Direct Air vs Bypass Air confusion

[n0oxy]

weight of power nozzles

Actually, I think it was sptyks's post that you are disagreeing with rather than mine. Like you, I'm a big fan of canisters like we talked about at the convention a few months ago. It was interesting hearing the tones of the different Hoover canisters at the museum.

 

[n0oxy]

swapping hoover power nozzles

Rob, I know you're a big fan of the Hoover power nozzle canisters, just curious, have you tried using a different hoover power nozzle than the one that came with each canister? I think you said you have 11 different Hoover power nozzle canisters, does each canister have a different power nozzle or are some the same? I guess it may not even be possible to do this, depending on if the hoses and wands are similar. I think it's kind of interesting to pair canister vacuums with other power nozzles than what they come with, for example, using a Riccar power nozzle with an Electrolux canister, or a Sebo power nozzle with a Panasonic. If a power nozzle has a pig tail cord, this is really easy to do, the nozzles that use direct connect are a bit more difficult, but can still be done if you make a pigtail cord with the right connectors.

 

[n0oxy]

weight of cleaning head

While uprights might be heavier, this also makes them harder to move I think. If a powernozzle's brush is at the right height, it should be able to clean as good as an upright. It's interesting that the volt cleans so well since it does not have a height adjustment setting.

 

[sptyks]

It all boils down to Airflow! The Bypass design of the canister does not supply enough airflow to pull the carpet up to the nozzle to form a complete seal to the carpet. And it is true that direct air uprights require a little more effort to push because of this, but that is why Kirby developed Tech Drive which reduces the effort to push the vacuum by 90%. The kirby G series vacuums can be pushed and pulled with only two fingers with Tech Drive engaged.

 

[anontemp123]

I have read this thread again and again, and I think I have the answers to all my questions. Thank you so much.

As far as filtering the motor cooling air in direct air vacuums: Why can't this air just be sent up to the bag with the dirt and filtered that way? I actually assumed this was the case, but now it makes sense why 'bypass' is said to have better filtration. I know for allergy sufferers this can be a huge deal. I was looking for used Riccars on Craiglist and asked a seller why she was selling her Riccar Vibrance. She replied her family members required even better filtration than a Riccar bypass. She ended up having to purchase a top-of-the-line Rainbow.

 

[anontemp123]

And where could I find an explanations on the importance of suction? I've read and seen so many explanations on the importance of airflow, but nothing that gives suction the spotlight. After all, suction does still matter. Sort of like an idiot's guide to understanding static pressure. How is suction generated. Etc.

 

[n0oxy]

suction and airflow

Suction is the actual pressure difference that is created, if you put your hand up to a hose and it grabs on really hard, than there is a lot of suction. Airflow is how much air is being moved. You actually need a decent amount of both to clean well. And, the more you have of one, the less you will have of the other. The clean air uprights generate a lot of airflow but not as much suction which is why they don't work as well with attachments. On the other hand, if you have very strong suction but don't move as much air, the dirt will not move towards the nozzle so the vacuum can pull it in. Again, you need a decent amount of both to clean well.

 

[n0oxy]

the tandom air concept

I know many think that the dirty air design actually cleans carpets the best, I do think that a good power nozzle canister will clean just as well as an upright though. Still, the tandom air uprights that Tacony produces do seem to do a really good job at cleaning carpets. And of course there is the volt power nozzle, really this gives you the best of both worlds if you hook it up to a canister, backpack or central vacuum. You have the high airflow of the dirty air design, but you also have the extra suction or lift provided by the canister motor, the only thing that concerns me about the dirty air design is that everything picked up goes through the fan. I know fans have improved to prevent breaking, but I would think after a while, dust would become caked on the fan blades in this design.

 

[anontemp123]

Let's take it one step back. For me it's easy to understand airflow. Fan moves, generates airflow. Bends reduce airflow.

However, what is generating suction? Is it also the fan? Some other part of the design? I have a notion that for suction, it doesn't matter how long the path is, or how many bends you have, suction remains constant. Does that sound right?

 

[kirbysthebest]

Suction: the production of a partial vacuum by the removal of air in order to force fluid into a vacant space or procure adhesion.


Hence, the fan pushes air away, and the atmospheric pressure forces air or fluid (air is actually a gaseous fluid ) into that space.  Remembering that nature abhors a vacuum. 


 


 Suction as we would define it is created in a vacuum cleaner  by placing a restriction between the fan casing and the nozzle or hose.  Where through the Beurnoulli Principal there is a low side and a high side.  The speed of the air increases through the restriction and thus we have a vacuum cleaner, or a suction sweeper.  Basically air traveling from atmospheric pressure, speeds up through the restriction to fill the vacuum created by the fan and then returning to atmosphere.


 


Air flow would be the speed in which the air is moving, and suction would be the force in which it is being removed.

 

[n0oxy]

creating suction

In order to create suction, you need at least somewhat of a seal, if everything is totally sealed, you then have maximum suction but no air flow at all which is not very useful. To see the difference a seal makes, if you have access to a canister vacuum, open the bag compartment and turn it on. You will probably feel lots of air flowing but not a lot of force, in this state, nothing is really sealed, so you have a large amount of air but it's not moving with much force. Again, to clean well, you need a decent amount of both suction and airflow. This also gets in to the difference more than one fan stage can make. If you have more than one fan in series, it increases the suction, on the other hand, if you have fans in parallel, the airflow is increased. Airflow will also be restricted by things such as the hose diameter, that's why in applications such as central vacuums works best with a wide diameter hose. I'm actually thinking of trying a commercial 1.5 inch hose on my central vacuum units to see how it works.

 

[sptyks]

Suction vs Airflow and Filtration

Harley and Mike, you gave excellent definitions and descriptions of Suction vs Airflow in the previous posts.


 


I have another description of these two forces. First off, always remember that as one increases, the other decreases. However as stated earlier, you do need both to clean a carpet.


 


I own several Kirby's which are Direct Air or Dirty air machines. The Kirby has a huge amount of Airflow at 127 -130 CFM (cubic feet per minute) but low suction measured at 32 inches of water. This is because the opening to the fan chamber is a full 2 inches in diameter allowing all that air to move very quickly through the machine.


 


I also own a Hoover WindTunnel Air vacuum which is a bypass air bagless vacuum. In contrast to the Kirby, the Hoover has lots of suction but much less airflow because the diameter of the hose and internal piping is a narrow 1 1/4 inches. The Hoover has only 60 CFM airflow but the suction measures at 80 inches of water.


 


So therefore assuming the size of the motor and type of fan is the same, it is mainly the diameter of the opening which the air passes through that determines the amount of suction and airflow.


 


Now lets talk about how the length of the hose or internal piping affects suction and airflow. So the LONGER the hose, the less suction and airflow you will have. This is why Central vacuums typically located in a basement or garage have very powerful 240 volt motors. These huge motors are needed to overcome the loss of suction and airflow caused by the very long internal piping that is located inside the walls of a home. These pipes can be 50 to 150 feet long depending on the size of the house.


 


As far as filtration goes, the difference between Direct Air and Bypass Air vacuums is insignificant. Both can have synthetic cloth HEPA bags which filter the air down to particles of less than a Micron which is excellent. The fact that Direct Air vacuums use a separate fan to cool the motor does not really affect their ability to filter well. The exhaust air coming from the cooling fan contains only a few microns of carbon coming from the motor's carbon brushes. As far as I know no one is allergic to carbon because our bodies are made up largely of carbon.


 


The Kirby is a Direct Air machine which has the Gold Seal of Approval from CRI (Carpet and Rug Institute.) To get a Gold Seal, CRI measures these two things: the amount of dirt removed from several different types of carpet and the quality of air exiting the machine (filtration). If you are not familiar with CRI here is a link so you can check any make and model vacuum. The first link is CRI testing standards. The second link is a list of certified vacuum cleaners and their ranking.


 


http://www.carpet-rug.org/vacuums.html

 


http://www.carpet-rug.org/certified-vacuums.html

 


 


 


 


 


 

 

[Mike81]

What is good airflow rating?
One very powerful canister is Philips Performer Pro bagged canister vacuum. It has 108 cfm and 500 airwatts of suction/airflow. Something that is excellent for canister vacuum. It is measured from the hose end by the consumer reports.
This 2100 watt vacuum is now discontinued due to the too high wattage motor. For US people it is 18 amps.
I bet that Kirby or Royal will produce more cfm, but for canister TRUE 108 cfm seems very good.
My parents have that Philips now (my ex vacuum). It has powerhead outlet, so I might test it with the full-size Wessel Werk powerhead.
And what it comes to canister vs upright, I personally like both.

 

[sptyks]

Mike81,


108 CFM is excellent for a canister vacuum.


 The Kirby Avalir has close to 130 CFM and the Royal 8300 has close to 150 CFM but those are both Direct Air upright vacuums.


 


You can still use the canister with 2100 watt motor in Finland correct?


This canister would be illegal in the US. Our maximum wattage for vacuums is 1440 watts or 12 amps.


 


 

 

[Mike81]

Well 18 amps / 2200 watts is now illegal in EU because of new regulations. It is only that stores can't sell those high wattage vacuums. Of course we can keep them.
Only vacuum that comes close to it is the last high wattage Electrolux Ultraone with 465 airwats.
One note is that Philips uses large diameter hose. Also Electrolux has fairly large diameter hose.
These vacuums has very straight airpath to keep the good airfow.

 

[anontemp123]

Ok, so the length of the hose *does* affect suction? I thought as long as the system is sealed, suction should not be affected by the hose length. Another hurdle for me is to understand why, even with a dirty filter, I don't get loss of suction with my current bypass. Is it the nature of suction, or something to do with Dyson's cyclone system.

I found these videos useful: (second one was the best)



(I tried to make the videos a link, but I couldn't figure it out. The messageboard software embeds them like this.)

Although, in this one, can you really just add the two figures like that?

 

[tolivac]

I have not heard of any "regs" prohibiting vacuums in the US over 1400W.If the vac draws more than this it would have to be equipped with a 20A 120V NEMA plug.-Like any other 20A device.I have a Blendtec "Titan" blender that has a 20A motor-what is on the blender nameplate-it has a NEMA 20A plug.Many central vacuum units draw 15A @ 120V.1800W.Have such a unit.Then there are the 240V central units that would need a NEMA 15A or 20A 240V plug and outlet.Many shop tools like table saws have this,too.Know a friend that has a woodshop in his garage and his 7Hp planer runs from a 60A 240V "stove" outlet.

 

[n0oxy]

decreases of suction and airflow

In theory at least, as the pipe runs get longer and there are more twists and turns, the airflow will decrease, but the pressure difference would stay the same, assuming that the system is sealed well. There are some central vacuum units that have two motors, if the motors are in series, you will increase the pressure difference, however if the motors are in parallel, you will increase airflow, but remember that airflow is also restricted by a narrow path, so if the maximum amount of air is already flowing through a hose, adding another motor will not increase the performance unless the hose is wider. This is why on some canister vacuums such as the Sebo, the hose becomes wider as you move towards the end that connects to the vacuum itself. The most powerful central vacuum unit I have in my apartment is the Purvac Barracuda, it has 144CFM and 151 of suction, and connecting a central vacuum hose directly to it, or any central vacuum unit is really awesome, like a super powerful canister vacuum. I have several central vacuum units throughout my apartment, a total of 7 of them. In the United States, the maximum power an appliance is allowed to pull is 12 amps, that's for a standard 120 volt outlet, I do think some central vacuum units actually draw more though. In Europe, they use a 220-240 volt system, and if you have higher voltage, the motors will draw less amperage. If I had a 220 volt outlet, I would consider getting a 220 volt unit, they are quite powerful. Hmmmm, all this talk about central vacuum units has made me want to connect the hose and fire up a few of them, so I'm going to go do that.

 

[n0oxy]

more airflow with open bags

So, as I stated in my last post, I did fire up a couple of my central vacuums, and then I pulled out my sanitaire backpack vacuum. Backpacks are interesting because the bags they can use are a bit different from most canister and upright bags. This backpack came with a paper bag, the first thing I did was to replace that with a cloth bag, many backpacks can use the same bags, and 10 quart cloth bags are easy to find. I tried running the vacuum without the lid on, quite a bit of airflow, it almost felt like a regular table fan, but of course, you really could not clean with that, there was no seal, the air was allowed to flow freely. Once you put the lid back on, it creates a semi-seal, and that's where you get your suction. For backpacks, you can choose to use closed or open bags, apparently the main advantage of open bags is that you can dump them out and reuse them. I would never reuse any bag, even if you dump out everything that is visible, dust will still clog the pores of the bag. The main reason I use the open bags in my backpacks is because they allow more airflow through the bag. Interestingly, the central vacuums made by MD manufacturing also use this approach for their bags, the bag goes in to the top of the unit and provides a lot of surface area for air to flow. Since the Kirby vacuums have so much airflow, I'm wondering if the bags they use are similar to this, or do they use the close bags like what you see on most canisters, where the only opening is for the tube to be inserted.

 

[sptyks]

Kirby and Royal airflow

N0oxy,


The Kirby and Royal bags have only one opening near the top of the bag. The large volume of airflow is because the bags are quite large so there is a lot of surface area for the air to pass through. The full line is only halfway up the bag so the top half of the bag remains empty so that dirt does not block the pores in that part of the bag. The outer bag on the Kirby and Royal also allows air to pass through and acts as a secondary filter. This is quite different than canister vacuums and some other upright vacuums where the bag is totally enclosed inside a solid enclosure further restricting airflow.