Airflow with cloth outer bag

I think we could probably improve airflow on cloth-bagged vacuums which have inner paper bags, by leaving the zipper slightly ajar.

I bought a new replacement Outer Bag for my Kirby Tradition.
Its not as well made or nicely finished, as earlier bags; no Kirby label, Bag Topper too deep, raw white fabric edges alongside zip, internal strap is velcro & too long, and there's no felt strip inside to protect from catching the paper bag and to seal the zipper area from dust.

The original need for this Felt Strip, and the absence of it on the new cloth bag, led me to question it:

The original purpose of the cloth bag was obviously to keep fine dust contained within the fabric. It had to be the right strength, the right weave, and it was important to empty it frequently, and to scrape stubborn crusty bits, to maintain proper airflow.
Otherwise, air pressure would build up inside the cloth bag, and resist the flow of new air coming in. The degree of pressure is evident in the way dirt is compacted into a near-solid brick if unemptied for too long.

Now that we have paper bags (double-ply, hepa filtration etc.) the purpose of the cloth bag today is just to serve as a container, like a net, to stop the paper bag from bursting.
It doesn't need to filter or resist airflow at all - but it was designed to!

I'm suggesting the degree of resistance, and restriction of airflow, caused by the outer cloth bag, is now hindering performance of the inner paper bag.

You can see the pressure build-up within the cloth bag, when it instantaneously inflates to a solid, as soon as you turn the machine on. This isn't purely because the paper bag is pushing from the inside, sometimes paper bags are folded-over at one end and never fully inflate, or the fill-tube impedes the paper bag, yet the cloth is always fully inflated in all areas, and solid.

It appears to me that there must be air pressure caused by the cloth bag, acting against the paper bag, restricting airflow.

I think the faster the (clean) air is allowed to escape the cloth bag, the easier it will be for new (dirty) air to enter the paper bag.

Modern upright vacuums with plastic housings and paper bags, all have significant air-vents in the plastic housing to allow air to escape as quickly as possible once its left the paper bag.

I tried leaving the cloth bag zipper slightly ajar, zipper undone an inch or two, and it seemed to improve performance.

I have no way to measure air-flow, pressure, vacuum etc.
So I cannot tell whether this is really a significant improvement or just my imagination.

I'd welcome your thoughts on this.


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Post# 403113 12/26/2018 at 01:42 (1,941 days old) by Rowdy141 (United Kingdom)
Checkrate/Likes I think we could probably improve airflow on cloth-bagged vacuums which have inner paper bags, by leaving the zipper slightly ajar. I bought a new replacement Outer Bag for my Kirby Tradition. Its not as well made or nicely finished, as earlier bags; no Kirby label, Bag Topper too deep, raw white fabric edges alongside zip, internal strap is velcro & too long, and there's no felt strip inside to protect from catching the paper bag and to seal the zipper area from dust. The original need for this Felt Strip, and the absence of it on the new cloth bag, led me to question it: The original purpose of the cloth bag was obviously to keep fine dust contained within the fabric. It had to be the right strength, the right weave, and it was important to empty it frequently, and to scrape stubborn crusty bits, to maintain proper airflow. Otherwise, air pressure would build up inside the cloth bag, and resist the flow of new air coming in. The degree of pressure is evident in the way dirt is compacted into a near-solid brick if unemptied for too long. Now that we have paper bags (double-ply, hepa filtration etc.) the purpose of the cloth bag today is just to serve as a container, like a net, to stop the paper bag from bursting. It doesn't need to filter or resist airflow at all - but it was designed to! I'm suggesting the degree of resistance, and restriction of airflow, caused by the outer cloth bag, is now hindering performance of the inner paper bag. You can see the pressure build-up within the cloth bag, when it instantaneously inflates to a solid, as soon as you turn the machine on. This isn't purely because the paper bag is pushing from the inside, sometimes paper bags are folded-over at one end and never fully inflate, or the fill-tube impedes the paper bag, yet the cloth is always fully inflated in all areas, and solid. It appears to me that there must be air pressure caused by the cloth bag, acting against the paper bag, restricting airflow. I think the faster the (clean) air is allowed to escape the cloth bag, the easier it will be for new (dirty) air to enter the paper bag. Modern upright vacuums with plastic housings and paper bags, all have significant air-vents in the plastic housing to allow air to escape as quickly as possible once its left the paper bag. I tried leaving the cloth bag zipper slightly ajar, zipper undone an inch or two, and it seemed to improve performance. I have no way to measure air-flow, pressure, vacuum etc. So I cannot tell whether this is really a significant improvement or just my imagination. I'd welcome your thoughts on this.

Post# 403122 , Reply# 1 12/26/2018 at 16:57 (1,941 days old) by Lesinutah (Utah)
Checkrate/Likes *Hey* I'm going to disagree. I could understand shakeout bag yes but bag assembly no. I modified my tradition to use newsest sentria bags. The original 1.25" fill tube is where resistance comes to play. The paper micron magic bags maybe. If you use setup I use the motor is almost as strong as sentria. The breathability of the bag makes no difference. If you're fill tube is sealed you could take cloth bag off or keep it on. There should be no dust coming from anywhere. If you do it's a hole in your fill tube or not sealed correctly. Its like saying someone with long hair is going to have more resistance running. The bag doesn't restrict airflow. Run your vacuum with no cloth bag you will see no higher rpms no higher amps no more stress on anything. I do have a video of a 561 with no cloth bag at all testing my setup using newsest Kirby bags. Just my 2 cents Kes

Post# 403128 , Reply# 2 12/26/2018 at 20:05 (1,941 days old) by Rowdy141 (United Kingdom)
Checkrate/Likes Hi Les, Thanks for your take on my 'theory'. Ah, so the Vents in new plastic canisters are just to prevent the door from blowing open, not to improve airflow through the paper bags? Gotcha. I'm sort-of throwing this idea out there, whilst still trying to get my head around the dynamics, so I can improve my understanding of bag/tube/roller set-up. I'd be the first to admit I don't know much, and there seems to be little or no statistics regarding bag/tube/speed/roller/carpet efficiencies. I think most users tend to judge their own configuration/circumstances. I could buy a Vacuum Meter, Pressure Gauge, Flow Meter, and use my Ammeter, and test different bags and carpet types, but I'd still be out-of-my-depth trying to understand it all. Especially where the wider Tube also means a drop in airspeed and pressure. That's my stumbling block. I didn't mention the Fill-Tube diameter factor (Tradition v Heritage/Legend) because we don't have that problem on our 240v machines. Ours are permanently on High (hose) speed. Fitting the Legend II emptor & tube & bag on our Traditions, makes no discernible difference. But again, no real evidence either way. I figured the bag must have been restricting airflow, because it blows-out, like a sail in a wind. If air passes through freely, it would remain limp? Do you suppose the Felt was just to stop the Zip from jamming with dirt? Not a sealer? Should I sew one into the new Cloth Bag? Thanks Les. Happy New Year

Post# 403131 , Reply# 3 12/26/2018 at 20:39 (1,941 days old) by Lesinutah (Utah)
Checkrate/Likes *Hey* I done tests on empty shakeout full shakeout f&g no anything and my adaptor setup. Empty shakeout no bag and cloth HEPA setup I made no resistance. F&G was 20-25 percent loss full shakeout 33 percent full HEPA no resistance. The HEPA bags do breath better as there not paper. The classic 3 bag tradition and first heritage bags are trash. The build quality and fabric is worthless. The old shakeout bags were 562 through classic are good. There is a classic bag with pin stripes that leaked air. The brownish bags breathe well. The tradition had shakeout and first disposable. It was restrictive because where emtor goes is 2.25 or around that of airflow. The exit is 1.25 inches. It's going to strain.later on heritage it almost same in and out causing little resistance. The new emtors have streamline air path no resistance. It's what I have gathered. Les

Post# 403182 , Reply# 4 12/27/2018 at 18:40 (1,940 days old) by texaskirbyguy (Plano, TX)
Checkrate/Likes 1 *In the name of science...* ...I did a quick 10 minute test on my stock Tradition using paper bags. Tests were done on low speed with open intake, as the rug nozzle has much less air restriction than the hose. This would represent a realistic mode of operation. Bag was a tad less than half full and inside temperature was been 69*F. With zipper closed, after a 10 second warmup to stabilize current: RPM 12677 Watts 443 With zipper fully open after 10 seconds to stabilize: RPM 12608 Watts 451 Increased airflow equals more load on the motor, slowing the speed and increasing current. As I expected, opening the zipper DOES increase airflow, just not very much. In fact you will most likely not notice any usable performance gains. Opening the zipper only an inch or two will yield even less usable performance gain.

Post# 403184 , Reply# 5 12/27/2018 at 18:57 (1,940 days old) by Lesinutah (Utah)
Checkrate/Likes *Hey* So basically there's a 1-1.5 percent difference. Like I said bag makes no difference it's the seal or air leaks but with no leaks no difference. Les