pressure drop across air filter

|
| Don Stauffer wrote:
| > Matt wrote:
| >
| > > In "Experiment 1" I found that both the used filters developed a
| > > differential pressure near 40mm H20 and that the new right filter
| > > developed about 19mm H2O.
| > >
| > > For "Experiment 2" I made some improvements in the vacuum setup
(cleaned
| > > the shop-vac, used a shorter cord, straightened the vacuum hose).
Then
| > > the DP was about 58mm for the used filters and 44mm for the new
filter.
|
| > That is a couple of inches of water. I am trying to remember what
| > atmospheric pressure is in inches of water. Seems to me it is abut 16
| > feet, right? That would be 192 inches. If so, those filters are not
| > lowering pressure at intake by all that much, as would be expected.
| > Most air cleaners really are quite efficient devices.
|
| The static pressure of one foot of water is 0.433 inches...
|
| So 40 millimeters times 0.0394 = 1.576 inches
|
| 1.576 divided by 12 = 0.131
|
| 0.131 X 0.433 = 0.056 PSI
|
The static pressure of 1 foot of water is 12" WC....... 12"=1'

ED3

 

|
| | |
| | Don Stauffer wrote:
| | > Matt wrote:
| | >
| | > > In "Experiment 1" I found that both the used filters developed a
| | > > differential pressure near 40mm H20 and that the new right filter
| | > > developed about 19mm H2O.
| | > >
| | > > For "Experiment 2" I made some improvements in the vacuum setup
| (cleaned
| | > > the shop-vac, used a shorter cord, straightened the vacuum hose).
| Then
| | > > the DP was about 58mm for the used filters and 44mm for the new
| filter.
| |
| | > That is a couple of inches of water. I am trying to remember what
| | > atmospheric pressure is in inches of water. Seems to me it is abut 16
| | > feet, right? That would be 192 inches. If so, those filters are not
| | > lowering pressure at intake by all that much, as would be expected.
| | > Most air cleaners really are quite efficient devices.
| |
| | The static pressure of one foot of water is 0.433 inches...
| |
| | So 40 millimeters times 0.0394 = 1.576 inches
| |
| | 1.576 divided by 12 = 0.131
| |
| | 0.131 X 0.433 = 0.056 PSI

The static pressure of 1 foot of water is 12" WC....... 12"=1'

Possibly you meant 0.433psi?
Standard Atmosphere is 29.92" hg / 14.9psi/ 34.7' / 416" WC
ED3

 

I should have written that the static pressure of one foot is water is
0.433 pounds per square inch.

 

Ok, I must be missing something basic here....

Why not just use a run of the mill cheapie dial vacuum gauge from a
cheap tune up kit and measure it like 'ported' vacuum?????

At idle it is going to be really low, open it up and you get 'manifold'
vacuum. Change the shape of the air filter and the ported will change
radically. The manifold vacuum is the one I would be watching....

Or if you are really serious about playing around, just drill a hole and
tap a nipple into each manifold so you get the manifold vacuum at all
times?

Other than that, the vacuum cleaner will give you an idea of the
differences, but in real life, well....

I keep track of my gas mileage and when it starts to climb, I start
checking things like filters......

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

 

If you want to make really accurate measurements, you have to be sure that
you are measuring the parameter you really want to evaluate, at the exact
and
reproducible conditions that you would use across the range of filters, and
that
your measurement method is accurate.

Temperature, air density, atmospheric pressure, humidity, air velocity, etc
might all be important. If you want to measure the restriction imposed by
the filter, these parameters, in the same range as what you would experience
on the road, might be all you need.

If you want to measure the efficiency of the filter to remove particles of
different sizes, other tests would have to be carefully devised. Ability of
the filter to continue to function as the particles accumulate may be
important.

This is why it is hard to give a definite answer when asked 'Is K&N the best
filter out there?'

The more you try to get a test that gets usable data, normally the more
difficult
it is to obtain the data, and the more expensive and complicated it becomes.

 

I get Standard Atmosphere is 29.92" hg / 14.7psi / 33.9' / 406.8" WC /
1013.25 millibars / 76 cm hg
Stan

 

I was thinking the same thing about an orifice plate. Not sure whether
the filter DP data are meaningful unless the air flow rate is known
and/or known to be comparable to air flow rates at top speed.

 

Atmospheric pressure is 760 mmHg. The density of mercury is 13.6 times
that of water.

0.760m * (39.37 in/m) * 13.6 = 407 in = 33.9 ft.

 

But manifold vacuum is not what you want. That includes the drop across
the air cleaner PLUS the drop across the throttle and venturi. You need
to put the meter in between the filter and the carburetor (or throttle
assembly). Further, the drop will be small in inches of mercury, so a
normal manifold pressure gauge will show very little movement, and will
be hard to read.

 

While you're up to your ass in technical jargon like static pressure
and differential pressure and universal gas constant, absolute
pressure, gauge pressure, temperature in degrees Rankine, Newtonian
physics, Bernoulli, Kutta-Jukowski, Coanda effect, standard atmosphere,
Boyle's Law, Charles Law, Gay-Lussac's Law and associated formulae,
don't lose sight of your original intent, which was to correct the
relentless carbon fouling problem in your CJ-360...

Have you tried riding with the one new filter installed and checking
the spark plug, or what? Please do that test, before I succumb to
senile dementia...

 

I won't be likely to contradict you on that---it seems to make sense to me.

My bowls are vented to atomsphere. In each bowl there is a little
"standpipe" that is open to the headspace and passes through the fuel
and down through the bottom of the bowl. The bottom end of that pipe is
equipped with a foot-long rubber hose that extends approximately to the
bottom of the frame. When the bike is moving, the open ends of the
hoses have wind blowing past them. I've been running without the hoses
lately because they tend to get in the way when I am doing carb work. I
don't expect that running without the hoses matters much.

 

If a given filter acts virtually like an orifice plate, then the flow
rate is proportional to the square root of the differential pressure.

Then for either of the used filters, the flow rate increased by a factor
of sqrt(58/40) = 1.2 in Experiment 2 (E2) compared to Experiment 1 (E1).
So flow increased by 2/10.

For the new filter, the flow rate increased by a factor of sqrt(44/19) =
1.5 in E2 vs. E1. Flow increased by 5/10.

Thus the new filter was able to accomodate an increased load better than
either of the used filters.

 

Sorry to make us all wait ...

 

Here is a rough estimate of the air demands of an engine cylinder.

If a two-cylinder bike consumes a gallon of gas in thirty miles at
90mph, each cylinder is using a gallon in sixty miles, or 60miles/90mph
= 2/3 hours = 2400 seconds. A gallon of gas weighs about 5 1/3 lb, so
if the fuel mixture ratio is 14, its burning requires about 75 lb of
air. So air is needed at a rate of about 75 lb(453g/lb)/2400 sec = 14
grams/sec. The density of air being about 1/780 that of water, the
cylinder uses about 14g/sec * (0.780 liter/g) = 11 liters/sec = 11 l/sec
(0.0353 cu. ft/l) = 0.39 cubic feet/sec.

Thus an air filter needs to pass a cubic foot of air in about 2.5 seconds.

Now to measure the flow rate of my shop-vac ...