NATIONAL BUREAU OF STANDARDS REPORT

2322

PERFORMANCE TESTS OF CLEANABLE

IMPINGEMENT TYPE AIR FILTERS

TYPE VS AND TYPE VR

(VORTOX)

by

Henry E. Robinson

Thomas 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

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003 -20-4715 March 4, 1953 2322

PERFORMANCE TESTS OF CLEANABLE

IMPINGEMENT TYPE AIR FILTERS

TYPE VS AND TYPE VR

manufactured by

Vortox Company

Claremont, California.

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 I 3 O-OOI

The publication, reprin'

unless permission Isobt:

25, D. C, Such permiss

rally prepared If that i

Approved for public release by the *'*' Director of the National Institute of

has been speclD- Standards and Technology (NIST) , on October 9, 2015.
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PERFORMANCE TESTS OF CLEANABLE

IMPINGEMENT TYPE AIR FILTERS

TYPE VS Km TYPE VR

I„ INTRODUCTION

At the request of the Bureau of Ships, Code 327, Navy Department (NPO-I5479, Index No« NSM I 3 O-OOI) 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-I6552 (Ships) dated 1 October 1951 as modified by

Amendment 1 dated 15 April 1952«

The tests were performed on specimen filters 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 SPECIMENS

The two filters submitted were manufactured by the Vortox

Company of Claremont, California, and were of the cleanable viscid

type, 20x20x2 inches in nominal size. They were identified by

their nameplates as Type VS and Type VR air filters.

The media of the filters consisted of multitudinous helical

coils, about 5/16 inch in diameter formed from 0,011 inch iron or

steel wire flashed with copper, apparently poured with random

orientation into the space between the faces and the edges of the

air filter frame.

The Type VS filter was composed of the following elements,

starting at the upstream face: two layers of expanded metal

l/4xl/2 mesh; heltical wire media; one layer of flat screen 14x1^

mesh; one layer of expanded metal l/l+xl/2 mesh. The filter had

actual outside dimensions of 19“9/l6xl9"9/l6xl-7/^ inches, leaving a free opening lSxlS-l/l6 inches (2,26 ft^ net face area) and

weighed 11,0 lb, when clean and oiled.

The Type VR filter was similar in construction to the Type VS

except that another layer of expanded metal l/4xl/2 mesh was used

in lieu of the 14x1^ mesh flat screen. The filter had actual outside dimensions of 19-l/2xl9“l/2x2-l/S inches, leaving a free open

ing 17~7/^x17“‘15/16 inches ( 2,23 ft“^ net face area) and weighed

12,7 lb, when clean and oiled.

The manufacturer submitted an adhesive designated, as ^’9974"

for oiling both filters. This was done in preparation for the

test by immersing the filters in the liquid and letting the excess oil drain off with the filters standing on edge for a minimum

of 16 hours prior to the test.

III. TEST METHOD AND PROCEDURE

The dust-ai^resting 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 jfeet

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^)0

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 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 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 in- > creased to approximately O.OO4 inch W. G. per gram of dirt mixture fed per square 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 drops of the clean oiled filters, in inch W.G,

,

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

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

in Table 1.
V
- 3 - TABLE 1

Face Velocity, fpm 300 600 900

Type VS

At start of 300 fpm test 0.040 . 144 .316

At start of 600 fpm test .041 .160 .372

At start of 900 fpm test . .04^ .19^ .450

After 900 fpm test ,073 . 25 ^ .555

Increase in P.D. after

3 cleanings, percent ^3 79 76

Type VR

At start of 300 fpm test 0,064 .207 .422

At start of 600 fpm test .064 .217 .443

At start of 900 fpm test ,064 .215 .437

After 900 fpm test .067 ,225 .456

Increase in P.D, after

3 cleanings, percent 5 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, for each of the filters.

TABLE 2

Filter Face Velocitv ..Dirt Xoad=^= Pressure Drop Efficien

fpm grams/6 q ft inch WG percent

VS 300 0 .040

2 .040 43

5 .041 44

7 .041 45

34

' ,052 47

63 ,067 — 102 .0^7 51(P)

104 ,0^6 50 (A)

135 ,107 56

190 „161 56

221 ,200 59

237 ,225 6l(P)

240 ,217 61 (A)

252 ,250 64

294 .352 6?^

326 .512 73

^I'Average mixture :

' 0^ lint, 96^ Cottrell precipitate by weight.

Average rate of dirt loading: 19.7 grams per square foot per hour.

- 4 -

Filter

VS

Face Velocity

fpm

600

TABLE 2 - continued

Dirt Load* Pressure Drop Eff iciencv

grams/sq ft inch ¥G percent

0 ,160

6 .162 55

12 .170 5 ^

2 ^ .199 59

64 .252 61

119 .347 67

137 .393 65 (P)

143 .390 61(A)

150 .420 63

177 .503 60

223 .672 71

250 .^10 75

^'Average mixture: 3,9^ lint, 96.1^ Oottrell precipitate by weight.

Average rate of dirt loading: 23.9 grams per square foot per hour.

0 .450 - 9 .46S 63

1 ^ .475 63

46 . 5 SS 6 S

73 .713 74 (P)

S3 .710 74 (A)

110 .S4£> 75

13s .995 75

147 1.060 SO

157 1.143 79

=<'Average mixture: lint, 96^ Cottrell precipitate by weight.

Average rate of dirt loading: 20.1 grams per square foot per hour.

0 .064 —

3 .064 45

6 .064 4 S

S . 064 46

26 .073 51

73 .101 53

101 .llS 57 (P)

104 .122 57 (A)

132 .150 5 S

166 .205 62

169 ,206 62

IS9 .251 62

22s .354 64

259 .507 74

^'Average mixture: 4«0^ lint, 96% Cottrell precipitate by weight.

Average rate of dirt loading: 17.6 grams per square foot per hour.
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Filter Face Velocity Dirt Load* Pressure Drop Efficiency

fpjn grams/sq ft inch WG percent

VR 600 0

6

12

4 ^ ^5

110

116

144

176

.217

,220

.225

. 2^5

.350

.396

.425

.510

.633

52

55

61

64

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63(A)

69

73

214 .Sll 73

^'Average mixture: 3.9^ lint, 96.1 Cottrell precipitate by

Average rate of dirt loading: 20. 6 grams per square foot

VR 900 0 .437

9 .450 5^

.458 65

2^ .500 69

74 .655 70

121 .835 72

130 .880 73(P)

140 .^25 74(A)

159 1.032 75

=^Average mixture: 4.0^ lint, 96^ Cottrell precipitate by weight.

Average rate of dirt loading: 21.2 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. S\]mkRY OF RESULTS

A. Performance

The test data are plotted in Figure 1 and Figure 2, which

show the variation of the pressure drop and of the efficiency of

the filters as they were 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.j, in

percent, as taken from the curves of Figure 1 and Figure 2, at

various specific dirt loadings.

TABLE 3

Spec. Dirt Ldg, 0 100 200 300

grams/sq ft (Initial)

Face Vel . . fpm P.D, Eff. P.D, Eff. P.D, Eff. P.D. Eff.

- - VS

300 0,04 43 ,0B 51 !17 57 .3,^ 69

600 ,16 55 .31 65 .55 65 - - 900 .45 63 .79 74 - - - -

VR

300 0.06 45 .12 57 ,2?^ 62

600 .22 52 .37 64 ,74 74 - - 900 .44 5^ .75 71 - - - -

B. Cleanability

The pressure drops of the clean oiled filters at 300, 600 and

900 fpm face velocity recorded in Table 1 imder Test Results indicate that, after the Type VS filter had been subjected to three

loadings with the dust-lint mixture and three cleanings and re-oilings,

its average pressure drop showed an average increase of about 79

percent. This increase in pressure dron indicates that the Type VS

filter v/as not satisfactorily cleanable by the method employed. The

Type VR filter had an average increase in pressure drop of about 7

percent over its original measurement. This change is within the

uncertainty with which the cleaning operation, which is necessarily

involved in the process of ascertaining cleanability, could be perform.ed. It is believed the Type VR filter can be considered as

satisfactorily cleanable.

It should be noted that the initial resistance (0,450 inch W.G.)

of the Type VS filter at the start of the 900 fpm velocity'' test was

considerab.1 higher than the initial resistance ( 0 , 316 ) of the same

filter hefr'rp the 300 fpm velocity test. The increase was due to

dirt in tl e filter which could not be removed by the cleaning operation; its effect was to cause the filter to start the 900 fpm loading test at a relatively high resistance, and therefore to reduce the

dirt-holding capacit 3

/- reckoned for any selected final resistance.

The difference in cleanability of the two filters appeared to

be due chiefly to the 14xlB mesh flab screen just downstream of the

filtering media in the Type VS filter, v/hich made it difficult to

flush water into, or dirt out of, the media on that side.

Mo visible evidence of shifting or compaction of the helical

coil filtering media was observed in the course of these tests.
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C, General

The fact that efficiencies determined at the end of a day

of loading of the filters (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 filters were subjected did not overtax

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

surfaces to become "dry".

PRESSURE

DROP

V OR T 0 X

100 200 300 400 500

LOAD, GRAMS PER SQARE FOOT FIG. I

u_

Lli 40

PRESSURE

DROP,

INCH

W

G

EFFICIENCY,

PERCENT

VORTOX VR

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 hy Congress in Public Law 619, 1950.

These include the development and maintenance of the national standards of

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and various consultation and information services. A major portion of the

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The results of the Bureau’s work take the form of either actual equipment and

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Washington 25, D. C.
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