Technical data

18
Each "T" junction increases the effective length of the tube to which it is mounted by 3
metres. For example, if the junction is fitted to a 2 metre fumes tube, when calculating
the pressure drop you must deem the total length of the tube to be 5 metres. Each 5°
bend increases the effective length of the tube to which it is mounted by 1.2 metres. For
example, if the bend is fitted to a 2 metre air tube, when calculating the pressure drop
you must deem the total length of the tube to be 3.2 metres.
Table 3.3
APPROXIMATE ADMITTED MAXIMUM LENGTHS [m] - by TYPE of installation
B23 C13 C33 C53
fumes tube
separate
tubes
coaxial wall-mounted coaxial roof-mounted
separate
tubes
dia. 80 dia. 80
dia. 125
O-SCR007
dia. 180 O-KTC004
dia. 125
O-SCR008
dia. 150 O-SCR009 dia. 210 O-KTC001 dia. 80
Horizontal Vertical - dia. 80 tubes dia. 130 tubes dia. 80 tubes dia. 100 tubes dia. 130 tubes -
fumes fumes air/fumes air/fumes air/fumes air/fumes air/fumes air/fumes air/fumes
30 30 25+25 20+20 N/A 25+25 30+30 N/A 1+25
Approximate maximum lengths.
The above maximum admitted lengths are to be considered APPROXIMATE and apply
to installations in which the tubes (air and fumes) are routed linearly as shown in Figure
3.5 → 17; Figure 3.6 → 19 and Figure 3.7 → 19. If this condition does not apply, you
must calculate the pressure drop (see "EXAMPLE CALCULATION" below): the installation
is permitted only if the total pressure drop is less than the admitted pressure drop
(see 3.1 → 17).
EXAMPLE CALCULATION
We are to install a B15 with separate tubes, dia. 80, as follows:
7 metres of fumes tube dia. 80;•
2 90° bends dia. 80 on the fumes tube;•
6 metres of air tube dia. 80.•
We can now calculate the pressure drop (see Table 3.4 → 18), bearing in mind that the
total admitted pressure drop is 60 Pa.
Table 3.4
COMPONENT Quantity [m] Pressure drop [Pa/m] Pressure drops [Pa]
Dia. 80 fumes tube 7 x 0,7 = 4,9
90° bends 2 x 1,0 = 2,0
Dia. 80 air tubes 6 x 0,4 = 2,4
TOTAL PRESSURE DROP = 9,3
Example numerical calculation.
The total pressure drop is less than the admitted pressure drop (9.3 Pa less than
the maximum admitted figure of 60 Pa) and hence the installation is PERMITTED.
If the installation had turned out to be not permitted due to excessive pressure drop, we
could have adopted one of the following measures:
reduce the length of the air/fumes tubes;•
increase the diameter of the tubes to dia. 100.•
For special installations, phone ROBUR Presales at +39.035.888.111.