NATIONAL BUREAU OF STANDARDS REPORT

It 620

PERFORMANCE OF A DONALDSON OIL BATH

AIR CLEANER MODEL A 1057l|

Report to

of Chief of Transportation

Air Transportation Service

Department of the Army

Washington 25, D.C,

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

by

Carl W. Coblentz
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

1003-20-l483« April 65, 1958

NBS REPORT

I162O

PERFORMANCE OF A DONALDSON OIL BATH

AIR CLEANER MODEL A IO57I4

by

Carl W, Coblentz

Heating and Air Conditioning Section

Building Technology Division

To

Office of Chief of Transportation

Air Transportation Service

Department of the Army

Washington 25 , D.C,

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, rep . n part, is prohibited

. Approved for public release by the a a w w > unlesspermission Is

. , ^ ndards, Washington 25 |D,C. Such pert DirCCtOr of tllC National Institute of lort has been specifically prepared If tt Standards and Technology (NIST) port for its own use, on October 9, 2015.

PERFORMANCE OF A DONALDSON OIL BATH

AIR CLEANER 5 MODEL A 10S7k

by

Carl W, Coblentz

Abstract

The specimen filter was charged with 13dOg

of dust and the pressure loss, due to this

dust load, increased from 7,9 inches W,G,

to 9.. 5 inches W, at an air flow rate of

315 cfm, and the filtering efficiency

decreased only slightly at the end of the

test, averaging 9l\% for A,C. Spark Plug

”flne" dust and 99^ Por A,G. Spark Plug

"coarse" dust. Tilting of the filter up

to 30 degrees had no effect on the fil-*

terlng efficiency and did not produce a

noticeable carry»over of the oil. The dust

holding capacity of this filter corresponds

to the dust load produced during 7. 3 hours

of operation at the design air flow rate

with a dust concentration of 10 mg/cu ft.

1. INTRODUCTION

As a part of the research project, "Air Filter Systems

for Army Aircraft", the performance characteristics of an

oil-bath air cleaner manufactured by the Donaldson Company

of St. Paul, Minnesota, were determined with a view to comparing this type of filter with others as s.n induction air

cleaner for helicopter or other small aircraft engines.

2, SPECIMEN AND TEST APPARATUS

The test specimen was a Donaldson model A 10571] air

filter designed for an air flow rate of 315 Por use on

tractors and built oP substantial sheet steel. The device

weighed 27 pounds, including 3"l/2 quarts of oil. The outside shell was a cylinder 16=3/4 inches high and 10-3/1^^

= 2 -

inches in diameter, with a short inlet pipe protruding from

the top and an outlet near the top on one side. The lower

part, the oil pan, was detachable^

An inverted truncated cone was welded to the bottom of

the oil pan and, for use, the cup so formed was filled with

oil until the oil surface vjas flush with the upper rim of

the cup. When assembled, the inlet aj.r duct leading down

the center of the shell reached about l /2 inch below the

oil level. According to the manufacturer's description,

the dusty air mixes with the oil and then passes through a series of wire mesh screens where the oil and dust are

captured and allowed to drain back into the outer part of

the oil pan. Here, the dust settles to the bottom and the

clean oil flows over into the inner cup to be entrained

again by the air streams By this process the air cleaning

medium, the wire mesh, is continuously scrubbed as it cleans

the air. The screen elements serve as a trap for the airentrained oil, rather than as a simple filter for the dust.

The air cleaner was connected to a ^-Inch test duct

through which air was drawn by means of an exhaust blower.

The air flow rate through the air cleaner could be adjusted

in a wide range by a valve installed in the test duct between blower and air cleaner. The air flow rate was measured with an orifice flow meter designed in accordance with

A.S.M.E,. Research Publication, "Fluid Meters, Their theory

and Application." The orifice flow meter was equipped with

a water-filled U-tube manometer ' and an inclined gage connected in parallel. The latter was used to obtain more

precise measurements at low air flow rates and was closed

off at higher air flow rates when readings were taken on

the U-tube manometer.

For each test run, a measured amount of dust was placed

in a small hopper which fed the groove of a turntable to a

predetermined level. This turntable was mounted on a variable speed Graham transmission and the test dust was drawn

from the groove by a high pressure aspirator which broke up

most of the agglomerations and supplied the dust to the open

inlet of the test duct. By changing the speed of the turntable, the dust feed rate could be varied in the range from

zero to 30 grams per minute to provide the desired dust

concentration in the test duct.

The dust used was classified air cleaner test dust produced by the A.C. Spark Plug Division of General Motors

Corporation. Both the "fine" and the "coarse" types of dust
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were used and a few test runs were made with a mixture of

50^ of each of the two kinds.

The efficiency of the test specimen was determined by

drawing equal volumes of air out of the test duct upstream

and downstream of the test specimen. By using identical

sampling nozzles Installed at the center of the duct and

adjusting each sampling air flow rate to produce ’’isokinetic” flow in the duct and nozzle, it was assured that

the dust concentration in the samples was representative of

that in the main dust. "Isokinetic" sampling is obtained

when the air flow rate, in feet per minute, in the entrance

to the nozzle is equal to that in the main test duct at the

entrance to the nozzle.

The sampling air flow rates were measured with two

identical orifice flow meters which had been previously

calibrated with a gas meter. The manometers o,f these flovj

meters were mounted on either side of a graduated scale to

I’acilitate the adjustments for maintaining a constant

sampling air flow rate during each test.

The sampling air was drawn through an absolute filter

of glass fiber paper whose smallest fibers were about 0»3

micron thick. Tests of the air cleaning efficiency of

similar paper by the Atomic Energy Commission indicated

that such paper retained more than 99 <>99 per cent of all

particles of O.3 micron size and larger. These glass fiber

papers were, therefore, selected as absolute filters for

the air sampler, and the dust collected on these filters

was determined by weighing the papers before and after each

test to the nearest 0.1 milligram.

The efficiency of the air cleaner was ca3.culated from

the formula e x 100

where; E = filtering efficiency, per cent,

U = weight increase of upstream sampler,

D = weight increase of downstream sampler.

The validity of tills test method was ascertained by

operating the test duct without an air cleaner and determining that the amount of dust collected by both samplers

was equal. Further, in every test run, it was checked that

the weight increase of the upstream sampler was close to the

anjount of the total dust introduced into the test duct multiplied by the ratio of the sampling air flow to the total

air flow.
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-k3 . TEST PROCEDURES AND OBSERVATIONS

The first series of tests was made to determine the

dust holding Jcapaci ty, the pressure loss, and the efficiency of the test specimen at its Resign air flow rate of

315 cfm by using both types of the c^ssified test dust and

also a mixture of $0fo of each* Approximately 50 grams of

dust were introduced into the test duct during each of 2 b

individual test runs. Table 1 shows the results of these

tests arranged in groups; of two to six runs of the same

type of dust. It will be noted that the pressure loss does

not increase consistently, in one case even showing a

decrease although 100 grams of dust were introduced 1 into the test specimen. This fluctuation was of a magnitude of up to ±0,1 inch W.G, and was probably caused by the

change of viscosity of the oil and air due to the change of

temperature in the laboratory. Figure 1 shows the curves of

least mean distances of the points of observation. The

pressure loss increased from 7 oQ 7 inch W.G. to 9 «I|5 inch

W*G. , as the filter was loaded with a total of 1379*8 grams

of dust. The filtering efficiency averaged 99 per cent for

coarse dust and dropped little due to the Increasing filter

load. The efficiency observed for fine dust was 95 per cent

at the beginning of the test and dropped to 6b, 3 per cent

when the filter was fully loaded. The efficiency for the

mixture of ^0% fine and coarse dust appears well in between

those of the two test dusts used alone,

TABLE 1

Pressure Loss and Efficiency at

Increasing Dust Load

No.

of

Tests

Dust

Cum. Load

Type g

Air Plow

Rate

CFM

Pressure

in. W

Start

Loss

,G,

End

Efficiency

6 50/50 276,8 315 7.67 8,07 97 .

5

2 Fine 377.1 315 8,15 8,07 95.0

2 Coarse 1* 77 . Ij 315 8,11 B.35 99 . 14 2 Fine 577.6 315 7.95 8.143 94.6

2 Coarse 677.9 315 8.35 8,82 99.1

2 Coarse 77 b ,

2

15b 2.91 3-07

3 Coarse 92b ,

6

315 boll 9.37 99.0

3 Fine 1079.0 315 80 43 8,98 94.2

3 Coarse 1229 0I4 315 8,90 9.29 9 bc 8

3 Fine 1379,

b

31s 8,98 9.1*5 88,3

ipSiSiBiSiSvJ:

5rs.m

5

°

The pressure loss of the test specimen at various air

flow rates from 100 cfm to 3?0 cfm was determined. These

measurements were made at about room temperature with a

clean filter and motor oil SAE 30 and are summarized in

Table 2 below:

TABLE 2

Pressure Loss at Air Plow Rates from

100 cfm to 370 cfm

Air Flow Rate, cfm Pressure Loss in. W.G.

100 l .«9

130 2.13

200 3.51*

222 k -33

278 5.63

293 60 01

315 7.87

370 10.21}

The upper curve of Figure 2 shows the curve of

the least mean distances plotted from these points of obser*

vation. The lower series of curves of Figure 2 represent

the efficiency of the test specimen at different air flow

rates according to the data shown in Table 3« The values

for the 315 cfm air flow rates are taken from Table 1« The

efficiency of 97*2^ of the mixture of $0% fine and coarse

dust was taken from the extrapolated value of Figure 1 at

a dust load of i|00g® The points of observation shown in

Figure 2 represent average values of the test results shown

in Table 3 » It will be noted that the change of the efficiency at the dust loads used in this series of tests was

insignificant as indicated by the small slope during the

first part of the load capacity test.

To determine the effect of tilting, a series of tests

was made in which the test specimen was tilted alternately

15 , 30 and [15 degrees. Table I4 shows the results obtained

when the air cleaner was tilted 15 degrees and 30 degrees

from the vertical. By comparing these values with Table 1,

it will be noted that the pressure loss at 1^ degrees

tilting is about 1 inch W, G, higher than in the vertical

position and at 30 degrees tilting the difference is about

2 inch W, G.. at corresponding dust loads. The efficiency

observed at these angles was practically the same as

observed when the test specimen was in a vertical position.

At a tilting angle up to 30 degrees, no carry-over of oil

v/ AI^FWr RA'PE

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: j idiktk

-=6

was noticed. However, when the test specimen was moved to

degree position, it was noticed that oil was carried

over and no test of the efficiency was conducted in this

position

TABLE 3

Pressure Loss and Efficiency at Different

Air Flow Rates

Air Flow Pressure Loss Dust

Rate In, W o G

Efficiency Cum, Load

CFM Start End i Type g

100 1.89 1.97 98.1 ; Coarse 50.1

100 1.89 1.97 88.3 Pine 127 .it 100 1.97 1.97 97.6 Coarse 276.3

100 1.97 1.97 86.7 Pine 301.4

100 1.89 1.97 97.8 Coarse 326.6

200 4.02 4.17 98.6 Coarse 152.5

200 4.10 4.10 89.3 Pine 202.8

200 4.02 It. 13 97.8 Coarse 227.9

200 4.02 4.10 89.4 Fine 253.0

315 8.15 8.07 95.0 Pine 377.1

315 8.11 8.35 99 .it Coarse lt77.1i

315 7.95 8.43 94.6 Pine 577.6

315 — — 97.2 50/50 400.0

TABLE 4

Tilting of Filter at 315 c fill Air Flow Rate

Pressure Loss Dust

Degrees in

W.G. Efficiency Cum. Load

Tilting Start End Type g

15 8.86 9.06 99 .it Coarse 377.6

15 8.90 8.98 94.4 Fine 426.7

30 9;t(5 10.31 98.3 Coarse 476.8

30 9.37 9.65 9lt.l Fine 427.0

DISCUSSION AND CONCLUSIONS

The tests conducted with the Donaldson oil bath air

cleaner showed average efficiency values of 99 per cent on

A.C . Spark Plug Division air cleaner test dust "coarse" and

94 per cent on "fine" dust. The efficiency decreased with

the dust load while the pressure loss increased f rom 7o87
Lrc'U
in* W.G. when the filter was clean to 9oli5 in* WoG* when the

filter was loaded with 1379«.8 grams ( 3 «Ol4 lbs,) of dust*

This dust load was considered as the dust holding capacity

because of the noticeable loss of efficiency and the sharp

increase of pressure drop at this point* Tilting the air

cleaner up to 30 degrees did not appreciably affect its

performance

The dust load so established corresponds to a service

period of 7«3 hours of continuous operation in a dust con>= centration of 10 mg/cu ft at the design air flow rate of

315 cfm.

The performance characteristics of this air cleaner

are among the best so far observed in this laboratory. The

dust holding capacity in particular is superior and may^, in

service, suffice for a 1000 hour operation under normal

conditions.

The test specimen was built of steel for rough use on

tractors and weighed 27 pounds. This weight could prO“

bably be cut in half by constructing the air cleaner

entirely of light weight metal. The use of this type air

cleaner for helicopters, then, appears feasible since the

desired maximum three per cent power loss will not be much

exceeded as indicated by the following computation? The

315 cfm design air flow rate is appropriate for a 2I4 O H, P,

engine which would have a total lift of approximately

2l|00 pounds, so that 13 - 1/2 pounds weight of the air

cleaner would require 0*5^ per cent of the total power.

Since a power loss of approximately three per cent of the

maximum engine output is expected for each 10 in, ¥,G,

pressure loss in the 'air cleaner, the average 8,5 W*G,

pressure loss observed on the test specimen would produce

215 cent power loss; this adds up to a total loss of

3.06 per cent.

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