NATIONAL BUREAU OF STANDARDS REPORT

4110

PERFORMANCE TESTS OF A DOLLINGER

STAYNEW AUTOMATIC AIR FILTER

MODEL A-4 (TYPE HD PANELS)

by

Henry E„ Robinson

Thomas W* Watson

Report to

General Services Administration

Public Buildings Service

Washington 25, D. C.

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

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1000-30-4230 May 25, 1955 4110

PERFORMANCE TESTS OF A DOLLINGER

STAYNEW AUTOMATIC AIR FILTER

MODEL A -4 (TYPE HD PANELS)

by

Henry E, Robinson

Thomas W 9 Watson

Heating and Air Conditioning Section

Building Technology Division

to

General Services Administration

Public Buildings Service

Washington 25, D 0 C„

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication,

unless permissio

25, D, C. Such

|

cal ly prepared I

* , r , . , ,, or in part, is prohibited Approved for public release by the

„ ,

_. T • , T r

Standards, Washington Director of the National Institute of

report has been specln- Standards and Technology (NIST) report for its own use. on October 9, 2015.

PERFORMANCE TESTS OF A DOLLINGER

MODEL A -4 3TAYNEW AUTOMATIC FILTER

1, INTRODUCTION

At the request of the Public Buildings Service, General

Services Administration, the performance characteristics of

self-cleaning automatic oil-type air filters were determined

to provide information to assist in the preparation of new- air filter specifications.

The test results presented herein were obtained on a specimen automatic oil-type air filter submitted by its manufacturer at the request of the Public Buildings Service and

included determinations of dust arresting efficiency with two

aerosols (atmospheric air and Cottrell precipitate), pressure

drop, dirt load and cleanability of the specimen.

2. DESCRIPTION OF THE FILTER SPECIMEN

The filter was manufactured by the Dollinger Corporation

Rochester 3, New York, and was identified by the factory representative as a Dollinger Staynew Automatic self-cleaning

air filter Model A-4, capacity 1715 efm 0 The drive motor cur

rent characteristics were stated as follows: 1/6 HP; 1 PH;

60 CY; 115 volts; 3.0 Amps; 1?25 RPM.

The test unit had a housing with actual outside dimensions of 2? 3/4 inches in width, 52 inches in height and 19

5/3 inches in length. The exposed face of the curtain media

on the upstream side was 21 3/4 inches wide by 23 1/2 inches

high (3.55 sq.ft, gross face area). The unit was rated at

1715 cfm air delivery at a face velocity of 550 fpm based on

the net air-passing exposed area of the upstream curtain

(3.12 sq. ft.). Special upstream and downstream transitions,

12 inches in length with flanges 30 inches square matching

those of the duct of the test apparatus, were used to adapt

the unit for test. The openings formed by these transitions

at the duct flanges were 2 4 inches square upstream and downstream. The downstream curtain face had an exposed area

21 3/4 inches wide and 23 1/2 inches high ( 3.55 so. ft.).

The filter consisted of Type HD panel sections 23 inches

in width and about 10 1/4 inches in height, consisting of a layer of 12 -mesh bronze screen to which were attached several

layers of woven copper mesh. The panels were joined together

by 1 l/4x23 -inch metal strips (which reduced the net face
'

,

‘

'
area of the curtain to 87.$% of the gross area) and attached

to two endless chains forming an endless curtain that rotated

over sprockets on horizontal shafts located in the top and

reservoir assemblies. There were two endless curtains, one

upstream approximately 102 1/2 inches in length and one downstream about $0 inches in length. Both curtains rotated downward on their upstream face and upward on their downstream

face. The lower end of the upstream curtain in passing around

its lower sprocket dipped into a reservoir of oil for cleaning

and re-oiling the media. The downstream curtain did not enter

the oil bath, but was scrubbed at the lower sprocket by a rotating cylindrical nylon brush when the curtain moved.

The curtains were shifted intermittently by a timercontrolled motor and gear box. The synchronous electric

timer was set by the factory to actuate the drive motor for

a period of 20 seconds every 15 minutes, resulting in a curtain movement of approximately 2 1/2 inches per shift. For the

dirt-loading tests the timer was re-adjusted for a curtain

movement of 3 inches per shift, or 12 inches per hour.

The manufacturer furnished an adhesive designated as

"Pingene 50". Approximately 25 gallons were required to fill

the reservoir to the indicated level.

3. TEST METHOD AND PROCEDURE

Efficiency determinations were made by the NBS "DustSpot Method" using the following aerosols: (a) outdoor atmospheric air drawn through the laboratory without addition of

other dust or contaminant; and (b) Cottrell precipitate,

dispersed in the outdoor atmospheric 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$). The

test duct and arrangement are shown in Figure 1. A baffle

made of two 3-inch wide slats at right angles to each other

was located in the duct about 3-1/2 ft. downstream of the test

assembly to intermix the air discharged from it.

For these tests, the unit was installed in the test duct

and its exterior housing was carefully sealed to prevent inleakage of air. The desired rate of air flow through the air

cleaner was established and samples of air were drawn from the

center of the test duct, at points one foot upstream and eight

feet downstream of the air cleaner assembly, at equal rates

for equal times, and passed through known areas of Whatman No.

3

41 filter paper. The filter papers used in the upstream and

downstream positions were selected to have the same light

transmission readings when clean, as determined by means of

a photometer using transmitted light. Using filter paper

sampling areas downstream equal to 30 percent of the filter

paper area upstream, an efficiency of 70 percent would be indicated if the upstream and downstream dust-spots on the

papers had the same opacity, as indicated by the change in

the light transmissions of the dust-spot areas before and

after the sample was drawn. If the opacities of the dustspots differed, the efficiency was calculated by means of

the formula

Efficiency

,

percent - 100 1 -

where A

p and A2 were the areas of the dust-spots upstream and

downstream, respectively, and Q]_ and 02 were the opacities of

the dust-spots upstream and downstream respectively.

In testing the unit, it was desirable to subject it to a dirt-loading condition that would simulate a service condition

and that would allow the results to be applicable for a wide

range of unit sizes.

In service, a unit having an upstream exposed curtain

height of H ft, and receiving air containing a dust concentration of C grams per 1000 cf, at face velocity V, shifts its

curtain periodically or uniformly at an average rate of S

inches per hour. Under these conditions, the curtain, when it

leaves the air stream entering the front face of the unit, will

have received a "burden" of

12H x 60V x C or 0.72 HVC grams of dust per square foot . S x 1000 S

The average pressure drop of a unit, and to some extent its efficiency, regardless of its size provided the face velocity is

the same, depend on the average dirtiness of its curtain, and

therefore on the magnitude of the "burden" as defined above.

On this basis, a test of a small-sized unit can be expected to

be reasonably representative for a much larger unit, if the

"burdens" are the same.

To evaluate a burden reasonably representative of what

might be experienced in actual service, the following in-service

- 4

-

conditions were assumed: H = 7 ft; 3=7 inches/hour; C = 0.065 gram per 1000 cf (1 grain per 1000 cf) ; V = 500 fpm.

Using these values, a representative service burden was computed to be

B = = 23*4 grams/sq.ft.

In selecting conditions for the test it was desirable to

increase the curtain shifting speed S to 12 inches/hr, to

shorten the time required for several revolutions of the curtain. Assuming that the test should be conducted with a burden B = 23.4 grams/sq . ft . , and that for the unit tested the

height of exposed face = I .96 ft.; width = 1.8l ft.; curtain

shifting speed S = 12 inches/hr; and velocity V = 550 fpmi

then

23 . 4

- ^72_HVC

S

or C = 23 .4 x 12

0.72 x 1 .96 x~ 550 x 0.87&

“ 0.413 gram per 1000 cf.

The air flow capacity of the unit was 1.81 x 1.96 x O .878 x

550 = 1715 cfm, and the appropriate average rate of dust feed to

the unit was therefore 0.71 gram per minute. With 4% by weight

of lint added, the average rate of dirt feed to the filter was

0.74 gram per minute.

The following procedure was employed in these tests. The

clean unit was installed in the test duct, its oil reservoir

was filled to the indicated level, and all discoverable air

leaks into its housing were sealed. The timer control was adjusted to shift the curtain 12 inches per hour. During a period

of 36 hours immediately prior to the tests the curtain was allowed to shift automatically for a total of approximately 4 revolutions through the oil reservoir, with no air flow, to saturate the curtain media. The initial resistance of the clean

filter at various rates of air flow was then measured. Next,

three determinations of the efficiency of the clean unit were

made at rated velocity, using as the aerosol outdoor air drawn

into the test duct through a nearby open window.

Following these, three efficiency determinations were made

at rated velocity, using as the aerosol outdoor air in which

was dispersed Cottrell precipitate at a concentration of approximately 0.99 gram per thousand cubic feet of air, i.e., a

CiO B

net dust feed rate of 1.7 grams per minute. The sampling times

for the efficiency tests with Cottrell precipitate as the aerosol were 10 minutes each and the curtain made one shift during

each test. When these had been obtained, the process was begun of loading the unit with a mixture of 4 percent cotton

lint, and 96 percent Cottrell precipitate, by weight, separately dispersed into the air stream. The lint used for this

purpose was No. 7 cotton 1 inters previously ground in a Wiley

mill with a 4 “ millimeter screen; the lint was dispersed into the air stream every 15 minutes (immediately after each

curtain movement) through an aspirator operating at approximately 35 psi inlet air pressure. .. At suitable periods as

loading progressed, the efficiency of the unit was determined

using 100 percent Cottrell precipitate in outdoor air. The

pressure drop was recorded at intervals during the tests.

In order that the dirt-loading process simulate continuous operation of the unit in service at the desired burden,

the curtain-shifting timer mechanism was deenergized during

all periods when the air flow through the unit was stopped -- e.g., overnight, or at lunch periods. Similarly, the increased rate of dust feed occurring during efficiency determinations was in effect reduced to the desired average net

rate of feed (0.71 gram per minute) by operating the unit without dust feed for ten minutes following each ll}. -minute efficiency determination.

The dirt-loading process was continued until the curtain

had made two or more revolutions under the imposed dust burden conditions. Although some variation of pressure drop

occurred as a result of the periodic changes of curtain position, an equilibrium of efficiency and pressure drop appeared

to have been substantially attained at this stage of the test.

At the conclusion of the dirt-loading tests the efficiency was determined again using laboratory air as the aerosol

In order to ascertain the self-cleaning performance of the unit

the curtain was left running intermittently for a period of 17

hours (two revolutions) with no air flow through the unit. The

resistance of the cleaned filter at various air flows was then

observed.

4. TEST RESULTS

Tabulated in Table 1 are measurements, at four different

face velocities, of the pressure drops through the filter when

it was clean, and when it had been allowed to clean itself

- 6 - after the dirt-loading test 0 In each case, the observed values

apply for a particular position of the curtain,, As may be seen

from the pressure drop data in Table 2 for the clean unit tested with atmospheric air (which could have caused no significant

change in curtain resistance) the pressure drop of the clean

unit was observed to vary from 0.2?S to 0.303 inch W.G., depending upon curtain position,,

The operating performance of the unit at 550 fpm net

face velocity is summarized in Table 2„ The table gives data

on the efficiency of the unit in arresting Cottrell precipitate, and on its pressure drop, as the curtain was progressively loaded, from a clean condition to an operating equilibrium condition corresponding to a "dirt burden" of 24 „ 3 grams

per soo ft., with a mixture of approximately 4 percent lint

and 96 percent Cottrell precipitate by weight. It is believed

that the unit was operating substantially at the equilibrium

condition for this burden after the curtain had turned more

than 1.5 revolutions. This is indicated by the trend of the

efficiency and pressure drop curves plotted from the data of

Table 2, as shown in Figure 2, Also, the efficiency of the

unit in filtering atmospheric air is given for the clean

unit, and for the unit when its media was loaded with a dirt

deposit corresponding to a "dirt burden" of 24,3 grams per

S 0 o ft

,

5. SUMMARY

A, Performance

Due to the self-cleaning action of the unit, which

occurs periodically during operation, the performance of the

unit depends on, and must be related to, the dirt deposit on

the curtain, expressed in this report by means of the "dirt

burden" on the curtain as it leaves the airstream on the upstream side. On this basis, at 550 fpm net face velocity,

the efficiency of the unit in arresting Cottrell precipitate

was about ?6 percent for equilibrium operation at a dirt burden of 24,3 grams per sq« ft. The corresponding pressure

drop averaged 0,35 inch W,G, , with a plus or minus variation

of about 0.02 inch depending upon the curtain position.

The effect of the magnitude of the burden is shown by

the corresponding figures obtained when the curtain was

practically clean, even though the rate of dirt feed was the

same, i„e 0

, at the start of the dirt-loading test. The

- 7

-

efficiency and pressure drop of the unit at this stage were

about 75 percent and O. 3 O inch W.G. , respectively. As the

deposit on the curtain increased to the equilibrium condition,

the efficiency and pressure drop rose to the values given in

the preceding paragraph.

The efficiency of the clean unit in arresting the dust

in the atmospheric air at the test laboratory was on the

order of 9 percent, individual values ranging from 7 to 11

percent. Its efficiency appeared to be approximately the same

with the curtain clean, and with a dirt burden of 2I4.3 grams

per sq. ft.

At conclusion of the tests, examination of the test duct

downstream of the unit showed no evidence of oil carry-over.

Some oily patches were observed on the downstream face of the

downstream curtain at the conclusion of the tests. It is concluded that oil carry-over would be negligible for a unit operated at curtain shift speeds not greater than 12 inches per

hour.

B. Self-Gleaning

Automatic self -cleaning of the curtain by its intermittent motion through the oil reservoir appeared to be effective.

At the conclusion of the dirt-loading test, the curtain was allowed to move intermittently through the oil at a rate of 12

inches per hour for 17 hours with no air flow for a total of

two revolutions. The pressure drop of the unit, at 550 fpm

face velocity, was reduced from its value when dirty (about

0.35) to a value of O. 3 O 6 inch W.G., as compared with the

initial average value of 0.289 for the clean filter as indicated in Table 2. On inspection of th© unit after the test

and this self-cleaning operation, the upstream curtain appeared

to be quite clean except at the edges of the 1 l/l^-inch metal

junction strips, some dirt deposits remained in a few places

on the media. This type of deposit is considered to be of

little practical importance. The downstream curtain had a

slightly dusted appearance, and a few small oily areas, but

no significant dust deposits.

The lint and dust removed from the filter curtain settled

to the bottom of the oil reservoir as a heavy sludge, leaving

the oil substantially clear. The sludge was readily removed

from the reservoir by means of the catch pan provided.
.. ••

-

-
- s -

C . General

The following observations were made concerning particulate matter downstream of the test unit.

(1) Cellophane tapes stretched across the duct 15"

downstream of the unit with the adhesive side facing upstream,

and exposed for several hours each during the dirt-loading

test, showed on examination under the microscope that many

particles from 15 to 5 microns, and smaller, in size were

caught* Relatively few larger particles, ranging from 20 to

200 microns, were found on the tapes* No lint fibres were

observed; late in the tests 4 or 5 small droplets of what

appeared to be oil were found on a tape, but it is believed

this was of little importance since none was observed in the

downstream duct at the end of the tests c

(2) A cellophane tape exposed at the downstream dust

sampling station 8 ft. from the test unit throughout the

entire test showed many fine particles, and relatively fewlarge particles of dust; no lint was observed.

(3) Examination by microscope of the downstream filter

papers from efficienc3

'

r determinations showred that almost all

of the particles on the paper were under 20 microns, with

most under 5 microns; a few up to 50 microns were observed*

(4) Examination of the downstream duct of the test

apparatus after the tests indicated no observable oiliness

of the duct. Upon careful sweeping of the downstream duct,

no observable quantity of dust was obtained from it.

A cloth was wetted with the oil submitted with the

unit, and taken outdoors and ignited with a wooden safety

match.. The cloth did not ignite readily, but^once** ignited it

burned strongly with a smokey flame.

No difficulty was experienced in setting the adjustment

of the curtain-shifting timer as desired. The intermittent

shifting action of the curtain occurred smoothly and without

objectionable noise.

TABLE 1

Net Face Air Pressure Pressure

Velocity Flow Drop* Drop**

fpm cfm inch W. G. inch W.Go

321 1000 0.112 0.116

432 1500 .233 = 239

550 1715 .296 .306

642 2000 .400 .407

302 2 500 .530 .623

* Initial resistance of the clean filter,, ** Resistance of the unit after the dirt-loading test and 1?

hours of intermittent self-cleaning action (approximately

two turns) without air flow.

TABLE 2

Face Inlet Total

Velo- Aero- Total Curtain Dirt Pressure Efficcity sol# Time Movement Fed## Drop iency

fpm minutes revolutions grams inch Wo Go percent

550 A _ 0 0o278 8

- 0 0 .285 11

C3 0 0 •303

0,289 avg„

7

550 C 10 0o02 17 .315 74.5

34 0 0? 3U ,308 75»7

58 oil 51 .305 74.5 (PM)

82 o!6 70 ,316 75.0 (AM)

- 1*35 085 313 0 34® 75°5 (PM)

460 o90 330 o3X9 77.1 (AM)

634 lo 24 476 .325 74.7

838 lo 64 626 .347 76,3 (PM)

864 1c69 644 .356 74.7 (AM)

1050 2 + 0$ 773 .349 74.9

A =, <=> 773 .335 13 . - - 773 ,326 1 0

#A = Particulate matter in atmospheric air at NBS

C = Cottrell precipitate in atmospheric air

Average mixtures 3<>9 percent linty 96,1 percent

Cottrell precipitate by weight,, (The dirt fed corresponds to

a "dirt burden” on the curtain of 24,3 grams per sq 0 ft, on

leaving the airstream)

o

_ I CVS

Filter Frame

VERTICAL SECTION

Air Filter Test Apparatus

Figure I
,

*

'
iN30H3d AON3IOIdd3 '9M HON I

IOO

200

300

400

500

600

700

TOTAL

DIRT

FED,

GRAMS

Fig.

2

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

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Standards, Washington 25, D. C.
II

•*)