CFM test for Atlanta

[Andy]

Ever since I have been in this industry the salesman have been saying there is only so much CFM you can get through a 2 inch hose. That is like saying there is only so many GPM you can get through a 1/4 inch hose but if you crank the pressure up what happens? You get more GPM.
My theory is that with a bigger blower and more inches of lift the CFM can always increase unless the hose collapses.
So to test my theory at Atlanta ( I probably won't be there). I am assuming that you will have small and big truckmounts there. Run out 150 ft. of hose and test the CFM. If the salesmen are right, that you can only get an x amount of cfm through a 2 inch hose, the CFM should plateau at a certain point no matter what blower, rpm or lift. that the machine is running at.
Give you something to think about before the bears come out.

 

[Mikey P]

But do you trust the cfm meters in this application?

 

[Andy]

If the same CFM meter is used on all the machines and hoses the question can still be answered.

 

[Mikey P]

Which meter and where do you want it placed?

 

[Andy]

I will leave that up to someone that knows more about meters than I do.

 

[dgardner]

That is like saying there is only so many GPM you can get through a 1/4 inch hose but if you crank the pressure up what happens? You get more GPM.

Andy, welcome to MB! Have you observed this personally? Can I get, say, 100 GPM through a 1/4" hose with enough pressure?

 

[TConway]

I believe this test will be possible, I can say that the cfm will more than likely climb to a certain point my best guess is in the high 300's. I believe what will happen is that the 2.0 hose will start to raise the lift factor on the bigger machines and this will start to activate the truck mounts safety feature.....the blower relief valve.
My legend is set at 16 hg but the VRV does not really VENT, it only leaks because it is a sub par unit. Now on my buddies 870 and 570 they are always leaking even MORE when the wand is on the carpet cleaning you can hear is opening and closing with every wand stroke.
What I can also say is even though my PC L is set at 16 Hg and you plug the hose 100-150-200 it will climb to that, but it takes its time and that time varies with hose length, the 870 because the hose is under much greater vac load just due to it creating so much vacuum in the hose itself it MUCH MUCH faster to hit that level almost instant.
I have taken this into account as I am working on our new wand. The results are pretty awesome, and interesting also.

 

[TConway]

Mikey has stated before "There is a difference working with a big blowered machine it is hard to explain but it is different" I can tell you with my experience with the 870, 570, and even my VWTM, there is a difference, it is NOT what you think, the wand did NOT get way louder as I was expecting, I am not saying the noise level didn't increase it did but not nearly as much as I was thinking it would compaired to my PC L
What does change is the quickness that the wand starts to lock or suck down to the carpet, the larger machines have already pretty much vacated all the free moving air in the 2.0 hose, the bigger machines are not needing the wand to be on the carpet to create a vacuum they have already basically done it, and when the wand hits the carpet....GAME ON the vac is there it is not needing to build it.

 

[TConway]

I set out to see if the "30" minute drytimes was really truely possible, you read it all the time on the forums, I also get a bit of guys that have called me for filters and telling me they have a custom tm's producing 800+ cfm. I am NOT saying they don't, what I do know is it is NOT possible to get with a 2.0 hose.
I am also fairly convenced that 30 minute dry times are more of a myth than a overall reality...Yes it is possible if you live in a very DRY climate area, but as I say the overall it is just not reality.
I would go as far to say if a guy is getting TRUE DRY times in 4 hours or less they are more than likely better than 75% of the carpet cleaners out there. I also tell them if they are getting this and they are running in bone stock set up, spending 100's of dollars on hose, cuffs, filters, or modding there machines is NOT going to give them more of a bang in dry times than just adding some sort of airmover or fan to there cleaning process. (AND POSSIBLY CHARGE FOR THIS STEP)
Carpet has the ability to HOLD ON TO a certain amout of water, just like guys with a whole head of thick hair, they can towel dry but once the free amount of water has been towed out a blow dryer is needed to get that final carpet cleaning hairdo.

 

[dgardner]

I believe this test will be possible, I can say that the cfm will more than likely climb to a certain point my best guess is in the high 300's.

Tom nailed it - that is if you measure accurately. Here's an online flow calculator set up for standard atmospheric conditions at sea level (the best possible scenario) with 100 feet of 2" open hose and a blower pulling 16 inHg at the inlet - it calculates 292 cfm:

 

[Pioneer Floorcare]

Tom nailed it - that is if you measure accurately. Here's an online flow calculator set up for standard atmospheric conditions at sea level (the best possible scenario) with 100 feet of 2" open hose and a blower pulling 16 inHg at the inlet - it calculates 292 cfm:

View attachment 11872

Where is this calculator? Can you do it at 13" of lift

 

[dgardner]

It's here:

http://www.pipeflowcalculations.com/pressuredrop/

Since it's designed to figure pressure drop you have to work it kinda backwards to figure cfm. If you're really interested I could type out a procedure (unless it's obvious), but here's the screen for 13" Hg:

Warning - don't get too excited over these numbers - they are for an open hose. Things change drastically when you connect a wand and drop it on the carpet and you can't calculate that from where I sit.... You have to measure it in the field.

 

[Cleanworks]

I believe the meters have to be calibrated for the diameter of the hose. The area in a 2 in hose is 3.14 in multiply by 600 in (50ft) you get 157 cubic feet of air in a 50 ft hose. If you have a blower working at 157 cfm, it will take 1 minute to evacuate all the air from that 50 ft hose. If you have a blower working at 314 cfm, it will take only 30 seconds and so on. The more cfm you have, the faster you move that air, creating faster vacuum ( higher velocity at the wand) a good example, I have a custom made portable with 2 high performance vac motors in parallel. It only pulls 14 in hg. My old ninja pulls the same with 2 much vac motors in series. Allthough the suction is the same, I can use 5 times the length vac hose because I am moving the air much faster. The rate of cfm that can be moved through a 2 in vac hose depends on the size of blower. Bigger is always better

 

[Cleanworks]

Excuse me where I said 14hg, I meant 10

 

[dgardner]

I believe the meters have to be calibrated for the diameter of the hose.

No, unless I'm not understanding your point. A flowmeter measures volumetric flow regardless of what hose it is hooked up to. Now if you're really measuring velocity inside the hose and converting to flow, then knowing the hose area is crucial to get correct numbers. But (this is a biggie) only if your measuring the velocity inside a straight run of the actual hose. And only if your instrument has a small enough area compared to the hose, otherwise the very act of measuring will affect the results. For example, the common procedure of using a funnel and turbine anemometer is hugely inaccurate if you use the area of the funnel big end, because the area of the anemometer is a significant percentage of the funnel's area (not to mention several other issues that affect the reading).

I have a custom made portable with 2 high performance vac motors in parallel. It only pulls 14 in hg.

Really? What vacs are you using? They pull 190 inches of water each? The new Ametek 8.4 inch vacs only run 146 inches. Seriously - I'm interested in what part number you are using.

Edit - I see you meant 10 - makes more sense....

Allthough the suction is the same, I can use 5 times the length vac hose because I am moving the air much faster

Sealed suction means nothing - lift and volumetric flow with wand on carpet defines performance.
When you are measuring your sealed vacuum, not only aren't you moving air faster, you aren't moving any air at all, so you're right, even though the sealed suction may be the same that doesn't tell you how the two units will perform.

The more cfm you have, the faster you move that air, creating faster vacuum ( higher velocity at the wand)

What you are describing is rise time, and it does affect performance for the first second or so after you slap the wand down, until the system has reached equilibrium.

If you are running 600 feet of hose and you lift the wand off the carpet on every stroke then yeah - you may notice a performance hit. But 150' and a reasonably sized blower? Not so much. It's not as bad as you think because your calcs are wrong.

3.14 square inches of area times 600 linear inches (50 feet) of hose equals 1884 cubic inches of volume, not 157 cubic feet. Since there are 1728 cubic inches in a cubic foot (12 X 12 X 12 = 1728) then your hose's volume is really only 1.09 cubic feet:

3.14 square inches X 600 linear inches = 1884 cubic inches

1884 cubic inches / 1728 = 1.09 cubic feet of volume in the 50', 2" hose.

So, using your example, your 157 cfm vac will take .0069 minutes (0.41 seconds) to reach equilibrium, while the 314 cfm vac will take 0.21 seconds. Not a huge difference as it turns out. There are lots of good reasons why you might want the bigger blower, but shaving less than a quarter of a second off your rise time might not be at the top of the list...

Edit: I used your example, but in real life the vac isn't removing all the air, only about half (at 15" Hg), so the rise time to reach equilibrium would be faster. In actuality the waste tank is the largest volume in the system, it has a much greater effect than the hose. A 60 gallon tank has a volume of around 8 cubic feet, still way shy of your 157 cubic foot example.

Now the V/AT guys with a 250 gallon waste have to contend with almost 34 cubic feet, maybe that's why they need the big blower...

Bigger is always better

Somewhat true, but only up to a point. Once you reach the vacuum limit set by your relief (to avoid imploding your waste tank) adding a bigger blower will just relieve more air - you won't get any more flow through the hose/wand.....

(BTW - You guys (and gals) probably think I'm nuts for enjoying such a nerdy subject, but providing, installing, and calibrating flow instruments is a big part of my corporate day job - I installed my first flowmeter in 1979...)

 

[Captain America]

Larger engines and larger blowers get faster dry times...guaranteed.....
4.5 blower should be used with a 30 hp minimum for vacuum......
With a zipper and correct heat I can get 2 hour dry time on commercial carpet...30 minute with a fan.
Residential carpet is variable...4 hour ++++
But I only have a 4.5 blower...I wouldn't buy another truckmount with less than a 4.7 blower......
Cap

 

[Cleanworks]

I see where my calculation is off, I am dividing 1884 cubic inches by 12 to get 157 cubic ft. I bow to your expertise but it seems obvious that bigger is better up to a certain limit. What is that limit?

 

[dgardner]

What is that limit?

 

[Cleanworks]

All dry times should be measured with a moisture tester.

 

[J Scott W]

I have flow meters we used for testing. I might be able to get them to Atlanta. But they are abit pricey (at least by my budget) so, I would need someoen to watch over them.

 

[Andy]

Let see if we can answer the wand to carpet airflow. CFM and Lift are opposite numbers, if lift goes up cfm goes down. let us work with a known. The VRV is set at a given amount closed of at the machine, let's say 14hg. When you put the wand on the carpet the lift is less because their is air moving through the carpet extracting the dirt and water in the process. With the wand on the carpet have someone record lift. Now remove the hose from the wand and cap it. start drilling holes in the cap until the lift equal what was recorded when the wand was on the carpet.
Can the airflow be calculated by multiplying the number of holes by the diameter of the holes using that area in the equation. If that doesn't work, can you use a flowmeter with the holed cap in place to see what the airflow is?

 

[dgardner]

Ever since I have been in this industry the salesman have been saying there is only so much CFM you can get through a 2 inch hose.

it seems obvious that bigger is better up to a certain limit. What is that limit?

The following is primarily for Andy and Ron, others wade in at your own peril.

Andy, there is a limit, it is determined by available atmospheric pressure and air velocity through the hose. I deal with some of these principles every day, but until I started playing what-if with the flow calculator I never put everything together in my head. Thanks for getting me to think this through.

Unfortunately what follows still applies only to an open length of hose, but it's a start. It doesn't directly answer Ron's question, assuming he meant a cleaning set up including wand, but it does set a limit. The blower for maximum performance in an actual cleaning situation would be smaller than this.

I created a special new flow calculator screen to go with the discussion:

This screen is again with 100' of 2" hose. I increased the cfm as high as I could without the calculator crashing, I got to about 305 cfm. Notice the velocity v2 - this is how fast the air is exiting the hose as it's going into the blower. Let me tell you, 52,500 feet per minute is screaming! In fact, the speed of sound is not far away, 67,560 fpm. Any higher than 305.03 cfm and there wasn't enough atmospheric pressure to move the air, the velocity became infinity, and the calculator crashed. Things get pretty goofy as you approach the speed of sound, and I don't pretend to understand the physics, for that you need a real rocket scientist!

So, at first blush you might be tempted to say that 305 cfm is the most flow you can get through a 2" hose - but not so fast.

Cfm is a volumetric measurement - a cubic foot is a volume. If I have a box that is 12" by 12" by 12" it would enclose a cubic foot of air. How much air (by mass/weight) is in there? Ah - it depends. If I'm at sea level it will contain more air than at the top of Mount Everest, because at lower pressures the molecules spread out. Put another way, if I fill a balloon with one cubic foot of air at sea level then take it up the mountain the balloon will get bigger. As the pressure is lowered a given mass of air will expand to fill a larger volume. Ever buy a bag of chips in LA then drive up into the mountains and had the bag blow up? same principle.

Here's the rub - the 305 cfm that the calculator came up with is air at atmospheric pressure - basically like the air around you now. But as the air enters the open hose the pressure starts to drop. It drops evenly with distance until it's at the lowest pressure going into the blower. As the pressure drops, the air expands, or occupies a greater volume.

Blowers are rated using acfm, or actual cfm. This means the volume is measured as the air flows into the blower, at the lowest pressure, meaning also at the highest volume!

Look again at the flow calc screen. Notice that the vacuum at the blower inlet is reading 21.86" hg. It took that much vacuum to achieve our max flow - but - this means the air pressure went from 29.92 (standard atmospheric pressure) to 8.05" hg at the blower inlet - a factor of 3.76 to one. This means that the air volume increased by the same factor (assuming the temperature remains the same, different discussion). So, the 305 cubic feet of atmospheric air entering the hose expanded to 3.76 times it's size, or 1147 cubic feet by the time it entered the blower. Since the blower is rated in acfm, our hypothetical blower would have to be rated at 1127 cfm/21.86" hg to achieve maximum flow through the 100' of 2" hose (on earth, anyway).

So, What is the maximum flow? if you're talking about acfm as measured at the blower inlet, it's 1147 (or thereabouts). if you're measuring at the hose inlet it's 305 cfm (which is also called scfm - standardized to sea-level atmospheric conditions).

If you're looking to find a truckmount that will achieve terminal flow through 100' of open hose you probably won't find one at the show. But it's a moot point - the really interesting question is what's the answer for a complete cleaning setup with hose and wand, sitting on carpet? Which wand? Which carpet? How much hose?, 2 or 2-1/2"? Probably why there are so many different TM designs out there....

 

[Mikey P]

Marty can you repeat that in pig latin?

 

[Cleanworks]

I'm getting dizzy now, numbers just swirling around in my brain. Let me run this by you. You are using 50ft of 2in vac hose. This is capable of handling a certain capacity of air. One hundred feet has double that capacity and so on. Using a 3 blower pumps out the air at a certain volume and pressure. Using a 4 blower must pump it out at a greater volume and so on. There has to be a maximum volume somewhere. We see tm's with small #3 blowers to large #6 blowers and even larger. For a single wand unit, there has to be a size where you get your maximum performance where any more is just a waste.

 

[dgardner]

You are using 50ft of 2in vac hose. This is capable of handling a certain capacity of air. One hundred feet has double that capacity and so on.

Nope - think about that. The longer hose will have more pressure drop and thus less capacity. And it's not linear, meaning not exactly half or double.....

 

[dgardner]

For a single wand unit, there has to be a size where you get your maximum performance where any more is just a waste.

Absolutely! But when you add in a wand, (maybe 12", maybe 14", maybe a Zipper) and carpet (what kind of carpet?) it gets a little fuzzy.

I can't calculate it, but they can measure it.

You pick a maximum vacuum atm, say 15", pick a "standard" wand, say a PC Quad with glide, some "standard" carpet, say a medium cut-pile, a "standard" hose, say 120' of 2" - and move the whole setup from machine to machine until you find the smallest one that will hit 15" with wand on the carpet. Now you've found the maximum performance with the smallest machine - until you change the setup! Different carpet? different wand? Different hose length? Start all over.

 

[GeneMiller]

Ever since I have been in this industry the salesman have been saying there is only so much CFM you can get through a 2 inch hose. That is like saying there is only so many GPM you can get through a 1/4 inch hose but if you crank the pressure up what happens? You get more GPM.
My theory is that with a bigger blower and more inches of lift the CFM can always increase unless the hose collapses.
So to test my theory at Atlanta ( I probably won't be there). I am assuming that you will have small and big truckmounts there. Run out 150 ft. of hose and test the CFM. If the salesmen are right, that you can only get an x amount of cfm through a 2 inch hose, the CFM should plateau at a certain point no matter what blower, rpm or lift. that the machine is running at.
Give you something to think about before the bears come out.

The limit of the 1/4" hose is 3 gpm. You can turn the pressure up as high as you want. It's easy to do a bucket test and see for yourself. As far as blowers you have to overcome the friction created inside the hose. The chart really doesn't help because we don't use the hose open. A bigger blower able to maintain higher lift handles the friction loss plus the weight of the water better. Remember the blower has to lift the water which is heavy. It's really just that simple.

 

[Doug Rice]

it gets a little fuzzy.

Blooming
couldn't resist

 

[dgardner]

The limit of the 1/4" hose is 3 gpm. You can turn the pressure up as high as you want.

How high can you go Gene? The silly flow calculator I've been playing with suggests that a 100' 1/4" hose with a #12 jet on the end will flow a touch more than 4 gpm if you can pump out 1700 psi while flowing (as long as you don't have any super-restrictive fittings). It would be interesting to test in real life....

 

[dgardner]

Blooming
couldn't resist

Lol...