. The downside with a straight is less efficiency at lower pressure so more amp draw. At higher pressures it outperforms the BI so it is a good choice with a vfd to monitor the amp draw. The Oneida smart is more of a way to juice a smaller DC than a way to max out a 5 hp system. It mates a little larger impeller with a little smaller inlet and uses the vfd to control the amp load. You can do the same thing yourself with a three phase motor and vfd. You will find that you only will vary the speed by about 5 hz to keep the FPM the same at most size machine ports. I'm always surprised more choices aren't out there for people who want to customize their system to their ducting sizes. We aren't given much credit for doing homework. Dave

[Michael W. Clark]

The Oneida smart is more of a way to juice a smaller DC than a way to max out a 5 hp system. It mates a little larger impeller with a little smaller inlet and uses the vfd to control the amp load.

I thought about that too. Basically, the fan is too much for the motor if the system were running "normally". When you connect the smaller hoses, you choke the flow, and the motor speed increases to maintain FLA (or to 100% output on the VFD). Still not sure how this is a benefit over connecting a 2.5" hose from the shopvac. You would need to run the small hose back to the collector or else dust could settle out in your larger main ducts (or you could blead in air, but now your fan would slow down). The cyclone efficiency is also going to be greatly reduced at 400 CFM if it was intended to operate at 800-1000 CFM. I could definitely see the VFD to protect the motor when you have machines of similar size and you want max flow without overamping when you go to the branch with the least resistance.

I think for the smaller stuff, a shop-vac or DE will be a better solution. If your connecting a hand-held sander to the Smart system, you have a lower cyclone performance, high air:cloth with the Oneida systems, and very fine dust. Seems like it would tend to plug the DC filters even quicker, you know more fine dust would be getting through the cyclone since the efficiency is lower.

[Joe Jensen]

Shop vac pull about 100 cfm so I doubt a shop vac is better. A shop vac would do about 90" of pressure though. I think the ideal setup for an overhead blade guard would be a shop vac mounted up in the attic. Seems to me that I read that the 5HP Smart Pro had a straight fan but I am now 50 and my memory isn't what it once was. I am hoping to chat with the Oneida folks at IWF in August.

[ian maybury]

As ever in these matters it's got to come down to matching the fan curve of the collector to the system curve. Trouble is that we can fairly easily estimate the system numbers, but typically have no means of including the resistance of machine hoods. (it'd be perfectly practical for machine makers to include this information in their specs)

And as ever too obtaining solid and reliable data that hasn't been goosed to make the xyz dust collection kit look good is often a problem. The Cincinatti Fan tables seem as before to be a pretty good source of trustworthy fan performance numbers (CFM vs pressure vs RPM) for many types of impeller. It's possible to pretty clearly figure the effect for example of an extra inch in impeller diameter.

It's clear that most machine hoods are restrictive, and that short of surgery/running older machines like David K does that dust collector performance is often improved by extra pressure capability. Even with the option of hood mods there seem to be places where the it's necessary to generate fairly decent air speeds through tightish gaps to get good collection. e.g. ref our recent discussion on saw top and bottom guards.

What I was driving at in the earlier post is that the simple solution to getting quite a decent amount of extra pressure (there may still be times where upping the RPM with a VFD will be needed - if the extra noise is OK) that often gets overlooked is simply to use a larger diameter moderately backwards inclined fan such as the 16in Clear Vue or something similar. (this will also produce a bit more noise)

There will be probably times where it's overkill in terms of its CFM capability (e.g. on a router table with a small cutter), but running restricted is no problem unless the ducting is ginormous, and in the meantime having the extra suction available can really pay off. In that the air flow is much higher than would be the case with a smaller diameter/lower pressure capability fan.

Think also of the benefit of having some cushion to cover for filter blinding....

ian

[Michael W. Clark]

Shop vac pull about 100 cfm so I doubt a shop vac is better. A shop vac would do about 90" of pressure though.

I'm not sure that I am in agreement here. The Oneida 3HP system (didn't see the link for the 5HP) has a max SP of 24"wg. A 3HP, 6 gallon shop vac has a max SP of 57"wg (according to the Shop-Vac website) and a Festool CT36 has a max SP of 96"wg (according to Festool specs). The most that the Oneida system will pull in a 1.25' flex hose, 10' long is about 65-70 CFM because it is limited by the max SP of 24"wg. When you add hood losses, bends in the hose, etc., this flow will go down because you cannot generate any additional SP. The shop-vac has over 2X the max SP and the Festool has almost 4X the SP. I'm sure the shop-vac and Festool are not going to develop their maximum flows (147 CFM and 131 CFM, respectively), but they certainly have the potential (SP) to draw more flow through the system. Like Ian stated, the volume flow is completely dependent on the relationship of the system losses to the fan's capability.

From an operations standpoint, its usually not recommended to operate a fan at the max SP because this is an unstable point on its curve and it can surge. Also, I would not want to run a long length of flex back to the collector and start a large motor everytime for all of my smaller bench operations. If you connect the small hose into your existing system flowing only 100 CFM, then a lot of the material would certainly drop out in the duct.

I think the smart system would work as a compromise if you didn't have a shop-vac, but I don't see it as replacing the shop-vac which is where their advertising leads you. I have experience with two industrial applications where the owner wanted to us to use the DC as a housekeeping system. Both of those attempts failed, despite a lot of effort. We were ultimately able to get one of the systems to work by replacing the exhauster with a Roots PD blower with a max SP of 24"Hg (327"wg). The other system, the owner replaced the centrifugal fan with a pressure blower capable of about 24 osi (42"wg). This system never really worked even though all the duct was reduced to 4" diameter from 10" and all joints were caulked and sealed as much as possible.

Back to the OP, I would get the 5HP system and run it full out. You can always reduce the volume if necessary (not sure why on most stationary tool applications) but it is difficult to add SP and flow that your fan/motor is not capable of handling should you acquire something in the future that required the flow. The difference in price between a 3 and 5HP system is minimal.

Mike

[Alan Bienlein]

Say what you will but you wont regret going with the higher horsepower unit.

I started out with the 1 hp delta dust pump when I didn't know any better. It didn't take long to see how inadequate it was. I did some research and bought the 16" impeller from clearvue and the 5 hp motor from electric motor warehouse. I figured it was cheaper doing that than wishing I had done it for when I might add some more machines in the future.

Think of it like this it's easier to choke off the dust collection to a machine with and oversize collecter than it is to add and wish you had more suction with and under size unit!

[David Kumm]

I think the differential is even greater than Michael's example. I doubt the type of impeller used by most hobby collectors will pull at 24". Once you get under a 3" hose a strong vac provides more cfm. I run a 7.5 hp motor with a straight blade and doubt the velocity in a 2.5 hose will equal the shop vac. I'll test it when I get home and let you know. Dave

[ian maybury]

I'd be dead interested to hear the result of that Dave. It's hard to predict, and I'm not sure how it would do re. Michael's point about instability - but digging around in fan curves suggests that for example the 16in Clear Vue might just be able to shift enough air at 24in to match a vacuum. I can't remember the diameter of your fan, but knocking even an inch off the impeller diameter looks like it might drop the pressure by a few inches..

ian

[Ryan Brucks]

i've compared my 16in clearvue impeller running through a 2.5" line to my 5hp "peak" rigid shopvac... they were really close, would need testing to be able to tell the difference for sure, but I still thought the shopvac had a bit more, and of course more suction.

[Joe Jensen]

I'm not sure that I am in agreement here. The Oneida 3HP system (didn't see the link for the 5HP) has a max SP of 24"wg. A 3HP, 6 gallon shop vac has a max SP of 57"wg (according to the Shop-Vac website) and a Festool CT36 has a max SP of 96"wg (according to Festool specs). The most that the Oneida system will pull in a 1.25' flex hose, 10' long is about 65-70 CFM because it is limited by the max SP of 24"wg. When you add hood losses, bends in the hose, etc., this flow will go down because you cannot generate any additional SP. The shop-vac has over 2X the max SP and the Festool has almost 4X the SP. I'm sure the shop-vac and Festool are not going to develop their maximum flows (147 CFM and 131 CFM, respectively), but they certainly have the potential (SP) to draw more flow through the system. Like Ian stated, the volume flow is completely dependent on the relationship of the system losses to the fan's capability.
Mike

I think we agree, I just wasn't clear. Take my 2HP Oneida Super Dust Gorilla. Generates a max of 11 or 12" of pressure with no cyclone, filter, or duct losses. I've read that the cyclone is .5", filters in use about 1.5", and my typical duct run is about 5-6". That leaves me with only 4-5" of pressure at the machine port. If it's a 3" or larger port a dust collector will be better. With the smart system I would get a net of 16-17" of pressure at the port, that would pull about 2X the CFM. But, take for example the Sawstop overhead guard with a 1.25" port, or the Felder overhead guard with a 1.5" port. Both of those would probably do better with a Festool vac or my WAP vac.

[Michael W. Clark]

That leaves me with only 4-5" of pressure at the machine port.

I think we ultimately have the same veiw. I was confused by your pressure statement and reference to the small port scenarios earlier in the thread. I'll explain what I mean, and I do not intend to talk over or under you as I am not sure how deep your understanding is for these systems.

The pressure at the machine port is related to the fan capabilities, but it is not necessarily the subtraction of the system losses from the max SP rating of the fan. The fan has a performance curve such that it produces less CFM at the max SP and more CFM at a SP less than the max SP. This curve, or relationship, is primarily dependant on the fan type, wheel type, size, and speed, and is usually referred to as the fan curve.

The system requires a certain amount of SP to move a given volume of air through the system. Air will flow from an area of higher pressure to an area of lower pressure. The fan's job is to generate the negative pressure to cause the air to move. The amount of SP it takes to move a certain CFM through a system is dependant on the system losses. The small hoses we are talking about require a lot of SP because of the resistance. A larger hose requires less SP to move the same volume of air because of less resistance. This CFM/SP relationship for the system is referred to as the system curve.

The SP at the hood will be dependant on the hood configuration and the force required to accelerate the air up to the duct velocity. The pressure at the duct opening, will be approximately equal to ambient or 0"wg. If you take SP measurements closer to the fan inlet, the SP gets more negative. As you pull more flow through the system, the SP requirement increases with the square of the increase in CFM. If you double the CFM, you need 4x the SP to generate that flow in the same system. This square relationship is how the system curve is generated.

Ultimately, the system curve and the fan curve have to find a common point to coexist. This is known as the system operating point. Take your 2HP fan for example. If you connect it to a 1" hose, you will likely operate at the max SP and the flow will be the CFM that can be drawn through that hose with 12"SP applied at the outlet of the hose. This would be one operating point on your fan curve. If you connect your fan to a 10" diameter duct, you will likely not produce anywhere near 12"wg of SP because the 2HP fan cannot generate enough flow to cause 12"wg SP worth of losses in the 10" duct. This would be a different operating point on your fan curve. The pressure at the inlet of the 10" duct would not be your fan max SP minus the losses of the 10" duct. It would be dependant on the flow and inlet configuration of the 10" duct.

All this is why it is generally advisable to go with a larger DC fan given the opportunity. The larger fan will tolerate additional flow and system SP requirements (system losses). If you have a system with a lot of losses and the fan is marginal or slightly undersized, the fan's CFM will be reduced. This translates to more dust getting airborne at the hood, and reduced efficiency at the cyclone. As the cyclone efficiency drops, more fine dust is carried over to the after filters, starts plugging them and reducing the volume further.

Mike

[Alan Bienlein]

Hey Michael didn't I say the same thing in my post that it's easier to choke off the dust collection to a machine with and oversize collecter than it is to add and wish you had more suction with and under size unit!

[ian maybury]

Thanks Ryan, that's about what i'd expect. That while it's not got quite the same pressure capability that you can get fairly decent airflow from a 16in impeller compared to a vacuum - even on a small hose provided it's not too long.

Quite a bit probably comes down to specifics. The brochure for the 5HP Smart unit shows a heavily backwards curved impeller, but doesn't seem to specify the diameter or the RPM range. The fan curve shows pressure at the inlet (so it includes the filter and the cyclone), but only goes to 15in WG/586 cfm.

I'm not sure how heavily BI impellers respond to increased RPM, but they tend not to do so well at higher pressures.

I've been banging away on the impact of quite small changes in impeller diameter on pressure capability.

They don't publish curves, but the 16in Clear Vue seems from other's fan curves like it should get to about 24in WG. That may not be any more than the Smart, or it could be - it depends on what pressure drop you factor in for the cyclone and filter.

My recollection is bit fuzzy, but i think that tip speed is probably a fairly good indicator of pressure capability in a centrifugal fan. By that measure a 15in dia fan is about 7% faster than a 14in, and a 16in about another 7% faster than the 15in.

It's meanwhile i suspect fairly unusual to run a fan all that much faster than 3,450RPM on a VFD - not because it's not possible mechanically, but because of noise.

Shout if you know better, but i'm guessing that if the Smart impeller was more than an inch or so smaller in diameter than say a 16in dia item run at 3,450RPM that it could struggle to do much better on pressure.

Put another way. Whether you achieve the tip speed through extra RPM or through extra diameter is it possibly the noise that sets the practical upper limit?

Anybody?