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5.11
Flue gases recirculation piping system
–
Normally the pipe would be connected to the flue stack as
shown in Fig. 26, forming an angle of 45° facing the flow of
the flue gases and with the centre of the angle located at the
centre of the flue. The pipe can be connected to the flue gas
chamber, but should anyway be kept at the same angle of 45°
facing the flow of the flue gases and with the centre of the an-
gle at the centre of the flow.
–
The pipe should be prepared so that the number of elbows is
reduced to a minimum and the normal expansion and con-
traction of the piping is ensured.
Long piping can excessively dilate and place a very heavy
load on the connection points, causing the components to
break eventually.
The arrangement should take into account misalignments
that allow the necessary movement of the piping without the
exercise of undue force on the burner or the flue.
–
The expansion and contraction of the pipe can be managed
using two relatively long pipes next to each other at 90°.
A small movement of the angle between these two pipes will
provide the space necessary for absorbing the expansion
and the contraction. The ends of the flue gases recirculation
pipes should be fixed securely to allow it to work correctly and
avoid the application of high load on the burner or on the flue.
–
A channel for draining the condensate should be provided
upstream of the flue gases recirculation control valve and the
relative shut-off valve (if being used). There should be con-
densate drain valves and a collection space (drain channels
volumes) sufficient enough to prevent the condensate flowing
through the control valves and inside the fan.
If there is a lot of condensate it might be necessary to have a
drain channel on the bottom of the casing to remove it all.
3
7
1
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11
Key to layout (Fig. 26)
1
Burner
2
Induced flue gases recirculating modulating damper
3
Flue gases recirculating pipe
4
Boiler flue
5
Alternative "T" configuration
6
Flue gases pressure test point upstream of damper 2)
7
Boiler
8
Discharge valve (manual ball valve, stainless steel)
Installation
–
Establish whether reduction joints are needed to connect the
flue gases recirculation control valve and the relative shut-off
valve.
–
The pipe should be adequately supported in order to manage
its weight and to control its thermal expansion and contrac-
tion. It might be necessary to fix the supports to ensure the
flue gases recirculation pipe is stable.
CAUTION
–
The flue gases recirculation pipe is generally composed of a
Schedule 40 pipe since it can easily be found and is inexpen-
sive.
For this application it is possible to use a Schedule 20 pipe.
–
The pipe components should be welded airtight, flanged or
screwed together to ensure it is airtight.
Any leaks of air in the pipe will prevent the system from oper-
ating correctly. You only need to check the seals, without
checking for any leaks.
WARNING
WARNING
4
8
9
9
Discharge line
10 Condensate syphon
11 Main gas feeding input
WARNING
WARNING
23
GB
Uncontrolled accumulation of condensate could
cause an untimely malfunction of the control
valves, the fan and the motor.
Suitable means should be provided for removing
the condensate from the system.
Cold starting will generate a great deal of conden-
sate.
The pipe and fittings need to be suitably insulated
to prevent accidental scalding.
6
2
10
The FGR system is only provided for gas opera-
tion.
3
5
8
8
Fig. 26
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