NATIONAL BUREAU OF STANDARDS REPORT

14569

Report to

Engineering and Development Branch

Office of the Chief of Transportation

Department of the Army

Washington, D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

AIR-MAZE AIRCRAFT FILTERS

Carl W. Coblentz

William F. Goddard, Jr
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NEBS REPORT

IOO3

-2O -4838 March 16, 1956 4569

AIR-MAZE AIRCRAFT FILTERS

by

Carl W. Coblenta

William F. Goddard, Jr.

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»

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, re

unless permission Is

25, D. C. Such per

cal ly prepared If t

. , r , , 1 In part, is prohibited Approved ror public release by the

andards, Washington Director of the National Institute of ...

port has been specifi- Standards and Technology (NIST) !port for its own use . on October 9, 20 1 5.

AIR-MAZE AIRCRAFT FILTERS

by

Carl W. Coblentz and William F. Goddard, Jr.

Abstract

The characteristics of a group of twelve AirMaze aircraft engine filters were determined

with different aerosols and air flow rates.

Tests were made with the filters oiled, dry

and as received. The group consisted of new

filters of two different designs and of filters which had been worn to various degrees

in service. The filtering efficiency with

A.C. Spark Plug Division ’'coarse” dust

reached 98.7$* This type filter is small and

light and its pressure loss moderate when the

filters are clean; but the pressure loss

increases sharply when the filters become

loaded with dust. The advantages of the two

different designs are described and the effect

of the length of service and the value of

proper maintenance are explained. The

attainment of adequate maintenance appears

to be extremely difficult in military use.

1. INTRODUCTION

The performance characteristics and service requirements of the Air-Maze aircraft engine air filters were

determined as a part of the research project "Air Filter

Systems for Army Aircraft". This type filter is being used

in the L-19 Army aircraft. It is an oiled-impingement type

filter consisting of pleated flock covered wire screens.

This filter is mounted on the air-intake of the carburetor

and may be removed for cleaning or replacement.

2. FINDINGS

The filtering efficiency, using A.C. Spark Plug

Division "coarse" dust reached 98.7^» Efficiency is about

equal with A«.€* "fine" dust and with Cottrell precipitate.

The efficiency determined with '’coarse 11 dust was considerably higher than that obtained with n fine” dust; the filtering efficiency of the $0%> mixture of fine and coarse

dusts was w ell in between the efficiencies of these dusts

alone, as could be expected. The following table shows the

gravimetric efficiencies determined for the first two test

runs with 15>.lg dust each, after the filters had been

cleaned and oiled.

TABLE 1

FILTER EFFICIENCY WITH DIFFERENT DUSTS

Tests Filter Dust

No. No.

Efficiency Average

l.Run 2. Run

2181-2

21149-10

4044-5

4051-2

1187-8

6 A.C. Fine 96.5 97.5 97.0

7 n 96,7 97.

k

97.0

7 50$ Fine 4 Coarse 97.8 98.1 98.0

6 A.C. Coarse 98.6 98.7 98.7

6 Cottrell Precipitate 95.8 98.2 96.9

Tests made with the filters "as received” show values

of efficiency lying between those determined for the

cleaned filters when tested oiled and those when tested

dry. It can be assumed that part of the oil had been lost

in storage due to absorption by the wrapping paper, or had

been run out of the flocking, indicating the importance of

careful oiling for obtaining the highest possible efficiency

of this type filter. If the filters are not properly oiled

after being cleaned, the filtering efficiency drops to

about one-half and the dust holding capacity is reduced.

The importance of the oiling of the filters is expressed

in the following table which compares the efficiencies of

two filters oiled and not oiled for three consecutive dust

charges of 15. lg A.C. ’’fine" dust.

During the third test run, the oiled new filters

passed 2.1% of the dust introduced into the system, whereas,

under the same conditions, the filter when dry passed 60,6%

or about 30 times as much dust as when it was oiled.

Fig. 1 presents the values of the following table as a

graph.
•:

.
GRAVIMETRIC EFFICIENCY OF OILED AND DRY FILTERS

USING A C. SPARK PLUG DIV. DUST "FINE

DUST CHARGE, GRAMS

NBS

-3-

TABLE 2

GRAVIMETRIC EFFICIENCY OF OILED AND DRY FILTERS

Tests No.

Condition

of Filter 1. Charge

Efficiency

2. Charge 3- Charge

2181-3 New, oiled 96.5

1288 , 1311-2 New, dry 62.4

2151-3 Used, oiled 94.0

1181-3 Used, dry 37.6

97.5 97.9

56.6 39.4

96.1 96.2

39.0 33-2

The effect of filter wear was determined by comparing

three filters of the same design with different lengths of

service. Table 3> below, shows the number of the filters

and their length of previous service and the values calculated for the efficiency with A.C. ’’fine” dust and Cottrell precipitate using the gravimetric as well as the dust

spot methods. The effectiveness of the filter decreases

sharply when the flock wears off as a result of repeated

cleanings and due to the air stream in operation.

TABLE 3

EFFECT OF FILTER WEAR ON EFFICIENCY

Filter Hrs. of A.C. Fine Cottrell Precipitate

No . Service Gravimetric Dust Spot Gravimetric Dust Spot

6 New 97.0 97.8 96.9 96.5

3 331 88.0 81.7 95-2 92.9

5 1226 84.5 79.7 90.2 91.2

These values, which are plotted on a graph in Fig. 2,

indicate the loss of efficiency not only to be a function

of the wear, but also, to be different when different

aerosols are used. When Cottrell precipitate was used,

the efficiency decreased almost linearly with the hours of

service, whereas, with A.C. "fine'’ dust, the decrease of

the efficiency was more than twice as much during the

first 300 hours of service as it was during the succeeding

900 hours.

EFFECT OF FILTER WEAR ON THE EFFICIENCY.

-CQTTSSL

j-j j-J-4 -j [-

fJalLgER: l £FgIClENCY

: ___ -j- 4_LL l-LL.

Table I4 presents a summary of the efficiency and

pressure loss for both the old and the new design filters

at air flow rates of 200 CFM, 3^5 CFM, and 2,60 CFM, using

A.C. "fine" dust as an aerosol. As it had been noticed

that the specimen filters of each type did not produce

identical test results, all tests of this series were conducted with at least two specimens of each type. The

average values from the duplicated tests are more representative than the individual tests would be, as they

alleviate the deviation of test observations resulting

from certain construction differences in the filters,

as well as from slightly varying conditions that may

affect these observations.

These average values are shown as a graph in Fig. 3,

indicating that the pressure loss and the efficiency are

higher on the old design filters for any comparable air

flow rate and dust charge.

The filtering efficiency of the older design with two

flocked screens was found to be better than that of the

new design which has only one flocked s creen. The

efficiency of the old design at 305 OFM exceeded 9 and

decreased for both higher and lower flow rates.

The pressure loss of the Air-Maze filters stays

rather low as long as the filters are not overloaded, but

increases fast once a certain load has been reached.

It was noted that neither the weight nor the pressure

loss presented a positive criterion of the condition of

the used filters. It was noted, however, that a pressure

loss of less than 1 inch W.G* at the design air flow rate

occurred only when the flock had worn off to such a degree that the filtering efficiency had dropped considerably and the filter should have been replaced.

3. SPECIMEN AND TEST APPARATUS

The test specimens were products of the Air-Maze Corporation of Cleveland, Ohio. The Office of the Chief of

Transportation furnished 12 filters for testing, all

having the same outside dimensions of 7 | x 7 x 1 inch with

a free filtering area of 6 - 3 /I4 x 6 -I/I4 inches or 0.293

square feet. According to the manufacturer's catalog,

these filters are designed for a face velocity of 1050

ft/min. corresponding to about 305 CFM air flow rate.
.

&/-V.
GRAVIMETRIC

EFFICIENCY

AND

PRESSURE

LOSS

OF

NEW

AND

OLD

DESIGN

FILTERS

AT

DIFFERENT

AIR

FLOW

RATES

WITH

A.G.

SPARK

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DIV.,

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.
EFFICIENCY AND PRESSURE LOSS OF OLD AND NEW DESIGN FILTERS

DUST CHARGE - grama

-5

-

Some of the test specimens were new and others had

different lengths of service. The used filters had two

pleated flock covered wire screens as the filter media.

There were two new filters of this same construction and

two new filters of a new design - one flocked screen,

the other screen being bare. The cotton flock had worn

off considerably on some of the used filters leaving a

practically bare wire mesh.

Table £ shows a listing of the test specimens giving

the consecutive numbers, time of service as reported by

the Transportation Corps, their weight as received after

removing the holding clips and gaskets, and their pressure

loss at 305 CFM air flow.

Fig. I4 is a photograph of the test apparatus, showing

the 20 ft. long duct made of 5 inch brass pipe in the

middle of which is an adapter to hold the rectangular

test specimen. The two halves of the adapter are equipped

with foam rubber strips so that any outside air leakage

is prevented when the two halves are pulled against the

specimen with I4 steel bolts. Vertical and horizontal

stops are provided to assure proper alignment of the test

specimen in the adapter. The air is drawn into the duct

by a blower installed in a room behind the test panel, and

the air flow rates are measured with orifice flow meters

designed in accordance with the A.S.M.E. Research Publication "Fluid Meters, Their Theory and Application."

For each test run, a measured amount of dust is

placed in a small hopper which feeds into the groove of

a turntable to a constant level. The turntable is mounted

on a variable speed Graham transmission and the dust is

picked up from the groove by a high pressure aspirator

which breaks up any agglomerations and supplies the dust

to the open inlet of the test duct, at the desired feed

rate. By changing the speed of the turntable, infinite

variations of dust concentrations can be obtained for any

air flow rate and can be maintained constant during each

test run.

The test dust used is classified air cleaner test

dust produced by the A.C. Spark Plug Division of General

Motors Corporation. Most tests were made with "fine" dust

for comparative purposes, a few tests were made with

"coarse" dust and also with a mixture of each fine and

coarse dust and also with Cottrell precipitate.
-

.

’

.

.
TABLE 5

No.

1

2

3

4

5

6

7

S

9

10

11

Length of Service

Hrs.

Used

986

330

Used

1225

New

New

200-300

434

200-300

New

New

Weight

&

Pressure ! 305 CFM,

234.9 1.38

239.7 1.14

24g.4 1.12

222.9 0.75

237.6 0.83

218.4 1.97

220.6 1.93

288.2 2.36

221.7 1.22

227.6 1.07

249.0 1.26

12 236.4 1.26
. •
Pig.

~ 6 ~

The efficiency of the test specimen is determined by

sampling the air upstream and downs tr earn of the air cleaner

with identical sampling nozzles installed in the center of

the duct. A representative sampling is assured by maintaining isokinetic flow between nozzle inlet and duct.

The dust drawn through the sampling nozzle is collected on

glass fiber paper whose smallest fibers are about 0«3

micron in diameter. Tests of the air cleaning efficiency

of similar paper by the Atomic Energy Commission indicate

that such paper retains more than 99.99 per cent of all

particles 0.3 micron and larger and it can, therefore, be

considered an absolute filter for these tests.

Figo 5 i s a photograph of this sampling device. It

shows one nozzle installed in a 3 inch duct, chosen for

ease of photography, and three others with different

openings to compensate for a wide range of air velocities

in the test duct. One sampling paper holder is shown

with the nozzles and another one is installed between the

two bell caps. These holders consist of aluminum rings

between which the glass fiber paper is clamped tight.

The air flow rate through the upstream and downstream

samples is measured with two identical orifice flow meters

which were calibrated with a gas meter. The manometers

connected to these flow meters are mounted on either side

of a graduated rule to facilitate the adjustments for

maintaining equal flow through the two samplers during

each test. The filter efficiency was calculated from the

formula

e g = (l - 2 ) X 100$

where E^ = gravimetric efficiency, per cent,

D = weight gain of downstream sampler,

U = weight gain of upstream sampler.

In order to ascertain that the observed sampler gains

are representative for the prevailing dust concentrations

in the duct, the test apparatus is operated without filter,

at frequent intervals, in which case the upstream and

downstream filter gains must be equal.

The efficiency of the filter was also determined by

another method based on the discoloration caused by the

dust. This method is known as the ’’National Bureau of
> ’ '
Fig. 5

-7-

Standards Dust Spot Method" and is described in the paper

"A Test Method for Air Filters" by R. S. Dill, ASHVE

Transactions, Vol. I4I4, p 339, 193&» In this method, equal

air samples from upstream and downstream of the filter are

passed through known areas of Whatman #141 filter paper®

The areas of the upstream and downstream filter papers are

selected by repeated trials to obtain an approximately

equal change of light transmission through these papers

for a given test c ondition.

4® TEST PROCEDURE AND OBSERVATIONS

All filters were tested at the design air flow rate

of 305 CFM and Table 6 shows a summary of the more indicative test results. In order to determine the characteristics of this type filter, tests were made under nine different c onditions:

A/ Filters oiled; tested with A.C. "fine" dust.

B/ Filters as received; tested with A.C. "fine"

dust.

C/ Filters dry (cleaned and not oiled); tested

with A. C. "fine" dust.

D/ Filters as received; tested with A.C. "coarse"

dust.

E/ Filters oiled; tested with A.C. "coarse" dust.

F/ Filters oiled; tested with 5

0

% each A.C. "fine"

and "coarse" dust.

G/ Filters oiled; tested with Cottrell precipitate.

H/ Filters oiled; tested with A.C. "fine" dust and

200 CFM air flow.

i/ Filters oiled; tested with A.C. "fine" dust and

360 CFM air flow.

Between two and four individual test runs were made

with each filter for every condition tested to observe the

change of its characteristics with the increase of the

dust load. 15 g to 20 g of dust were used for each run and

the filter weight was determined before and after each

test run so that an approximation of the filtering

efficiency was obtained as the ratio of the weight

increase of the filter to the weight of the dust introduced into the duct. This efficiency, Ep, was mostly lower

than the efficiency Eq computed from the weight increase of

the samplers because dust dropped off the filter when it

was removed from the test duct to be weighed.

- 8 -

The pressure drop across the filter was observed and

the duration of the tests was noted. From the latter, the

dust concentration upstream of the filter was calculated.

This concentration was maintained at about 10 mg/cu ft,

equivalent to a heavy dust cloud.

A comparison of the efficiency of the filter resulting

from the use of dust of different mean particle size was

made. Sufficient tests with the four different dusts used

were conducted on the two new filters, numbers 6 and 7, to

obtain average value for each dust.

The new design filters were loaded with 60g of dust

for all three air flow rates showing a minimum efficiency

of 86.9$ and a maximum pressure loss of 9.5^4 in. W.G.

The old design filters w ere charged with I45g of dust for

the 200 CFM and 305 CFM tests at which dust loads, the

desired maximum pressure loss of 10 in. W.G. was exceeded.

At the design air flow rate and using A.C. "fine"

dust, the efficiency of the new type filter was 90.2$ for

the first I5g of dust introduced after cleaning and oiling

the filter, and 96.6$ under the same condition of the old

type filter. This means that almost three times as much

dust passes through the new filter than the old one.

Under conditions as indicated above, the pressure

loss of the new design filters was 1.^8 in. W.G. against

2.58 in. W.G. for the old design. This margin in favor of

the new design increased significantly as the dust load

increased. Whereas, the pressure loss of the old design at

a load of 45g increased to 12.L[5 in. W.G. , the pressure

loss of the new design reached only 7.35 in. W.G. with a

dust load of 60g.

The weight of these filters appeared to vary less

with the condition of the screen flock than the amount of

residual dust which had not been removed from the filter

in recent cleaning operations. The pressure loss of any

one filter at a constant air flow rate depends on the

condition of the screen flock and its oiling, and the

amount of dust load accumulated on the filter.

- 10 - The light weight and small space requirements, however,

make the use of this kind of filter attractive as an induction air cleaner for small aircraft.

SUMMARY

OF

TEST

RESULTS

A/

FILTERS

OILED,

A.C.

"FINE",

305

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1

SUMMARY ( A/ FILTERS OILEI

Filter Number

Test Number 2151

Filter Gain g 1^*5

Dust Introduced g 15 «1

Duration of Test Min. 4.22

Pressure Loss

Start In. WG 1.51* Pressure Loss

Finish WG 1.97

Sampler Gain

Upstream ®g 70*4

Sampler Gain

Downstream mg 4.2

Dust Concentration Cu. ft. H.7

Efficiency - Eq

Gravimetric $

94.0

Efficiency - Ej.

Filter Gain $

96.1

Efficiency - ED

Discoloration

12

2144 2145 2146 2147 2148

331.2 274.4 288.3 302.7 ,316.8

13.7 13.9 l4.4 l4.1 14.2

15.1 15.1 15.1 15.1 15.1

4.62 4.35 4.42 4.12 4.63

4.17 1.57 1.93 2.64 4.06

6.93 2.01 2.68 4.o6 7.76

47.9 52.4 55.8 68.4 59.8

2.8 5.6 3.2 2.8 2.0

10.7 11.4 11.3 12.2 10.7

94.1 89.3 94.3 95.4 96.6

90.9 92.2 95.5 93.4 94.2

91.7 88.9 90.0 91.8 94.0

TABLE 6

SUMMARY OF TEST RESULTS

A/ FILTERS OILED, A.C. "FINE", 305 CFM

Filter Number

Test Number 2151

1

2152 2153

2

1121 1122 1123

5

1127 1128

Filter Weight

Start g 299.6 314.1 328.2 272.2 — 269.1 —

Filter Gain g 14.5 l4.l l4.0 Total 40. 5 Total 26.1

Dust Introduced g 15.1 15.1 15.1 15.1 15.1 15.1 15.1 15.1

Duration of Test Min. 4.22 4.89 4.45 5.57 >+.89 4.98 5.05 4.86

Pressure Loss

Start In. WG 1.54 2.05 2.87 0.96 1.97 2.87 0.95 l.l4

Pressure Loss

Finish In. WG 1.97 2.91 4.85 1.97 2.83 5.75 1.14 1.30

Sampler Gain

Upstream mg 70.4 67.2 52.8 68.9 67.8 73.4 73.4 71.0

Sampler Gain

Downstream mg 4.2 2.6 2.0 9.2 6.1 4.0 11.1 11.6

Dust Concentration

mg/

Cu. ft. 11.7 10.1 11.1 8.9 10.1 9.9 9.8 10.2

Efficiency - Eg

Gravimetric % 94.0 96.1 96.2 86.7 91.0 94.6 84.9 83.7

Efficiency - Ej,

Filter Gain i 96.1 93.5 92.9 Average 89 ..6 Average 86.4

Efficiency - ED

Discoloration i — — 79.6 83.3 77.9 76.6

6 7

2181 2182 2183 2l4g 2l4lO 2l4ll

OBSERVED VALUES

267.7 291.4 306.2 296.3 3H.1 325.5

14.7 14.8 14.8 14.8 14.4 l4.8

15.1 15.1 15.1 15.1 15.1 15.1

4.30 4.07 4.80 4.55 4.18 4.37

2.44 3.39 4.88 2.68 3.98 6.38

3.42 4,88 9.68 4.10 6.38 15.29

57.2 59.0 62.9 55.2 58.0 58.6

2.0 1.5 1.3 1.8 1.5 1.0

COMPUTED VALUES

11 12

2l4l 2142 2143 2144 2145 2146 2147

289.0 303.1 317.1 331.2 274.4 288.3 302.7

l4.i l4.0 l4.l 13.7 13.9 l4.4 l4.i

15.1 15.1 15.1 15.1 15.1 15.1 15.1

4.57 4.67 4.93 4.62 4.35 4.42 4.12

1.57 2.09 2.83 4.17 1.57 1.93 2.64

2.09 2.87 4.22 6.93 2.01 2.68 4.06

60.0 51.7 38.2 47.9 52.4 55.8 68.4

5.4 3.4 2.9 2.8 5.6 3.2 2.8

11.5 12.2 10.3

96.5 97.5 97.9

10.9 11.0 11.3 10.8 10.6

96.7 97.4 98.2 91.0 93.4

98.1 95.5 98.1 93.6 92.8

91.6 93.9 96.5 87.7 86.8

10.0 10.7 11.4 11.3 12.2

92.4 94.1 89.3 94.3 95.4

93.5 90.9 92.2 95.5 93.4

89.1 91.7 88.9 90.0 91.8

2148

316.8

14.2

15.1

4.63

4.06

7.76

59.8

2.0

10.7

96.6

94.2

94.0

97.5 98.1 98.1
-

K
Filter Ni

Test Num'

Filter Wi Start

Filter &

Dust Int: Duration

Pressure

Start

Pressure

Finish

Sampler ( Upstrea

Sampler ( Downs t:

Dust Com

Eff iciem

Gravimt

Efficient

Filter

Efficient

Discolt

B/ FILTERS AS RECEIVED, A.C. "FINE", 305 CFM (Continuation of TABLE 6)

Filter Number

Test Number 1251

2

1252 1253

Filter Weight

Start g 239.7 — —

Filter Gain g Total 53..0 Dust Introduced g 20.1 20.1 20.1

Duration of Test Min. 7.5U 10.25 6.22

Pressure Loss

Start In. WG l.l4 1.69 2.52

Pressure Loss

Finish In. WG 1.77 2.71 6.42

Sampler Gain

Upstream mg 88.8 90.0 93.0

Sampler Gain

Downstream mg 19.8 14.4 12.8

Dust Concentration

mg/

Cu. ft. 9.1 6.7 10.6

Efficiency - Eg

Gravimetric £ 77.6 83.8 86.2

Efficiency - Ej.

Filter Gain t

Average 8J,.8

Efficiency - E

D

Discoloration i 69.8 76.8 83.5

3 5 9

12154 12155 12161 12162 1281 1282

OBSERVED VALUES

248.4

Total

20.1

5.45

34.4

20.2

6.36

237.6

16.9

20.1

5.84

254.5

16.5

20.1

6.80

221.7 232.8

11.1 13.8

15.1 15.1

4.73 4.55

1.18 1.57 0.79 1.02 1,22 1.57

1.69 2.36 1.02 1.30 1.57 2.16

97.4 93.2 54.4 48.2 82.4 67.4

25.0 19.2 11.8 l4.6 16.0 16.4

COMPUTED VALUES

12.1 10.4 n.3 9.7 10.5 10.9

74.3 79.4 78.3 69.3 81.6 75.6

Average 8 5.0 83.9 82.1 73.5 —

76.1 77.5 64.3 68.1 — —

11 12

1283 1264 1265 1266 1267 1268 1269

246.6

n.3

15.1

4.68

249.0 259.8

10.8 12.0

15.1 15.1

4.92 5.08

271.8

11.0

15.1

5.18

236.4 245.9 255.4

9.5 9.5 7.7

15.1 15.1 15.1

4.85 5.08 5 .I 8

2.05 1.26 1.89 3.50 1.26 1.73 3.19

2.91 2.09 3.86 H*O O 1.81 3.31 5.99

60.6 69.6 69.8 71.7 72.2 71.4 74.0

18.0 21.0 15.2 16.0 27.3 26.6 32.6

10.6 10.0 9.7 9.6 10.2 9.7 9.5

70.3 69.8 78.2 77.7 62.2 61.3 56.0

75.0 71.6 79.6 72.9 63 .O 63.0 51.0 — 84.5 84.4 88.3 83.6 83.1 80.8
>

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•
, D/ FILTERS AS RECEIVED,

C/ FILTERS DRY (NOT OILED), A.C. "FINE", 305 GFM A.C. "COARSE", 305 CFM

(Continuation of TABLE 6)

E/ FILTERS OILED,

A.C. "COARSE", 305 CFM

Filter Number

Test Number

Filter Weight

Start S

Filter Gain e

Dust Introduced g

Duration of Test Min,

Pressure Loss

Start In. WG

Pressure Loss

Finish In. WG

Sampler Gain

Upstream mg

Sampler Gain

Downstream mg

Dust Concentration “«/

Cu. ft

Efficiency - Bq

Gravimetric $

Efficiency - Ip

Filter Gain %

Efficiency - ED

Discoloration $

1 6 10 6

1181 1182 II83 1288 1311 1312 1313 . ’"1284 1285 12.76 4051 4052

OBSERVED VALUES

243.6 — 211.1 - 227.6 238.4 247.2 266.0 281.1

Total 17.; 9.2 — — — 10.8 8.8 8.3 15.1 15,1

15.0 15.1

' 15.1 15.1 15.1 15.1 *5.2 16.5 15.1 15.1 15.1 15.2

5.10 5.21 5.10 5.83 4.65 4.44 1.44 3.45 2.95 2,97 2,4o 2.53

1.50 1.61 1.73 2,08 2.25 2.28 — 1.14 1.26 1.42 2.4o 3.27

1.61 1.77 1.81 2.75 2.91 2.83 — 1.30 1.50 1,54 3.23 4.10

69.5 73.4 71.6 72.8 78.8 68.6 31.5 72.2 77.2 84.4 73.4 63 .O

43.4 44.8 47.

27.4 34.2 41.7 22.8 19.3 28.4 2

7 .2 1.0 0.8

COMPUTED VALUES

9.6 9.5 9.7 8.5 10.6 11.1 11.5 l4.6 15.6 15.5 20.7 19.6

37.6 39.0 33.2 62.4 56.6 39.4 27.6 73.2 63.2 67.8 98.6 98.7

Average 38 .1 61.0 — — — 65.2 58.4 55. 100 99.3

50.6 55.0 53.2 — — — — — — — —

Filter

Test Ni

Filter

Star

Filter

Dust I Durati

Pressu

Star

Pressu

Fini

Sample

Upst

Sample

Dowr

Dust C EfficJ

Grat

Effici

Fill

Efficj

Disc

F/ FILTERS OILED,

50^. "FHHL-COARSB", 305 CFM

Filter Number

Test Number

6

4053 4o43 4o44

7

4o45 4o46

Filter Weight

Start g 296.2 292.8 267.9 282.7 297.0

Filter Gain g 14.8 15-H 14.8 14.3 15.1

Dust Introduced g 15.1 15.1 15.1 15.1 15.1

Duration of Test Min. 3.42 3.07 2.28 3.42 3.50

Pressure Loss

Start In. WG 4.10 4.84 3.30 3.46 5.00

Pressure Loss

Finish In. WG 6.34 8.78 3.30 5.00 9.60

Sampler Gain

Upstream mg 59.8 78.4 86.2 86.2 81.8

Sampler Gain

Downstream mg 1.2 1.0 1.9 1.6 1.0

Dust Concentration mg/

Cu. ft. 14.5 16.2 14.5 14.5 14.2

Efficiency - Eg

Gravimetric i 98.0 98.7 97.8 98.1 98.8

Efficiency - Ej.

Filter Gain i 97.7 100 97.7 94.4 100

Efficiency - Ep

Discoloration $ — — — —

G/ FILTERS OILED,

COTTRELL PRECIPITATE, 305 CFM

Continuation of TABLE 6)

5 6 3 1

1184 1185 1186 1187 1188 1189 11810 1174 1175

OBSERVED VALUES

284.5

Total 40.2

15.1 15.1 15.1

6.78 5.44 5.62

330.6

Total

15.1

5.20

27.6

15.1

5.38

318.7

Total

15.1

5.62

28.4

15.1

5.32

237.0

Total

15.1

5.34

9.7

15.1

5.62

0.98 1.10 1.34 3.90 5.31 1.57 2.04 1.38 1.54

1.14 1.38 1.96 5.42 7.98 2.08 5.79 1.6l 1.65

79.5 77.4 70.8 76.7 66.6 65.1 57.8 68.2 69.2

8.0 7.4 9.4 3.4 1.2 3.2 2.8 49.6 50.6

COMPUTED VALUES

7.3 9.1 8.8 9.5 9.2 8.8 9.3 9.3 8.8

90.0 90.4 86.7 95.6 98.2 95.1 95.2 27.3 26.9

Average 88 .8 Average 91.4 Average 94.0 Average 31.2

90.0 92.4 91.5 95.9 97.1 92.1 93.6 54.1 61.6
L

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FILTERS

OILED,

A.C.

"FINE",

200

CFM

(Continuation

of

TABLE

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m r— MO CM r— J » • rH CM on • • • • i CM l i in • • • on on o on 1 i in 1 f: <—t r— CM on in rH CT\ r i H

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rH CM in ON • i • ON o 60 in CO Jt H O o in MO in cr» rH . - r— G£j | • MO on 00 * • | • • i CM K i Hin • • • CT\ r— j cn in 60 i in P 1 © rH r— rH t—t

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r— 1 nt • CO on tH • • • • i CM l in • • • t

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FILTERS

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A„Ce

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360

CFM

(Continuation

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TABLE

6)

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m cr> • • • • l 0 1 in 1 • • • cn 0 O r

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THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.