FIELD OF THE INVENTION
The present invention relates to air dampers in general and particularly to air
flow diverting dampers used in association with working and standby air fans
delivering low pressure air. More particularly the invention relates to an air flow
diverter damper device for an air-delivery system in heat recovery steam
generators (HRSG) to reduce the pressure required to operate the damper flap.
BACKGROUND OF THE INVENTION
In steam generators, low pressure air is required for providing cooling, sealing or
for combustion. Cooling air is required for flame scanners. In case of gas
ignitors, air is required for cooling as well as for combustion. In addition, if the
combustor or furnace is pressurized, air is also required to seal the openings
such as view ports, manholes etc., preventing the flow of hot gases out of
combustor to the environment.
Accordingly, a prior art arrangement for air delivery system (Figure 1) supplying
low pressure air required for said applications, comprises one working air fan (1)
and one standby air fan (2). Air delivery header (3) of the working air fan (1)
and a delivery header (4) of the standby air fan (2) are connected to a common

delivery air header (5) through a self-actuating diverter air damper (6). The self-
actuating diverter air damper (6) serves to connect the working air fan (1) to the
common delivery header (5) while isolating the standby air fan (2) from the
common delivery header (5), thereby eliminating the cross flow of air from the
working air fan (1) into the standby air fan (2).
As per the prior art air delivery system (Figure 2), when the standby air fan (2) is
put in service and the working air fan (1) is made out of service, the self-
actuating diverting air damper (6) allows connection of the standby air fan (2)
with the common delivery header (5) while isolating the working air fan (1) from
the common delivery header (5).
As per prior art air (Figure 1), the self-actuating diverting air damper (Figure 3),
has a damper body (7), with a flap (8) which is pivoted strategically in the
damper body (7), a couple of inlet pipes (9, 10) and a delivery pipe (11). When
the inlet pipe (9) is closed by the flap (8), the delivery pipe (11) is connected to
the inlet pipe (10) and when the inlet pipe (10) is closed by the flap (8), the
delivery pipe (11) is connected to the inlet pipe (9). The closure of inlet pipes (9,
10) by the flap (8) is achieved by the pressure difference between the two faces
of the flap (8). The self-actuating diverting air damper (Figure 3), experiences
considerable pressure drop across it.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention is to propose an air flow
diverter damper device for an air-delivery system in heat recovery steam
generators (HRSG) to reduce the pressure required to operate the damper flap.

Another object of the present invention is to propose an air flow diverter
damper device for an air-delivery system in heat recovery steam generators
(HRSG) to reduce the pressure required to operate the damper flap which
reduces the fan delivery pressure corresponding to the service requirement so as
to reduce the auxiliary power consumption of the plant.
Yet another object of the present art is to propose an air flow diverter damper
device for an air-delivery system in heat recovery steam generators (HRSG) to
reduce the pressure required to operate the damper flap which is also mountable
in any orientation.
SUMMARY OF THE INVENTION
Accordingly, there is provided an air flow diverter damper device for an air-
delivery system in heat recovery steam generators (HRSG) to reduce the
pressure required to operate the damper flap, the air flow diverter damper
connecting one at least each working and another stand by air fans delivering air
at low pressure to a common delivery header. The present invention provides a
means to reduce.the pressure required to operate the damper flap. The principle
of balancing of mass with spring is suitably employed to the present invention to
enable self-actuation of the diverter air-dampers with a considerably lower
pressure. The weight of the swinging flap is balanced so that the flap can be
located in any position overcoming the force due to gravitation. Even a slight
increase in the pressure on one side, will swing the flap to other side. Pressure is
required to swing the flap only upto the middle of the diverter air-damper, after
that by virtue of the spring force, the flap swings to reach its ultimate position.

To enable swinging of the flap with the lowest pressure possible, the flap is
provided with a flexible sealing member which assumes a concave contour. With
the said provisions, the pressure required to swing the flap is set to be the
lowest possible. In normal conditions, the flap of the air damper is held in the
position to close the delivery side of the standby air fan. When the standby air
fan is put in service, the pressure on the closing side of the flap increases while
the pressure on the other face of the flap is reduced.. This pressure difference
enables the flap to swing so as to close the delivery side of the air fan which is
put out of service.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 : Arrangement of an air delivery system with a working air fan in service
according to the prior art.
Figure 2 : Arrangement of an air delivery system with a standby air fan in service
according to yet another prior art.
Figure 3 : Present art of a self-actuating air diverter damper in the air delivery
system.
Figure 4 : A spring biased arrangement for the air-diverter damper for HRSG
according to the present invention.
Figure 5 : Flap assembly of the air diverter damper of Figure 3 .

DETAILED DESCRIPTION OF THE INVENTION
According to the invention, the principle of balancing of mass with a spring is
strategically employed to suit the self-actuating diverter air-dampers. The
weight of the swinging flap is balanced so that the flap can be located in any
position overcoming the force due to gravitation. Even a slight increase in
pressure on one side, will swing the flap to other side. Pressure is. required to
swing the flap only up to the middle of the diverter air-damper, after that by
virtue of the spring force, the flap is made to swing to reach its ultimate position.
To enable swinging of the flap with the lowest pressure possible, the flap is
provided with a flexible sealing member which has a concave contour. With
suitable provisions, the pressure required to swing the flap is set to be the lowest
possible. In normal conditions, the flap of an air damper is held in the position to
close the delivery side of the standby air fan. When the standby air fan is put in
service, the pressure on the closing side of flap increases while the pressure on
the other face of the flap is reduced. This pressure difference enable the flap to
swing so as to close the delivery side of the air fan which is put out of service.
The spring biased self-actuating air-diverter damper (Figure 4) of the present
invention, includes a damper body (12) with a plurality of flap assembly (13)
bolted to the damper body (12), a first inlet pipe (9), a second inlet pipe (10)
and a delivery pipe (11) welded to the damper body (12). The first inlet pipe (9)

is connected to a delivery header of one air fan and the second inlet pipe (10) is
connected to the second air fan. The delivery pipe (11) is connected to the
header leading to the user ends . It is possible to dismantle the plurality of flap
assembly (13) as it is bolted to the damper body (12) using a mounting flange
(14).
As per the present invention, the flap assembly (Figure 5), comprises a mounting
flange (14) with a hinge bracket (15) welded to it. A flexible sealing member
(18) and a Sealing washer (19) are attached to the flap (17) with a couple of
tightening rings (20) and a plurality of fasteners (21, 22). The flexible sealing
member (18) assumes a shape depending on the air flow delivered from the air
fans. The assembly of the flap (17) with the sealing members (18 and 19) is
mounted to the hinge bracket (15) using a plurality of pivot pins (16). The flap
(17) and an adjusting screw (24) are connected using at least two torsional
springs (23). Lock nuts (25) are provided for fixing the tightness of the torsional
springs (23). The flexible sealing member (18) facing the higher pressure air
from the working air fan, assumes a concave contour and swings the assembly
of the flap (17) with sealing members (18 and 19) closing the delivery side of the
non-working air fan. Using the adjusting screw (24), the flap is accurately
balanced demanding lesser pressure for its movement.

WE CLAIM :
1. An air flow diverter damper device for an air-delivery system in heat
recovery steam generators (HRSG) to reduce the pressure required to
operate the damper flap, comprising :
a spring balanced flap assembly (13) essentially consisting of an assembly
of a flap (17), a flexible sealing member (18), a sealing washer (19) and
at least two numbers of torsional springs (23) connected to an adjusting
screw (24) wherein the torsional springs (23) and the adjusting screw
(24 enable to balance the forces exerted by the flap (17) with a minimum-
possible bias and reduce the pressure required to swing the flap (17).
2. The device as claimed in claim 1, wherein the flap 17 is designed to
have an opening at its center to reduce its weight and accommodate
the inflating flexible sealing member (18).
3. The device as claimed in claim 1, wherein the flexible sealing member
(18) is made of flexible canvas material and inflatable to form a
concave shape when viewed from the delivery side of the working fan.
4. The device as claimed in claim 1, wherein the flexible sealing member
(18) forms a cup shape further upon application of air pressure and
reduce the pressure required to swing the flap (17).

5. The device as claimed in any of the preceding claims that the
centers of swing for the flap (17) and spring (23) are offset so that
the force required to swing the flap (17) is only up to half of its swing,
after that the flap (17) advances its swing with the force provided by
the springs (23).