Direct Air vs Bypass Air confusion

[anontemp123]

I've read a lot about the technical difference between the two. What I can't understand is how the bypass method filters better than direct air. Why does the fan placement -- before or after the "filter" -- matter if it all goes through the filter eventually? And if having the fan before the filter, like with direct air, gives you less filtration, wouldn't that automatically make tandem air as "worse" as direct air, because it has both?

When I use the vacuums we currently have, I always notice that not only is the vacuum sucking, but there is also air blowing out of the vacuum. I suspect that air that's blowing out might have something to do with the difference between the two, but I can't find an explanation that delves into those details.

Also, I've read certain Miele canisters will "filter the air around you". Is this just a way of saying "bypass", or does this mean they have an air purifier built-in that runs at the same time as the vacuum?

Recently upgraded carpet and our Dyson wouldn't run. Started reading about vacuums and couldn't resist going down the rabbit hole. It's a whole other world down here. Currently can't decide between four models, wish I could get them all. Hope I made sense. Thanks for any help.

 

[eurekaprince]

The primary objective of a bag-first configuration in an upright vacuum cleaner is to protect the fan and motor from damage by dirt and debris passing by the fan blades. Fan-first uprights require all dirt and debris, including stones, sand, paper clips, pins and other hard objects to pass through the fan before being blown into the bag. By putting the bag first in the pathway of the dirt, and having the airflow sucked into the bag (instead of being blown into the bag) the fan is protected from damage.

As a secondary benefit, an onboard hose can be used to provide suction to the brush roll cavity as well as for above the floor cleaning.

You can have good filtration in a fan-first vacuum and in a bag-first upright vacuum. Neither configuration guarantees better filtration of the exhaust air. Some say the classic, fan first upright vacuum configuration exhausts cleaner air because most dirt falls away from the path of the air flow, whereas in a bag-first upright, as in most canister cleaners, the air is always fighting its way through, over and around the collected dirt in the bag.

 

[anontemp123]

Thank you for the clarification. I don't know why every online resource informs the reader that bypass equals better filtration.

Is there a thread or section of the forum where we can ask for help choosing between different models? I don't want to violate forum rules but I couldn't find any such section.

 

[eurekaprince]

I think you'll find as many opinions about "what's the best vacuum?" as there are posters here at Vacuumland. Everyone has a favourite brand or certain set of criteria that determines their answer to "what's the best vacuum?"

Though many at Vacuumland disagree with the methodology and results of Consumer Reports tests, I personally have found them to be quite helpful. I always take into consideration their "brand reliability" survey results along with their test results.

My current "best vacuum" advice to others is actually a pair of vacuums - one upright to clean carpets and one canister to clean everything else. My upright of choice is the lightweight Hoover Platinum Bagged upright (rated "excellent" for carpet cleaning by CR). My canister of choice is the quiet, versatile Miele C3 Alize (rated "excellent" for airflow through the hose and for noise suppression by CR.) These 2 are a dynamic duo that gets the job done easily and effortlessly. And the combination cost me under $1000.

 

[sptyks]

Anontemp123,


 


If you want your new carpet to be as clean as it possibly can be, then you should get a Direct Air machine. Direct Air vacuums such as Kirby, Royal and Riccar Tandem have the most airflow and best agitation of any Bypass air vacuum.


 


It's a known fact that Airflow and Agitation is what cleans carpet. These Direct Air machines have more airflow and clean better because the fan is located only 3 inches from the carpet. In a Bypass machine the fan is placed after the bag and the air must travel through 3 to 5 feet of hose and internal piping with numerous twists and bends before reaching the bag. This reduces airflow by more than half as measured with my Baird Airflow meter.


 


It is true that with a Direct Air vacuum all the dirt and whatever other objects you pickup such as small stones, sand, paper clips, screws and coins must pass through the fan on the way to the bag. This is not the problem that it once used to be when fans used to be made of metal which is actually quite brittle. Foreign objects hitting a fan spinning at 18,000 RPM would most likely break one or more blades of a metal fan. The newer Kirby and other Direct Air vacuums have fans made out of Amodel which is similar to Kevlar but 300% stronger than Kevlar, so they are now pretty much Bullet Proof. Royal still uses a metal fan but it is designed with very curved fins which pass most objects through the fancase with little problem.


 


Other things to consider is that most Direct Air vacuums can be configured to be used as a powerful (leaf) blower. Bypass Vacuums do not have this option. Another fact which may clear up some confusion is that most all vacuums (Direct and Bypass) now have as an option top use the new cloth type HEPA bags which filter the air exiting the vacuum so well that it is cleaner than the air you are breathing in. In other words it is filtering the air around you.


 


I hope this video helps you to better understand the differences between Direct and Bypass Air vacuums:


 

 

[sptyks]

Anontemp123,


 


The two best Direct Air vacuums are Kirby and Royal. You saw the all metal Royal in action in the video I posted in Reply #4 above. I am posting the Kirby Sentria user's guide so you can not only see the Kirby system in action, but also see all the things the Kirby system can do. The performance is equal to or better than the Royal.


 


New Kirby's cost anywhere from $1500 to $2995 but you can get a fully reconditioned - like new Kirby system with all the attachments including carpet shampoo system for a fraction of that cost on ebay. Typically $300 to $500.


 


I own several Kirby's and I can truly say it is the best vacuum I have ever used.


 

 

[anontemp123]

More confusion

Thanks, eurekaprince and sptyks, for your assistance. I have read many of your posts, sptyks, but thanks for the refresher. I particularly enjoyed your lively debate with another member on airflow vs suction. (The Avalir announcement thread was also a favorite of mine.) I was completely oblivious to this world, but for the last two weeks, I have spent all my spare time reading about and looking at vacuums. If I may be so bold, I hope to soon write my perspectives and share my experiences. I also have some further queries for you, too, eurekaprince. First, I would graciously ask if someone could help clear up my confusion on a couple of other topics.

The owner of a vacuum store told me that a beater bar is the best at cleaning carpet. (Before, I always took beater bar and brushroll to mean the same thing.) He further explained that folks would keep ruining their hardwood floors, so residential vacuums no longer have beater bars. I thought, "Wow, that's what I need!" Another vacuum store owner, however, told me a beater bar would ruin my new dense carpet. Any thoughts?

Also, I'm still a bit unclear on adjusting the height of a brush roll vs suction power and how that ties into agitation. When I can't move a vacuum on a sample of my carpet, I can reduce the suction power (on vacuums that allow this) and the vacuum will move. But now I am sucking less. Or I can raise the brushroll and it will move. But now I feel like I'm not getting as "deep" a clean; that the brushroll is only combing the top half of my carpet, if you will. If a better agitation machine agressively hits my carpet to make up for only combing the top half of the carpet, won't that ruin the carpet (like that one store owner told me the beater bar would)? Now, on my previous low density, low pile carpet, was the brushroll over-combing and hitting the carpet backing? Just having some difficulty grasping these concepts. It sometimes makes sense to me that I would raise the brushroll on low pile carpet to avoid hitting the backing, and lower the brushroll on high pile carpet to get a deeper clean. But then carpet density enters the equation and I'm confused again.

For bonus points, how is a metal brushroll superior to a wooden brushroll superior to a plastic brushroll? (I know that's not a sentence, but you know what I mean.) Aside from replaceable brushes, I remember reading or hearing something about bearings, but couldn't find information on it.

 

[eurekaprince]

Hi anontemp,

I don't think you can focus on one element of a vacuum cleaner to guarantee good results. Good cleaning performance is a result of the right combination of mutiple features. There are excellent upright vacuums with wooden brush rolls, and poorer performers with steel brush rolls. This is why I like Consumer Reports tests - each vacuum in the test group undergoes identical testing and the results are compared. It's the final result that counts. In deep carpet cleaning, the tests measure how much material is removed from identical carpets by each vacuum. Each stretch of carpet is "dirtied" in the same controlled manner before the vacs are tested on them.

Beater bars are also not a guarantor of better deep carpet cleaning. The vibration and agitation provided by a bristle-only agitator can do as good a job of disengaging dirt from a carpet pile. The only thing to watch out for are overly soft bristles as these may not provide sufficient vibration. But again, the "proof is in the pudding" so to speak.

Setting the height of an upright on it's lowest setting will not always guarantee a better cleaning of the carpet. The nozzle needs to be able to "breathe" to prevent "suction lock" and allow airflow to carry away the dirt. As long as the brush roll is somehow making contact with the top of the nap, that is all the vibration you are going to need to dislodge the dirt. You will remove more embedded dirt by going over the same area a few times with the nozzle height set just right, than going over once with the nozzle set at its lowest setting.

For delicate carpets, I would recommend a weaker cleaning mechanism - best use an airdriven turbo nozzle with a canister cleaner. These will provide a gentler sweeping action than a motor-driven brush roll.

 

[sptyks]

Hello Anontemp123. You have many good questions.


 


Let's start with the brushroll. Brushrolls no longer have beater bars on them, but that is not a problem because the newer brushes are now stiffer and beat the carpet just as well as beater bars. The second store owner is wrong! Hoover used beater bars in their vacuums for decades without causing any damage to carpets. But beater bars did have a problem with damage to wooden flooring.


 


The new stiffer brushrolls have plenty of vibration but pose no danger to 99% of today's carpets. Wooden brushrolls are best and are used on the most expensive vacuums. Wood is best because it allows for a magnet to be imbedded into the brushroll. The magnet is used to activate the BPI (brushroll performance indicator) light which is present in the newer Kirby's and Royals. Metal is Ok but doesn't allow for a magnet. They also have a tendency to rust if used on a damp carpet or stored in a damp area. Stay away from plastic brushrolls which may not be well balanced and have inferior bearings.


 


If you should purchase a Kirby or Royal vacuum, you will not need to worry about setting the correct nozzle - brushroll height as it is a foolproof process no matter what type of carpet you have. When set properly, Kirby's and Royals are designed to do a deep clean every time without doing any damage to the carpet. It is a fact that no vacuum cleans any better than a newer (less than 10 years old) Kirby or Royal. Here's how the height is properly set:


 


Kirby: With the motor running, lower the nozzle one click at a time with the Toe-Touch control, until you hear a change in the motor sound when the brushes first contact the carpet, then lower one more click which will form a seal between the nozzle and carpet. You are now at the proper height. The BPI light should be on steady green. If BPI starts to flicker or goes out, you have gone too low and/or the belt needs to be replaced. On the Kirby, the very lowest setting is for use with the Carpet Shampoo system.


 


Royal: With motor running, turn the Height Adjustment knob clockwise. When the Adjust-O-Rite button on the front of the nozzle sucks in, you are at the correct height. The BPI light works the same way as the Kirby BPI.


 


I have tried to answer all of your questions but if you have more, then ask away. I check in here every morning.


 I am wondering if you have had a chance to watch the two videos I posted earlier, especially the first one which does a great job of explaining the difference between Agitation Airflow and suction.


 


~Stan

 

[hooverkid]

Let me see...

So let me see if i can answer all your questions in one go, for a vacuum to work well on carpet you need 3 things, airflow (the amount of air the machine moves), agitation(the vibrating and grooming the brushroll does on the carpet) and suction (the amount of force the air is pulled through the machine).I along with many others agree that airflow is the most important element of a vacuum,the direct air or fan first style of vacuum uses a fan placed a few inches from the cleaning nozzle and as a whole will produce more airflow than a bypass or bag first machine, agitation is the second most important element to how well a vacuum will clean carpet and you get the best agitation when you have a combination of good airflow to pull the carpet up to the nozzle,a good brushroll which typically the best brush rolls are made of wood or metal Examplesof thesetype of brushrolls include metal beater bar brushes like what is found in traditional direct air vacuums like a sanitaire, a metal brushroll with brush stiffener like in riccar and simplicity tandem air vacuums or a wooden brushroll like royal or kirby bell nozzle direct air vacuums use and the third element in agitation is height adjustment that puts the nozzle at a balance between good airflow and good brush contact to the carpet if the nozzle is too low the vacuum won't have good airflow and if it is too high the brush won"t give the best agitation. Suction is less important in direct air vacuums but in clean air vacuums the suction pulls the dirt from the tube to the bag. Hope this helps!

 

[anontemp123]

Yes, in fact I had already watched those videos, and part 2 of the first one, too. (In part 2, he does the tug of war again.) But I like reruns so I watched them again. Just going to let your responses bounce around in my head for a day, then I'll be back.

Eurekaprince, would you consider a used basic C1 Delphi canister to be a reliable investment? I mean like how, with a Kirby, you can buy any old beat up one and get it to work. I am being offered a C1 Delphi, no attachments, just the powered floor brush it comes with. I couldn't find videos on dissecting it like I did with Kirby models.

 

[anontemp123]

hooverkid, in a directair, the path the debris takes up until it "hits" the fan, isn't that the same type of suction as in a bypass? In my very limited understanding, it's the larger diameter airflow in directair that is creating greater suction than with bypass. I see it as: with bypass, the fan is so far away it has to work so much harder, and the airflow diameter has to be smaller, to get good suction. Whereas with direct air, the fan is right there, so it doesn't have to be as powerful to get good suction. I hope I explained my (probably wrong) intuitions clearly.

 

[vacuumlad1650]

Ok gather round kids and I'll post the real way a Direct Air vacuum works...or at least how Hoover designed it. Let me dig out my copy of Fabulous Dustpan by Frank G Hoover
Andy

 

[vacuumlad1650]

"Fabulous Dustpan"
Chapter 11
The day they moved the wheels back
Pages 107 and 108

Andy

 

[anontemp123]

Thanks for the great read!

I don't understand why a bypass also can't "lift" the carpet and comb it? My DC14 Dyson definitely lifted my old carpet a little. (Maybe it was poorly installed carpet.) Does direct air lift the carpet better in some way?

Again, I have no doubt direct air is preferred for carpet, just trying to make sure my concepts are somewhat sound.

 

[hooverkid]

On a bypass machine all the suction is going to the nozzle through a 1 1/4" hose normally placed on the side of the cleaner this makes the vacuum not pick up well in the side opposite the intake hose and because the hose is small the hose also reduces the amount of air. Think of it like this if you have a lot of dirt in a work bench and your using a shop vac you'll pick up more dirt in one pass if you use a tool with a wide opening, on a direct air vacuum there is a wide opening to the fan that helps to move more air.

 

[eurekaprince]

Hi anontemp,

The Miele Delphi is a fine cleaner, though it rates only average for carpet cleaning. If you are getting it for very little money, why not? You can always upgrade, improve and enhance the cleaner gradually by buying easily available genuine Miele attachments and filters. I'm not a big fan of power nozzle canisters because I find the electrified hose, handle and wands too heavy and bulky and prone to electrical problems like cutting out. But you can always buy a regular non-electrified hose and wand and bare floor brush and attachments to make this your primary cleaner for everything but carpets. For carpets, I much prefer a basic, classic lightweight upright as a companion to the canister. Even a cheap grey Eureka DialaNap Boss will do the trick!

 

[eurekaprince]

On the other hand, why bother with a used C1 Delphi missing most of its attachments when you can get a brand new "suction-only" Miele Olympus for $330? It's the identical vac without the power nozzle configuration for deep carpet cleaning. The suction only carpet nozzle is fine for removing surface litter from carpets. I still prefer the more deluxe Alize over the Olympus.

See below for a nice summary of the Olympus:



http://https//youtu.be/qVFnybNxsF4

 

[vacuumlad1650]

You have to realize that airflow is lost when it goes through the twists and turns of a hose. This can be the difference between lifting a 1974 Buick with a 1974 Kenmore magic cord and lifting a Brick with a Kirby. The design is a huge part. Twists and turns of hoses are detrimental to airflo
Andy