NATIONAL BUREAU OF STANDARDS REPORT

46?7

PERFORMANCE OF TWO AIR-MAZE OIL BATH AIR CLEANERS

Carl W. Coblentz

William F. Goddard, Jr.

Report to

Office of the Chief of Engineers

Department of the Army

Washington 25, D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair W eeks, Secretary NATIONAL BUREAU OF STANDARDS

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

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C.. and its major field laboratories in Boulder. Colorado, is suggested in the following listing of

the div isions and sections engaged in technical work. In general, each section carries out specialized

research, development, and engineering in the field indicated bv its title. A brief description of

the activities, and of the resultant reports and publications, appears on the inside back cover of

this report.

WASHINGTON, I). C.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instru- ments. Magnetic Measurements. Process Technology. Engineering Electronics. Electronic

Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenic Physics.

Engines and Lubrication. Engine Fuels. Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Phvsies. Electron Phvsics. \lomic Physics. Nuclear Physics. Radioactivity. X-rays.

Betatron. Nucleonic Instrumentation. Radiological Equipment. AEC Radiation Instruments. Chemistry. Organic Coatings. Surface Chemistry. Organic. Chemistry. Analy tical Chemistry.

Inorganic Chemistrv. Lleetrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry . Spectrochemistry . Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics.

Mass and Seale. Capacity, Densitv, and Fluid Meters. Combustion Controls.

Organic anti Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Poly mer Structure. Organic Plasties. Dental Research.

Metallurgy. Thermal Metallurgv. Chemical Metallurgv. Mechanical Metallurgv. Corrosion.

Mineral Products. Ceramic Engineering. Porcelain and Potterv. Glass. Refractories.

Enameled Metals. Concreting Materials. Constitution and Mierostrueture.

Building Technology. Structural Engineering. Eire Protection. Heating and \ir Conditioning. floor. Bool, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical \nalvsis. Compulation. Statistical Engineering. Mathematical Phvsies.

Data Processing Systems. Components and Techniques. Digital Circuitry. Digital Systems.

\nalogue Sv stems. Applications Engineering. • Office of Basie Instrumentation • Office of Weights and Measures

BOl EDER. COLORADO

Cryogenic Engineering. Crvogenie Equipment. Crv ogenie Processes. Properties ol Materials.

Gas l.iquelaet ion. Radio Propagation Physic's. I pper Atmosphere Research. Ionospheric Research. Regular

Propaga I ion Serv ices. Rudio Propagation Engineering. Erequencv l tilization Research. Tropospheric Propagation

Research.

Radio Standards. High Erequencv Standards Branch: High Erequencv Electrical Standards.

Radio Broadcast Service. High Erequencv I mpedance Standards. Microwave Standards Branch:

Extreme High Erequencv and Noise. Microwave Erequencv and Speetroscopv . Microwave

( '.ircuit Standards.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1000-30-4301 May 16, 1956 4637

PERFORMANCE OF TWO AIR-MAZE OIL BATH AIR CLEANERS

by

Carl W. Coblentz

William F. Oxoddard, Jr.

Heating and Air Conditioning Section

Building Technology Division

to

Office of the Chief of Engineers

Department of the Army

Washington 25, D. C„

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publicatio

unless permiss 25.D.C. Sue

cal ly preparec

Approved for public release by the °r p*r r is prohibited Director of the National Institute of »f standards, Washington Standards and Technology (NIST)

on October 9, 2015.

i a report has been specifilar report for its own use.

PERFORMANCE OF TWO AIR-MAZE Oil BATH AIR CLEANERS

by

Carl W. Coblentz and William F. Goddard, Jr.

Abstract

The operating; characteristics of two oil

bath air cleaners of the same type but of

different size were determined for an air

flow rate of 50 CFM. Using A. C. test dust

"fine” the filtering efficiency of the

larger model, designed for an air flow rate

of 143 CFM, was 03% and the efficiency of

the smaller unit designed for 03 CFM was

92%. Both specimens employed a rubber like

diaphragm as a relief valve which opened

to let air flowing from the ripe 1 ine

by-pass the oil bath and closed during- the

intake part of the cycle. The free floating

diaphragm on the larger model performed well

at -30 F ambient temperature, whereas the

diaphragm of the smaller model, which was

riveted to the valve seat, did not close at

temperatures below -13 F, permitting dusty

air to by-pass the filter element during

intake . cycle

1 . INTRODUCTION

Upon requests by the Office of the Chief of

Engineers, Department of the Army, dated April 5 and

May 1, 1956, two specimen air cleaners were tested to

determine their performance characteristics as filters

of the ventilating air for elevator oil tanks.

It is essential that a filter for this purpose

shall have a high efficiency when air is being drawn

into the tank. Filters tested were equipped with

rubber flap valves designed to by-pass the oil bath

when air was being expelled from the tank.

- 2 -

2 . FINDINGS

The first specimen tested was designed for an air

flow rate of 143 CFM. The efficiency of the device at

the operating air flow rate of 50 CF? was only and

an examination of the effluent air indicated t> at dust

particles of £0 micron size had passed the filter; this

was the maximum size of dust particles in the test dust

used for testing this specimen. The pressure loss

increased from 1.9 in. W. G. with clean oil to 2.5 in.

W. G. after the introduction of 260g of dust. These 260g

of dust are equivalent to the total dust which would have

been introduced into the air cleaner during 1040 operating

cycles at a dust concentration of 10 mg/cu ft. The

pressure loss during the discharge portion of the cycle,

when pushing air from the oil tank through the device, was

0.5 in. W. G. No change in the flexibility of the diaphragm,

that served as a relief valve, was noticed when it was

cooled to -33F ; at -36F some stiffening was perceptible and

at -51F the rigidity of the material was such that it could

no longer be expected to operate properly. When operating

the device with the recommended oil, MIL-0-60#3» the loss

due to splashing during 100 operating cycles was 22. 2g.

A flame test revealed that at an oil temperature of

147. 2F no back flash occurred when the filter screen of the

device in operation was touched with a burning torch.

Further tests made with this specimen showed that

using a heavier oil, SAE-20W-30, instead of MII-0-60#3,

did not change the filtering efficiency. The loose fit

of the brass grommet in the relief valve, which enabled

the same to float on the center stem, did, not produce

an air leakage that Effected the efficiency to a noticeable degree. No change in the performance of the relief

diaphragm could be noticed when the ambient temperature was

reduced from 70F to -30F.

The other test specimen was designed for an air flow

rate of ^3 CFM and showed a fitering efficiency of 92 %> at a 50 CFM air flow rate and using A. C. test dust ''fine”.

When using A. C. test dust u coarse T? which contained dust

particles up to 200 micron size the largest particles

observed in the effluent air stream were $0 micron size.

-3-

'The pressure loss with clean oil, MIL-0-6-$3 , was

2.$ in. W. G. and increased to 3.2 in. ¥• G. after 50ft

of dust had been introduced into the device. The oil

lost during 100 operating cycles was 29. 2g.

The relief valve of this model was riveted to the

valve spider and the dianhragm wrs curled up. At room

temperature, the suction caused by the air flow would

securely close the valve: however, when the device was

operated in a -30F ambient air the dianhragm remained

in its curled shape permitting in-flowing dusty air to

by-pass the oil bath. After increasing the ambient

temperature slowly to -13F the diaphragm commenced to

operate properly.

3. SPECIMEN AND TEST APPARATUS

The test specimens were manufactured by the Air-Mag,e Coruoration of Cleveland, Ohio, as their models FV143S an6^

FV$3S. They were supnlied to the Office of the Chief of

Engineers by the Wayne Pump Company of Salisbury, Maryland,

as prototypes for filtering the ventilating air1 of elevator

oil tanks. The latter specimen was furnished after the

performance of the first one had been tested by this

laboratory and found to be not satisfactory.

Both specimens were oil bath air cleaners provided

with a relief valve to by-pass the air around the oil

supply in the filter during the discharge portion of the

cycle. The first model was designed for a 143 CFM air

flow rate and weighted 2.$f0kg (6 lbs 6 oz). The

other model was designed for -3 CFM and weighted 1.256kg

(2 lbs 12 oz). The design of both devices was very similar,

the difference being only their size and the construction of

the air relief valve. These relief valves had a diaphragm

of about 1/16 inch thick, flexible, rubber-like material.

In the larger model, the diaphragm was provided with a brass grommet which centered the same to the snider seat

and avowed the diaphragm to float free when air was

blown into the air cleaner from the oil tank. Fig. 1 is

a photograph of the components of this filter. It shows

the tank into which the oil is filled to a stamped-in

mark: the filter element consisting of several lavers of

corrugated wire mesh screen surrounded by a steel jacket

and with the spider seat of the relief valve in its upper

part, the cover with the stem, and the base, which had a

f i.e; . 1

-4-

2in SFT, to connect the air cleaner to the pipe line and

a cork washer as an air seal to the tank. The diaphragm

was placed on a glass beaker for photographic reasons;

this beaker -a-dversely shows below the diaphragm.

The oil supply of the large device was 491 and that

of the smaller model was 144g.

Fig. 2 shows the FVF3S model assembled and fig. 3 is

a view into the filter element to show how the diarhragrri

was curled up due to the distortion of the material by the

center rivet that holds it to the spider seat.

For test purposes an enclosure was designed and built

that completely covered the device so that the amount of

test dust introduced into the air cleaner could be determined. Fig. 4 is a photograph of the arrangement used for

determining the filtering efficiency. On the left side

is the dust feed apparatus which consists of a variable

speed drive onto which a turntable with two concentric

grooves is mounted. A weighted amount of test dust is

placed into the hopper from which it fills one of the

grooves to a constant level. The dust is then picked up

by a high pressure aspirator which breaks up any ag'-lomerations and introduces the dust in a stead}^ stream of

air into the inlet ripe of the air cleaner enclosure.

By varying the speed of the turntable any desired dust

fe^d rate can be obtained. By dividing the dust feed rate,

in grams per minute, through the flow rate of the air

drawn through the device, in OFF, the concentration of the

dust, in g per cu ft is obtained. This concentration

was maintained at about 0.01 g/cu ft during the efficiency

tests

The air was drawn through the filter with an exhaust

blower and the air flow rate was measured with orifice

flow meters designed in conformance with the ASFE Research

Publication ,

T, Fluid Feters, Their Theory and Appl i cat ion :I

<,

4. TEST PROCEDURE AND OBSERVATIONS

The efficiency of the air cleaner was determined by

drawing a small amount of air from the center of the duct

downstream the filter. The sampling air was blown through

a glass fiber paper whose smallest fibers were about 0.3
.

V.

'

' !|j3
•v

*

IR-MAZE

ath air fiitUU*

stY

*EF

l'n

TI ON<C

niif WEEK, DAILY IN VERY jjJJvYL.

S A L‘

L WiTHU

'ltP OIL AND DIRT F *?IV uS6

CAUt 'OnS

J N CRANKCASE. eE m - °N: FELTED END OF SCRE*

ELEMENT must be in

Air. MA2E CORP. CLEVELAND. OHIO U S A

fig, 2

fig - 3
<5?
[H

|S 1 ^ 1 » •"' "V^' ’ y

-5-

micron thick. Tests of the dust retention ability of a similar material by the Atomic Energy Commission indicated

that this paper would retain more than 99 * 99% of all

particles 0.3 micron and larger and could, therefore, be

considered an absolute filter. The filtering efficiency

was determined from the formula:

E = (1 100

¥] -W?

where E = R =

3 =

efficiency, %> ratio of filter flow rate to

sampler flow rate,

weight gain of sampler, g.

weight of dust introduced into

filter enclosure, g.

weight of dust fallen out in

enclosure and collected after

test

.

The test dust used for determining the filtering

efficiency was Arizona road dust classified by the

A. C. Spark Pluy Division of General fetors Corporation

and nationally accepted as a standard air cleaner test

dust. It had the following particle size distribution

by weight.

0 to 5 microns 99% ± 2%

5 to 10 microns 18% ± 3%

10 to 20 microns 16% ± 9%

20 to 40 microns 18% ± 9%

40 to F0 microns 9% 1 9 %> The filtering efficiency of the specimen was determined as the average value of four test runs in each of

which 20g of dust were introduced into the filter. I'he

efficiency of the larger model FV143S was 89 % and that

of the smaller one FY 89 S was 92% at 50 CFI air flow rate.

These efficiency values were determined on both models wi th

light oil, FIL-0-60&3/ and heavier motor oil, SAE-20W-30,

and no difference could be noticed at room temperature.

The pressure loss of the test specimens was determined

as the pressure drop between the base flange and the

inside of the enclosure for the air flow during the air

intake portion of the cycle, i.e., during the efficiency

- 6 -

test runs. This pressure loss increased on the larger

model from 1.9 in. W. G. with clean oil to 2.5 in. W. G.

after introduction of 260g of dust. This dust load did

not exhaust the dust holding capacity of the device,

however, as the 260g of dust corresponded to the total

amount of dust that could reasonably be expected to be

introduced into the air cleaner during 1040 operating

cycles, it was felt that an earlier servicing of the

device would be advisable and the full dust holding

capacity would not be needed. The pressure loss during

the discharge portion of the cycle, when flowing air

from the oil tank, was 0.5 in. W. G. This pressure loss

was independent of the dust load in the air cleaner,

which indicated that the main flow of air was through

the by-pass valve.

The pressure loss of the FV$3S model at 50 CFM

flow was 2.F in. W. G. and increased to 3.2 in. W. G.

after 50ft of dust was introduced into the device and

when oil MIL-0-60&3 was used. Using heavier oil,

SAE-20W-30, the pressure loss with clean oil was 3.3 in.

W. G. at room temperature.

It was investigated whether a back-flash could occur

when the air cleaner was heated due to solar radiation

and then touched by a flash. For this purnose the

specimen FV143S was installed in the enclosure shown in

fig. 4. A plexiglass window was then built into the

center of the lid of the enclosure, the cover of the

air cleaner was removed and the rubber diaphragm replaced

with a Plexiglass plate, so that the inside of the filter

screen could be observed while the device was in operation. Three thermocourl es were installed at the air

inlet, the air outlet and one in the oil to measure the

temperatures at these points. Air was then drawn in from

an electric heater at a rate of 50 CFM. After reaching

an air outlet temperature of 130F the filter screen was

touched with the tip of a welding torch introduced through

the inlet pipe of the enclosure. As no flash could be

noticed the temperature was further increased until the

inlet temperature was 150. OF, the oil temperature was

147. 2F and the outlet air temperature 145. OF. Mo back

flash was observed under this condition.

-7-

The flexibility of the diaphragm of the 143 CFM unit

at low temperatures was observed by mounting it on a stand

and placing it in a low temperature chest. The flexibility

of the disk at room temperature was then compared with that

after exposure to the low temperature, for several minutes.

It was noticed that the flexibility had not changed at

-33F- At -36F some stiffening was perceptible and at -51F

the rigidity had become such that a proper operation

could not be expected. When operating this specimen in

a -30F ambient temperature the operation of the by-pass

valve appeared to be the same as at room temperature.

The operation of the smaller model FVF3 S in a -30F

ambient showed that the curled up diaphragm did not

clo se when air at a flow rate of 50 OFF was drawn into

the filter. (In actual oreration the dusty air would

have by-passed the oil-filter and ^lown into the oil

tank), the air temperature was then slowly increased while

the direction of the air flow was continuously altered.

The diaphragm commenced to close when the ambient temperature had increased to -13F.

An examination of maximum size of dust particles in

the effluent air was made by inserting a microscopic

slide into the air duct. This slide was prepared with

an adhesive made up from Canadian balsam and castor oil.

The larger model was tested with A. C. dust "fine'’

that contains dust particles of up to £0 micron size,

whereas the smaller unit was tested with A. C. dust

"coarse” having particled up to 200 micron size. A

microscopic examination of the slides showed particles of

up to SO micron size from both models. This revealed that

the smaller model did retain all particles larger than

SO microns.

4. DISCUSSION AND CONCI USI0N5

The performance tests revealed the apparent usefulness of this type of air cleaner for the intended purpose.

The comparatively low efficiency of S3 percent on the

larger model, rated at 143 CFN, is attributed to the fact

that it was being used at less than 30% of its design

air flow. The filtering efficiency of this unit was too

low. Experience with other oil bath air cleaners has shown

that the efficiency decreased with the air flow rate. It

was therefore, to be expected that the efficiency would be

higher on the smaller unit designed for f3 OFF and being

utilized at 60% of this air flow rate. The efficiency of

92%o of this model compared favorably with the other

acceptable oil bath filters.

If this smaller model FV&3S can be procured with a floating diaphragm similar to that being employed on the

larger model, it is recommended that it be used. Unless

this modification can be obtained, the installation of

paper air filters should be considered.

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

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project

or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

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

the National Bureau of Standards ($1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office, Washington 25, D. C.

Inquiries regarding the Bureau’s reports should be addressed to the Office of Technical Information, National Bureau of Standards, Washington 25, D. C.