Air flow..is it a finite CFM number?

[Dolly Llama]

This talk of restricting blowers on the exhaust end for more heat and how it relates to airflow has me wondering...

HOW does it restrict CFMs?

Is blow by/air slip on the lobes created with positive displacement blowers?
if not, won't it push out the same amount whether restricted or not?
The only requirement would be more HP to over come the greater load.

next...the wand end is where the real restriction to the vac system occurs, no?

How many CFM is even possible at 15HG thru a typical 14" unglided wand?
How many CFMs are possible thru a hole glide?

am I missing sump'um?
or is the exhaust end really not the choke point to be concerned with "as long as" it's equal to or greater than the wand slot?


.L.T.A.

 

[Larry Cobb]

Larry;

As I have stated before, the major restrictions to TM airflow when cleaning are, in order of importance:

1. Carpet-Wand Interface -most restriction
2. Long 2" Hoses - substantial
3. Silencers - substantial to moderate
Depends on design path and corrosion effects
4. Heat Exchanger - moderate in good designs, high in typical designs
5. Vac Tank & filter - moderate to slight with no baffles
6. Plumbing Fittings- slight

I have seen flow charts for 2" tubing that went to 800 CFM. It just takes more pressure or vacuum to deliver that amount.

In the real world we run out of lift, and start opening the relief valve.

I previously measured w/flowmeter a 14" CMP wand w/glide at slightly over 200 CFM on commercial level-loop carpet.

(Edited - The lift @ the wand was ~11" for the 200 CFM)

Larry Cobb
Mikey Board Supporting Member

P.S. Steven- CFM's at the wand do vary with hose lengths. Lift is lost for each 50' of hose.

 

[Dolly Llama]

Wouldn't the CFM's to the wand vary with hose lengths ?

yea, I'm sure there's some restriction/friction involved with longer the hose run, 'Dink

To make it easy on the fizzicks majors, maybe they could calculate how many CFM can possibly be pulled through a typical 14" wand slot with no hose attached. (at 15HG)
it must be a finite number, no?

we'll dispense with the variables of adding recovered water to the mix, and just start with clean air only

edit.... thanks Larry
so how many CFM can flow thru a typical wand interface (WI) at 15HG?
The rest of the numbers, bends etc shouldn't matter "if" it's equal to or greater than the WI

Yes? no?


..L.T.A.

 

[Dolly Llama]

I hear what you're saying 'Dink, but regardless of blower, there should be a finite number of CFMs that can be pulled thru a finite sized space at a finite 15HG.

Lets say a wand opening is 1/4" x 14"
That equals 3.5" Sq In...I think...
15HG vac pressure

Those are the constants that should be able to be calculated, no?

Shouldn't matter if the blower is rated at 290 CFM or 700 CFM, cause I'm "guessing" that's more CFM than can possibly be drawn thru 3.5" sq in at 15HG


..L.T.A.

 

[Lee Stockwell]

Absolutely on the right track Larry. We throw around "cfm" without specifying other variables which make a huge difference.

more...after supper and a movie

 

[sweendogg]

After I'm done plowing.. I'll sit down and give this some thought.. Larry you are on the right track. For a set amount of lift ie vaccuum there "should" be only a finite amount of cfm available. I'll do a little research and maybe if I come up stumped I'll send it to some of my physics proffessors.

 

[Rex Tyus]

I hear what you're saying 'Dink, but regardless of blower, there should be a finite number of CFMs that can be pulled thru a finite sized space at a finite 15HG.Lets say a wand opening is 1/4" x 14"
That equals 3.5" Sq In...I think...
15HG vac pressure

Those are the constants that should be able to be calculated, no?

Shouldn't matter if the blower is rated at 290 CFM or 700 CFM, cause I'm "guessing" that's more CFM than can possibly be drawn thru 3.5" sq in at 15HG


..L.T.A.

I am in such agreement. I think this is what T has been saying for quite some time as well.

One way to test with all variables included would be to isolate the exhaust, measure CFM. Isolate the vac relief intake,measure the cfm. Do the subtraction and BINGO what ever is left is coming through the wand slot (or leaks in the system). :shock:

 

[Shawn Forsythe]

A few tidbits have been left out of the discussion here.

1. Traditional spring loaded vacuum relief valves begin to creep open at just a few inches of lift, thereby bypassing an enormous amount of CFM. Far more than many of the items on Larry Cobb's list. Air going into the vac relief valve is CFM NOT going through the wand lips. Only the Kunkle/Bayco or SOVC is available to remedy this.

2. Air is elastic and density varies with temparature, so the CFM ratings of a blower's capability only exist at an optimum temperature with a calculated restriction measured in backpressure or vacuum AT THE BLOWER'S PORTS.

3. A not very much discussed variable is the "high heat clearance" option that a great many TM manufacturers specify for their supplied blowers, which both yields markedly different CFM ratings than the stock ratings, but also creates a slippage factor never referenced or specified in the ratings.

As a result, CFM is a commodity that is determined by actual reading, and not in any way practically calculated by a combination of published performance data for the components. Rex's method is one means surely, but remember CFM will vary with temperature and pressure of the air in various positions of the device, such as heat exchangers, which is in constant change itself.

 

[Larry Cobb]

A few tidbits have been left out of the discussion here.

3. A not very much discussed variable is the "high heat clearance" option that a great many TM manufacturers specify for their supplied blowers, which both yields markedly different CFM ratings than the stock ratings, but also creates a slippage factor never referenced or specified in the ratings.

Now you are talking about "Industry Secrets".

Care to tell the board members all the TM manufacturers who utilize the "high clearance"
blowers?
I remember the day when the Sutorbilt rep was surprised that Dynachem was using the "standard clearance" blower.

Larry

 

[Shawn Forsythe]

I'd say that the majority, if not most HX units sport the High Heat Clearance blowers.

My only point is that CFM ratings are for a standard blower at a standard condition. No unit, I repeat no TM unit exhibits the stated rating of the blower under typical operating conditions (after warm up).

It should also be noted that a High Heat Clearance Blower is made as such so that when the blower is used under the particular application with the temperatures and pressures present, the blower, which naturally heats up (and expands), will exhibit near normal operating parameters and operate within design limits. The practical end result is that the blower will have NORMAL or nominal clearances when under typical and maximum load.

In other words, a cold High Heat Clearance blower will NOT put out spec CFM, but in fact may put out the same CFM as a standard blower at operating temp, while the standard blower may be experiencing overheat symptoms under the same (TM) conditions.

 

[lance]

Would a blower HX work very well if it didn't choke down the plumbing sizes?

If the blower was 3 inch out and the hx was the same it seems the exhaust would move faster thru it making lower temps.

Are all engine exhaust HX's choking down the plumbing from the engine? If so, does it affect the engine's performance (especially running all out while loaded with a blower running near it's max)????

 

[Dolly Llama]

Are all engine exhaust HX's choking down the plumbing from the engine? If so, does it affect the engine's performance (especially running all out while loaded with a blower running near it's max)????

HX back pressure on engines is a concern, Lance.

as i understand it, the engine manufactures have standards of acceptable back pressure limits
.................................................................................................................................................


OK, you smart guys, so due to ambient temps, humidity etc, we're unable to calculate a finite amount that fits everywhere.

Maybe someone could give a "general" rule of thumb of how many CFM can be pulled thru a 3.5 sq in opening at 15hg?

it doesn't matter what marketing hype is used to for blower CFM spec

"about" how may freekin CMFs can be pulled thru the straw at 15hg??


..L.T.A.

 

[Able 1]

Great thread Meat!

 

[Walt]

Larry;

4. Heat Exchanger - moderate in good designs, high in typical designs
5. Vac Tank & filter - moderate to slight with no baffles

Number 4. - is that a restriction on the motor or on the blower? Please explain. I'm very curious.

Number 5. - that doesn't surprise me. I think it's one of the real secrets of the vortex - a round tank. How did you ascertain this? Can this be reduced by large holes in the baffles? Or is a baffle a baffle.

 

[Lee Stockwell]

I'm going to give you a number...and you're NOT going to like it.

First of all let's understand that "lift" or vacuum is just another way to describe air pressure below atmospheric pressure. You can't get below absolute zero pressure, no matter how strong the device, you can only approach it.

Vacuum gauges show a range of 0-30 hg, but 30 hg doesn't exist. 29.92 hg is close to zero absolute pressure. Therefore it is accepted that 0.4912 psi is close to 1.0 hg.

ANSI has standards for air piping that reliably indicate how many standard cfm can flow through 2" pipe at various pressures. This is a curve, and you can plot it on graph paper.

5 psi 80 scfm
10psi 125 scfm
20psi 215 scfm
40psi 385 scfm
60psi 560 scfm
80psi 720 scfm

Some manufacturers claim cfm numbers near the top end of that scale, but there's a big problem. Look at it and tell me if you see it?

 

[Shawn Forsythe]

It is a little worse than that....

Look what actually happens at about 13" of lift. The CFM rise flattens out. At anything over 15", the CFM rises insignificantly.

The hose length will act as further restriction, potentially lowering the available CFM for the smaller wand orifice.

Source: Gast Manufacturing

 

[Greenie]

Numbers and charts are fun.

But I got $100 right now that says you ain't gettin' 300cfm through ANY wand in production with any TM in production using 2" hose....end of story.

What some miss in all of this debate is 150cfm at 15"hg AT the carpet wand interface is awesome for actual recovery, you don't need 300 cfm.

But I'm just an average guy, not one of the educated ones.

 

[Larry Cobb]

Walt;

Heat Exchangers can have both engine exhaust and/or blower exhaust running thru them.

If they utilize blower exhaust, the air flow capacity has to be greater.

Ideal Tank design for minimizing vacuum loss would be NO baffles.

The round tank design is just better at separating the water from the airflow.

Larry

 

[Shawn Forsythe]

I got $100 right now that says you ain't gettin' 300cfm through ANY wand in production with any TM in production using 2" hose....end of story.

While that may be true, the point is that with enough 2" hose and the inherent restrictions of just the hose, you may not even have 300 CFM available no matter what the wand characteristics are.

 

[bob vawter]

'dink.......LOL!

so i GUESS yous don wanna hear about me "locking" my spring valve down wit duct tape...right?

 

[Shawn Forsythe]

Bawb,

Your unit probably has so many air leaks that you risk encroachment on one of Nick's "patents". :wink:

 

[bob vawter]

Not true Shawn.....i'm very persnicketty about my lid gasket......and keep a constant eye on my marine hose clamps.......like i sED i duct tape my relief valve down to ONE HOLE.......

I SUCK...BIGTIME!

 

[Greenie]

Bawb,

Your unit probably has so many air leaks that you risk encroachment on one of Nick's "patents". :wink:

holy crap...contender for banner quote of the month!

 

[Ron Werner]

I was just thinking of science experiments. As already mentioned, and what was shown on Shawn's chart, were the qualifications or standard environment (darn, I've forgotten the term) which you need to duplicate in order to have a frame of reference. Ie having a standard temp and air pressure. The numbers may change based on elevation, thinner air.
So there will be ONE number, at one temp, at one air pressure, etc. It will vary from there.

Then you get into the restrictions and variables in equipment. Too many variables to get just one finite number.

 

[B&BGaryC]

Not true Shawn.....i'm very persnicketty about my lid gasket......and keep a constant eye on my marine hose clamps.......like i sED i duct tape my relief valve down to ONE HOLE.......

I SUCK...BIGTIME!

I saw a van drive by about 8 months ago that said, "Persnicketty Cleaners"

The tag line was, "Persnicketty people choose persnicketty cleaners"