NATIONAL BUREAU OF STANDARDS REPORT

4022

PERFORMANCE OF FRAM PAPER FILTERS, MODEL CA-IOOPL

by

C. W. Coblentz

T. W. Watson

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards is suggested in the following listing

of the divisions and sections engaged in technical work. In general, each section is engaged in specialized research, development, and engineering in the field indicated by its title. A brief

description of the activities, and of the resultant reports and publications, appears on the inside

of the back cover of this report.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instru- ments. Magnetic Measurements. Process Technology. Engineering Electronics. Electronic

Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenic Physics.

Engines and Lubrication. Engine Fuels.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid

State Physics. Electron Physics. Atomic Physics. Nuclear Physics. Radioactivity. X-rays. Betatron. Nucleonic Instrumentation. Radiological Equipment. AEC Radiation Instruments. Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics.

Mass and Scale. < Capacity, Density, and Fluid Meters. Combustion Controls.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Mineral Products. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. Components and Techniques. Digital Circuitry. Digital Systems.

Analogue Systems.

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials.

Gas Liquefaction.

Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular

Propagation Services.

Radio Propagation Engineering. Frequency Utilization Research. Tropospheric Propagation

Research.

Radio Standards. High Frequency Standards. Microwave Standards. • Office of Basic Instrumentation • Office of Weights and Measures
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003-20-4^3^ April 5, 1955

PERFORMANCE OF FRAM PAPER FILTERS, MODEL CA-IOOPL

by

C. W. Coblentz

T, W. Watson

Heating and Air Conditioning Section

Building Technology Division

To

Engineering and Development Branch

Office of the Chief of Transportation

Department of the Army

Washington, D, C,

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprl

unless permission Is ol

25, D.C. Such permi

cally prepared If that

Approved for public release by the

Director of the National Institute ot

Standards and Technology (NIST)

on October 9, 2015.

part, is prohibited

dards, Washington

rt has been specifirt for its own use.

4022
' , 't-ry

' t' *- ’’ ' ' ’ . ’ ’ 'J. 'E'* ..I^ ' & '/ni S^'4T^ '

•' » '" « ''ktS '''5. Sii\-t’A ,8 .7 |V'%- -rtS ;' i f

; j^ ^.iiifj;-v .

’

X-i!

A

; '. 5^*^, .

... '•‘>hjV.‘»^-v;.',"3L • '

’&&••. '/•«'.

, fc

,;siww5i ^

/ y,i

:'*<! .

,' •

:>W' *%'! ,''

•<? .' jV *

. V *^'i.: . .'••

' / <«»

• ^ ... f . *.- .•'>. :• .- V . v4»y ‘

, .

' ,,; • A'’Wr\’ -ri ' r:X''-j ‘ - ^ §}\

' .,l

" “ -

-Irmt'

' X Av>

' '; .

...

•• -v/Ai .i -rt .

., /• ,0 '- • '

- .• •' <..• •

•f,

X, u'.f

,' r XT’.

'.V s

''*

''>* '«»’«!•<• r f .«• x»jl *1' ^>{:» *» .» w;»irti«l«i » n

:<i '^i* ' 4.j*i|AH' ,’ ‘it \'‘ - ft (< jiiVi.*.

'. • .’>.'

. it ft,:,. . nt-4 It i , '.,

, (J *|*-i^( V**!**

• ' ' . '1 ' ’"

•, i'
Performance of Pram Paper Filters, Model CA-IOOPL

Abstract

Several specimens of the Fram filter, Model CA-IOOPL

were tested to determine the efficiency and pressure

drop characteristics for a range of air flow rates

from 1+0 to 150 cfm using coarse and fine test dust

prepared by the AC Spark Plug Division. The dust filtering efficiency was found to be on the order of

9 S to 99 percent for most test conditions by the

gravimetric test method. Efficiencies obtained by

weighing the filter element were about 2 1/2% lower

on the average than those obtained by the gravimetric sampling method. Efficiencies obtained by the

dust-spot method corroborated those obtained by

weighing the filter element on one specimen. The

small size and especially the light weight of this

filter would make it practical for aircraft. However, the dust-holding capacity was found to be

low, so that application of this type of filter

appears to be restricted to an after-filter when

the bulk of the dust has been removed by an effective pre-filter. The pressure drop across the filter at design air flow rate of 120 cfm and a suggested maximum dust load of I6 grams was about 2 3/4

inch W.G.

I INTRODUCTION

As part of the project ”Air Filter Systems for Army Aircraft", the performance characteristics of a Fram CA-IOOPL paper

filter were determined to establish the feasibility of using

this type of air filter as an induction air cleaner for helicopter or other small aircraft engines,

II SPECIMEN AND TEST EQUIPMENT

The test specimens were manufactured by the Fram Corporation

of Providence, Rhode Island, and furnished as representative of a series of induction air cleaners for mobile and stationary combustion engines. The test specimen consisted of a filter holder with

several replacement filter cartridges. The cartridges, one of

which is shown in ^^ig. 1, were cylindrical, made of a pleated

paper ring, with woven wire screens on the inside and outside,

and held rigid by two flat metal rings that covered the ends.

The dusty air was to pass through the filter from the outside

to the inside and the dust could collect on the surface or in

the pores of the filter.

FIG.l
VA
- 2 -

The manufacturer had furnished a holder for this filter

suitable for attachment to the carburetor intake of an automobile

and for operaticnas an intake air noise silencer. This adapter

was not practical for installation in the test apparatus and a special adapter was designed for this purpose. It is shown assembled in Fig. 2 and disassembled in Fig. 1.

The dusty air entered at the bottom of the adapter through

a 3 inch pipe. The filter was sealed against the upper half

of the adapter around the rim of the filter and the dusty air

was prevented from entering directly into the center of the filter by means of a cover plate at the bottom as shown in Fig. 1

This arrangement provided that all dust particles which fell off

the filter were again picked up by the air stream. It was found

that practically no dust accumulated underneath the filter or in

the adapter during the various tests. The pressure drop across

the filter was determined by taps installed in the filtered-air

pipe near the upper adapter and in the lower adapter shell as

shown in Fig. 2.

The air was drawn through the filter with an exhaust blower

and the air flow rate was measured with an orifice flow meter desired in conformance with the A.S.M.E. Research Publication

’'Fluid Meters, Their Theory and Application”. The test dusts

used were AC Spark Plug Div. classified air cleaner test dusts

"coarse" and "fine”. The dust concentration was maintained at

a desired value by feeding the dust from a hopper into the

groove of a turntable mounted on a variable speed Graham transmission, A high pressure air aspirator picked up the dust from

the turntable, breaking up most of the agglomeration, and supplied it to the inlet of the test duct.

The efficiency of the filter was determined by sampling the

air upstream and downstream of the filter with identical sampling

nozzles installed in the center of the duct through which air was

drawn at the velocity prevailing in the duct. The dust was collected on glass fiber paper whose smallest fibers were about 0.3

micron in diameter. Tests of the air cleaning efficiency of

similar papers by the Atomic Energy Commission indicate that this

paper would retain more than 99*99% of all particles 0.3 micron

and larger and could, therefore, be considered an absolute filter.

The air flow rate through the upstream and downstream samplers

was measured with two orifice flow meters that had been calibrated with a gas meter. Manometers connected to these flow meters were mounted on either side of a srraduated rule to enable

the operator to maintain equal flow through the samplers during

each test. The filter efficiency was calculated from the formula
' • v,^

...:• '/r'

,s*

j ••••• •' •(» Ktwl'i .:.: >r :

')^

^ r*

*•

:. . 'C' I »•>.' ^ - I.’;, Vi^ “'W •-A riflfi 15 ^ ilAV

;;• '1 p

I

'V <

J;' •Vt

V '^!i

' L 4^

r'.

•

» '.-'

"

\\i‘ i. \fr- J ,. A » J. o'*

•;'

its lU-

v<1 att

IV

' i ! f J:, '1-s

^ . r ' /V

' i

•' i?*TCk

',. <•

'

!

1 5 r : \' J ' ' i ’V

. \ -. ,

' ' '

< . •

; '.(

! '•,"

1.' '.

' \

' V • '

I

!'P

v* n r

» ^ • u.

'

: I

\ 4

- ‘'. m-

'"v

. .. (

. .

, ' 't '.

.. t>-.ni] 'fr, ' ' ‘A ' f ^, *• *'

^**

\' t /:/'

/

•'••

1.)-^ v.ijil 4' '-.

. s' ,-?>j .. :•-.1 'i.'o;

t ^

: I V ', '>

I j.Lj

'. i

' :>>s ^ '!«:

' , ' ; "f r< ‘l’»3-'*'"

,1

' ' '

.- .\r

/ y S' '^c*

' . . fi ' •'T

/s '^ b:tf

. . Tsi

' >f '. ; 1- -i ""u V

,;:Vf-. -it/. . ’/ . 1, ,

•*; :-... 1 ;,i :S

s

. , ••,

!' pi. ; V :i ^^l ^

•' - ,

'

;••( • ' OM'.j.lP- .., :. ..

' '

, ,*'.).t» r 1 .•

‘ '. _ , . ,

;

. » .. (-^V,

1
FIG
A.. i
- 3 »

Eg^

= (1 - D) X 100%

u

where Eq = gravimetric efficiency, %> D = weight increase of downstream sampler,

U = weight increase of upstream sampler.

By weighing the filter cartridge before and after the tests

another value for the filter efficiency was obtained as the

ratio of the weight increase of the filter to the total amount

of dust introduced. This value Ep was found to be consistently

lower than Eq which was attributed to the unavoidable loss of

some dust from the filter as it was taken out of the adapter.

Ill TEST PROCEDURE AND OBSERVATIONS

The filters were tested both with AC Spark Plug Division’s

classified air cleaner test dust ’’fine’’ and with a mixture of

50^ each ’’fine” and ’’coarse” dust. The efficiency of the filter

was determined at an air flow rate of 120 CFM and the pressure

drop was observed at six different air flow rates ranging from

45 CFM to 150 CFM. For each test between S grams and 10 grams

of dust were introduced into the duct system. It was found that

this was the smallest amount that would produce an indicative

weight increase of the downstream sampler. The weight increase

of the samplers was determined with a laboratory balance to ±

0,1 milligram.

The dust concentration was determined as the ratio of the

total dust introduced and the total volume of air circulated

through the system during the test. The latter value was the

product of the duration of the test and the air flow rate. As

it was considered improbable that the concentration would have

any appreciable effect on the efficiency of this type of filter

no determination of the change of efficiency with varying concentrations was made. The average concentration used was about

20 mg/cu.ft.

Table 1 shows a summary of the results of 13 tests conducted

to determine the efficiency of these filters. It will be noticed

that part of the tests were conducted with AC Spark Plug Division

dust fine and part with 50^ each fine and coarse. Filter 1 was

first loaded with fine dust, then rapped on the floor to remove

as much as possible of the dust collected on the filter, and then

loaded again with mixed dust. Whereas the average efficiency,

Eq, of 98,4% of the first two tests on filter 1 with fine

dust equaled that of the three tests with filter 3, the

tests of this same filter after being cleaned using mixed dust

Filter

Test N

Type 0

Weight

Durati

Dust C

Pressu

IP

Wei^t

U

D

Effici

Wei^t

lilt

Effici

(a) A

(t) A

TABI£ I

SUMMAHY 07 EIStJlTS

EFFIOUNCT TBSTS OF 7BAM FILTBH MODBL OA-IOOPL BY OHAVIMBTHIO METHOD

(AIE FLOW HATE 120 CFM)

Filter Ho. 1 2 j U

Test No. 1 2 3 4 1 2 3 1 2 3 1 2 3

Type of Bust Used fine (a) half & half (B) half & half (b) fine (a half 4 half(b)

Weight of Dust g 10.112 10.109 10.120 10.132 10.144 8.070 8.147 8.669 8.658 8.675 8.010 8.022 8 . 02I Buratlon of Test min 5 ‘22 5'24 4'43 4-33 3 '09 3'06 3'39 4,59 4'09 U'4i 3'03 2'48 2'53

Bust Concentratlozi mg/ft^ X5.7 15.6 17.86 18.53 24.1 21.7 18.6 15.5 17.4 15.4 21.9 23.9 23.2

Pressure Drop across Filter

Initial In. wo 1.38 2.56 1.97 5.32 1.4l 1.97 3.25 1.50 2.05 3 . 58 1.58 1.87 2.76

Final In. WO 2.56 7.73 5.32 13.7 1.97 3.25 6.98 2.05 3.58 6.86 1.87 2.76 7.01

Wel^t Increase of Sampler

Upstream mg 181.6 183.4 135.2 132.0 145.8 128.4 121.0 168.4 195.0 169.2 165.3 197.8 171 .: Bovnstream mg 1+.4 1.6 3.3 2.6 5.0 2.2 2.6 4.0 1.6 1.4 2.9 0.6 0.5

Efficiency, S(j $ 97.6 99.1 97.6 98.0 96.6 98.3 97.9 96.7 99.2 99.2 98.2 99.6 99.6

Weight Increase of

filter g 19.5 19.4 25.3 24.5 23.3

Efficiency, Ep 1 96.5 95.8 95.8 94.1 96.9

(a) AC Spark Plug Division classified test dust ’fine"

(t) A mixture of 50/( fine and 30^ coarse AC Spark Plug Division classified test dust.
I. » .

.' ‘

•r^sSv 'r$l. .d" ^

‘ ,. “

? . :

. . . - : ,('•

I!)

'-^ v»‘ -u

sM j

' > '*Ji' y

^5.vb'^

'"

' ^’^Z J

yf’-fi.'l - a. .rv : 1".^:’ ' ...2

< --fl ‘-'i-'-^ V .i^;K .-

. i.:.- * •*'-’ - '.>•, »• 1' : ( .•!efc*> V i*-S ..._.» ..i^ic-- -rf.’ ?--» /*'

.r«‘ <•.• / i_. ;.«»• <4* ‘^-f '^>

'V . ii .'^**’ '!*'’• '«*»' k!^'v.

•^}

.1 '-•

\

. --

' ' " ' -CT A" ' '. TTT'^Tt • -.iZl’i ''• '.^ • * n'D .T

iU ... I<I4.M|# 1.-4 '"Ifts#

'»

I’ 'H^ A.

If^'f.x :ftf^lkk... ,1 S(-»» >

4'*' ' ^• aM-
showed an average efficiency Eq of only 97.^^ as compared to

99.1^ average efficiency of filter 4 (a new filter) when operated under the same conditions. This comparison seemed to indicate that filter 1 must have been somehow damaged by the rapping

process used for cleaning. The effect of structural damage

likewise was apparent in filter 2, the average efficiency, Eq,

of which was only 97-9% compared with 99*1^ of filter 4 under

equal conditions. It was noticed after the test that there was

a small dent in one of the rims of filter 2 which apparently

caused a leak of dust between the rim and the corrugated filter

element.

The average efficiencies, Ey, obtained from the weight 'increase of the filters are about 2 1/2^ below the efficiencies,

Eq . , The effltjiencies’cdetermi'n-ed from the filbbr weights,- 'are

considered to corroborate. approximately the results observed by

the gravimetric method.

The efficiency of a fifth filter was determined using the

NBS "Dust-Spot Method” as described in the paper ”A Test Method

for Air Filters” by R. S, Dill (ASHVE Transactions, Vol 44, p

379, 193^). In this method equal air samples upstream and downstream of the test filter are passed through known areas of

Whatman No. 41 filter paper. The areas of the filter papers upstream and downstream are selected to obtain approximately equal

change in light transmission through the filter paper spots.

The filter specimen used for this test had been loaded with

dust and cleaned prior to the test. Its weight at the start of

the test was about 7.6 grams higher than its weight new indicating that some dust remained on the filter element after

cleaning.

The results of the dust spot test are shown in Table 2.

Table 2 shows an increase in efficiency from 96.5^ at a load of

6 grams to 9^.1^ at a load of 14 grams corresponding to an increase in pressure drop from an initial value of 2.17 in. W.G.

to a final value of 11.77 in. W.G. at the end of the test. The

efficiency, Ep, determined from the increase in weight of the

filter was 9^oS% for this test.
'T

*

;*»n

'

. U'i

' ‘ V jil VV I r - .

c 4

I > 'jl ,4

.

I’d' ' ,.

,

. *r. X-

•

/?, : 'T,

V# '/k

»'. V-. \. X ,5 £f

jj*

;

> '•>'

X I >: f I

. b;

’; > . I '» :'

' .'.'^‘'ri '' "•

._,

i

• • ' -I /

• - » • .1'IV'' t

; n i lV^ '

'

' . ..

li;,'

I '

)
« 5 " TABLE 2

SUIVIMARY OF RESULTS

EFFICIENCY TESTS OF FRAM FILTER, MODEL CA-IOOPL

BY THE DUST SPOT METHOD

AIRFLOW RATE 120 CFM

Dust Pressure Dust EffiLoad Drop Concentration ciency

Grams in W. G. Aerosol Grams/lOOO cu.ft. Ed 1o

0 2,17

6.1 3.04 A.C. Fine 7,2 96.5

9.2 4.69 tf 7.7 97.5

14.3 11.77 ft S.3 9?^ol

Ep (from change in filter weight) =

The relation of the pressure drop to the accumulated filter loads and the air flow rate was determined by measuring the

pressure drops across filter 4 at different air flow rates before each test and after it was loaded to capacity. Table 3

shows the values observed and Fig, 3 shows these values plotted

on semi-log paper. This family of four curves shows that the

rate of increase of pressure drop with increased air flow rate

was greater at higher dust loads than for the clean filter or

at lower accumulated loads.

TABLE 3

PRESSURE DROP vs AIR FLOW RATE (OBSERVED VALUES)

FRAM PAPER FILTER, MODEL CA-IOOPL

Air Flow Pressure Drop Across Filter, in. W.G.

Rate Load on Filter Element

,

grams

CFM none 7.7 15.5 23.3

45 0.35 OE « 2.05

70 0.59 0.S3 1.13 3.46

^0 0.79 4.13

90 0.95 - 4.76

120 1.5^ 1.S7 2.71 7.01

150 2.32 2.72 3.43 8.94
£

j...

4:m

^'i ' '

'>- H

m JTi

g. f

‘4 •

' ->• Mt

' ""'i

. .. .

, t/, ^.‘=, r- ',. .. ' ' ' •; *_ '

' i'"/;^^'

?. * >.ri «flO* tSJkaSfei'iii ’’i.

*.

* / ,f

.'

; ’'V ,: ,. *'i' '''' "'

r^. \ .4

V. S -P ,>•,

,'

.,t, ,?

••: *T

V . " f^r >;)a

r if

>v

<1011!?'/ '; '^!i Pd.*A ',;/

-•

•*4?‘

»>T

*-;/ / « - ... "

'i

'’’ ‘fii< “* *' >.6«» 'WSSnaltK /dsel >i9i

'

. 'i '*f, .*f^ a*w,^

; .Af% « 4 ' ' V- 4. '

r -f'

' •

• <‘. S’W

-ffi

/'i-'l' isr loaa

n^.OOI-i^ ^StfJeH -,t?{5Y.ila .teiAil. MAt» "’ ' ''^&;'’jaf«

:;:•

. jra;, T. S.\^'

0yr: ^ vUU

t

E

"

''ik'^'C-il

« ,#'‘'31l

It,

"C>0

. /«m-

i ^

' „ /

‘

(:«,

*v*

'. ':yAa


6 •=

Table 4 shows the values of the pressure drop at the

observed filter loads and at selected air flow rates determined from s:raph Fig, 3. By plotting this table in Fig, 4

a family of five curves is obtained for each of five air flow

rates between l+O and 160 CFM, This family of curves shows

that the pressure drop increased almost linearly up to about

l6 grams filter load for all air flow rates.

TABLE 4

FILTER LOAD vs PRESSURES DROP OF FRAM FILTER MODEL CA-IOOPL

(VALUES DETERMINED FROM FIG, 3,

BASED ON OBSERVED VALUES TABLE 3)

Load Pressure Drop Across Filter, in W.G,

Grams Air Flow Rate, CFM

40 70 100 IIP 160

0 0,31 0.63 1,15 1,^0 2.60

7.7 0.43 0,^3 1.45 2,25 3.1

15.5 0,60 1.13 1.90 2.S5 3.5

23o3 1.^5 3o46 5.5 7,5 9oS

At dust loads in excess of 16 grams all curves bend to the right

which indicates that the increase of the pressure drop, then, is

no longer directly proportional to the dust load. The sharp

change of curvature in the pressure drop curves in Fig, 4 at a

load of about l6 grams suggests that the filter should be considered to be loaded to capacity when it has accumulated about

l6 grams of dust.

The pressure drop across the fifth specimen, tested by the

dust spot method, appeared to begin to increase more rapidly at

a total load of about S grams of dust. However, when the disparity between the initial weight of this filter at the start

of the test and its weight new is taken into consideration, its

pressure drop characteristic is similar to that of the fourth

specimen plotted in Fig.4o

The true pressure drop across the filter element may be

slightly less than the measured values because of the difference in velocity head of the air at the two points of measurement. This error is probably less than 0,25 in W.G,
ft

'^:^-*^e.Ci‘t*? . ’^v r/^

..4;

1.,- ' ! •’>^ *fc-..

' j;

’ j I’.MA t'i'” t*a«tl*«S(|^ -T^'o

, • -.^.^’i .linc'f.'' ‘n.'S-

\f

ja -cSi

'W

i^hVx'

:v I, i, s-

MX-;)' :.i:x

Mut.

V K fc'Mi -•iScTjW , --y. ..V,

i

'^.

•Cf>Q

' mt'^

.!

.'

* i. < /-

.V: X H-

.

.

‘ ^^v'l •^. ^ > L.Z^f’ ;,': iFp,u *<f

* -. ^ I jy^S^ .- ^

J.v ’' -^' '

' ‘

Vi., ‘fv . .v4f. ~.?:vvi- ,if.-wti .9 »j'..'<i^-. - C-, ;# ,J,.S -^i'

-

. -) f\ •'* f M *»

•

' ’'* -

'

' '? • fe.3 i* HVKvM^ -fv^l',^ t'v

?;;: ,•/•; /-t».f .>»v 2b 4 .^-.i

.-- .fd • u-jftri ->/r

'•

r yiij.' , . iff,iH^^?.;"\;u'.-;^'.r t»?..' .‘1

“ '> t.rl ’

, '*•’

rt

* V-.' - iV>.

_

••;^t ft* . .'1

rf.^, * V-. - iv7.*P'^'.:><:d'3 '!'' i.i't ‘^-;!

a." v • ;''' ^1='.*. r fer *40

’> > f;1 <

' - » *•’<. . '*i ui(_ '('•^

y.. !«. 'tv'>

• .! (’i 'A*i.#i f.r • ^v •''•-!*«!?

,

’

'

'V qr

‘i^ ' .fMl; ’i-.:.Tri

* •

:'l. #

,;:,y

^

\?'fVi*.-‘:|-:- T»l -I .'“^."i ‘o-i
"FRAM" PAPER FILTER No . GA-IOOPL

24

22

20

IS

16

001.4

w

^2

ao

o

05 3®

3

« 6

4

2

L+jXI

_n“

Preaaure Drop acroe* Filter, In.W.G.

Dust

Load

of

Filter,

grams

„ 7

-

IV DISCUSSION AND CONCLUSIONS

The efficiency of this type filter, tested under simulated

operating conditions, was found to be when using AC Spark

Plug Division’s classified air cleaner test dust ’’fine” and

99.1^ with a mixture of 50% ’’fine” and 50%> ’’coarse” dust. This

filtering efficiency is believed to be a satisfactory protection

against engine wear due to dust in the induction air of aircraft

engines under any conditions. The pressure drop across the

filter was moderate if the dust load did not exceed about l6

grams

.

The filter cannot be readily cleaned, by rapping the filter on a solid surface as recommended by the manufacturer.

This cleaning method damaged the filter frame in some instances

which resulted in a loss of efficiency during subsequent operation. The dust holding capacity was rather low. At a design

air flow rate of 120 CFM this filter would be filled to capacity

in less than 7 minutes in a dust concentration of 20 mg/cu.ft.

which can occur on dusty air fields.

This type of filter may have application, however, as an

after-filter provided the bulk of the dust has been removed by

an effective pre-filter and a further removal of dust is desired for ultimate extension of the life of the engine.