Question for engineers and the mathematically brilliant here

[truckmount girl]

I'm no engineer, but I maintain that lift is dynamic throughout the system and should not be measured at only the blower. In fact, it seems to me that lift and CFM readings are moot EXCEPT at the wand/carpet interface, because that is the only place it matters. The problem being there seems to be no accurate way to measure those figures at that crucial point. If we could find a way to test these forces just inside the lips of the wand, it would be ideal. Even at the wand handle would be better than at the machine.

There are a lot of people here more educated than I....and this industry has a lot of people who came from other industries....so I ask, what is the ideal instrument to get these figures at the crucial points?

Also can lift and cfm be dynamic at different areas of the system?

One more question, is the ratio of lift and cfm constant or can it be changed with restrictions? In other words if CFM is raised or dropped by 100, how much will that change the lift reading? If I then raise or lower the CFM by 200 or 500, will that lift ratio stay constant or will it be dynamic?

These are the kind of discussions Greenie and I have over morning coffee...sad huh?

Take care,
Lisa

 

[Rex Tyus]

Lisa,

I am no engineer and the term brilliant has never been used when describing me (unless smart ass counts).

I agree with pretty much everything in your post (at least the parts I understand).

One way to measure AVAILABLE lift is to modify a hose cuff with a vac gauge inserted at the end of the hose run. You could experiment with different diameter hose as well as runs. You could do it with a wand if someone was willing to sacrifice one to be drilled and tapped.

To check C F M you could measure the blower exhaust and the vac relief intake and subtract.

Just a couple of thoughts.

The Vac gauge reading on the machine is as useful as teats on a boar hog in my opinion.

 

[Duane Oxley]

I posted this on the ICS board, but here goes...

"...can lift and cfm be dynamic at different areas of the system?

CFM will be constant, IMO, throughout the system. In other words, although CFM will fluctuate, it will be the same at any time, from one end to the other of the vacuum system. (i.e., what goes in, will come out, and they will be equivalent to each other)

But lift will vary with distance from the blower, smoothness of plumbing & hose, diameter of hose, etc. The interesting thing is, that if you do have a "perfect lock" on the vacuum inlet, the lift will read the same throughout. As soon as there's a break on that lock, lift will vary, with the greatest reading being at the blower, and the least at the end of the hose.

"... is the ratio of lift and cfm constant or can it be changed with restrictions?

The relationship between the two is not constant in that orifice size affects them... so does, as a result, hose diameter, etc. It's virtually the mirror- image of a pressure system, but there is another variable thrown in: "internal slippage". Although a blower is said to be, "positive displacement", it is far from that, when compared to a solution pump. Blower parts do not come into contact with each other as they turn and create vacuum... clearances between rotating parts is a must. That clearance results in internal slippage that allows more air to "slip" as resistance to that air (i.e., inches of lift) is encountered.

In a solution system, as pressure increases, so does GPM (the, "mirror" of CFM). And that increase is pretty constant. So, increasing the pressure increases the GPM.at a constant rate (increasing the pressure by 4 times, doubles the GPM). This is because a pump doesn't have internal slippage in the way that a blower does... (and, IMO, because water, cleaning solution, etc., is more viscous than air).

Try this: Measure PSI with a pressure gauge ATW and compare to the gauge on the machine ("ATM"). Without the trigger pulled, they will read the same. <u>As soon as you pull the wand trigger, they will not read the same.</u> This same principle applies to airflow and blower CFM / lift, and it's, "dynamic" tendencies.

"... if CFM is raised or dropped by 100, how much will that change the lift reading?"

Too many variables to consider to give you a straight, concise answer on that one. You'd have to specify everything from type, RPM and condition of the blower, to the diameter and straightness of the system plumbing, to the length, diameter and smoothness of the vacuum hose... and the leak- tendencies of the vacuum relief, to even begin to get at the information needed.

" If I then raise or lower the CFM by 200 or 500, will that lift ratio stay constant or will it be dynamic?

I believe that, if the system is sealed ("locked", as I mentioned above...), it will be constant. As soon as a leak (lack of perfect "lock") is present, it's not constant any more...

 

[Duane Oxley]

"...The interesting thing is, that if you do have a "perfect lock" on the vacuum inlet, the lift will read the same throughout. As soon as there's a break on that lock, lift will vary, with the greatest reading being at the blower, and the least at the end of the hose. "

 

[The Cleaning Artist]

drill a hole and weld a bung on the face of an old wand and install a vacuum gage. Start testing. with/without glides ect. A pitot tube could be used for cfm if you have the software to go with it. It measures airspeed and then the software converts to cfm from port area. Port being area of hose ect.

 

[truckmount girl]

So tell me the answers Terje. I know you've got an engineering degree.

Take care,
Lisa

 

[truckmount girl]

I know that if I have 2" hose run from the truck to a 1.5" whip hose, the more I shorten that 1.5" whip hose the better performance I will get, everything else being the same, so having a short restriction is better than having a long restriction. Explain that.

Also, If you measured lift and CFM at the blower, and then at a restriction point, and then after the restriction point, what would the differences in lift and CFM be at each point along the way? Say, you had 10' of 1.5" hose in the middle of a 100' run of 2" hose?

Take care,
Lisa

 

[The Cleaning Artist]

lift inside the 10' 1.5" hose would be higher with an open hose. CFM would be less. Now on out past the 1.5 hose in the 2" hose the lift would be far less cause the restriction. Plug the end and the lift will start to equalize.

 

[Duane Oxley]

The term, "lift" is being used 2 different ways in our industry, it seems...

"Lift" is the available force to pull vacuum.

"Lift" <u>on a gage</u>, indicates the amount of that available force that's being "consumed".

Restriction of any kind consumes available lift. There's <u>more</u> restriction introduced by smaller diameter hose.

Therefore, the larger the hose (up to the size of the blower intake port... possibly slightly larger, but I'm not so sure about that one...), the less the restriction.

Smaller hose consumes more of the available lift...

 

[Rex Tyus]

Duane Oxley said

The term, "lift" is being used 2 different ways in our industry, it seems...

"Lift" is the available force to pull vacuum.

"Lift" on a gage, indicates the amount of that available force that's being "consumed".

Restriction of any kind consumes available lift. There's more restriction introduced by smaller diameter hose.

Therefore, the larger the hose (up to the size of the blower intake port... possibly slightly larger, but I'm not so sure about that one...), the less the restriction.

Smaller hose consumes more of the available lift...

THANK GOD!!!

I can finally agree with someone on the "lift" topic.

 

[The Preacher]

how come Shawn doesn't have his pointy hed stuck in here???

will this be SOA certified when it's figgered out??? LOL


PS i admire you folks who know and apply good science/physics for our benefit, THANK YOU!

 

[Rex Tyus]

It has to do about Volume.

Is that what they mean by CUBIC FEET PER MINUTE? :roll:

 

[truckmount girl]

Okay, but what about velocity? If the lift is higher at the restriction, it is pulling harder and moving the air through the hose faster, right? Or not?

When we were working with Dri-Eaz on the Rover project, with their tests we learned some incredible things about holed glides....

The smaller the hole, the better water was extracted ABOVE the backing. Even a hole as small as 1/8".

The larger the hole, the better water was extracted from BENEATH the backing.

But holes always pulled more water than slots or mini-slots, even from below the backing, so an open slot was inferior to holes.

Please explain this in terms of lift, cfm and velocity. What would you expect to see for figures at the wand?

Why is a short restriction less damaging to performance than a longer restriction? Does the friction of the long hose run slow the velocity of the air?

Take care,
Lisa

 

[Bob Foster]

http://www.technicalspecialties.net/Def ... PL'&M='DW'

 

[Duane Oxley]

"Why is a short restriction less damaging to performance than a longer restriction?"

Longer hose = more restriction. Shorter hose = less... that's why...


"Does the friction of the long hose run slow the velocity of the air?"

IMO, "Yes"... as a by- product of "consuming" lift, which decreases CFM...

 

[The Cleaning Artist]

the hose we use causes restriction because it is not smooth on the inside and the connectors and cuffs. Turbulence and friction. I loose way less cfm through pvc pipe. Velocity plays a big role in how the water enters the glide. Velocity also is a key factor to keeping that water moving in the hose to the tank. John Sales told me it takes 150 cfm in a 2" hose to keep the water airborne so it doesn't puddle by his testing. I have never tested it though.

No doubt that holes dry faster with my testing.

Keeping everything the same, when the vac gage reads less HG there is more available cfm, less restriction. The more HG the less cfm. Now in real world cleaning when every part of the cleaning changes, the above is not always true. Example, The more available lift a machine has the more cfm you'll have at the end of the hose on a long run.

 

[Duane Oxley]

Terry...

I don't think that it's an environment for "laminar" flow inside of a vac hose, except maybe a smooth bore or similar. That being the case, there's a real can of worms there, trying to calculate the effects, I'm guessing. I'm no engineer, but even the hose itself changes over time. I've seen everything from continuous scratches for as far as you care to examine... to a layer of grease about 1/2" thick (from doing a lot of restaurants) in vacuum hose...