0 pah F;\e TO* a~q-23 

A mining research contract rep.qrt 

AUGUST1983 

REVERSE PERFORMANCE 

CHARACTERISTICS OF 

MAIN MINE FANS 

Contract 50308044 

Engineers International, Inc. 

BUREAU OF MINES 

UNITED STATES DEPARTMENT OF THE INTERIOR Fvzy wrw7 6, %A. -..A+ A 
DISCLAIMER 

The views and conclusions contained in this document are those 

of the authors and should not be interpreted as necessarily representing the official policies or recommendations of The Interior 

Department's Bureau of Mines or the U. S. Government. 

Reference ,to specific brands, equipment, or trade names in this 

report is made to facilitate understanding and does not imply endorsement by the Bureau of Mines, the U. S. Government, or Engineers 

International, Inc. 

ClassBook 

*GPO 7.1-18. 

ENGINEERS INTERNATIONAL, INC. 
Reverse Performance Characteristics of Main Mine 

Fans -- 7.Ar~hor(s) N.F. Dunn, S. Bhattacha-S-T Rajaram 

som - ror 

--- PP-~~. 

9. P.doming 0rf.niration Name and Addross 

Engineers International, Inc. 

98 E. Naperville Road 

Westmont, IL 60559 

REPORT DOCUMEMATiON 

PAGE 

It Sponsoring Organization Name and Address 

Bureau of Mines 

U. S. Department of the Interior 

Pittsburgh Research Center, P. 0. Box 18070 

Pmsbur~h. - PA 15236 

4. mi. and SUMWO 

'- 

15. Supplementary Not2. 3. Recipient's Accession No. 

5 Report Date 

August 1983 

6. 

--- I. Performing OrganIration Rept No. 

1050 10. Proieet/Task/Work Unit No. 

- 

11. ContnctfC) or CranttG) No. 

(a 50308044 

(GI 

13. Type of Report 6 Period Covemd 

FINAL 

5/80 - 4/83 14. 

16. Abstnct (Umit: 200 rods) 

During a mine fire or other emergency, it may be desirable to reverse 

the airflow in order to provide an escapeway or to isolate a fire. Also, 

in colder areas, the airflow may be reversed to prevent ice buildup. When 

reversing main mine fans, the mine operator usually does not know what 

operating characteristics of flow and pressure to expect. Laboratory a~d 

field tests of vane axial main mine fans in the 7- to 9-ft diameter size 

range wese conducted to establish forward and reverse performance characteristics under controlled conditGons and at typical mine installations. 

The data obtained suggest that reverse performance characteristics are 

dependent upon the blade angle and the hub to tip ratio. There is also 

evidence that reverse performance can be predicted for a family of blade 

angles and a given hub to tip ratio. Generally, quantity of air is 30% to 

65% less in reversethanwhen operating in the normal forward mode. 

--- - - - - . -- - - --- - - p--- - 

17. Document Analyls a. Descriptors 1 

Ventilation, Vane Axial Fans, Mines 

b. Identlfterr/Open-Endd Terms 

=. COSATI fi.~d/~~~~ Field 08 /~roup I 

18. Availability Statement 

Unlimited 

Gee ANSI-239.18) See Instructions on Reverse OPTIONAL FORM 272 :C77! 

(Formerly NYIS351 

Department of Cohmeme 

19. Security Class (This Report) 

Unclassified 

20. Security Class (This Page) 

Unclassified 

21. No. of Prges 

65 

22. Price 
FOREWORD 

This report was prepared by Engineers International, Inc., under 

USBM Contract No, 50308044. The contract was initiated under the 

~etal/~onmetal Mine Health and Safety Program. It was administered 

under the technical direction of the Pittsburgh Research Center with 

Mr. E. D. Thimons acting as Technical Project Officer. 

Mr. Alan G. Bolton was the contract administrator for the Bureau 

of Mines. This report is a summary of the work recently completed as 

a part of this contract during the period May 29, 1980 to April 29 

1983. This report was submitTed by the authors in August, i983. 

The work on the project was significantly aided by the contributions of Mr. William Bruce of MSHA Technical Support in Denver, CO; 

Messrs. Ray Schilz and William Meakin of Joy Manufacturing Company; 

and by the mining companies whose personnel were both patient and 

cooperative during field testing. 

This project was conducted under the technical supervision of 

Dr, V, Rajaram, with Mr. Michael F. Dunn as Project Engineer and Vr, 

Swapan Bhattacharya as Staff Engineer, who are the authors of this 

report. Mr. Francis S. Rendorski provided technical supervision 

during Phase I and the initial portions of the Phase I1 field tests. 

Dr. Madan M. Singh provided overall direction for the project. 

4 ENGINEERS INTERNATIONAL, INC 
TABLE OF CONTENTS 

Pane 

REPORT DOCUMENTATION PAGE .................. 3 

FOREWORD .......................... 4 

TABLE OF CONTENTS ...................... 5 

LISTOFFIGURES ....................... 6 

LIST OF TABLES ....................... 7 

1.0 INTRODUCTION ........................ 8 

1.1 Purpose ........................ 8 

1.2 Objectives ....................... 8 

2.0 VANE-AXIAL FANS ....................... 9 

2.1 Characteristics and Use ................ 9 

q.2 Reversal Characteristics ................ 9 

3.0 LABORATORY TEST RESULTS ................... 12 

3.1 AMCAStandards ..................... 12 

3.2 Project Test Facilities ................ 12 

3.3 Test Results ...................... 12 

3.4 Conclusions ...................... 18 

4.0 FIELD TEST PROCEDURE .................... 21 

4.1 Apparatus Required ................... 21 

4.2 Preliminary Data Collection .............. 23 

4.3 Equipment Use ..................... 25 

4.4 Fan Testing Procedure ................. 28 

4.5 Computations ..................... 31 

5.0 FIELDTESTS ......................... 34 

5.1 HineNo.1 ....................... 34 

5.2 Mine No . 2 ....................... 37 

5.3 Mine No . 3 ....................... 41 

5.4 Summary of Field Results ................ 50 

6.0 GUIDELINES FOR REVERSING FANS ................ 54 

6.1 Data Trends from Present Work ............. 54 

6.2 Guidelines ....................... 54 

6.3 Applicability of Guidelines .............. 55 

7.0 CONCLUSIONS AND RECOMMENDATIONS ............... 56 

7.1 Conclusions ...................... 56 

7.2 Recommendations for Future Work ............ 56 

8.0 APPENDIXA ......................... 57 

ENGINEERS INTERNATIONAL. INC . 
LIST OF FIGURES 

Figure Page 

1 . Vane-axial fan ...................... .PO 

2 . Definition of blade angle .................. 1 B 

3 . AMCA laboratory standard for testing fans .......... 13 

4 . Laboratory fan testing arrangement ............. 14 

5 . Test data sheet (from Joy Manufacturing Co.) ....... -15 

6 . M96-43 reverse performance summary at various blade angles .. 16 

7 . M96-58 reverse performance summary at various blade angles ..i 7 

Fan average performance versus blade angle for laboratory 

data ........................... 20 

Pitot tube ......................... 22 

Field altimeter ...................... 24 

Pitot tube traverse plane ................. 30 

Fan installation at Mine No . l ............... 3% 

General ventilation arrangement. Mine No.2. . .. ..... 38 

Schematic of fan installations in Mine No.2 ........ 39 

Schematic of fan installations in Mine No.3 ........ 46 

Computation of total pressure from characteristic curves . . 49 

Fan average performance versus blade angle ......... 52 

Fan performance with 10' blade angle ............ 58 

Fan performance with 20' blade angle ............ 59 

Fan performance with 30' blade angle ............ 50 

Fan performance with 35' blade angle ............ 61 

Fan performance with 12' blade angle ............ 62 

Fan performance with 22O blade angle ............ 63 

Fan performance with 32' blade angle ............ 64 

Fan performance with 42' blade angle ............ 65 

ENGINEERS INTERNATIONAL. INC . 
LIST OF TABLES 

Table Title -5 

1 . Calculated and laboratory test data comparison ... 19 

2 . Performance comparison for fan 1. ......... 36 

3 . Performance comparison for fan 2 .......... 40 

4 . Performance comparison for fan 3 .......... 42 

5 . Performance comparison for fan 4 .......... 43 

6 . Performance comparison for fan 5 .......... 44 

7 . Performance comparison for fan 6 .......... 47 

8 . Performance comparison for fan 7 .......... 48 

9 . Field test data summary .............. 51 

ENGINEERS INTERNATIONAL. INC . 
1.0 INTRODUCTION 

Ventilation is an essential part of any underground mining 

operation. The principal functions of the ventilating air consist of 

providing oxygen to persons and equipment, dilution of gaseous pollutants, transport of dust, and cooling (or heating). The mine fan 

supplying the ventilating air may be either a forcing or an exhausting type and, under normal operating conditions, is run in one direction only. 

During a mine fire or other emergency, however, it may be desirable to reverse the airflow in order to provide an escapeway or to 

isolate a fire. Additionally, ice buildup in a shaft can be detrimental and many mines that employ vane-axial fans reverse their 

airflow during winter in order to course warm exhaust air (heated by 

the mining equipment or natural rock temperature) through the shaft 

and adits thereby limiting such buildups. However, when a mine 

reverses its airflow by electrically reversing its main mine fan, it 

usually does not know what operating characteristics of flow and 

pressure to expect. The laboratory and field testing in this project 

helped provide such answers. 

1.1 Purpose 

The project was accomplished in two phases. The purpose of 

Phase I was to test and establish main mine fan characteristics in 

the reverse direction, under laboratory conditions. To carry out 

this work, EI subcontracted with Joy Manufacturing Company of New 

Philadelphia, Ohio, to test two (2) common main mine fans each of 56- 

in. (2.4-m) diameter but with different hub to tip ratios. The 

laboratory testing was conducted within the first two weeks of March 

1981. 

The purpose of the second phase was to estimate reverse characteristics of mine fans under actual mining conditions. To that end, 

seven (7) fans were tested at several mines around the country. 

1.2 Objectives 

The objective of the laboratory testing was to develop performance data in forward and reverse directions under reasonably controlled conditions. From these data, reverse fan performance estimates were made. The laboratory data also served as a base for 

comparing results of similar fan testing in the field. A secondary 

benefit from developing these data was that they served as a good 

comparison to the calculated performance scaled from smaller fans 

tested in the laboratory (by means of fan law relationships). 

The objective of the field testing was to verify the laboratory 

results by testing under actual mining conditions. Tt was anticipated that multiple fan installations, air doors and regulators, and 

auxiliary fans would affect reverse fan performance and its predictability. Consequently other parameters not found in the laboratory 

would need to be considered when evaluating field tests. 

8 ENGINEERS INTERNATIONAL, INC. 
2.0 VANE-AXIAL FANS 

2.1 Characteristics and Use 

Vane-axial fans, first developed in the 1930s, are the most 

common type of fans used in mines today. In order to cause airflow 

these fans create a pressure difference in an airway. Vane-axial 

fans accelerate the air through the fan, which rebults in both a 

pressure and velocity increase. Fans must supply enough pressure to 

overcome system pressure head losses and deliver the required air 

quantity. Therefore, one reason for vane-axial fan popularity is the 

versatility of adjustment to a wide range of performance requirements. These fans basically consist of a cylindrical impeller within 

a fan housing. The impeller has air-foil blades causing airflow 

through the fan axially, that is, paraiiei to the rotation axis. 

Figure 1 illustrates the basic design of a typical vane-axial 

fan. The inlet bell and outlet cone help to improve the efficiency 

of moving air by reducing turbulence. The main fan parts are the 

blades, rotor or hub, diffuser tail, straightening vanes, and drive 

shaft . 

The hub to tip ratio, which will be referred to often, is simply 

the ratio of the hub radius (distance from the fan center to the base 

of the blade) to the tip radius (distance from the fan center to the 

blade tip). The vane-axial fans tested have variable pitch blades 

which can be set to a particular angle. An illustration of the blade 

angle setting is shown in Figure 2. 

Blade settings on fan manufacturers' characteristic curves are 

often expressed by a number which corresponds to a blade angle. The 

number and corresponding angle varies among manufacturers, hence 

reference is made to blade angle rather than blade setting throughout 

this report. 

2.2 Reversal Characteristics 

Mines often use vane-axial main fans because sf fl.exibility in 

installation and performance, and lower power consumption. However, 

these fans perform very inefficiently when reversed, their output 

being reduced considerably. 

Problems involved with reversed main fans go beyond the limitations of the fan itself. With the main mine fans reversed, auxiliary 

fans in the mine could still be circulating air in their normal 

direction, adding increased resistance to the main fans. After 

reversal of the main mine fans, the previously established airflow 

movement in the mine must be overcome which could take some time to 

reach steady-state flow. Any natural ventilation effect present can 

either aid the fan or add increased resistance depending on conditions. Thus, the field testing of main mine fans involves many other 

factors that could influence performance. 

9 ENGINEERS INTERNATIONAL, INC. 


3.0 LABORATORY TEST RESULTS 

Laboratory tests of vane-axial fans, in both forward and 

reverse, were conducted at the Joy Iianufacturing ~ompany's facilities 

in Ohio. Test procedures and results are provided in this secti~n of 

the report. 

3.1 AMCA Standards 

The Air Moving and Conditioning Association, Tnc. (AMCA) has 

developed standards for testing fans which include testing equipment 

and testing facilities'. The purpose of such standards is to assure 

uniformity of fan ratings. Figures 3a and 3b illustrate test facilities according to AMCA Standard 210-74 for laboratory testing of fans 

in both forward and reverse directions. 

3.2 Proiect Test Facilities 

Figure 4 shows the fan test arrangement at Joy Manufacturing 

Coppany (Joy). Two fans were tested at 720 rpm for four different 

blade angles in both the forward and reverse directions. A minimum 

of six determinations were taken at each blade angle. For each 

determination, readings of pressure heads, power input, rpm, wet and 

dry bulb temperature, and barometric pressure were recorded. All 

information was recorded on standard data sheets similar to the one 

shown in Figure 5. 

3.3 Test Results 

A series of performance curves, for each fan tested, are presented in Appendix A, showing forward and reverse performance (with 

reverse flow shown as a percentage of forward flow), and input horsepower for each blade setting. Tn addition to these fan curves, 

reverse fan performance summary curves showing the relationship 

between reverse and forward flow, for each fan and blade angle, are 

presented in Figures 6 and 7. Data points for these figures have 

been obtained from the corresponding performance curves included in 

Appendix A. 

3.3.1 Calculated Versus Test Data 

To accurately establish the percent of reverse flow (as compared 

to forward performance), it was decided that the forward performance 

should first be established, rather than accept the data presented in 

Joy's catalog. 

The catalog data were found to be reasonably accurate when compared to the test results. Nevertheless, the curves presented in 

this report are derived from actual tests and not taken from the mine 

'~ir Moving and Conditioning Association, Inc. Laboratory Methods of 

Testing Fans for Rating Purposes. AMCA Standard 210-74, ASHM 

Standard 51-75, 1975. 

1050-3 

R1050A l2 ENGINEERS INTERNATIONAL, INC. 
I I I 

-----I 

1 0 D3 M IN . ------t1 I 

F -'L 

I 

I FAN 0 f I 

PITOT TUBE 

STRAIGHTENER TRAVERSE 

\ 

TRANSFORMATION PIECE 

(a) Pitot traverse in outlet duct 

TRAVERSE 

TRANSFORMATION PlECE 

(b) Pitot traverse in inlet duct 

FIGURE 3. - AMCA laboratory standard for testing fans. 
- REVERSE FLOW FORWARD FLOW - - 

\ I 

I - 

- 

- 

-- I - 

- 

- 

- SHAFT I - 

- 

- TO MOTOR 4 - 

REVERSE FLOWING FORWARD FLOWING 

TRAVERSE TRAVERSE 

FAN PLANE PLANE 

\ 

AIR STRAIGHTENERS 

BELL HOUSING 

LOCATION 

SCAL

I in =I

FIGURE 4. - Laboratory fan testing arrangement.. 
DATE -- 

SHEET -- OF SHEETS 

BLOWING OR EXHAUSTING TEST - -- -. 

12 . 0.075 , 

13 Density 

2 

3 

4 

5 

15 Duct _ Ft2 Duct _ 16 Area Ilia . 17 

18 Duct Friction P 

19 - - 

20 P Correction 

21 

2 2 SHUTOFF 

AMPS - 

23 

20 VOLTS - RMP 

TOTAL WATTS - avc 1096 . . . . (1) Vel - (Av. P, xiAir 

(2) Vol - Vel x Duct Area . . . . . . - 

(3) pt - Av. Pa + Av. Pv . . . . . --- Mu ,G, Sneed RPP 

(6) PV - Av. Pv x 0.075 -- "W.C. VoI. CIT EiiK ......- (5) Pvl - Pv x P Correction . . . . - "W.G. Pt "\J.c. 

"W.C.. Pv 'IN.(:. (6) pt - pt x !?L!&!? + (pv x pf) . . - - Dens. 

(7) P, = Pt - P" . . . . . . . . . = 

(8) AHP - 't . . , . , . . . . = I 

(9) IHP - ~aft?!~~ 0.0751Dens. . . . . = IHP 11fP .---+- 

(10) BHP - IIIP x c~C:,,~~~ _ , . . ~11~ ~IIP k--+--y --, t-- 

(11) EFF~,~,~ = (AI{PIBHP) x 100 . . . = I 1 I 4 

CONDITION 

TEST 

(12) EFFstatic = EFFt x (Ps/Pt) . . . - stn~ irz I 

/ 

(13) EFF - (AHPIIHP) x 100. . . a_- '" AWATTS 

FIGURE 5. - Test data sheet 

(from Joy Manufacturing Co,), 

AMPS VOLTS RPFl 


fan catalog. Table 1 is the result of a random comparison between 

calculated and laboratory test data for the M96-58 fan at ckr tested 

blade angles. The difference between the corresponding calculated 

and tested data points is consistently less than 10%; often less than 

5%. 

3.3.2 Forward versus Reverse Performance 

Analysis of Figures 6 and 7 reveals an hzv~ra~ rC2l;tioi'!shi~ 

between performance and corresponding blade angles. However, due to 

limitations of data, the applicability of this relationship to other 

types of fans and hub to tip ratios is not known. 

Analysis was carried further by plotting the average reverse 

percent of forward performance, from curves in Figures 6 and 7, 

against blade angle, as shown in Figure 8. The results show s well 

defined curve for each hub to tip ratio tested. Adopting these 

curves to fans of other hub to tip ratios may be premature at this 

time, although, the data strongly suggest that such a relationship 

may exist for a given hub to tip ratio. 

3.3.3 Pressure and Volume 

In general, the results indicate that fan static pressure CP j 

changes as the square of the volume (Q): S 

For example, if the volume in the reverse direction is reduced ro 60 

percent of the forward value, the pressure available from the fan 

will be reduced to about 36 percent. This relationship has been 

reported in previous studies of smaller fans2. 

Laboratory testing has shown that reverse flow is not cl const;int 

percentage of forward flow but depends upon blade angle and hub .so 

tip ratio. In addition, the fan law governing the pressure.-volume 

relationships in vane-axial fans appears to be valid rsr reverse 

flow. Field testing of main mine fans was undertaken to assess the 

validity of these generalizations over a wider range of hub to tip 

ratios. The results are presented in the f0110wi~g sections. 

--- .- ----..--- 2~estern Engineering and Manufacturing Company. Product 1nf ormati%% 

Handbook. Bulletin No. H-78, 1978, p. 7.18. 

ENGINEERS INTERMATIOI!AL, IliiC. 
TABLE 1. - Calculated and laboratory test data CCJIIIP~~~.~~G~? ---- fyc.lcy Model M96-58 fan in forward mode 

Blade Angle, 

degrees (rad) 

Volume, cfn (m3/s) - -- 

Calculated lleasurec -- 

104,000 (49.1) 105,090 ($9.5) 

130,000 (61.4) 140,972 (6t.5) 

185,000 (87.3) i4bY38E (92.71 

212,000 (100.0) 230,416 (108.79 

27C,OOO (127.4) 270,278 (12765k 

300,000 (141.6) 315,000 (148.6) 

310,000 (146.3) 301,386 (142.2) 

365,000 (172.2) 359,722 (1 70.0) 

19 ENGINEERS INTERNATIONAL.. INC 

4.0 FIELD TEST PROCEDURE 

Field tests were conducted on seven (7) main mine fans located 

in three (3) mines in the United States. Details of the field test 

procedure used in these tests is provided in this section. 

4.1 A~~aratus Reauired 

The following test equipment were used: 

pitot tube 

Magnehelic gauge 

sling psychrometer 

electric thermometer 

altimeterlbarometer 

stroboscopic tachometer. 

4.1.1 Pitot Tube 

The pitot tube is a standard air velocity instrument, especially 

suited for measuring high velocities encountered with main mine fans. 

The pitot tube is made of two concentric tubes, one inside the other, 

with one end bent at a right angle and the other end provided with 

fittings for each tube, to which a pressure gauge or manometer can be 

attached (Figure 9). The inside tube receives the total pressure of 

the airstream and the outer tube, closed on the end, receives the 

static pressure of the airstream through a number of pinholes set 

back from the end. When the leads from the pressure gauge are 

attached to the pitot tube, the gauge registers the difference in 

pressure between the inner and outer tubes, namely, the velocity pressure. With one lead from the pressure gauge open to the atmosphere, 

connecting the other lead to the outer tube yields static pressure, 

and to the inner tube gives total pressure. 

Pitot tubes are commercially available in a wide range of sizes. 

Since the diameters of the fans tested were between 7 to 9 ft, a 5-ft 

long pitot tube was used to ensure that the pitot tube was of sufficient length to reach all necessary measuring points in the air duct. 

4.1.2 Magnehelic Gauge 

The Magnehelic gauge was used with the pitot tube for the pressure measurements. This aneroid type gauge is suitable for measurement of the relatively low pressures encountered in ventilation 

studies. Taking a pressure reading simply involves connecting the 

high pressure lead from the pitot tube to the high pressure inlet 

connector on the gauge, the low pressure lead to the other connector, 

and reading the position of the pointer on the dial. The principal 

advantages of this type of gauge over the more commonly used U-tube 

ENGINEERS INTERNATIONAL, INC. 

manometer are easy reading, portability, and absence of fluid which 

leads to easier maintenanc-e and use in any position. 

4.1.3 Sling Psychrometer 

Humidity measurements were taken using the sling psychrometer, 

which consists of two thermometers mounted side by side on a rigid 

frame. One of the thermometers, referred to as the wet bulb, is 

covered with a wick of muslin cloth moistened with distilled water. 

A handle is provided at one end, which is used to rotate the instrument to increase the rate of water evaporation from the wick causing 

a cooler temperature reading. Based on the dry- and wet-bulb read= 

ings, the relative humidity of the air can be calculated. 

4.1.4 Electric Thermometer 

The electric thermometer was used to measure the air temperature 

within the fan ducting by inserting a temperature sensitive probe 

through a hole in the ducting. 

4.1.5 Altimeter 

The American Paulin System altimeter was utilized to measure 

barometric pressure at the test sites. This precision instrument 

works on the principle of aneroid barometers but is free from most of 

the instrumental errors inherent in the ordinary aneroid. Figure 10 

shows the component parts of a Micro-series altimeter having an 

accuracy to the nearest foot. 

4.1.6 Stroboscopic Tachometer 

Fan speed was measured with a stroboscopic tachometer. This 

device emits a flash of light having a high intensity but short duration. An electronic pulse generator controls the frequency. The 

unit is hand held, and flashes are bright enough for use in daylight. 

The fan speed is related to the frequency of the strobe, and can be 

read directly on a scale. 

4.2 Preliminary Data Collection 

Before fan testing, some preliminary data were gathered at each 

mine site. First, the mine map was studied in detail with special 

emphasis on the overall ventilation scheme. Pertinent data included: 

location of shafts and adits 

location and layout of intake and return 

airways 

distribution of seals and stoppings 

a position of main mine fans 

23 ENGINEERS INTERNATIONAL, INC. 
RESET CONTROL 

(raise and turn) 

'GRADUATED SC 

BALANCE MARK \ 

BALANCE INDICATOR 

ALE 

FIGURE 10. - Field altimeter. 
a position of auxiliary fans and their 

capacities 

location and type of ventilation doors 

prior mine experience on fan reversal. 

Where a mine had more than one operating fan, the possible influence 

that the reversal of one fan would have on the others was examined 

before planning the test sequence. For instance, if two fans were 

operating in parallel, both would be reversed simultaneously, while 

fans located on two corners of the property could be reversed separately. 

Second, specific information of the fan installation was 

recorded. This included knowledge of: 

a type of fan - blowing or exhausting 

a position of the fan - vertical or horizontal 

fan ducting 

accessibility 

a location of access holes for pressure 

survey purposes 

location of guide vanes. 

Finally, fan details were obtained from fan manufacturers, mine 

personnel and name plates mounted on the fan assembly. Briefly, this 

included : 

fan performance curves 

dimensions of the component parts of the 

entire fan installation, such as, blade tip 

diameter, hub diameter, duct diameter and 

length, blade angle, and bell angles. 

drive motor specifications. 

4.3 Equipment Use 

4.3.1 Pressure Readings 

Reference marks were made on the pitot tube corresponding to the distances of the measurement points from the circumference of the air 

duct. The pitot tube was introduced through an access hole in the 

ducting, and was positioned at each measurement point with the nose 

of the tube pointed upstream. The Magnehelic gauge was connected to 

the pitot tube by means of two flexible tubes. By making the appropriate connections, velocity pressure, static pressure and total 

pressure were measured. This process was repeated until measurements 

at each traverse point were completed. 

ENGINEERS INTERNATIONAL, INC. 
Since the airflow at the traverse plane was never steady, pressure readings indicated on the Magnehelic gauge fluctuated considerably. Each pressure reading was, therefore, averaged on a time 

weighted basis. 

The following precautions were observed during the test: 

the pitot tube was checked before use 

to ensure that it was thoroughly clean 

the Magnehelic gauges were calibrated prior 

to testing 

pitot tube perpendicularity to the airstream 

was closely watched 

care was taken in connecting the pitot tube 

to the Magnehelic gauge with regard to 

anticipated pressures, that is, whether the 

pressures were negative or positive and 

whether the scale was appropriate 

kinks in the flexible tubing were avoided. 

4.3.2 Measurement of Temperature and Humidity 

The wet bulb of the sling psychrometer was soaked with distilled 

water before proceeding with the temperature readings. With the 

handle held firmly, the instrument was rotated at an uniform rate 

until both the wet- and dry-bulb readings remained constant. The 

readings were repeated after 5-10 minutes. Wet- and dry-bulb temperatures were recorded at the time of each fan test. 

While testing fans in the exhausting mode, wet- and dry-bulb 

readings of the intake air were taken by inserting the psychrometer 

through one of the traverse holes into the duct. 

The following precautions were observed in the course of making 

the temperature measurements: 

when the thermometers were read, neither the 

frame nor the thermometers were allowed to 

come directly in contact with the hand 

the wick on the wet-bulb was thoroughly 

wetted after making sure that it was clean 

and closely fitted 

both thermometers were read with minimum 

time delay 

the psychrometer was held away from the body 

or any other source of heat 

the thermometers were calibrated before the 

test to ensure that the readings were accur0 

ate to 2 F. 

ENGINEERS INTERNATIONAL, INC. 
4.3.3 Measurement of Barometric Pressure 

The following procedure was adopted for the measurement of barometric pressure: 

a) At the place of known elevation: 

a the altimeter was placed on the benchmark 

a approximately 10-15 minutes are allowed 

to elapse for the altimeter to adjust to 

the ambient temperature 

a the altimeter was leveled by means of the 

circular level 

a the instrument was balanced by bringing 

the balance indicator needle to the 

center of its run by turning the pointer 

knob 

a the pointer needle was set at the elevation of the benchmark by turning the 

Reset Control knob. 

b) At the test site: 

a the altimeter was placed in the airstream 

for exhausting fans if possible, or 

placed outside the airstream for blowing 

fans 

a the altimeter was allowed to adjust to 

ambient conditions and leveled 

a the instrument was balanced by means of 

the pointer knob 

a the altitude and pressure as indicated by 

the pointer was recorded. 

The following precautions were taken to ensure accuracy: 

a the altimeter was protected from the 

direct rays of the sun 

a care was taken when placing the altimeter 

at the test site so that the temperatures 

at the top and bottom of the altimeter 

did not vary significantly 

a the instrument was always balanced from 

the positive side of the window 

a parallax errors were avoided while reading the position of the pointer needle 

a since two observers seldom obtain exactly 

the same reading from a particular altimeter, one person was assigned to the 

j ob 

ENGINEERS INTERNATIONAL, INC. 
a the test value of barometric pressure 

was determined by averaging measurements 

made at the beginning and end of the test 

period. 

4.3.4 Measurement of Fan Speed 

Fan rpm was estimated using a stroboscopic tachometer. The 

basic requirement for this test is that the fan blades should be 

visible by the strobe light. Where the fan installation was vertical, measurement of fan speed was not possible. 

The stroboscope was held before the rotating fan and the strobe 

light allowed to shine on the blades. The adjusting screw was turned 

until the fan blades appeared stationary. Knowing the approximate 

range of rpm from manufacturer's data, the fan speed was measured and 

recorded. 

4.4 Fan Testing Procedure 

The fan test at any field site was a two-step operation - first 

with the fan operating normally (forcing or exhausting, as the case 

may be) and later upon reversal. Fan reversal was normally achieved 

by interchanging the electrical connections. Sufficient time was 

allowed to elapse after reversal for the entire airflow through the 

mine to reach steady state. 

The operations performed during each step of the test were identical and basically consisted of determining the fan flow rates and 

pressure heads developed, by means of a pitot tube traverse. Concurrently with the pitot tube traverse, measurements were taken to 

determine air density. This included wet- and dry-bulb thermometer 

readings, and barometric pressure. In addition, with the fan in 

operation, voltage and current readings were taken to determine fan 

power input. Finally, the fan speed was measured by means of the 

stroboscopic tachometer. All information was recorded on field data 

sheets. Details on the various parts of the test follow. 

4.4.1 Pitot Tube Traverse 

4.4.1.1 Location of Traverse Plane 

Choice of the traverse planes for the pitot tube survey were 

made judiciously to ensure accuracy. Guidelines for location in the 

duct include3 : 

'~ir Moving and Conditioning Association, Inc. A Guide to the Measurement of Fan-System Performance in the Field. AMCA Fan Application Manual, Part 3, Publication 203, 1976. 

ENGINEERS INTERNATIONAL. INC. 
a "the velocity distribution should be 

uniform throughout the traverse plane. It 

is recommended that the uniformity distribution be considered acceptable when more 

than 75% of the velocity pressure measurements are greater than 1/10 of the maximum 

measurement" 

the airstream should be as nearly at right 

angles to the traverse plane as possible, 

although a 10 degree (0.17 rad) deviation 

is acceptable 

a the cross-sectional shape of the airway 

in which the traverse plane is located 

should be uniform 

a the traverse should be made 7.5 duct 

diameters or more downstream from any 

major air disturbance such as a bend or 

constriction 

a the traverse plane should be located such 

that the effect of leakage between the fan 

and the plane is minimized 

a the location of the traverse plane on the 

inlet side of the fan should be at a 

distance not less than 112 of the fan 

inlet diameter. 

In general, most mine fans are equipped with access holes 

for fan testing, and these were considered adequate for the purposes 

of the test. 

4.4.1.2 Selection of Measuring Points 

Selection of measuring points on a traverse plane were based on 

the principle of equal area traversing, that is, the cross-sectional 

area of the duct was divided into equal areas with several sampling 

points within each area. Figure 11 shows the position of traverse 

points in a circular air-measurement section for a 5-area, 20-point 

traverse. Due to the difficulties in conducting pitot tube surveys 

in the field where conditions cannot be easily controlled, a 20-point 

traverse was chosen in preference to the 24-point traverse employed 

during laboratory testing. 

4.4.2 Fan Power Input Determination 

Typical motor performance data was used to determine the power 

input to the fan. These data are referred to as typical because a 

good correlation exists between the measured values and the 

ENGINEERS INTERNATIONAL, INC. 
)+- 0.342 dir. 4 

FIGURE 11. - Pitot tube traverse plane. 
corresponding values supplied by the fan manufacturer. The field 

measurements simply consisted of taking current and voltage readings, 

once with the fan operating in forward and once in reverse. If 

significant fluctuations were noted, several observations were made 

and an average value calculated. 

4.5 Computations 

4.5.1 Air Density 

The following equations were used to calculate the density of 

air: 

where, = partial vapor pressure, in. Hg, (inches of mercury, Pp f rorn tables ) , 

p = density of air, lb/ft3, 

tw = wet-bulb temperature, OF, 

td = dry-bulb temperature, OF, 

pb = barometric pressure, in. Hg, 

and Pe = saturated vapor pressure at t in. Hg. wY 

Alternatively, special charts are available to determine the 

approximate value of air density based on t w' t d and p values 

obtained in the field. b 

4.5.2 Conversion Calculations 

The following formulas were applied to convert the field results 

to the speed and density conditions of the fan performance ratings: 

31 ENGINEERSINTERNATIONAL, INC. 
where, P = fan static pressure, in. W.G. (inches of water 

S gauge) , 

P = fan velocity pressure, in. W.G., v 

Pt = fan total pressure, in. W.G., 

N = fan speed, rpm, 

p = air density, lb/ft3, 

and subscript c designating the value of the parameters after being 

converted to specified conditions. 

4.5.3 Fan Quantity 

The average velocity at the plane of traverse is given by: 

where, V = average velocity, fpm, C 

'v = fan velocity pressure converted to specified C conditions, in. W.G., 

and Po = standard air density at sea level and 70°F, lb/f t3. 

The flow rate is simply: 

where, 

Q=V cxA, 

Q = fan quantity, cfm, 

A = effective area, ft3, 

and Vc = average velocity, fpm. 

The flow capacities were determined for a fan operating in the 

forward mode and in reverse, and the percent reduction of flow rate 

due to fan reversal was calculated, as follows: 

1 reduction in capacity =I - %Ir LOO, 

where, Qr = fan quantity in reverse, cfm, 

and Qf = normal fan capacity, cfm. 

ENGINEERS INTERNATIONAL, INC. 
4.5.4 Static Pressure 

As shown earlier, the fan static pressure under specified 

conditions is given by equation 4. The percent reduction in static 

head due to fan reversal is simply: 

X reduction in head = 11 - 'sr ( x 100, 

where, P = converted static head of fan while in 

sr 

reverse, in. W.G. 

and Psf = converted static head of fan operating 

in the forward mode, in. W.G. 

ENGINEERS INTERNATIONAL, INC. 
5.0 FIELD TESTS 

Field tests on seven (7) main mine fans were conducted at three 

(3) mines located in different parts of the United States. Details 

of the tests along with the results are provided in the following 

sections. 

5.1. Mine No. 1 

The first fan test was performed at a room-and-pillar limestone 

mine in the Midwest. Auxiliary mine ventilation included two 60,000 

cfm (28 mS/s) centrifugal fans operating at low pressure. No air 

doors or regulators that could affect main fan reverse performance 

were present. The large open area of the mine and low pressure 

auxiliary fans suggested little interference with the performance of 

the main fan. 

Mine air was exhausted by an 81-in. (2.1-m) diameter 8112-C 

Chicago Blower vane-axial fan, having a hub diameter of 27 in. 

(0.7 m), mounted vertically over a 15-ft (4.6-m) diameter mine shaft. 

A schematic of the fan installation is shown in Figure 12. 

5.1.1 Test 1 

5.1.1.1 Test Conditions 

Due to limited accessibility and absence of ductwork, only one 

pitot tube traverse plane was available. Very little air turbulence 

was detected at this plane, possibly due to the absence of elbows, 

straightening vanes, or offsets. Fan reversal was accomplished by 

simply reversing the electrical connections leading to the fan motor. 

5.1.1.2 Test Results 

Performance comparison data for forward and reverse fan operation is listed in Table 2. The operating point in the blowing, or 

reverse mode, was at a considerably lower volume and static pressure, 

compared to forward performance. Air quantity in reverse was 55 percent of the capacity in the forward mode, at 36 percent of the static 

pressure. 

This fan was of a different manufacture compared to those tested 

during the laboratory phase, suggesting that blade design was probably based on a different philosophy. Hub to tip ratio was also 

higher than the laboratory fans, having a value of 0.33. It was 

assumed that the blade angle was that listed on the nameplate, 17 

degrees (0.3 rad), as access to the blades was not possible. 

34 ENGINEERS INTERNATIONAL, INC. 
OUTLET CONE 

---- 

FIGURE 12. - Fan inst-allation at Pfine :.L>= 1. 

35 
TABLE 2. - Performance comparison for fan 1 

Parameter Forward 

Volume, cfm (m3/s) 227,242 (107) 

Static Pressure, in. W.G. 

(Pa) -3.75 (-933) 

Total Pressure, in. W.G. 

(Pa) 

Velocity Pressure, in. W.G. 3.18 (791) 

(Pa) 

Current, amps 151 

Reverse 

ENGINEERS INTERNATIONAL, INC. 
5.2 Mine No. 2 

Tests on four (4) main mine fans were performed at a room-andpillar copper mine in the Midwest. The mine was fairly extensive and 

consisted of five (5) intake shafts, one (1) intake portal, and four 

(4) exhaust shafts. The relative positions of the intake and exhaust 

shafts and the layout of ventilation stoppings are shown schematically in Figure 13. 

Each exhaust shaft was equipped with a M96-50D Joy Axivane fan, 

rated at 900 RPM and 700 hp. These were 96-in. (2.4-m) diameter 

vane-axial fans, with 50-in. (1.3-m) hub diameters, mounted horizontally and connected to 40-ft (12.2-m) long evases. Figure 14 

shows the essential features of the fan instaiiation along with the 

locations of the pitot tube traverse planes. 

5.2.1 Test 2 

5.2.1.1 Test Conditions 

This test was conducted on fan 2, the location of which is shown 

in Figure 13. The traverse planes were located on either side of the 

fan blades. Minimal air turbulence was detected at the traverse 

planes. 

Testing this fan in the exhaust mode was done with the other 

three (3) fans also operating in the exhaust mode. During reverse 

testing, fan 5 was reversed, while fans 3 and 4 were in the normal. 

mode. The air damper doors within the fan housing and the underground air doors were kept open by means of bolts during reversal. 

This test scheme was considered by mine personnel to represent 

emergency action for existing mining conditions. 

5.2.1.2 Test Results 

Performance comparison data for forward and reverse fan operation are listed in Table 3. As expected, a drop in both quantity and 

static pressure was noted following reversal. Volume of air handled 

decreased to 39 percent, while static pressure was only 11 percent of 

the forward value. The blade angle for this fan was found to be 37.5 

degrees (0.65 rad), and the measured fan rpm was 920. 

5.2.2 Test 3 

5.2.2.1 Test Conditions 

This test was conducted on fan 3. Forward testing was performed 

with all fans operating in the normal mode. During reverse testing, 

fan 4 was reversed, fan 2 was operating in the normal mode, and fan 5 

was inoperative due to mechanical difficulty. This test scheme was 

considered by mine personnel to represent emergency action for 

existing mining conditions. 

37 ENGINEERS INTERNATIONAL, INC. 


TABLE 3. - Performance comparison for fan 2 

Parameter Forward 

Volume, cfm (m3/s) 455,196(215) 

Static Pressure, in. W.G. 

(Pa) -16.44 (-4091) 

Total Pressure, in. W.G. 

(Pa) -7.85 (-1953) 

Velocity Pressure, in. W.G. 

(Pa) 8.59 (2138) 

Current, amps 86 

Reverse 

ENGINEERS INTERNATIONAL, INC. 
5.2.2.2 Test Results 

Performance comparison data for forward and reverse fan operation are listed in Table 4. Air quantity in reverse was 37 percent 

of that in the forward mode and at 9 percent of the static pressure. 

The blade angle was 36 degrees (0.63 rad) and fan speed was 920 rpm. 

5.2.3 Test 4 

5.2.3.1 Test Conditions 

This test was conducted on fan 4. During fan testing in the 

exhaust mode, the other three exhaust fans were also operating in the 

exhaust mode. During reverse testing, fan 3 was reversed. Fan 2 was 

in the normal operating mode, and fan 5 was inoperative due to 

mechanical difficulty . This test scheme was considered by mine 

personnel to represent an emergency action for existing mining 

conditions. 

5.2.3.2 Test Results 

The performance comparison between forward and reverse flows is 

presented in Table 5. Reverse air quantity was 35.5 percent of the 

capacity in the forward mode, while the static pressure was about 9 

percent of the forward value. The blade angle of the fan was determined to be 39 degrees (0.7 rad) and fan rpm was 920. 

5.2.4 Test 5 

5.2.4.1 Test Conditions 

This test was performed on fan 5. During fan testing, all fans 

were operating in the normal mode. During reverse testing, fan 2 was 

reversed, while fans 3 and 4 operated in the exhaust mode. This test 

scheme was considered by mine personnel to represent an emergency 

action for existing mining conditions. 

5.2.4.2 Test Results 

The comparison between forward and reverse performance is listed 

in Table 6. Reverse air quantity was found to be about 40 percent of 

the quantity in the forward mode, while the static pressure developed 

was about 14 percent of the forward value. The blade angle was 

found to be 37 degrees (0.65 rad) and fan speed was 920 rpm. 

5.3 Mine No. 3 

Tests of two main mine fans, placed in parallel, were conducted 

at an oil shale operation in the western United States. The mine 

operated on three levels. The main access drifts at each level 

branched from an 8-ft (2.4-m) diameter circular shaft. Each of these 

ENGINEERS INTERNATIONAL, INC. 
TABLE 4. - Performance comparison for fan 3 

Parameter Forward Reverse 

Volume, cfm (m3/s) 480,868 (227) 177,139 (84) 

Static Pressure, in. W.G. 

(Pa) -16.05 (-3994) -1.44 (-358) 

Total Pressure, in. W.G. 

(Pa) -6.47 (-1610) -0.14 (-35) 

Velocity Pressure, in. W.G. 

(Pa) 9.58 (2384) 1.30 (323) 

Current, amps 9 1 78 

E?JGINF:ERS INTERNATIONAL, INC. 
TABLE 5. - Performance comparison for fan 4 

Parameter Forward 

Volume, cfm (m3/s) 516,446 (244) 

Static Pressure, in. W.G. 

(Pa) -16.70 (-4156) 

Total Pressure, in. W.G. 

(Pa) -5.65 (-1406) 

Velocity Pressure, in. W.G. 

(Pa) 11.05 (2750) 

Current, amps 87 

Reverse 

183,169 (86) 

ENGINEERS INTERNATIONAL, INC. 
TABLE 6. - Performance com~arison for fan 5 

Parameter Forward 

Volume, cfm (m3/s) 458,296 (216) 

Static Pressure, in. W.G. 

(Pa) -15.08 (-3753) 

Total Pressure, in. W.G. 

(Pa) -6.34 (-1578) 

Velocity Pressure, in. W.G. 

(Pa) 8.74 (2175) 

Current, amps 96 

Reverse 

ENGINEERS INTERNATIONAL, INC. 
drifts were about 25-ft (7.6-m) high and 25-ft (7.6-m) wide and led 

to modified room-and-pillar working sections. The ventilating air at 

the two lower levels were regulated by free hanging brattice partially blocking the airways, while the upper level access drift was 

completely open. An auxiliary fan operated at the lower level during 

fan testing; however, the large cross-sectional area of airways suggested little interference with main fan performance. 

Mine air was exhausted by two 79-in. (2-m) diameter, 200 hp AMF 

2000-80-10 Spendrup vane-axial fans, each having a hub diameter of 31 

in. (0.8 m), horizontally mounted in a Y-connection off the shaft. 

Figure 15 shows the installation, which is heavily insulated to prevent ice build-up. 

5.3.1 Tests 6 and 7 

5.3.1.1 Test Conditions 

Due to limited accessibility and absence of substantial ductwork, only one pitot tube traverse plane was available. This plane 

was located at the junction of the fan housing and the evase. Some 

turbulence at the traverse plane was noticed, probably due to 

straightening vanes or fan motor supports. Fan reversal was accomplished by simply reversing the electrical connections to the fan 

motor. 

5.3.1.2 Test Results 

Performance comparison data for forward and reverse fan operation are listed in Tables 7 and 8. The static and total pressure 

readings obtained during forward fan testing at this mine were rather 

erratic and, contrary to expectations, the sum of static and velocity 

pressures at several measurement points did not equal the total pressure. This was judged to be caused by an unfavorable pitot traverse 

location. The velocity pressure readings, on the other hand, 

appeared less affected by the location and were fairly consistent. 

In order to eliminate the discrepancies in the pressure readings, the expected fan pressure at the inby side of the fan in the 

forward mode was estimated on the basis of the mine characteristic 

curve and the measured velocity pressure. The mine resistance, R, 

was calculated from the operating point data for the mine. The mine 

characteristic curve was plotted for different values of air quantity, Q, as shown in Figure 16, using the following relationship: 

ENGINEERS INTERNATIONAL, INC. 
PLAN VIEW 

OUTER 

INSULATW , 

FIGURE 15. - Schematic of fan installations at Mine No. 3. 
TABLE 7. - Performance com~arison for fan 6 

Parameter Forward Reverse 

Volume, cfm (m3/sec) 113,130 (53) 57,072 (27) 

Static pressure, in. W.G. -2.33 (-580) -0.55 (-137) 

(Pa) 

Total Pressure, in. W.G. -1.50 (-373) -0.36 (-90) 

(Pa) 

Velocity Pressure, in. W.G. 0.83 (207) 0.19 (47) 

(Pa) 

Current, amps 144 14 1 

ENGINEERS INTERNATIONAL, INC. 
TABLE 8. - Performance comparison for fan 7 

Parameter 

Volume, cfm (m3/sec) 

Forward Keverse 

127,463 (60) 54,983 (26) 

Static pressure, in. W.G. -2.99 (-7.44) -0.67 (-167) 

(Pa) 

Total Pressure, in. W.G. -1.93 (-480) -0.49 (-122) 

(Pa) 

Velocity Pressure, in. W.G. 1.06 (264) 

(Pa) 

Current, amps 150 144 

48 ENGINEERS INTERNATIONAL, INC. 
FIGURE 16. - Comptitation of total pressure from 

cl~aracteristic curves. 
where, P = the total pressure. 

The measured forward quantity for each fan was entered on the Q-axis, 

intercepting the mine characteristic curve. The corresponding total 

pressures were read. The static pressures were then calculated using 

the estimated value of total pressures and observed velocity pressures. 

In order to verify the validity of this approach, the observed 

reverse quantities were also entered on the Q-axis and the corresponding total pressures were compared to measured data. The calculated values were found to be reasonably close to observed data. 

It should be emphasized, however, that the calculation of mine resistance was based on anticipated fan duty for a specific fan and blade 

angle and does not necessarily reflect the actual resistance of the 

mine airways. The results obtained through this approach should, 

therefore, be considered merely as rough estimates of the actual conditions. The data did not accurately show the exhaust performance 

values, however, the data did allow differences between forward and 

reverse performance to be identified. 

The calculated static pressures appear in Table 9. The fan 6 

quantity in the reverse mode is 50.5 percent of that in the forward 

mode, at 23.6 percent of the static pressure in the forward mode. 

The prediction would be (0.505)~ or 25.5 percent. Fan 7 gave 43.1 

percent of forward flow when reversed, at 22.1 percent of the static 

pressure. The predicted pressure would be (0.431)~ or 18.6 percent. 

Therefore, these results are in good agreement with earlier data. 

These fans were of a different manufacture than those tested in 

the laboratory, suggesting that blade design philosophy was probably 

different. Hub to tip ratio was also higher than the laboratory 

fans, having a value of about 0.39. Blade tip angles were measured 

at 12 degrees (0.21 rad) and 15 degrees (0.76 rad) for fans 6 and 7, 

respectively. 

5.4 Summary of Field Results 

Table 9 provides a performance comparison summary for all the 

fans tested in the field (absolute values of static pressures are 

shown). Based on these results, Figure 17 was plotted to illustrate 

the relationship between reverse performance, the blade angle, and 

hub to tip ratio of vane axial fans. The laboratory data are also 

included in this plot to demonstrate the correlation between laboratory and field results. 

It is evident from Figure 17 that the results of fan testing at 

Mine 2 are in good agreement with the laboratory results. The field 

ENGINEERS INTERNATIONAL, INC. 
Test 

- 

TABLE 9. - Field test data summary 

Volume 

Forward, Reverse, 

cfm (m3/s) cfm (m3/s) 

Reverse performance as a percentage of forvard perfomance 

Static Pressure 

Forward Reverse R/F*. Blade Angle, 

in. W.G. (Pa) in. W.G. (Pa) % degrees (rad) 

ENGINEERS INTER
FIGURE 17. - Fan average performance versus blade angle. 

*Figures in parentheses refer to hub to tip ratios 

**Fan model number 
data are not as consistent as the laboratory data, due to the 

inherent inaccuracies in field testing arising from excessive blade 

wear, interaction between fans, and air turbulence. 

The data points from Tests 1, 6 and 7 however, do not exhibit 

any apparent correlation with the other test results. There are two 

possible explanations for these discrepancies. First, fan interaction during tests 6 and 7 could have affected results in that the 

fan junction duct was very close to the fan housing. This could 

permit one fan to interfere with the static pressure produced by the 

other. Second, fans 1, 6 and 7 were of a different manufacture compared to the laboratory and Mine No. 2 fans, suggesting perhaps that 

the blade design was based on a different philosophy. 

The inverse square relationship between pressure and air quantity obtained during laboratory testing (Section 3.3.3), appeared to 

hold true for the field results, within reasonable limits of error. 

The results from Mine No. 2 deviated from this relationship, probably 

due to interaction between the various fans and the complex ventilation system at this mine. 

ENGINEERS INTERNATIONAL, INC 
6.0 GUIDELINES FOR REVERSING FANS 

6.1 -- Data ?'re~.lds from Present Work 

Based on the laboratory and field test results, the following 

distinct trends are evident: 

a for a given hub to tip ratio and blade angle, 

there appears to be a definite relationship 

between the reverse fan volume as a percentage 

of forward volume of a vane-axial fan. This 

relationship is likely to be different for fans 

of different manufacturers 

a reverse performance of vane-axial fans is 

inversely related to their blade tip angles 

a in the absence of significant interaction from 

auxiliary fans within a gi.ven mine network, the 

percent of static pressure obtained during 

reverse operation varies as a square of the 

change in air volume. This may be expressed 

as: 

static pressure, fan reversed where Ps = static pressure, fan forward ' 

and reverse air quantit 

= forward air quantit;' 

6.2 Guidelines 

When fan reversal at a mine is anticipated, due to an emergency 

situation or otherwise, the mine operator should consider the effectiveness of fan reversal in correcting that particular situation. 

The following steps are recommended for this evaluation: 

1. Obtain fan data, such as: 

a type of fan (manufacturer) 

a forward fan quantity 

a blade angle (corresponding to blade setting number) 

a hub to tip ratio. 

2. Based on the above information, and with the help of a 

reverse performance chart (as shown in Figure 8 obtained from laboratory tests of the fan in reverse) for that fan type, estimate the 

fan quantity and pressure in reverse. 

ENGINEERS INTERNATIONAL, INC. 
3. Establish the quantity of air available to different parts 

of the mine and the overall airflow pattern based on the characteristics of the mine airways. 

This will enable the mine eperator to evaluate: 

in case of a fire, whether the fire can be isolated 

whether sufficient air would be available to 

persons in different areas of the mine 

whether gaseous pollutants can be adequately 

dissipated. 

On the basis of such evaluation, the mine operator would be able 

to effectively and efficiently determine if and how fan reversal 

should be done. 

6.3 Applicability of Guidelines 

The limitations of the results of this study should be 

understood before applying the guidelines to a particular mine. 

These are: 

in a situation where several fans are operating 

in close proximity to one another within a ventilation circuit, the effect of their interaction may influence the predictability of the 

reverse performance of an individual fan. The 

results of this study should, therefore, be 

used with caution when fan interaction is anticipa ted 

due to time and budget limitations, only a 

limited variety of fan types were tested. The 

study revealed that fans of different manufacturers had different reverse characteristics, possibly due to the blade design philosophy of each type. Kost of the conclusive 

findings of this study relate to fans made by 

Joy Manufacturing Compsny. The applicability 

of the results, therefore, is limited to Joy 

fans, or to fans identical to those tested in 

the field 

due to the nature of the fan installations at 

most of the field testing sites, ideal pitot 

tube traverse planes for pressure and flow 

measurement could not be found. This may have 

introduced inaccuracies in the field measurements, and could account for some of the discrepancies in the final results. 

55 ENGINEERS INTERNATIONAL, INC. 
7.0 CONCLUSIONS AND RECOMMENDATIONS 

7.1 Conclusions 

The following is a summary of the major conclusions reached 

from the results of this study: 

the study clearly demonstrates that it is possible to predict reverse performance of vaneaxial fans to a reasonable degree of accuracy, 

based on data obtainable from fan manufacturers 

the reverse performance of vane-axial fans is 

not a fixed percentage of forward performance, 

contrary to earlier belief. It generally 

varies between 30 to 65 percent, depending on 

fan make, blade angle, and hub to tip ratio. 

Static pressure during reverse rotation generally is reduced to values between 9 and 42 percent of the forward mode. 

fan laws governing airflow during the forward 

operation of mine fans appear to be applicable 

to reverse flow 

the field tests indicated that fan reversal 

does not have noticeable effect on the structural integrity of the fan and installation. 

In addition, provided that air doors and 

dampers (if present) are kept securely fastened 

during reverse operation, the safety of the 

mine is not endangered. 

7.2 Recommendations for Future Work 

The testing of two fans in the laboratory and seven in the field 

does not provide sufficient data from which to establish definite 

guidelines. Information from other operating mines that have performed similar tests is necessary to generalize the data trends 

observed in this study. This collection should include information 

from small diameter fans and from fans made by many different manufacturers. From this study, it is apparent that fans of different 

manufacture behave differently when reversed. 

.It would also be advantageous to test multiple fan installations 

in various ways to better establish the effect of fan interaction on 

performance. Another worthwhile area of research is to investigate 

the effect of fan reversal on airflow in underground airways in order 

to predict conditions during an emergency. 

56 ENGINEERS INTERNATIONAL, INC 
Fan Performance Curves 

Obtained in the Laboratory 

57 ENGINEERS INTERNATIONAL, INC. 
TEST PERFORMANCE 

FAN MOOEL: M96- 43 

JOY AXIVANE MINE FAN 

FAN SPEED: 720 RPM 

AIR DENSITY: 0.075 #/cu ft 

BLADE TIP ANGLE: 1 o0 

REVERSE FLOW IN PERCENT 

OF FORWARD FLOW 

FAN WERAiiiiC 34 SAME 

SYSTEM WITH REVERSE ROTATION 

, 

W 

tg it' 100, 

, 

3 W 

e a 

z e 

L! 

C 

FIGURE ~1. - Fan performance with lo0 blade angle. 
TEST PERFORMANCE 

FAN MODEL: M96- 43 

JOY AXIVANE MINE FAN 

FAN SPEED: 720 RPM 

AIR DENSITY: 0.075 # /cu ft 

BLADE TIP ANGLE: 20° 

REVERSE: FLOW IN PERCENT 

OF FORWARD FLOW 

FAN OPERATING ON THE SAME 

SYSTEM WITH REVERSE ROTATION 

FIGURE A2.- Fan performance with 20' blade angle. 
TEST PERFORMANCE 

FAN MODEL: M96- 43 

JOY AXNANE MINE FAN 

FAN SPEED: 720 RPM 

AIR DENSITY: 0.075 #/cu ft 

BLADE TIP ANGLE: 30 0 

REVERSE FLOW IN PERCENT 

OF FORWARD FLOW 

FAN OPERATING ON THE SAME 

SYSTEM WITH REVERSE ROTATION 

IHPN . SPN DENOTES NORMAL ROTATION 

IHP,, SP, DENOTES REVERSE ROTATION 

VOLUME FLOW, cfm in thousands 

FIGURE A3. - Fan performance with 30' blade angle. 
TEST PERFORMANCE 

FAN MODEL: M96- 43 

JOY AXlVANE MINE FAN REVERSE FLOW IN P

FAN SPEED: 720 RPM OF FORWARD FLdW 

AIR DENSITY: 0.075 #/cu It FAN OPERATING ON 

BLADE TIP ANGLE: 35 0 SYSTEM WITH REVE

FIGURE A4. - Fan performance with 35' blade angle. 

TEST PERFORMANCE 

FAN MODEL: M96- 58 

JOY AXNANE MINE FAN REVERSE FLOW IN 

FAN SPEED: 720 RPM OF FORWARD FLO

AIR DENSITY: 0.075 #/cu It 

BLADE TIP ANGLE: 22 o FAN OPERATING ON 

SYSTEM WITH REV

PN SPN DENOTES NORMAL ROTATION 

IHPR 9 SPR DENOTES REVERSE ROTATION 

\ / 

OA 

I I 1 1 II 1 

40 80 120 160 200 240 

VOLUME FLOW, cf'm in thousands 

FIGURE A6. - ?an performance with 2Z0 blade angle. 
TEST PERFORMANCE 

FAN MODEL: M96-50 

JOY AXNANE UIM FAN 

FAN SPEED: 720 RPU REVERSE FLOW N PERCEN

AR DENSITY: 0.075 */n, ft OF FORWARD FLOW 

BLADE TP ANGLE: 320 FAN OPERATNG (*I TM SA

SYSTEM WITH REVERSE R

FIGURE A7. - Fan performance with 3Z0 blade angle. 

8 

a^ 6- 

a 

V 

3 

3 

c' .- 

d 4- 

3 

a 

a 

W 

a 

a 

E 

; 2- 

0 

IHPN , SPN DENOTES NORMAL ROTATION 

IHP , SPR DENOTES REVERSE ROTATION R \ 

\ 

\ 

\ 

/ 

0 40 80 1 20 160 200 240 280 

VOCUME FLOW, cfm in thousand8 
VOClJME FL.OW, cfm ~r: thousands 

TEST PERFmMANCE 

FAN MOOEL: M96- 58 

JOY AXNANE MINE FAN REVERSE FLOW INPE

FAN SPEED: 720 RPM (X FORWARD FLOW 

'IR 0'075 *"" ft FAN OPERATMG ON T

BLADE TIP ANGLE: 42O SYSTEM WITH REVE

FTGURF A8. - ari perf orm,.rnce wi" t1-1 42" bl :id6 an~zle,