NATIONAL BUREAU OF STANDARDS REPORT

6404

PERFORMANCE TESTS OF

FOUR CLEANABLE IMPINGEMENT AIR FILTERS

TYPES 44 (TWO THICKNESSES), FS 304 AND FS 504

MANUFACTURED BY

THE FARR COMPANY

LOS ANGELES, CALIFORNIA

by

Carl W. Coblentz and Paul R. Achenbach

Report to

Bureau of Yards and Docks

Office of the Chief of Engineers

Headquarters, U. S. Air Force

Washington, D. C.

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
TOE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1000-12-4801 May 6, 1959 6404

PERFORMANCE TESTS OF

FOUR CLEANABLE IMPINGEMENT AIR FILTERS

TYPES 44 (TWO THICKNESSES), FS 304 AND FS 504

MANUFACTURED BY

THE FARR COMPANY

LOS ANGELES, CALIFORNIA

by

Carl W. Coblentz and Paul R. Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

Bureau of Yards and Docks

Office of the Chief of Engineers

Headquarters, U. S. Air Force

Washington, D. C.

IMPORTANT NOTICE

NATIONAL BUREAU OF

intended for use within I to additional evaluation a listing of this Report, eit the Office of the Director however, by the Governrr

to reproduce additional c

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

jr progress accounting documents

> formally published it is subjected

ing, reproduction, or open-literature mission is obtained In writing from

C. Such permission is not needed,

ally prepared If that agency wishes <NBS>

u. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PERFORMANCE TESTS OF FOUR FARR COMPANY AIR FILTERS

TYPES 44 (l IN. AND 2 IN. THICK),

FS 304 (l IN. THICK) and FS 504 (2 IN. THICK)

by

Carl W. Coblentz and Paul R. Achenbach

1 . Introduction

The performance characteristics of a group of cleanable

viscous impingement type air filters was determined to provide

information for evaluating the relative economy of cleanable

versus throw-away types -of filters. This investigation was

requested by the Defense Department through the Tri-Service

program of research and development at the National Bureau of

Standards to obtain required data for the preparation of new

air filter specifications.

The results presented in this report were obtained on 4

new filters and include determination of the arrestance and

pressure drop as a function of the specific dust load for face

velocities of 360 and 540 ft/min^and information on the cleanability of the specimens.

2 . Description of Test Specimens

The test specimens were of the cleanable viscous impingement type and were manufactured and supplied for this test by

the Farr Company of Los Angeles, California.

The filters were identified as types 44, 1-in. thick and

2-in. thick, type FS 304, 1-in. thick, and type FS 504, 2-in.

thick. The filters measured 19 1/2 in. square on the outside

and the face area of the media was 18 1/4 in. square, giving

them a net face area of 2.31 sq ft. The types 44 had an actual

thickness of 1 in. and 2 in., respectively; type FS 304 was

7/8 in. thick and type FS 504 was 1 7/8 in. thick. The type

44 was also marked "Industrial Filter".

The frames of all filters were made of aluminum sheet

pressed into U-shaped channels. The thickness of the material in the frame of the type 44, 2 in. thick, filter was 0.070

in.; all other frames were made of 0.044 in. thick sheet.

- 2 -

The filtering media of the 1-in. thick type 44 filter

consisted of 9 layers of V-crimped 14-mesh screen wire, the

crimps running at 90 degrees to each other in adjacent layers. The weight of the new filter was 6 lbs (2718 g), oiled

and ready for use.

The media of the 2 in. thick type 44 filter was made of

2-in. wide strips of V-crimped and flat screen wire piled up

in alternate layers with approximately four layers of each

kind per inch of thickness. The weight of this filter, oiled

and ready for use, was 10 lbs 6 oz (4725 g)

,

new.

The 1-in. thick FS 304 type had 2 layers of V-crimped

l4-mesh screen wire placed with the crimps at 90 degrees to

each other in the two layers and with a flat layer of the

same material on the downstream side.

The filter media of the 2 -in. thick FS 504 type consisted

of 3 layers of V-crimped 14-mesh screen wire, with the crimps

running at 90 degrees to each other in adjacent layers, followed by one layer of V-crimped 8 -mesh screen wire and a layer

of flat l4-mesh screen wire, on the downstream side.

An adhesive, furnished by the manufacturer and designated

as ’’Green B Loom 100”, was used for all tests. The filters

were immersed in the liquid and then drained for at least 16

hours before starting a test.

3 . Test Method and Procedure

The performance of the filters was determined at 360 ft/min

and 540 ft/min face velocity corresponding air flow rates of

8 l 6 cfm and 1224 cfm, respectively. The initial pressure drop

at each air velocity was measured and then the initial arrestance at the air velocity desired for that test 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^ 1938).

The aerosol used for the arrestance determinations was an

air-suspension of Cottrell precipitate which had been sifted

through a 100-mesh wire screen. In order to simulate actual

operating conditions when loading the filters, four percent by

-3-

weight of No. 7 cotton linters^ previously ground in a Wiley

mill with a four-millimeter screen were fed simultaneously with

the Cottrell precipitate.

The pressure drop of the filter was recorded after each

increment of 20 grams of dust introduced into the apparatus.

Whereas the arrestance measurements were made with 100

percent Cottrell precipitate,, cotton linters were added to retain a ratio of four parts by weight to every 96 parts of Cottrell precipitate., including that amount used for the arrestance

measurement s

.

Arrestance determinations were made at the beginning and

at the end of the loading period for each filter and at several intermediate load conditions. The filters were loaded

with a dust concentration of approximately 1 gram in 1000 cu

ft of air until the pressure drop reached 0.5 in. W.G. for the

360 ft/min face velocity tests and 0.8 in. W.G. in the tests

with 540 ft/min face velocity.

After the filters had been loaded to capacity they were

cleaned with water and allowed to dry; then,, oiled again as

previously described,, weighed and installed in the test apparatus for determining any change in pressure drop and in some

cases for a new performance test.

4 . Test Results

Tables 1 through 8 show the observed pressure drops and

the arrestance values for the four filters. The asterisks (*)

behind values of arrestance indicate that these values are the

average of two test runs.

-4-

Table 1

Performance of Type 44 Filter (2 in. thick) at

360 ft/min Face Velocity

Load Pressure Drop Arrestanc

g/sq ft in . W . G

.

0 0.045 - 3 0.046 59*

54 0.067 61*

122 0.092 63

173 0.130 64

223 0.198 68

274 0.319 - 315 0.515 80*

Table 2

Performance of Type 44 Filter (2 in. thick) at

540 ft/min Face Velocity

Load Pressure Drop Arrestance

g/sq ft in. W.G.

0 0.117 - 3 0.118 60*

49 0.156 63*

139 0.218 68*

220 0.335 74

265 0.480 75

310 0.710 81 * 325 0.855 81 *

Table 3

Performance of

360

Type 44 Filter (l in.

ft/min Face Velocity

thick) at

Load Pressure Drop Arrestance

g/sq ft in. W.G. ~~w~

0 0.070 - 3 0.073 60* 54 0.160 66

84 0.275 - 105 0.417 77

125 0.610 83*

-5-

Table 4

Performance of Type 44 Filter (l in. thick) at

540 ft/min Face Velocity

Load Pressure Drop Arrestanc ; - g/sq ft in. W. G. ~w~

0 0.143 - 7 0.148 63*

49 0.260 71

94 0.485 76

116 0.725 - 133 0.883 82*

Table 5

Performance of Type FS 504 Filter (2 in. thick) at

360 ft/min Face Velocity

Load Pressure Drop Arrestance

g/sq ' ft in. W.G. ~T~

0 0.040 - 3 0.042 49*

54 0.065 50

105 0.102 57

156 0.168 63

207 0.325 70

233 0.535 77*

Table 6

Performance of Type FS 504 Filter (2 in.

540 ft/min Face Velocity

thick) at

Load Pressure Drop Arrestanc

g/sq ft in. W.G.

0 0.075 - 5 0.076 50*

68 0.136 55

123 0.215 60

177 0.330 62

231 0.518 64

272 0.815 65 *

-6 -

Table 7

Performance of Type PS 304 Filter (l in. thick) at

360 ft/min Face Velocity

Load Pressure Drop Arrestance

g/sq ft in. W.G.

“1* 0 0.022 - 3 0.023 42* 37 0.042 47

80 0.085 50

126 0.156 55

168 0.340 66

190 0.575 77*

Table 8

Performance of Type FS 304 Filter (l in. thick

)

at

540 ft/min Face Velocity

Load Pressure Drop Arrestance

g/sq ft in . W.G.

0 0.055 - 3 0.055 43*

57 0.110 48

114 0.215 48

159 0.395 52

177 0.515 53

204 0.835 57

The preceding tables show the arrestance values and the

pressure drop as a function of dust load per square foot of

net filter area at face velocities of 360 ft/min and 5^0 ft/min.

Fig. 1 to 4 present these same values graphically using smooth

curves to approximately fit the individual points of observat ion

.

Fig. 1 to 4 show that both the pressure drop and the arrestance of all four models increased with increasing dust load; but

the rate of increase varied considerably.

The dust load indicated by these graphs at 0.5 in. W.G.

pressure drop for 360 ft/min face velocity and at 0.8 in. W.G.

for 540 ft/min face velocity have been tabulated in Table 9 as

-7-

Dust Holding Capacity. Also shown in this table are the mean

arrestance values for each filter and each face velocity during

the period in which the capacity dust load was being deposited.

Table 9

Dust Holding Capacity and Mean Arrestance

Type of Filter 44 44 FS 504 FS 304

Thickness of Filter,

inch 2 l 2 1

Face Velocity,

ft/min

Final Pressure Drop,

360 540 360 540 360 540 360 540

in. W. G. 0.5 0.8 0.5 0.8 0.5 0.8 0.5 0.8

Dust Holding Capacity,

grams/sq ft

Mean Arrestance,

315 318 113 124 233 270 187 200

% 66 70 69 73 59 59 54 49

This table shows that the dust holding capacity of the 2-in.

thick filters is higher than that of the 1-in. thick ones. The

difference,, though, is considerably greater for the two Type 44

filters where the mean arrestance of the 1 in. specimen was a little higher than that of the 2 in. filter. This is probably

the result of differences in the construction of the two filters.

Whereas the 2-in. thick filter media provided for dust collection

in the whole depth of the filter., the 1-in. Type 44 collected a heavy surface layer of lint that increased the pressure drop

rather rapidly but also improved its arrestance. The Type FS

filters contained fewa? layers of screen wire than the Type 44

filters which caused a larger amount of the dust introduced into

the duct to pass the filters. The fact that the arrestance determined on the Type 44 filters was higher at 540 ft/min face velocity than at 360 ft/min indicates that this type is well suited

for the higher velocity. The FS 504 (2 in. thick) showed equal

arrestance at the two face velocities. The arrestance of the

FS 304 type (l in. thick) decreased from 54 percent at 360 ft/min

to 49 percent at 540 ft/min perhaps because the higher velocity

carried more of the dust particles through the two layers of

crimped wire screen and one layer of flat screen comprising its

media.
'
-8 -

The cleanability of the filters is indicated by comparing

the weights and pressure drops after several loading and cleaning cycles with the original values when new. Table 10 shows

these values for the oiled and drained filters for both face

velocities

.

Table 10

Cleanability of Filters

Type and Condition of Filter

Type 44 (2 in. thick)

New

After 1 loading and cleaning

After 2 loadings and cleanings

Type 44 (l in. thick)

New

After 1 loading and cleaning

After 2 loadings and cleanings

Type FS 504 (2 in. thick)

New

After 1 loading and cleaning

After 2 loadings and cleanings

Type FS 304 (l in. thick)

New

After 1 loading and cleaning

After 2 loadings and cleanings

Weight Pressure Drop, in. W.G.

grams 360 ft/mi

n

540 ft/min

4725 0.045 0.095

4763 0.046 0.105

4867 0.052 0.105

2718 0.070 0.140

2740 0.070 0.135

2748 0.070 0.143

2677 0.041 O.O83

2687 0.036 0.075

2687 0.040 0.080

1622 0.023 0.046

1652 0.022 0.055

1640 0.023 0.055

All filters increased in weight by about one percent as a result of two loadings and two cleanings. This increase ranged

from 18 to 42 grams for the four specimens. In some cases the

pressure drop increased a little after two loadings and two

cleanings and in other cases it did not increase.

USCOMM-NBS-DC

FARR TYPE 44 ( 2 INCH THICK )

DUST LOAD

FARR TYPE 44 ( | INCH THICK )

/ MIN.

DUST LOAD > GRAMS PER SQUARE FOOT

FARR TYPE F-S 504 ( 2 INCH THICK )

DUST LOAD GRAMS PER SQUARE FOOT

FARR TYPE F-S 304 ( I INCH THICK )

*

» U)

r, 0

o 4

'< 51

DUST LOAD GRAMS PER SQUARE FOOT

tf. R. DEPARTMENT OK COMMERCE

f,*ovl« L, SttTMIM, SrcrflrU-y

NATIONAL mmftAU OK fWAMMHDH

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