NATIONAL BUREAU OF STANDARDS REPORT

2197

PERFORMANCE TESTS OF CLEANABLE

IMPINGEMENT TYPE AIR FILTERS

AIR MAZE TYPE P-5W

manufactured by

Air Maze Corporation

Cleveland, Ohio.

Henry E. Robinson

Thomas W. Watson

Heating and Air Conditioning Section

Building Technology Division

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Charles Sawyer, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

m% PROJECT NBS REPORT

1003-30-4715 January 15, 1953 2197

Performance Tests of Cleanable

Impingement Type Air Filters

Air Maze Type P-5W

manufactured by

Air Maze Corporation

Cleveland, Ohio,

by

Henry E. Robinson

Thomas W. Watson

Heating and Air Conditioning Section

Building Technology Division

to

Bureau of Ships, Code 327

Department of the Navy

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

The publication, i

unless permission

25, D, C. Such p

cally prepared If

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

or In part, Is prohibited

T Standards, Washington

a report has been speclfireport for Its own use.
:<
Performance Tests of an Air Maze Type P-5W 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 its 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 specimen

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 Air Maze Corporation of

Cleveland, Ohio, and was of the cleanable viscid type, 20x20x2

inches in nominal size. It was identified by nameplate as an

Air-Maze Type P-5W. The filtering media was composed of 16-mesh

screen wire cut in strips about 20 inches long and 2 inches wide,

crimped diagonally, and placed one on the other in the aluminum

metal edee-frame with the crimps reversed, the angle between reversed crimps being about 45°. There were approximately 6 layers

of strip per inch of pile. The media faces were covered by expanded metal sheet having diamond-shaped openings approximately

l-l/$x2-7/$ inches in size. The filter had actual outside dimensions of 19-5/#xl9-l/2x2 inches, leaving a free opening

lS-l/3xlS inches ( 2.26 ft^ net face area) and weighed 11.5 lb.

when clean, without oil.

The manufacturer submitted an adhesive designated as "Filterkote M

Tt 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 with the filter standing on edge for a minimum of

l£ hours prior to the test.

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«).
- - • . • • ;; " .
2

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 l+% 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 Noe 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, 600 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 , 600 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 percent lint and 96 percent 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

filter was determined using 100 percent 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 0.004 inch W.G. per gram of dirt mixture fed per

sauare foot of filter face area.

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 re-oiled 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 W.G.,

at 300, 600 and 900 fpm face air velocity, was measured at the

start of each of the tests, and after the 900 fpm test, as shown

in Table 1.
' ' ' ' - -

-

'

. . ,

*

.
- 3 -

Table 1

Face Velocity, fpm

At start of 300 fpm test

At start of 600 fpm test

At start of 900 fpm test

After 900 fpm test

In crease in P.D. after

3 cleanings, $

300 600 900

0.042 .148 .306

.045 .160 .338

.046 .162 .339

.045 .15$ .334

7 7 9

A summary of the test data obtained in dirt-loading tests

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/sqft inch WG percent

300 0 .042

4 .043 47

107 .074 - 192 .103 54

260 .149 62

309 .204 60

342 .25$ 63

375 .345 63

419 .51$ 64

* Average mixture: 4.0$ lint, 96 .0$ Cottrell precipitate by we

Average rate of dirt loading: 16.7 grams per square foot

per hour.

0 .160

6 .166 56

IS .172 59

25 .19$ 59

88 .250 63

115 .271 64(P)

121 .270 62(A)

212 .327 - 236 .350 64

272 .3$1 64 ( P

)

27$ .378 66(A)

34$ .490 65

423 .636 66( P)

429 .654 69(A)

4$4 .$64 73

* Average mixture: 4.1$ lint, 95.9$ Cottrell precipitate by weight.

Average rate of dirt loading: 20 .

8

grams per square foot per hour.
- «' : -C .

- ' /: •:

'hhjs- 3

'

v? ,^aH ^I.A iSTU^xxiTt
- 4 -

Table

Face Air Velocitv Dirt Load*

2 - continued

Pressure Drop Efficiency

fpm grams/sqft inch WG percent

900 0 .339 — 27 .364 61

&3 .506 67

110 .538 63 ( P

)

120 .543 66(A)

129 .578 70

175 .652 74(P)

134 .653 74(A)

230 .717 - 235 .788 73

332 .365 75(P)

341 .376 74(A)

387 .978 - 452 1.105 71

* Average mixture: 3.9$ lint, 96.1$ Cottrell precipitate by weight.

Average rate of dirt loading: 22.6 grams per square foot per hour

Note: Efficiencies marked (P) or (A) were determinations made

at the end of a day of loading, and at the start of the

next day of loading, respectively.

V. SUMMARY 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 loading.

Table 3

Spec. Dirt L

T d'g 0 100 200 300 400

grams per sq ft (Initial)

Face Velocity, fpm P.D. Eff. P.D. Eff. P.D. Eff. P.D. Eff. P.D.

300 0.04 .47 .07 51 .11 55 .19 60 » 44 63

600 .16 56 .26 63 .32 63 .41 65 .59 66

900 .34 60 .53 63 .63 74 .31 74 1.00 72
ta . : : '

liM

lim_ . gH
- 5 -

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 oilings,

its average percentage increase in pressure drop was about $ percent, or about 2.7 percent per loading and cleaning operation.

It is assumed that the factor of the care and thoroughness of

the cleaning operation, which is necessarily involved in the

process of ascertaining cleanability, was approximately constant.

It is believed the filter 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

rate to which the filter was subjected did not overtax the

wetting-rate of the filter adhesive and cause the filter surfaces

to become M drytT .
.

.

. . srftf b&v&ilsd 'Bit '

cKI:b s t as.tsoxor-x ( (A ) hsjH -as pi arttf) $ tibfefu %o
load, grams per square foot FIG. I
*
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

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

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Bureau of Standards (25 cents). Both are available from the 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.