-T&f3-"

NATIONAL BUREAU OF STANDARDS REPORT

69^7

PERFORMANCE TESTS OF A

’ROLL-O-MATIC" AUTOMATIC RENEWABLE MEDIA AIR FILTER

manufactured byAmerican Air Filter Company

Louisville, Kentucky

by

C. W. Coblentz and P. R. Achenbaoh

Report to

Public Buildings Service

General Services Administration

Washington 25 * D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FOR OFFICIAL USE ONLY
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

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of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS REPORT

Nil PROJECT NBS REPORT

1003-30-10630 August 25, I960 , 69^7

PERFORMANCE TESTS OF A

"ROLL-O-MATIC" AUTOMATIC RENEWABLE MEDIA AIR FILTER

manufactured by

American Air Filter Company

Louisville, Kentucky

by

Carl W. Coblentz and Paul R. Achenbach

Mechanical Systems Section

Building Research Division

to

Public Buildings Service

General Services Administration

Washington 25 j D. C.

IMPORTANT NOTICE

NATIONAL BUREAU OF ST Mended for uie within the

fo additional evaluation and r lilting cf this' Report, either I fhe Office of the Director) Na

r.ovevor, by the Government

to reproduce additional cople

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 201 5.

rogress accounting document!

mally published it Is subjected

eproductlon) or open-lltnraturo

Ion Is obtained In writing from

Such permission Is not needed'

jrepared If that agency wlshei <NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FOR OFFICIAL USE ONLY
V .

v* V V
PERFORMANCE TESTS OF A

"ROLL-O-MATIC" AUTOMATIC RENEWABLE MEDIA AIR FILTER

manufactured by

American Air Filter Co.^ Louisville, Kentucky

by

C. W. Coblentz and P. R. Achenbach

1 . Introduction

At the request of the Public Buildings Service, General

Services Administration, the performance characteristics of

an American Air Filter Company "Roll-O-Matic" air filter were

determined. The scope of this examination included determinations of the arrestance of the particulate matter in the

laboratory air and Cottrell precipitate at the rated air flow

the dust-holding capacity of the filter medium per unit area,

observation of the automatic advance of the filter mat, and

determination of the pressure drop for a range of air flow

rates and during the loading process at the rated air flow.

2 . Description of Test Specimen

The test specimen was manufactured and supplied in the

size required for test purposes by the American Air Filter

Company, Inc., of Louisville, Kentucky, and identified by

the trade name "Roll-O-Matic . ” It was intended to be representative of the equipment offered commercially in larger

sizes

.

The filter medium was a fiber glass mat about 2 1/4 in.

thick reinforced on the downstream side by longitudinal wires

The glass fibers appeared to be bonded by an organic plastic

material and were covered with tricresyl phosphate as an adhesive. The mat was supplied in a 3-ft wide roll on which

it was compressed to approximately 1/2-in. thickness. The

clean roll was suspended in the upper part of the housing,

and after passing the 24-in. square air flow opening, was

rolled up on another spool at the bottom of the housing by

an electric motor. In passing from the clean roll at the

top of the housing to the bottom roll, the medium was backed

up by a vertical stationary grid that prevented excessive

deflection of the filter mat when passing across the air

flow opening.

- 2 -

The movement of the blanket by the electric motor was

controlled by a time switch and a pressure switch which were

arranged to override each other. The time switch advanced

the filter mat at the minimum rate required to prevent the

filter from drying out and reducing the ability to arrest

the particulate matter. The pressure switch would activate

the advance mechanism when the pressure drop across the filter media had increased to a pre-set value before the time

switch had moved the media. The advance of the filter mat

would then continue until the pressure drop had decreased by

about 0.1 in. W.G. The specimen was designed to operate on

the time switch, and the pressure switch had been added as a safety device to avoid overloading of the filter media during

temporary extreme dust loads.

There was also an inclined gage arranged parallel to the

pressure switch that showed the difference of the total air

pressures upstream and downstream of the filter.

3 . Test Method and Procedure

The arrestance measurements were made in accordance with

the NBS ’’Dust Spot Method” described in a paper by R. S. Dill

and entitled, "A Test Method for Air Filters,” (ASHVE Transactions, Vol . 44, p. 379, 1938).

For test purposes, the housing with the filter medium in

place was installed in the test apparatus and carefully sealed

to prevent inward leakage of air except through the measuring

orifice. The desired rate of air flow through the filter was

established and samples of air were drawn from the center

points of the test duct two feet upstream and eight feet downstream of the test specimen at equal rates and passed through

known areas of Whatman No. 4l filter paper. The change of the

opacity of these areas was determined with a sensitive photometer which measured the light transmission of the same spot

on each sampling paper before and after the test. The two

sampling papers used for each test were selected to have the

same light transmission readings when clean.

For determining the arrestance of the filter, with Cottrell precipitate as the test dust, different size areas of

sampling papers were used upstream and downstream of the filter in order to obtain a similar increase of opacity on both

sampling papers. The arrestance, A (in percent), was then
'

. ’
- 3

-

calculated by the formula:

A

S D AD

S U AU

x 100

where Sp and Sp are the upstream and downstream sampling areas

and AU and AD the observed changes in the opacity of the upstream and downstream sampling papers,, respectively.

For determining the arrestance of the particulate matter

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

upstream and downstream samplers. A similar increase of the

opacity of the upstream and downstream filter papers was then

obtained by passing the sampling air through the upstream

paper only part of the time while operating the downstream

sampler continuously. This was accomplished by installing

one solenoid valve in the upstream sampling line and another

one as a by-pass. The 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 following formula:

A = 100 - T x —AU

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

through the upstream sampler, AU and AD being the changes of

opacity of the sampling papers, as previously indicated.

The pressure drop of an automatic renewable media air

filter of this type increases during operation with the media

in a stationary position, due to the accumulating dust load,

until it reaches the value at which the pressure switch was

set to operate the advance mechanism. The test was conducted

without the use of the time switch and the pressure switch

was set to commence advance at a value a little below 0.5 in.

W.G. The differential pressure was not adjustable.

When clean media was moved into the air stream, the

pressure drop decreased until the pressure switch stopped

the advance drive. The filter operated repetitively in the

on-off range of the pressure switch, the differential controlling the length of clean blanket that was moved into the

air stream and the rate of dust accumulation determining the

-infrequency of the cycles. The operation of this type filter at

a higher pressure drop would increase the dust load per unit

area of the filter medium. The saving on filter material, however, would tend to be offset by the increase of the required

blower power. The selected maximum pressure drop of 0.5 in.

W.G. corresponds to common operating practice for this type of

filter.

The following procedure was used for determining the performance of the test specimen: The pressure drop of the clean

filter mat was determined at the rated face velocity of 500 ft/

min, corresponding to an air flow rate of 2000 cfm, and also

at air flow rates of 20 percent above and below this value,

i.e., 2400 cfm and 1600 cfm. Thereafter, the specimen was

operated only at the rated face velocity, and three arrestance

determinations were made using the particulate matter in the

laboratory air as the aerosol, followed by two further arrestance measurements with Cottrell precipitate, after which

the loading of the filter with a mixture of 96 parts by weight

of Cottrell precipitate and 4 parts of lint was started. The

Cottrell precipitate had previously been sifted through a 100-

mesh screen and was dispersed into the test apparatus in a ratio nf 1 gram per 1000 cu ft of air. The lint was introduced

into the air stream separately and was prepared by grinding No.

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

Several more arrestance determinations were made later when

the blanket had advanced several steps using both aerosols. The

distance of each advance of the filter media was observed by

means of small markers fastened to the mat. These markers

moved alongside a yardstick mounted in the filter housing and

could be observed through a glass window in the test duct. A

pilot light was installed parallel to the advance motor and

enabled the operator to record the pressure drop of the test

specimen at the start and at the end of each advance of the

filter mat. The test was terminated when the media had advanced 32 1/2 in. At that time, a total of twelve arrestance

determinations had been made in addition to the five made

initially with the clean filter mat.

4 . Test Results

The test results are summarized in Tables 1 and 2 and

shown as graphs in Fig. 1 and 2. Table 1 gives the observed

values for dust load, total mat travel, pressure drop, and

the arrestance values determined with the particulate matter

in the laboratory air and with Cottrell precipitate.

-5-

Table 1

Summary of Arrestance, Pressure Drop., and

Mat Travel Determinations at Rated Air Flow

American Air Filter Co., ,T Roll-0-Matic" Air Filter

Dust Load Total Mat Travel Pressure Drop Arrestance Aeroso

g/ft width inches in. W. G. ~W~ **

0 0.103 18 * A

10 - 0.113 71* C

223 - 0.296 77 C

410 — 0.438 18 A

669 10 1/2 0.415 77 C

943 19 1/2 0.454 79* C

943 19 1/2 0.454 30* A

1099 28 0.371 28 A

1104 28 0.373 78 C

1218 32 1/2 0 . 366 78* C

* Average values of two or more tests.

* * Aerosol A - Particulate matter in the laboratory air.

Aerosol C - Cottrell precipitate in the laboratory air.

Table 2

Mat Travel, Dust Load, and Pressure Drop

Before and After Advance of Filter Media

American Air Filter Co., "Roll-O-Matic" Air Filter

at Rated Face Velocity of 500 ft/min

Dust Load Travel of Mat, in. Pressure Drop , in. W.G.

g/ft width Advance Total Before Advance After Advance

0 0 0 0.103

488 4 4 0.490 0.422

550 2 1/2 6 1/2 0.490 0.410

612 4 10 1/2 0.488 0.365

716 9 3/9 15 1/4 0.472 0.362

851 4 1/4 19 1/2 0.487 0.363

975 4 23 1/2 0.480 0.365

1089 4 1/2 28 0.478 0.361

1213 4 1/2 32 1/2 0.472 0.364

- 6 -

The dust load is reported in grams per foot width, referring to the 2-ft square air flow opening. At the end of the

test, 1218 g/ft width of Cottrell precipitate and lint had

been introduced into the test apparatus, corresponding to a total weight of 2436 grams. No fallout of dust could be found

in the test duct at the termination of the test.

The average arrestance of the particulate matter in the

laboratory air varied from l8 percent to 30 percent. The

lowest values were determined when the filter medium was

clean. After the filter mat had once started to advance, the

values of 28 and 30 percent were observed.

The arrestance values with Cottrell precipitate determined

on the clean filter mat were 72 percent and 71 percent and

varied between 77 and 79 percent after regular advance of the

filter media began. The average arrestance with Cottrell precipitate was 78 percent at steady state conditions.

The pressure drop of the clean filter mat at different

air flow rates is shown as follows in Table 3-

Table 3

Pressure Drop of Clean Filter

Air Flow Rate Face Velocity Pressure Drop

cfm ft/min in. W. G.

2400 600 0.132

2000 500 0.103

1600 400 0.077

The dust load values presented in Table 2 are the cumulative weight of dust and lint, in grams per foot width, that

had been introduced into the test apparatus at the beginning

of each advance of the filter medium. The values are interpolated between the 20-gram increments of Cottrell precipitate

and are correct to within ± 3 grams. The mat travel during

the advance varied from 2 1/2 in. to 4 3/4 in. It appears

that the first two advance cycles did not represent steady

state operation of the specimen since the dust load increments

after these two advances were only about one half as large as

for the later advances of the media. Since the positions of

the markers which indicated the travel distance of the mat

-7-

could not be observed much closer than ± 1/2 in., it can be

assumed that the advance distance during the six cycles that

followed the two initial cycles were practically equal. This

fact is also indicated by the nearly-constant values of the

pressure drop observed at the beginning and at the end of

each advance; namely, 0.481 in. W.G. ± 0.009, and 0.363 in.

W.G. ± 0.002, respectively.

The amount of Cottrell precipitate collected on a unit

area of filter medium during the steady state operation of the

test specimen provides a measure of the rate of consumption

of the media during actual use. Disregarding the insignificant mass of particulate matter collected on the filter during

the arrestance determinations with laboratory air, the dustholding capacity per unit area is expressed by the slope of

the straight line in Pig. 2 that best fits the individual

points of observation. According to this line, there were

1196 - 646 = 550 g/ft width of dust and lint introduced into

the filter mat while the filter mat advanced from the 12-inch

to the 32-inch position, a distance of 20 inches. Therefore,

the dust-holding capacity, then, was

550 x 12

20

= 330 g/sq ft.

Table 4 below presents a summary of the performance data

of this filter.

Table 4

Summary of Test Results

Pace Velocity, rated - 500 ft/min

Pressure Drop, clean

at 400 ft/min face velocity - 0.077 in. W.G.

at 500 ft/min face velocity - 0.103 in. W.G.

at 600 ft/min face velocity - 0.132 in. W.G.

Average range of operating pressure - 0.481 to O .363 in. W.G.

Arrestance, average

Mat clean, laboratory air - 18/

Cottrell precipitate - Steady state, laboratory air - 29%

Cottrell precipitate - 78/

Dust-Holding Capacity - 330 g/sq ft.

USCOMM-NBS-DC
{
ARRESTANCE v/s DUST LOAD

Figure 1

MAT TRAVEL v/s DUST LOAD

Figure 2

U.S. DEPARTMENT OF COMMERCE

Frederick U. Mueller, Secretary NATIONAL BUREAU OF STANDARDS

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

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

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