I have a 10 year old Jet 1200 dust collector. According to a radio shack decibel meter it runs at 85 decibels. When you add it to my unisaw the noise is 100 decibels, a dangerous level. I looked up the Gorilla 2 hp cyclone by Oneida and it is rated at 85 decibels. Are those numbers comprable? Are there quieter cyclones out there? ETR MD
Edited 8/29/2006 2:37 pm ET by wood masher
Replies
How many decibels is your unisaw alone? If it is the source of the 100 dB level, then a quieter cyclone won't necessarily help.
It also reads approx 85 (but a dinner conversation reads 62 and yelling at the machine reads 93 so I presume it works.)
I have the 3 hp Oneida cyclone and the bulk of the noise that I get is from air rushing in to the openings near the open blast gates. The cyclone isn't too bad, of course that is subjective. My TS drowns out most of it while the planers are the real noise makers. Two suggestions for a quieter setup:
1) Exhaust to the outside.
2) "Box in" the unit in its own little closet or put it outside the shop.
Best,
John
Well, I'm fixing to pull the trigger on a cyclone, so thought I'd jump in and get some opinions. I'm planning to route it outside into a small attached shed built for that purpose, for noise and space considerations, but I do have neighbors. I'm concerned about them being bothered by the noise every time I start it up. I'm currently a hobbyist, so most of my time spent in the shop is evenings and weekends. Opinions on brand, size, etc. will be appreciated and considered!
Paul,
Keep in mind that routing the exhaust of a dust collector to the outside also routs your air-conditioning or your heat to the outside. In other words, if you are cooling or heating your work area, while you are running the dust collector, you are cooling or heating the outdoors.
The noise from a dust collection system comes from the intake ports, the D/C machinery itself and the exhaust port.
Some of the intake port noise can be reduced by baffle design at each machine in the shop.
Mounting the entire dust collector outside the shop cuts down on the noise of the DC machinery, and the exhaust noise.
If the DC is going to run for long periods, any installation that vents the exhaust to the outside is going to drive up heating/airconditioning costs, as well as make the shop uncomfortable. If that's the case, it's a good idea to bring the exhaust back into the shop through baffling to reduce the noise.
Rich
Thanks for those insights Rich. If I understand your last statement correctly, you recommend having the dust collector outside, but you'd have the exhaust filtration unit on the inside? Say I got a 2hp Oneida Gorilla, the canister filter would be inside the shop while the rest of the unit would be outside? Does that filtration unit work well enough to allow for that type of installation?Paul
Paul,
I'm not familiar with that specific machine.
I'm designing a 600 sq foot shop. The DC will be entirely outside the main shop in its own enclosure. The exhaust gets routed back into the shop after filtration.
Rich
What DC system are you planning on using?
Probably the Grizzly 3 HP
http://www.grizzly.com/products/G1030
Rich
Ok, I currently am using a Jet with a Dust Dog canister filter, but I only have 480sf of space and it takes up too much room. I've pretty much made up my mind to go with the Oneida 2hp Super Gorilla (http://www.oneida-air.com/products/systems/2hp_super_gorilla/main.htm), so I'm going to have to ask their technical people how to route that exhaust back inside. I'm in Virginia, so it's a mild climate, but I do air condition the space in the summer time due to the high humidity here.Paul
I see what you mean about the difficulty in routing the exhaust back into the shop.
You may not have to in your climate.
I live in Northern Arizona. Last winter I "borrowed" a neighbor's shop space. His DC vents to the outside. Overnight temps were about 17-24 F. It warmed up a lot in the day, but it certainly wasn't comfortable enough for woodworking without heat.
Running the planer or jointer for long periods (typical use) really dropped the shop temp. Use of the table saw didn't make a big demand on the DC's time.
If you mount that cyclone unit outside and want to bring the exhaust air back, it looks like you would need to make provision for the arm holding the pleated exhaust filter to pass through the wall and come back into the shop, pleated filter and all.
I think that unit is all welded together, so it may be a choice between out or in...no in between. Thanks for your thoughts. It's been good talking with you. Good luck with your new shop.Paul
I have a 2 hp Oneida and originally used with an internal filter and a muffler that made the unit pretty quiet: with the cyclone alone running you could have a fairly normal conversation. I went to an external filter and enclosed the unit is a "closet" with baffled vents to relieve the back-pressure: even quieter.
Thanks for the information. Masher
Doug
I'm working on installing a ClearVue system in a closet and wondered where you got the baffled vents that you mentioned. Do you have a link handy? I tried doing a google search on 'baffle vent' and a few variations and couldn't really find anything. So far I'm at a whopping 101 dB before attaching the filters, ducting, collection bin or closet walls and soundproofing.
Thansk
Doug
If you build it he will come.
"So far I'm at a whopping 101 dB before attaching the filters, ducting, collection bin or closet walls and soundproofing."
This is a side issue, but in case your weren't aware, you're probably grossly overloading that motor by not having external resistance to air flow, and since it's moving too much air, it's making more noise than it will with ducting attached. The outlet is also wide open to your ears, which is where much (most?) of the noise is coming from. But do be aware that you risk burning out your motor with no duct network connected to either end.Be seeing you...
Thanks for the advice. So far I've only had it turned on twice for about 1-2 minutes each. The first time to just confirm the motor and remote switch got wired right, and the second to take a few dB measurements before starting to add insulation on an adjoining wall to find out how much noise reduction I get.
If you build it he will come.
TKanzler,I'm not sure I'm following your reasoning here about overloading the motor and burning it out when the intake or outlow are unrestricted.The motor is an induction motor. An unloaded induction motor (free running with nothing attached to its shaft) draws the least amount of current compared to any other operating condition and runs at its highest theoretical speed (ex 1725, 3450 rpm), governed by the line frequency of the AC supply. Under such conditions, the only cooler running condition is when it's off.With the least amount of restriction of airflow on the intake and outflow sides of the impeller, (the case you warned about), the motor will almost free run - it's least stressful state. No chance of burning out.If airway resistance is applied at the intake, the impeller will put stress on the motor, trying to overcome the air flow drag. If the motor is operated in that condition long enough, it is conceivable that heat could build up to damaging levels, but it is hard to imagine a motor would be supplied with the system that could not tolerate almost complete intake obstruction indefinitely.Interestingly, if the intake is completely blocked, the impleller will spin faster than with a partial obstruction as it will evacuate the impellar chamber and spin unobstructed in the partial vacuum. It will effectively be unloaded and draw less current in that condition.If the outflow is restricted or completely blocked, the impeller and motor will experience the most load possible and heating will occur. Again, it is hard to imagine a system designed with a motor incapable of running indefinitely with a completely blocked outflow.Rich
A propeller (axial) type fan will experience an increased load as the air flow is restricted, but a centrifugal blower will experience a decreased load as either the intake or exhaust is blocked.
For the axial fan, imagine the air is moving across the plane of the blade at the same speed as the pitch times rotational speed, with no slip. Or an airplane during a dive, such that the prop is just screwing it's way through the air, neither pushing nor pulling the plane. No power input to the blade. But sitting on the tarmac, with the engine run up and the blades at full pitch, it's moving the maximum amount of air that it can, which requires the maximum hp input to the blades. Try running a window fan, then closing the door while it's running, with no other way for air to get in (or box fan with the back blocked) - the speed will drop, and motor current will go up.
But a centrifugal blower (pumps work the same way) works by accelerating the air as it moves from the intake at the center of the wheel to the outer rim of the wheel thereby increasing its static pressure. The wheel turns at a constant speed, but as the air moves from near the center, the tangential speed of the blades is low, and increases as you move toward the rim. This air being sped towards the outer diameter is picking up static pressure from centripetal force.
If you block the air supply, the air inside is just being rotated around inside the housing, and only some small amount of friction from all that churning requires input power. As you allow air into the blower (or out of it, if it's the outlet that's blocked), the blower wheel will pass air, increasing it's static pressure as it moves out from the center to the rim. Many industrial blowers are not even rated at low static pressure, or free-air at the extreme, because they would overload the motor.
You're quite right about induction motors and how they behave (though with zero load they'll run just a couple of rpm shy of 1800 or 3600 rpm - 1725 and 3450 is fully-loaded), but the two different types of fans/blowers act opposite to each other.
I can't find an authoritative source on line right now that explains it better, but I'll look tomorrow.Be seeing you...
Both an axial fan and a centrifugal will move the most air and draw the least current when airflow is unrestricted. Your warning that an unrestricted fan is "moving all that air," therefore overloaded is wrong. It is moving all that air precisely because the flow is unimpeded. Any restriction decreases the airflow, no matter that such a condition increases the current that the motor then draws.Your example of the window fan is correct and defeats your argument. A window fan running unobstructed moves the most air and uses the least current. Close the room door, the fan slows down and draws more current - less air is moving.The airplane example does not pertain. A propeller driven by an internal combustion engine, of course moves the most air at the engine's maximum RPM. But that's because the power is being run up to maximum by forcing the engine to do that. A motor driven fan is operating differently. The energy supplied never changes. It uses the least amount when unloaded, under which case it is most efficient. In the case of the motor driving a fan blade (either kind) that's the very condition under which the most airflow happens.In no case does a dust collector design pose a danger to the motor's burning out when the fan is unobstructed.Rich
Let me try it this way. An axial fan, and an airplane propeller, is an air screw. If the air column is moving across the plane of the screw at the same speed it's pitch times rotational speed works out to (i.e. like it's winding through a solid, like a machine screw or lead screw with no force on it), then there is no pressure on either side of the blades, and therefore no tangential component (since there's no force at all), and therefore no shaft power into the blade. There is a little friction force from the air being cut by the blade or airfoil, but that's a parasitic loss that can't be helped, and it's minimal at typical low speeds of fans. That's a maximum theoretical air flow, which can't be obtained in practice since the fan is there to move the air, not spin idly in a moving air column. By resisting the air flow, positive pressure is induced on the outflow side, and/or negative on the inflow side, with a resulting tangential component which results in shaft torque, similar to the torque required to power a lead screw with a load against it.
In the case of the centrifugal blower, it operates on a different principle. Air static pressure is increased as the air column between blades is accelerated outward against the scroll. The power required is a function of flow rate and static pressure, so no flow requires no power input (other than some parasitic losses, as usual). A high flow rate at near-zero SP would also require little power, but since centrifugal blowers are designed to move air against some elevated resistance, they have a scroll with an outlet of a certain size through which the air is forced. There is always a minimum SP the air experiences internally, before the ductwork. That's one reason they make inefficient air circulators.
Fan curves and table for radial blowers are available from industrial manufacturers and suppliers. Look at these pages out of Grainger for radial blowers. You can see the bolded warning near the top-right of page 4056 against operating blowers with too little SP (resulting in too much air flow) for the motors they're equipped with. The "#" sign is used in the air delivery tables on the next page. The higher pressure radial blowers typically have such restrictions, and of course you could spin the wheel slower with a lower hp motor if you wanted (with a belt drive by using a different belt drive ratio, but that's a waste when you could just use a smaller, cheaper blower to do the same thing (unless sound is an issue). But the point is, the power input to the wheel increases as SP decreases, which results in air flow increases.
http://www.grainger.com/Grainger/wwg/catalogPDF.shtml Type in the page number to get the pages I've referenced. You can also look at page 4068 Terms and Tech Data, in the box at the bottom, last line of the first paragraph, where it says "As SP is increased, HP and CFM decrease."
Those small 1 to 2 hp stand-alone dust collectors can't be overloaded because there is too much intake and outlet restriction to overload the motor even with no hose attached. Performance suffers with hoses, bags, and ductwork connected, but they're generally made to not burn up. Open up the inlet, and remove the rectangular-to-round outlet hose adapter and see what current it draws, compared to with all that stuff on it, and compared to the motor nameplate.
In the case of the Clear View cyclone, that 14" Sheldon Engineering blower wheel has little restriction other than the cyclone separator itself until it's connected to some ductwork and filters. It's designed to work efficiently within a certain operating range, and like any radial wheel, it's optimized for a certain SP range. At a very low SP, a different wheel would be more efficient, but dust collection requires ductwork of some sort, so there is a reasonable range of SP the blowers are designed for, just like forward-curved furnace blowers (which also have minimum SP requirements to prevent overload when equipped with a motor of a given hp rating - see Grainger pages 4046 and 4047).
Other sources you can check include Bill Pentz's web site (starting at the bottom of the third paragraph) where he talks about having to limit the air flow to his experimental blowers to keep the motor current under the rated value.
http://billpentz.com/woodworking/cyclone/Blower.cfm
I have a pile of AMCA publications on my desk, but no way to scan and post them (they're copyrighted anyway, and management here frowns on that sort of thing). They are full of fan curves, both axial and centrifugal, including hp vs SP vs CFM for different fan types. Perhaps you can find them at a library. 201-90 is probably the most useful on this topic.
FWIW, I've also tested my own DC equipment, some forward-curved HVAC blowers, radial blowers, panel fans, and some other oddball stuff, and it all conforms to what I've said. Oh, yeah, I also used to fly airplanes.
I'm out of gas here.Be seeing you...
OK,
I'm out of gas, too.
The Grainger site will not load on my machine. I'm running IE v6. The Grainger site says I need IE 5 or later. Lord, I hate PCs.
I'll try the site later from home on my Mac.
I've looked at the Pentz site. Much too much to digest right now.
Film at 11.
Rich
Thank you for a very explicit and well written explanation of the workings of the two types of fans. Most of this, I have known but have missed some of the details. One thing kind of threw me was your use of "static pressure." Can you elaborate how static pressure relates to dynamic pressure in such systems.
In a nutshell, Total Pressure = Static Pressure + Dynamic Pressure
Static pressure is the pressure exerted on all surfaces by the fluid independent of it's motion. An air compressor tank holding air that isn't moving has the same static pressure everywhere inside it (not counting the effects of gravity).
Dynamic pressure is the impact pressure of a column of moving fluid. If you were to knock a wall down with a big fire hose and nozzle, the wall is experiencing dynamic pressure only, since the water is not contained and therefore has no static pressure.
In a DC duct system (or any pipe or duct system), if the fluid is moving, there is both static and dynamic pressure. Starting at the open end of a DC duct, the static pressure (compared to the air all around us) is zero, and the further along the ductwork you go towards the blower, the lower the static pressure goes (since it's suction we're talking about) due to the ductworks resistance to air flow accumulating. It's usually measured in inches of water, or Water Column, or Water Gauge, where 1 inch w.g. equals 0.0361 psi.
At the blower inlet there will be a static pressure that corresponds to a point on the blower's performance curve, and at that point the blower will be moving a certain amount of air. Higher static pressure (more negative on the suction side, or more positive on the outlet side) results in lower flow. The more you restrict the flow, the harder the fan pulls, but the less air it can move. Block it off totally, and you get the Static Pressure number makers of small DC's like to publish, but of course it's meaningless unless your using it for a vacuum press.
Remove some restriction, and it will move more air. Remove all restrictions, including the outlet adapter for the hose to the bag tree, and put a nice bell-mouth on the test duct, and you get a big air flow number. That's the air flow number makers of small DC's like to publish, but of course it's meaninless if you intend to actually use filter bags and some hose or ductwork.
The dynamic pressure will be the same along the whole length of the duct, as long as it's the same size and shape the whole way. The fluid flow rate in equals the flow rate out, so it has to be the same. A pitot tube isolates the dynamic pressure from the static pressure by putting the static pressure to both sides of a differential pressure gauge (or both ends of a manometer), and the dynamic pressure to only one side. You can also measure just static pressure, or even total pressure. Dwyer has some good pages on pitot tubes and flow measurement.
http://www.dwyer-inst.com/htdocs/airvelocity/AirVelocityIntroduction.cfm
http://www.dwyer-inst.com/htdocs/pressure/ManometerIntroduction.cfm
What the blower or fan (and pumps, for that matter) does is increase the static pressure of the moving fluid, from the fan inlet to it's outlet, while the dynamic pressure remains the same (if the outlet is the same size as the inlet). The total pressure in that case is also raised. This is the principle behind Bernoulli's equation.
http://www.grc.nasa.gov/WWW/K-12/airplane/bern.html
Hope that sheds more light than heat. Be seeing you...
I have two "vents" to relieve the back pressure and return the air. Both vents are "ported" towards a portion of the shop away from where I am usually working. Both are installed low to the floor. Over each vent I installed two high-quality furnace filters. They serve as baffles. The key is not to increase the back-pressure in the DC closet.
Edited 9/12/2006 10:16 am by DougF
Thanks - think I'll do the same thing with your furnace filter tip.
If you build it he will come.
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