NATIONAL BUREAU OF STANDARDS REPORT

7409

PERFORMANCE TEST OF A "CONOMATIC" AIR FILTER

MODEL 3-C90, WITH AUTOMATIC RENEWABLE MEDIA B-l-A

manufactured by

Continental Air Filters, Inc.

Louisville, Kentucky

C. W. Coblentz and P. R. Achenbach

Report to

Public Buildings Service

General Services Administration

Washington 25^ D. C,

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1003 - 30-10630 January 12, 1962

NBS REPORT

7409

PERFORMANCE TEST OF A "CONOMATIC" AIR FILTER

MODEL 3-C90, WITH AUTOMATIC RENEWABLE MEDIA B-l-A

manufactured by

Continental Air Filters, Inc.

Louisville, Kentucky

by

C, W. Coblentz and P, R. Achenbach

Mechanical Systems Section

Building Research Division

to

Public Buildings Service

General Services Administration

Washington 25, D. C.

NATIONAL BUREAU OF STAF

intended for use within the Gc

to additional evaluation and rev

listing of this Report, either in the Office of the Director, Natii however, by the Government af to reproduce additional copies

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

gress accounting documents

ally published it is subjected

production, or open-literature

n is obtained in writing from

jch permission is not needed,

epared if that agency wishes

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PERFORMANCE TEST OF A "CONOMATIC” AIR FILTER

MODEL 3-C90, WITH AUTOMATIC RENEWABLE MEDIA B-l-A

manufactured by

Continental Air Filters, Inc.

Louisville, Kentucky

by

C. W. Coblentz and P. R. Achenbach

1 . Intro duction

At the request of the Public Building Service, General

Services Administration, the performance characteristics of a "Conomatic" automatic renewable media air filter were determined. The scope of this examination included the determination of the arrestance and the dust holding capacity per unit

area of filter medium when operated at the rated face velocity

of 500 ft/min and at a pressure drop not exceeding 0.5 in. W.G.

using Cottrell precipitate and lint as the aerosol. The

arrestance of the filter media was also determined for steady

state conditions using the laboratory air as the aerosol.

2 . Description of Test Specimen

The test specimen was supplied by Continental Air Filters,

Inc., of Louisville, Kentucky. The mechanical part of the test

specimen was a "Conomatic; Model 3-C90 which had been modified

for installation in the N.B.S. air filter test apparatus. It

was the same device that had been used in testing other filter

media in 1958, as described in N.B.S. Report #6250,

The stock Conomatic apparatus had been enclosed in a sheet

metal housing and equipped with suitable transition sections so

that when it was installed in the air filters test apparatus no

air could enter the test system except through the measuring

orifice and all air had to pass through a 2 ft square area of

the filter medja. . A roll of clean media was mounted in the

upper portion of the housing and was unrolled as needed by a driven spool in the lower part of the housing. This lower

spool was connected to a 1/6HP electric motor through a reduction drive. The motor was controlled by a differential pressure switch built by the Republic Auto Gas Corporation. This

switch started the motor when the pressure drop across the filter media reached 0.5 in, W.G. and stopped it at a pressure
- 2 -

difference of about 0.45 in. W.G, The motor turned the lower

spool at about 1 RPM winding up the loaded media at a speed

ranging from 1 ft/min to 3 ft/min, depending on how much media

had beei wound up on the spool.

The filter media used for this test was manufactured by

the O^ens- Corning Fiberglas Corporation of Newark, Ohio, and

was identified as the Continental type B-l-A. The mat was

approximately 2 inches thick and was reinforced by a 4-mesh

cotton netting placed near the middle. The media was treated

with an adhesive, said to be a mineral oil with the trade name

"PUROCO". The weight of the media was approximately 4l grams

per square foot. A microscopic examination of the glass fibers

indicated that most were between 30 and 50 microns in diameter.

3 = Test Method and Procedure

The filter was tested at a face velocity of 500 ft/min,

corresponding to an air flow rate of 2,000 cfm. The arrestance

determinations were made using the NBS Dust Spot Method described

in a paper by R. S. Dill entitled M A Test Method for Air Filters”

(ASHVE Transactions, Vol. 44, p. 379^ 1938). The filter under

test was installed in the test apparatus and carefully sealed to

prevent any by-pass of air or air entry into the test apparatus,

except through the measuring orifice. After establishing the

correct air flow rate through the filter, samples of air were

drawn from the center points of the test duct 2 feet upstream

and 8 feet downstream of the test specimen at equal rates and

passed through known areas of Whatman No, 4l filter paper, Arrestance determinations were made with the particulate matter in

the laboratory air as the aerosol and also with Cottrell precipitate injected into the air stream at a ratio of 1 gram per 1,000

cu ft of air s The light transmission of the sampling papers was measured

before and after the test on the same area of each paper and the

two sampling papers used for any one arrestance determination

were selected to have the same light transmission when clean.

For determining the arrestance of the particulate matter

in the laboratory air, equal sampling areas were used in the

upstream and downstream samplers. A similar increase of the

opacity of the two sampling papers was obtained by passing the

sampling air through the upstream paper only part of the time
-3-

while operating the downstream sampler continuously. This was

accomplished by installing one solenoid valve in the upstream

sampling line and another one in a line by-passing the sampler.

The solenoid valves were operated by an electric timer and a relay so that one was open while the other one was closed during any desired percentage of the 5~minute timer cycle, reversing the position of the two valves during the remainder of the

cycle. The arrestance, A (in percent), was then determined

with the formula:

A = 100 - T x AD

AU

where T is the percentage of time during which air was drawn

through the upstream sampler, and AU and AD are the observed

changes in the opacity of the upstream and downstream sampling

papers, respectively.

For determining the arrestance of the filter with Cottrell

precipitate as the test dust, different size areas of sampling

paper were used upstream and downstream of the filter in order

to obtain a similar increase of opacity on both sampling papers

„

The arrestance was then calculated by the formula:

A - u - !§x ) x 100

where the symbols A, AU, and AD are the same as indicated above

and Sy and Sp are the upstream and downstream sampling areas.

During the course of the test, the filter media was loaded

with a inixture of 96 parts by weight of Cottrell precipitate

and 4 parts by weight of cotton linters,

Arrestance determinations were made at the beginning and

at the end of the test using Cottrell precipitate only, while

cotton linters were added during alternate time periods. The

Cottrell precipitate had been previously sifted through a 100-

mesh screen and the lint was prepared by grinding No. 7 cotton

linters through a Wiley mill with a 4-millimeter screen.

The pressure drop across the filter was recorded at the

beginning of the test, after eabh arrestance determination,

and after, every 20-gram increment of Cottrell precipitate that

was introduced into the test duct.
- 4-

The movement of the filter medium was determined by observing the vertical height of a small wire attached to the mat.

This wire was visible through a window in the duct and the

change of its position was noted after each movement relative

to a yard stick installed on the equipment wall adjacent to the

edge of the medium. The length of the individual as well as the

cumulative advances over a 2 ft length of the mat could be

observed to the nearest 1/2 inch.

The movement of 4l in. of the filter media starting about

6 ft from the end of the roll was observed, originally. In order

to determine the degree of uniformity of the roll of media another

section of 33 in. near the middle of the roll was tested in the

same way after winding approximately 20 ft of clean mat upon the

lower spool 9 The amount of Cottrell precipitate received per unit area

of filter media during the period when the media was being

advanced at fairly regular intervals was called the "Dust Holding Capacity" and provided a useful criterion for the consumption of filter media during actual use. The steady state

operation of the filter mat was considered to commence when

the mat had advanced more than one half of the exposed height

after the clean start. The dust holding capacity was determined by plotting the movement of the filter media against

the amount of dust introduced into the test apparatus and

finding the slope of the straight line that best fitted the

individual points of observation, representing essentially

steady operation of the system.

4 . Test Results

Table 1 shows the arrestance and pressure drop values

observed on both sections of the medium when clean and at steady

operating conditions. It will be noted that the arrestance

values determined with Cottrell precipitate for the clean mat

were 71.9 and 71.6 percent and at steady operating conditions,

86.4 and 86.2 percent, respectively. The arrestance of the

particulate matter of the laboratory air was only determined

for the first section and was 13.4 percent, at steady operating

conditions. Each of these reported arrestance values is an

average of two successive arrestance determinations.
-5-

Table 1

Arrestance, Dust Load, and Pressure Drop

Conomatic Model 3-C90 with Media B-l-A

Dust

g/ft

Load Pressure Drop Arrestance Aero;

width in. W. G. %

* Section One

8 0.170 71.9 C

840 0.458 86.4 C

840 0.464 13.4 A

; Section Two

8 0.162 71.6 C

678 0.429 86.2 C

* Aerosol A - Particulate matter in the laboratory air.

C - Cottrell precipitate in laboratory air.

Note: Each arrestance value is an average of two successive

arrestance determinations.

Tables 2 and 3 give the observed values for the mat travel,

dust load, and pressure drop before and after each advance of the

filter medium for the two sections of media tested. The pressure drop was observed to only 2 digits for the first half of

the section NolCl and to 3 digits, i.e. to the nearest 1/1000

in. W.G., during the rest of the test. The average pressure

drop at the start of the last eight mat advances of the first

section was 0.496 in. W.G. and that at the end was 0.443 in.

W.G., indicating an average differential of 0.053 in. W.G. The

.first advance was 4 1/2 in. whereas all successive advances,

except one of 1 1/2 in., were between 2 in. and 2 1/2 in.

The second section of the mat was operated at an average

pressure drop of 0.478 in. W.G. at the start of advancement of

the media and of 0.4l8 in. W.G. at the end of the movements,

corresponding to a differential of 0.060 in. W.G. The individual mat advance distances ranged from 2 to 5 ip.>with the

first movement being the longest^ and averaging about 2.6 in.

The adjustment of the pressure switch was not changed during

the entire test.
0

218

260

291

321

343

374

405

436

467

508

550

591

633

664

705

737

768

809

- 6 -

Table 2

Mat Travel, Dust Load, and Pressure Drop

Before and After Advance of Filter Medium

Conomatic, Model 3-090 with Media B-l-A

Section No, 1

Travel of Mat, in. Pressure Drop , in. W. Go

Advance Total Before Advance After Advance

0 0 0.165 _ _ 4 1/2 4 1/2 0.50 0,45

2 1/2 7 0.50 0o 45

oc. 9 0.50 0.45

2 11 0.50 0.45

2 1/2 13 1/2 0 o 50 0.45

2 15 1/2 0 o 50 0.45

2 17 1/2 0.50 0.45

2 19 1/2 0.50 0.45

2 21 1/2 0.50 0.45

1 1/2 23 0„ 50 0.45

2 25 0.497 0.445

2 1/2 27 1/2 0.498 0.440

2 29 1/2 0.497 0.442

2 31 1/2 0.495 0.440

2 1/2 34 0,496 0.439

2 36 0.495 0.441

2 1/2 38 1/2 0.496 0 e 44l

2 1/2 4l 0,494 0.442
7-

Table 3

Mat Travel , Dust Load and Pressure Drop

Before and After Advance of Filter Medium

Conomatic, Model 3-C90 with Media B-l-A

Section No. 2

Dust Load Travel of Mat, in.

g/ft width Advance Total

0 0 0

218 5 5

240 3 8

280 2 1/2 10 1/2

332 3 13 1/2

363 2 1/2 16

394 2 1/2 1'8 1/2

436 2 20 1/2

467 2 22 1/2

508 2 24 1/2

550 2 26 1/2

591 3 29 1/2

633 2 31 1/2

674 2 1/2 33

Pressure Drop,, in. W.G.

Before Advance After Advance

0.160

0.484 0.420

0.481 0.419

0.470 0.410

0.483 0.424

0.474 0.424

0.475 0.410

0.470 0.415

0.469 0.411

0.480 0.421

0.480 0.420

0.483 0.419

0.480 0.421

0.482 0.420

In spite of the differences in the pressures at initiation

and completion of the media movements for the two sections., no

significant difference in the dust holding capacity were observed for the two sections. Figure 1 and 2 show graphs of the

mat travel after an initial total advance of approximately l 6 in.

plotted against the dust load of the medium, expressed in grams

per foot width. Section No. 1, according to Figure 1, was fed

837-378 = 459 grams of dust while advancing from 16 to 42 in.,

a distance of 26 in. The dust holding capacity for the first

section, then, was:

^59 x = 212 g/sq ft

The corresponding value( of the dust fed to the second section

of the mat, as plotted in Figure 2, was 677-358 = 319 grams/ft

width, while the medium advanced from 16 to 34 = l 8 in. The dust

holding capacity for the second section was:

USC0MM-NBS-DC

319 x = 213 g/sq ft

Mat Travel vs. Dust Load

Mat Travel vs. Dust Load

Dust Load, grama per square foot

II. s. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, O.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

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its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover.

WASHINGTON, D.C.

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