NATIONAL BUREAU OF STANDARDS REPORT

2^46

PERFORMANCE TESTS OF CLEANABLE

IMPINGEMENT- TYPE AIR FILTERS

(Farr Type 44G)

by

Henry E. Robinson

Thomas W. Watson

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

A. V. Astio, Director

U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

cover of this report.

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003-20-4715 October 9, 1953 2^46

PERFORMANCE TESTS OF CLEANABLE

IMPINGEMENT-TYPE AIR FILTERS

(Type 44G)

manufactured by

The Farr Company

Los Angeles, California

by

Henry E. Robinson

Thomas W. Watson

Heating and Air Conditioning Section

Building Technology Division

to

Bureau of Ships, Code 32 ?

Department of the Navy

Reference: NPO - 15479 Index No. NSM 130-001

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, repr

unless permission isol 25.D.C, Suchperml

cally prepared If that

Approved for public release by the '

Director of the National Institute of

Drt has been specif}* Standards and Technology (N 1ST) on October 9, 20 1 5.
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PERFORMANCE TESTS OF A

FARR TYPE 440 AIR FILTER

I. INTRODUCTION

At the request of the Bureau of Ships, Code 327,

Navy Department (NPO-15479, Index No. NSM 130-001)

qualification tests were made to determine the performance of cleanable viscid-impingement type air

filters in accordance with Section 4.5 of Military

Specification MIL-F-16552 (Ships) dated 1 October

1951 as modified by Amendment 1 dated 15 April 1952.

The tests were performed on a specimen filter

submitted by the manufacturer at the request of the

Bureau of Ships, and included determinations of the

dust-arresting efficiency, pressure drop, specific

dirt load and cleanability of the specimens at three

face air velocities, namely 300, 600, and 900 feet

per minute.

II. DESCRIPTION OF THE FILTER SPECIMEN

The filter was manufactured by the Farr Company

of Los Angeles, California, and was of the cleanable

viscid type, 20 x 20 x 2 inches in nominal size. It

was identified by nameplate as a Farr Type 440.

The filtering media was composed of layers of

14-inch mesh screen wire in strips arranged and

piled in alternate layers of flat and v-crimped screen.

The media was held together at the edges by a steel

retaining frame. There were approximately 4 layers

of flat screen and 4 layers of v-crimp screen per

inch of pile.

The filter had actual outside dimensions of

19 1/2 X 19 5/8 X 2 inches, and had a free opening

1^ 3/^ X IS 1/4 inches in size (2.33 ft^ net face

area). It weighed 10.2 lb when clean, without oil.

The manufacturer submitted an adhesive designated as ’’Green Bloom 100” for oiling the filter.

This was done in preparation for test by immersing

the filter in the liquid and letting the excess oil

drain off at a temperature of 75° F or above, with

the filter standing on edge for a minimum of 24

hours prior to the test.
- 2 -

III. TEST METHOD AND PROCEDURE

The dust-arresting efficiency of the filter was

determined by the NBS "Dust Spot Method" using as a

test dust Cottrell precipitate at a concentration of

one gram per thousand cubic feet of air. The test

method is described in the paper "A Test Method for

Air Filters" by R. S. Dill (ASHVE Transactions, Vol.

44, p. 379, 193^).

Dirt-holding capacity was determined by supplying to the filter air in which were dispersed cotton

lint and Cottrell precipitate in the approximate proportions of k% and 96% by weight, respectively. The

average rate of feed of the contaminants was not more

than 25 grams per hour per square foot of net filter

face area at each face velocity. The lint used for

this purpose was No, 7 cotton linters ground in a

Wiley mill with 4 mm screen.

The efficiency and dirt-loading tests were made

at three different air velocities, namely, 300, 6OO,

and 900 fpm.

In the tests at each velocity, the following uniform procedure was employed. The clean filter, after

oiling and draining as described above, was installed

in the test duct and its initial pressure drop was

measured at 300, 6OO, and 900 fpm air velocity. The

initial efficiency of the filter at the test velocity

was then determined, following which the process of

loading the filter with a mixture of 4^ lint and 96%

Cottrell precipitate by weight was started. At intervals, the increasing pressure drop of the filter was

recorded. At suitable periods as loading progressed,

the efficiency of the filb.er was determined using 100^

Cottrell precipitate. In addition, the efficiency of

the filter was determined at the end of a day of loading, and at the start of the next day, to ascertain

whether the rate of dirt loading was overtaxing the

wetting rate of the filter adhesive. The dirt loading was continued, in general, until the rate of pressure drop rise increased to approximately O.OO4 ihch

W.G. per gram of dirt mixture fed per square foot of

filter face area.
3

The filter was then removed from the test duct

and cleaned by means of a stream of cold water from

a high-pressure hose nozzle, directed at and into

the filter media. After drying, the filter was reoiled for subsequent tests or for measurement of its

initial pressure drop after the final cleaning.

IV. TEST RESULTS

The pressure drop of the clean oiled filter, in

inch ¥.G., at 300 , 600 , and 900 face air velocity,

was measured at the start of each of the tests and

after the 900 fpm test, as sho\'m in Table 1 .

Table 1

Face Velocitv, fpm 300 600 900

At start of 300 fpm test 0.037 0.131 0.275

At start of 600 fpm test .041 .143 .299

At start of 900 fpm test ,043 .154 .31^

After 900 fpm test .043 . 155 > .325

Increase in P.D. after

3 cleanings, percent 16 15 15

A summary of the test data obtained in dirtloading 'bests conducted at 300, 600, and 900 fpm

face velocity is given in -Table 2

Table 2

Face Air

Velocity Dirt Load'!' Pressure Drop Efficiency

fpm grams/sq ft inch WG percent

300 0 0.037

3 .037 54

5 .037 53

72 .057 50 (P)

75 .053 52(A)

155 .076 — 196 .097 53 (P)

199 .091 53 (A)

251 .161 55

274 .215 64

259 .255 65

302 .342 69 (P)

305 .358 70(A)

323 .535 75

'•'Average mixture: 3 . 9^ lint . 96.1^ Cottrell precipitate by weight.

Average rate of dirt loading: 16.6 grams per square

foot ]per hour.
- 4

-

Face Air

Velocity

fpm

600

Table 2 - continued

Dirt Load'i' Pressure Drop Eff icien

grams/sq ft inch ¥G percent

0 0.143 _ _ _ 6 .145 60

12 .14s 62

62 .205 62

120 .250 63 (P)

126 .22^ 63(A)

161 .25S 62

232 .360 64

252 .393 64 (F)

25S .412 64 (A)

294 .525 71

338 .761 73

^'Average mixture: 4 . 0^ lint, 96^ Cottrell precipitate

by weight.

Average rate of dirt loading: 21.6 grams per square

foot per hour.

900 0 0.31^ —

_

9 .320 65

17 .32^ 63

106 .501 69

160 .571 70 (P)

169 .563 68(A)

240 .703 76

2^6 .^10 76 (F)

295 .^40 75 (A)

330 1.016 77

'•^Average mixture: 4 .< lint, 96^ Cottrell precipitate

by weight.

Average rate of dirt loading: 22.2 grams per square

foot per hour.

NOTE; Efficiencies marked (P) or

tions made at the end of a

at the start of the next day of loading,

respectively.

(A) were determineday of loading, and
- 5 -

V. SUMARY OF RESULTS

A, Performance

The test data are plotted in Figure 1 , which

shows the variation of the pressure drop and of

the efficiency of the filter as it was subjected

to increasing specific dirt loading at face velocities of 300, 600, and 900 feet per minute.

Table 3 presents values of the pressure drop

(P.D.) in inches of water, and of the approximate

efficiency (Eff.) in percent, as taken from the

curves of Figure 1 , at various specific dirt

loadings

.

Table 3

Spec. Dirt

Ldg. grams/ 0 100 200 3OO

sq ft (Initial’)

Face Vel.

fpm P.D. Eff. P.D. Eff. P.D. Eff. P.D. , Eff

300 0.04 54 0.06 52 0.09 53 0.33 69

600 .14 60 .24 63 .31 63 .55 71

900 .32 65 .49 69 .63 69 .^5 75

B. Cleanability

The pressure drops of the clean oiled filter at 300 , 600, and 900 fpm face velocity recorded in Table 1 under

Test Results indicate that, after the filter/had been

subjected to three loadings with the dust-lint mixture

and three cleanings and re-oilings, its average percentage increase in pressure drop was about 17.3 percent, or about 5 .^ percent per loading and cleaning

operation. However, although these readings seem to

indicate a gradual build-up of filter resistance,

thorough visual examination of the filter media after

cleaning at the end of the tests revealed no perceptible

dirt deposits not removed by the washing operation. The

adhesive furnished by the manufacturer and used for

oiling the media was unusually viscous - it was estimated

to have a viscosity not less than that designated as
- 6 -

SAE 50. It is possible that the changes in filter

pressure drop were due to variations in the amount

of the oil retained after the oiling and draining

' operation, which, however, was carried out in a

uniform manner. In view of the fact that the filter appeared thoroughly clean at the end of the

tests, it is believed it can be considered as

satisfactorily cleanable.

C. General

The fact that efficiencies determined at the

end of a day of loading of the filter (those marked

(P) in Table 2) were approximately the same as

those made at the start of the next day of loading

(those marked (A)) indicates that the dirt-loading

rates to which the filter was subjected did not

overtax the v/etting-rate of the filter adhesive

and cause the filter surfaces to become ^'dry”.
PRESSURE

DROP,

INCH

WG

EFF

1C

1E

N

C

Y

, P

E

R

CE

N

T

FARR 44 G

LOAD , GRAMS PER SQUARE FOOT

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

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

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

inside of the front cover.

Reports and Publications

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journals of professional and scientific societies. The Bureau itself publishes three monthly peri*

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

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available from the Government Printing Ofl&ce. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Ofl&ce of Scientific Publications, National Bureau of Standards, Washington 25, D. C.
NBS