FIELD OF THE INVENTION
The present invention relates to an improved Fan Throttling Device for Testing of
Fans adaptable to power and industrial boilers.
BACKGROUND OF THE INVENTION
Fans are used in power and industrial boilers to deliver the required flow of the
medium and impart adequate pressure to overcome the system resistance
depending on the functions of various types of fans used in the boilers.
Generally, fans are used in a boiler for providing primary air, (PA Fan),
Secondary air (FD fan) and to transmit the flue gas to a Chimney (ID Fan) of the
boiler.
As a process of design validation, the fans are tested to evaluate their
performance. These tests are carried out as per BS848 or AMCA 210 standards.
According to the prior art testing methods, the Fans are erected on a temporary
steel foundation and are run at a lower speed compatible with the temporary
foundation (since full speed would require a concrete and permanent
foundation). Standard norms are used to arrive at the actual performance of the
fan during operation by extrapolating the test results obtained by running the fan
at lower feed on the temporary foundation.

Fan performance curves are generally plotted with an Isentropic Head (a
measure of pressure) on Y-axis and Flow (a measure of quantity of medium
pushed by fan) on X-axis. Outlet of the fan is connected to a circular duct of
suitable size, so that the velocity of the flow medium in the duct is maintained
within the acceptable measurement range by the measuring instruments. In
order to simulate the system resistance and to vary the flow to arrive at the
correct operating point (particular point in the performance curve on X-Y plane
referred above), a throttling device is used to regulate the flow.
As shown in figure - 1, the existing throttling device (04) is generally supported
by rods (08) and rollers (09) from the circular duct (18). The device (04) being
fully supported on the circular duct (18), the device acts as a cantilever. With the
passage of time, the fan throttling device (04) due to its self-load creeps and
misalignment occurs. The misalignment leads to leakage in the fan flow through
the duct (18).
The existing ducts (18) are permissible for testing of fans (02) for thermal power
plant boilers up to 500MW. Thus, for testing of the fans (02) for the thermal
power plant boilers of higher capacity, larger diameter ducts are required. A
larger diameter duct calls for a correspondingly larger diameter cone (19) for the
new fan Throttling Device (03). Hence the new Fan Throttling Device (03) to be
rigid to accommodate a larger cone (19). As a higher force shall occur due to a
higher flow from the fan through the new duct (18), the new fan throttling
device can not be supported by the present arrangement of rod and rollers
(cantilever loading).

Further, it is very difficult to move the existing throttling device (04) because of
the higher frictional forces of the rod and roller arrangement.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose an improved Fan
throttling device for testing of fans adaptable to power and industrial boilers,
which eliminates the disadvantages of the prior art throttling devices.
Another object of the present invention is to propose an improved Fan throttling
device for testing of fans adaptable to power and industrial boilers, which is
capable of withstanding higher self-load including moments of inertia thereby
eliminating the use of counter-weights.
A still another object of the present invention is to propose an improved Fan
throttling device for testing of fans adaptable to power and industrial boilers,
which is enabled to achieve precise movement with a high positioning
repeatability to provide more accurate and error free testing results.
Yet another object of the present invention is to propose an improved Fan
throttling device for testing of fans adaptable to power and industrial boilers,
which can be remotely operated from the control panel.
A further object of the present invention is to propose an improved Fan throttling

device for testing of fans adaptable power and industrial boilers, which is capable
to carry-out the fan-testing process automatically with the provision of a
displacement transducer.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved Fan throttling Device that is
supported on a steel fabricated frame mounted on a concrete foundation. The
steel fabricated frame houses a Linear Motion Guide, a Lead Screw Assembly,
and an electric motor including a gearbox. A top frame assembly sits on the
Linear Motion Guides. The top frame assembly houses a cone, a vertical plate
with associated stiffeners. The top frame assembly further houses a drive
bracket. The drive bracket is mated to a lead screw flange. The lead screw is
mated to the electric motor including the gear box. The electric motor including
the gear box produces a rotary motion which in turn is converted into a linear
motion by the lead screw. The lead screw flange along with a nut moves linearly
over the lead screw. The linear movement of the screw flange moves the drive
bracket which constitutes a part of the top frame assembly. As explained above
the top frame assembly houses the cone, the vertical plate and associated plates
and stiffeners. Thus the linear movement of the cone with respect to the duct is
achieved.
The improved fan throttling device is supported on the Linear motion guide for

providing the axial movement. The linear motion guides have race ways like a
bearing to provide a smooth motion of the device over a linear motion rails.
The Linear motion guides provide the following advantages to the present device
over the rod and roller arrangement of the existing Fan Throttling Device :-
1. A larger permissible load
2. A highly rigid device in all directions
3. A high positioning repeatability.
4. A smooth operation with no clearance.
5. An easy maintenance.
6. Easily obtainable running accuracy.
7. Useable in various environmental conditions.
As described hereinabove, the motive force of the improved throttling device is
provided by the Lead Screw arrangement. The Lead Screw has the following
advantages for this specific application:-
1. The lead screw is made of high strength steel. It is manufactured by both
rolling and milling operation. It has both tighter tolerance and limited
clearance.
2. Normally ACME screws are used to convert a rotary motion to a linear
motion. Back driving is the result of the load pushing axially on the Screw

or Nut to create a rotary motion. Hence, the lead screw assembly is
capable to self-lock and resist back drive.
3. The Lead screw assembly of the invention is supported on both ends of a
double angular contact bearings to oppose the higher axial thrust on the
improved throttling device.
The motive power for the drive mechanism is provided by the electric motor with
gearbox. In the improved throttling device the electric motor with the gearbox is
mounted rigidly in the fabricated steel frame.
Structural analysis has been carried out for the improved Fan throttling device
using Ansys Finite Element analysis. The results have been found satisfactory
and meet the designed load parameters.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure - 1 shows a schematic arrangement of the existing Throttling Device
Figure - 2 shows an improved Fan Throttling Device Assembly according to the
invention.
Figure - 3(a) shows a steel fabricated frame of the improved device of the
invention.

Figure - 3(b) shows a linear motion guide of the improved device of the
invention.
Figure - 3(c) shows a lead screw assembly of the improved device of the
invention.
Figure - 3(d) shows a top frame assembly of the improved device of the
invention.
Figure - 3(e) shows a vertical plate with associated stiffeners of the improved
device of the invention.
Figure - 3(f) shows a cone with cone flange of the improved device of the
invention.
Figure - 3(g) shows the vertical plate with a bottom plate of the improved device
of the invention.
Figure - 3(h) shows a fabricated frame with linear motion guide and lead screw
assembly of the improved device of the invention.
Figure - 3(i) shows a fabricated frame with a top frame assembly of the
improved device of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The present invention is described herein below with reference to figure - 2. The
improved fan throttling device (03) is having a drive system which constitutes a
combination of a plurality of Linear Motion Guides (05), and a Lead Screw (10).
The Fan Throttling Device (03) is supported by a rigid steel fabricated frame (15)
supported on a concrete foundation (17).
The steel fabricated frame (15) houses the Linear Motion Guides (05), the Lead
Screw Assembly (10), and an electric motor (13) with a gearbox (14). A top
frame assembly (21) sits on the Linear Motion Guides (05).
The top frame assembly (21) houses a cone (19), a vertical plate (22) and
associated stiffeners. It also houses a drive bracket (23). The drive bracket (23)
is mated to a lead screw flange (24). The lead screw (10) is mated to the electric
motor (13) with the gear box (14).
The electric motor (13) with the gear box (14) produces a rotary motion which in
turn is converted into a linear motion by the lead screw (10). The lead screw
flange (24) along with the nut (11) moves linearly over the lead screw (10). This
moves the drive bracket (23) which is a part of the top frame assembly (21).

The top frame assembly (21) houses the cone (19), the vertical plate (22) with
associated plates and stiffeners. Thus the linear movement of the cone (19) with
respect to the duct (18) is achieved.
This improved throttling device (03) is adaptable to higher sizes of duct with
corresponding load-bearing capacity.
The following are the salient features of the improved fan throttling device (03)
1. It eliminates the rod (08) and roller (09) arrangement of the prior art
device (04) and replaces the function by providing a combination of Linear
Guides (05) and Lead screw assembly (10).
2. The total load on the Fan Throttling Device (03) is met by separately
using a combination of the Linear Motion Guide (05) and the Lead Screw
Assembly (10).
3. The Linear motion guides (05) are selected to take the self load of the
throttling device (03). The Linear Motion Blocks (07) are placed farthest
on Linear Motion Rails (06) from the point of application of the load such
that it can effectively oppose the moments of iinertia occurring due to the
airflow from the fan (02).

4. In addition, the Linear Motion Guides (05) provide smooth operation and
longer life to the device. It also can take higher permissible load.
5. The lead screw assembly (10) is designed to take the axial load due to the
airflow from the fan (02). The Lead Screw Assembly (10) has a self
locking feature. It will ensure that the improved fan throttling device (03)
will not move on its own when the full load of the fan (02) airflow acts on
the cone (19) of the throttling device (03).
6. The lead screw assembly (10) is operated by an electric motor (13, 14).
The lead screw assembly (10) is shaft driven thus eliminating
maintenance issue associated with chain drive system of prior art.
7. The Electric Motor (13, 14) has an integral brake to hold the Lead screw
flange (20) in a predetermined position opposing the load occurring due
to the fan airflow.
8. The electric motor (13 and 14) is rigidly mounted on the steel fabricated
frame structure (15).
9. The improved throttling device (03) can be remotely operated from the
control panel.

WE CLAIM
1. An improved fan throttling device (03) for testing of fans adaptable to
power and industrial boiler, comprising:
- a drive means comprising a lead screw assembly (10, 24) having a lead
screw (10) and a flange (24);, and a plurality of linear motion guides (05),
the lead screw assembly (10, 24) having a self-locking feature and
enabled to withstand the axial load due to air flow from the fan (02)
through a duct (18);
- a fabricated frame (15) for supporting the device (03) and
accommodating the drive means (05, 10) including a rotating means
comprising at least one electric motor with gearbox (13, 14), the rotating
means (13, 14) producing a rotary motion which is translated into a linear
motion by the lead screw assembly (10, 24), the lead screw (10) being
attachable to the electric motor (13); and
- a top frame assembly (21) disposed on the linear motion guides (05), and
accommodating a cone (19), a vertical plate with stiffeners (22), and a
drive bracket (23) attachable to the lead screw flange (24), the linear
movement of the lead screw assembly (10, 24) generating a linear
movement of the cone (19) in respect of the duct (18).

2. The device as claimed in claim 1, wherein the fabricated frame (15) is
supported on a concrete foundation (17).
3. The device as claimed in claim 1, wherein the self-locking feature is a nut
(11) which alongwith the lead screw flange (24) linearly moves over the

lead screw (10).
4. The device as claimed in claim 1, wherein the linear motion guides (05)
comprises linear motion rails (06).
5. The device as claimed in any of the preceding claims, wherein both ends
of the lead screw (10) is supported by a double angular contact bearing
(12).
6. The device as claimed in any of the preceding claims, wherein the lead
screw (10) is made of high strength steel manufactured through rolling
and milling operation.
7. The device as claimed in claim 1, wherein the frame structure (15)
comprises a fabricated steel structure.
8. The device as claimed in claim 1, optionally comprising at least one
displacement transducer attachable to the linear motion guides (05) to
enable the device (03) to automatically carry-out the testing process.
9. An improved fan throttling device for testing of fans adaptable to power
and industrial boiler as substantially described and illustrated herein with
reference to the accompanying drawings.

The invention relates to an improved fan throttling device (03) for testing of fans
adaptable to power and industrial boiler, comprising a drive means comprising a lead screw assembly (10, 24) having a lead screw (10) and a flange (24);, and a plurality of linear motion guides (05), the lead screw assembly (10, 24) having a self-locking feature and enabled to withstand the axial load due to air flow from
the fan (02) through a duct (18); a fabricated frame (15) for supporting the device (03) and accommodating the drive means (05, 10) including a rotating means comprising at least one electric motor with gearbox (13, 14), the rotating means (13, 14) producing a rotary motion which is translated into a linear
motion by the lead screw assembly (10, 24), the lead screw (10) being attachable to the electric motor (13); and a top frame assembly (21) disposed on the linear motion guides (05), and accommodating a cone (19), a vertical plate
with stiffeners (22), and a drive bracket (23) attachable to the lead screw flange (24), the linear movement of the lead screw assembly (10, 24) generating a linear movement of the cone (19) in respect of the duct (18).