Designation of centrifugal fans

Early USA Standards

Probably the first attempts at an industry wide standard were made by the US National Association of Fan Manufacturers in its Bulletin No 105 dating back to the 1930s. This bulletin cov­ered the designation of the discharge of centrifugal fans, the position of inlet boxes, the arrangement of fan drives, and the standard designation of motor positions. The relevant dia­grams for these designations are shown in Figures 9.1 to 9.4.

It is of interest to note that these standards have been used in the USA ever since, albeit with a few deletions and additions.

Arr 1

Arr 4

Arr 3


Arr 8


Cl la.

Arr 7

’ l


*rr 10


Arr 9

Fig 16 Counter Clockwise

Top Angular Up Bottom Angular Down Bottom Angular Down

Figure 9.1 Standard designation of fan discharge

Fig 13 Counter Clockwise Top Angular Up




Designation of centrifugal fans

Fig 1 Counter Clockwise Top Horizontal


Designation of centrifugal fans

Fig 4 Counter Clockwise Bottom Horizontal


Designation of centrifugal fans

Fig 3 Clockwise Bottom Horizontal




Designation of centrifugal fans

FigS Clockwise Up Blast


Fig 7 Counter Clockwise Down Blast


Figure 9.4 Standard designation of motor position


Fig« Counter Clockwise Up Blast


Fig 8 Clockwise Down Blast


The NAFM has been succeeded by AMCA International, which has been influenced to some extent by the subsequent ISO standards.

Early British Standards

Early efforts at the standardisation of nomenclature for dis­charge position and arrangements of drive etc were largely based on these American standards, but with some significant improvements.

Instead of “clockwise” and “counter-clockwise” for rotation, “right-hand” and “left-hand” were the designations perhaps on the basis that a right-hand thread is screwed clockwise to tighten. The position of the outlet was given an angular desig­nation starting at 0 for bottom horizontal and proceeding around the protractor i. e.


Fig 11 Fig 12

Clockwise Counter Clockwise

Bottom Angular Up Bottom Angular Up


Fig 9 Fig 10

Counter Clockwise Clockwise

Top Angular Down Top Angular Down


Designation of centrifugal fans

Designation of centrifugal fans Designation of centrifugal fans Designation of centrifugal fans Designation of centrifugal fans Designation of centrifugal fans Designation of centrifugal fans Designation of centrifugal fans Designation of centrifugal fans Designation of centrifugal fans Designation of centrifugal fans
















подпись: i i Designation of centrifugal fans Designation of centrifugal fansFor bottom angular down

Thus the designations become R0 or L0. R90 or L90 etc. These were standardised in both FMA 3:1952 and British Standard

Designation of centrifugal fans

Figure 9.7 Standard designation of fan discharge (Eurovent and ISO)

figure 9.7 standard designation of fan discharge (eurovent and iso)

L135 L90 R90 R135

Designation of centrifugal fans

B. Counter-clockwise a. Clockwise

Viewed from drive side

Figure 9.5 Standard designation of fan discharge (FMAand BSI — UK)

949:1939 and are best shown by reference to Figure 9.5. These designations were repeated in the 1963 and 1980 editions.

In like manner the designations for motor position were ap­pended to FMA3:1952 and BS 848:1963 and 1980. However, instead of the letters W, X, Y and Z, the letters B, C, D and A re­spectively were used, see Figure 9.6.

Designation of centrifugal fans

European and International Standards

With the growing Europeanisation of the fan industry the 1980s witnessed a demand for a more widespread standard. Eurovent (The European Committee of Air Equipment Manu­facturers) responded to this with document 1/1 of 1972. Whilst the British and American Standards were tabled as working documents, certain important changes were made in the inter­ests of acceptability. These were:

• Rotation would be identified by the letters LG (signifying Left, Gauche or Links) and RD (signifying Right, Droite or Recht). Thus the 3 main European languages were all re­cognised.

• An angular position would be identified by a number show­ing the degrees, but starting at 0 for vertical up outlet in­stead of 0 for bottom horizontal.

As in all the preceding standards, these designations were to be taken when viewed along the axis of the fan on the driveside. It should here be noted that the driveside was identified as the side opposite the inlet for a single inlet fan, no matter what was the actual position of the drive. This was stipulated principally for those occasions where a single inlet fan had a direct drive motor fitted in the fan inlet. There are however other rare in­stances of indirect drive on the inlet side. For double inlet cen­trifugal fans the direction of rotation is determined when viewed from the driveside.

These outlet positions are shown in Figure 9.7 and having re­cently been accorded worldwide recognition in ISO 13349. It should be noted that intermediate positions may be identified by an appropriate figure for the angle of the outlet. For the user, it is necessary to discuss with the manufacturer exactly what is available, depending on the constructional methods. All angles from 180° to 225° may require special constructions at extra cost.

The position of component parts of a centrifugal fan with volute casing are also standardised in Eurovent 1/1:1972 and ISO 13349 figure 20.

Whilst these diagrams indicate the angular position of a motor if mounted on the fan casing, they do not identify the alternative positions of a motor for an indirect drive (belt or chain) when at or near ground level. For these cases both Eurovent and ISO have adopted the American W, X, Y, and Z positions.

Fan specifiers are encouraged to specify ISO 13349 as this will obviate all possible ambiguities. However it has to be recognised that there are still some manufacturers using these earlier standards, albeit in diminishing numbers. For assistance in such cases, the following Table 9.1 of equivalents may be of help.

ISO 13349 Eurovent 1/1

BS 848 1939/63/80 FMA

AMCA Int. 99-2404

NAFM Bulletin 105 and early AMCA

LG or RD 0

L or R 90

CCW or CW 0


LG or RD 45

LorR 135

CCW or CW 45


LG or RD 90

LorR 180

CCW or CW 90


LG or RD 135

L or R 225

CCW or CW 135


LG or RD 180

L or R 270

CCW or CW 180


LG or RD 225

L or R 315

CCW or CW 225


LG or RD 270


CCW or CW 270


LG or RD 315

L or R 45

CCW or CW 315





Counter Clockwise






Up Blast



Top Angular Up



Top Horizontal



Top Angular Down



Down Blast



Bottom Angular Down



Bottom Horizontal



Bottom Angular Up

9.3.2 Designation of motor position

These are best determined from Figure 9.9. The codes used in ISO 13349 are for horizontal and vertical axes.

подпись: 9.3.2 designation of motor position
these are best determined from figure 9.9. the codes used in iso 13349 are for horizontal and vertical axes.
European and International Standards for fan arrangements

Until the 1980s the standardisation of fan arrangements was largely non-existent. Each company continued to use its own designations. Regrettably a small number still do. At that time BSI launched work on BS 848 Part 8 and had reached the stage of a working draft. This included a section on fan arrangements and these largely followed North American standards as exam — pled in what had now become AMCA Standard 99-2404. Since the original NAFM Bulletin No. 105 however, Arrangements 5 & 6 , which required flanged (rigid) couplings had become obso­lete and were no longer included. The BSI draft took advantage of this fact to use these two numbers for other purposes. Ar­rangement 5 was therefore proposed for direct drive without a motor supporting stool or pedestal, the motor being bolted to the fan casing by its flanged endshield. Arrangement 6 was uti­lised for the DIDW version of Arrangement 3 , which was re­stricted to SISW fans. There was certain logic in this — twice 3 equals 6!

Meanwhile UNI, the Italian standards organisation had also produced its standard UNI 7972 which had a very much more comprehensive range of fan arrangements, again using the American designations where possible.

At this point in time ISO determined that it would commence work on a “Vocabulary and definition of categories” which, as noted, was published as ISO 13349:1999, giving the drive ar­rangements for centrifugal fans. These are shown in Table 9.2.

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