FIELD OF INVENTION
The present invention relates to a mechanically actuated device to maintain flow
of water into steam generator through a bypass line. More particularly, the invention
relates to a mechanically actuated device placed in a bypass line which collects the feed
water from the upstream of the high pressure heaters (HPH) and releases water to the
downstream of high pressure heaters through a bypass line.
BACKGROUND OF THE INVENTION
In a thermal power plant water is converted to steam in a steam generator. This
steam when reached to super heated steam phase is allowed to impinge on the blades
of high pressure turbine which in turn rotates and makes the rotor connected to it to
rotate resulting in power generation.
The water required for generating steam is pumped by Boiler Feed Pump
(hereafter referred as “BFP”) which flows through the High Pressure Heaters (hereafter
referred as “HPH”), Feed water control station, Economiser and then into the boiler for
further conversion into steam.
The pipe connecting the BFP with HPH are called as, BFP discharge line. The pipe
connecting the HPH with Feed water control station is called as HPH Outlet line.

Temperature of feed water is increased from BFP discharge temperature to HPH
outlet temperature when flowing through the HPH by using heat exchange method.
Isolating valves are provided in the upstream and downstream of the HPH.
These valves are used to isolate the HPH when there is any maintenance requirement
in the HPH.
When there is any issue in the HPH such as leakage/blockage in the pipelines of
HPH, the flowrate of water through HPH will be reduced which leads to starvation of
economizer. In such circumstances, immediate action for the maintenance of HPH is
envisaged. Isolation valves which are available in the upstream and downstream of the
HPH are closed so that HPH can be taken for maintenance.
At this juncture it is necessary to maintain the required flowrate to the
economizer. This is achieved by bypassing HPH, by taking a bypass line already existing
in the system from BFP discharge line and connecting the same to HPH outlet.
However, there is a possibility of BFP shut off pressure being communicated to
the piping system through this bypass line, also, this line will feed economizer with
water at lower temperature when compared to water flowing through the HPH. This
temperature difference will affect the efficiency of the system.

Hence the requirement for controlling the flow through the bypass line arises.
This can be achieved by allowing the flow of feed water in the bypass line by
considering the differential pressure across the HPH.
The present invention meets the requirement by providing a mechanically
actuated device which can be used to maintain flow in High Pressure and High
Temperature Steam Generator by allowing the flow of feed water in the HPH bypass
line by considering the differential pressure across the HPH.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a mechanically actuated
device to maintain flow of water into steam generator through a bypass line, which is
capable of maintaining continuation of flow of feed water to the economizer and then to
the boiler.
Another object of the invention is to propose a mechanically actuated device to
maintain flow of water into steam generator through a bypass line, which can avoid the
possibility of BFP shut off pressure being communicated to the piping system through
HPH bypass line.

A still another object of the invention is to propose a mechanically actuated
device to maintain flow of water into steam generator through a bypass line, which is
able to control the flow of feed water in the HPH bypass line by considering the
differential pressure across the HPH.
A further object of the invention is to propose a mechanically actuated device to
maintain flow of water into steam generator through a bypass line, which ensures less
pressure drop across the body of the device.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
It is to be noted, however, that the appended drawings illustrated only typical
embodiments of the present subject matter and are therefore not to be considered for
limiting of its scope, for the invention may admit to other equally effective
embodiments.
The detailed description is described with reference to the accompanying figures.
In the figures, the left-most digit (s) of a reference number identifies the figure in which
the reference number first appears. The same numbers are used throughout the figures
to reference line features and components. Some embodiments of system or methods
in accordance with embodiments of the present subject matter are now described, by
way of example, and with reference to the accompanying figures.

Figure-1 illustrates the schematic diagram of the existing system in which feed
water is pumped in a High Pressure and High Temperature Steam Generator, in
accordance with an embodiment of the present subject matter;
Figure-2 illustrates the schematic diagram of the proposed Mechanically actuated
device used to maintain flow in High Pressure and High Temperature Steam Generator,
in accordance with an embodiment of the present subject matter;
Figure-3 illustrates a detail of one of the prime features–Disc- of the current
embodiment of the present subject matter.
Figure-4 illustrates one more detail of the same feature –Disc- illustrated in
Figure-3 of the current embodiment of the present subject matter.
Figure-5 illustrates a detail of one of the prime features – Spring Assembly- of
the current embodiment of the present subject matter.
The figures depict embodiments of the present subject matter for the purposes
of illustration only. A person skilled in the art will easily recognize from the following
description that alternative embodiments of the structures and method illustrated herein
may be employed without departing from the principles of the disclosure described
herein.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The subject matter of the present invention relates to a device comprised with a
globular body, a movable disk (3) with pressure balancing arrangement, a stationary
ring seat and with spring (22) actuation mechanism accommodating the flow
requirement, ensuring less pressure drop across the body and acting based on
differential pressure which is used to feed the economizer in the event of outage in the
HPH to prevent starvation.
According to FIG-1,The water required for generating steam is pumped by Boiler
Feed Pump which flows through the High Pressure Heaters, Feed water control station
and then into Economiser.
When there is any issue in the HPH such as leakage/blockage in the pipelines of
HPH, the flowrate of water through HPH will be reduced which leads to starvation of
economizer. In such circumstances, immediate action is required to maintain the
flowrate. This is achieved by bypassing HPH, by taking a bypass line from BFP
discharge line and connecting the same to HPH outlet.

This line will feed Economiser with water at lower temperature when compared
to water flowing through the HPH. This temperature difference will affect the efficiency
of the system.
The present invention as described in FIG-2 meets the requirement of a
mechanically actuated device which can be used to maintain flow in High Pressure and
High Temperature Steam Generator by allowing the flow of feed water in the HPH
bypass line by considering the differential pressure across the HPH.
In FIG-2, which depicts the current embodiment, feed water will be available on
both sides of the Disc (3). However, the direction of flow is always from the inlet to the
outlet side of the device. This device works on the basis of differential pressure i.e.
difference of pressure between the inlet and outlet side of the device, where the
pressure at the inlet of the device will always be on the higher side. When the
differential pressure reaches the set pressure of 7.5 kgf/cm2 at which the Spring (22) is
set, the Disc (3) will be moving in the upward direction which inturn pushes the Stem
(4) upwards, resulting in compression of the springs (22) where two springs are
arranged in series. This upward movement of the Disc (3) allows the flow through the
device and also stores a potential energy in the springs (22). When the differential
pressure across the device falls below the set pressure, the stored potential energy in
the spring pushes the Stem (4) which inturn pushes the Disc (3) in downward direction
against the flow of water, when the Disc (3) hits the seat (2) and arrest the flow.

One of the features of the current embodiment is that the Body (1) comprises of
a welded Seat ring (2) which is a metallic ring with hard facing on it and the seat is
machined such that a tapered seat arrangement is obtained which ensures positive
sealing by self-alignment of the Disc (3) ensuring contact during operation. If the hard
facing is done directly on the body, the body needs to be heat treated at higher
temperature for stress relieving, whereas in the current case hard facing is done on the
seat ring and stress relieving is done for the same. However, when a hard faced seat
ring is welded to the body, local heat treatment of the welded portion for relieving the
stress in the weld joint is sufficient. Hence welded seat ring arrangement ensures ease
of manufacturing by avoiding heat treatment of body and ease of maintenance of the
device if such a requirement arises.
In another feature of the current embodiment, the Disc (C) as indicated in FIG-3
is designed such that there is a conical nose like structure on the inlet and outlet sides
of the device, in which conical nose on the inlet side aids to controlled linear flow of
water parallel to the tapered seat and also maximizes the flowrate across the seat in a
short span of opening. The conical nose on the outlet side of the device is designed to
suit the spherical nose of the Stem (B) which aids in re-alignment of the stem force to
the center of the disc which further aids in positive sealing around the Seat (A).

The disc is further designed such that groove available on the disc, guides the
flow such that a back pressure is created on the disc which in turn provides a
cushioning effect on the disc when the disc tries to move in downward direction, which
further avoids chattering of the disc thus avoiding the damage to the disc and seat.
Also, the disc is designed with holes (more than 1) as shown in FIG-4, allows the
water inside the Disc (3 of FIG-2) to flow into the Body (1 of FIG-2) relieving the excess
pressure created by the water available inside the disc during its upward movement.
Thus these holes balance the pressure on the outer side and the inner side of the disc.
In another feature of the current embodiment, the Disc Guide (23 of FIG-2) is
designed such that the Disc (3 of FIG-2) is guided through this and at the same time
avoids any possibility of tilting of the disc.
In another feature of the current embodiment, the Stem (4) as indicated in FIG-2
is designed with the (i) Spherical nose, (ii) Spherical seating and (iii) length, of which
Spherical nose is designed to suit the conical nose in outlet side of the disc (3),
Spherical seat is designed to complement the tapered profile in the Spring Bottom
Washer (6) and the length of the stem is designed such that stem is guided inside the
Spring Adjuster (10). All the above specialities of the stem aids in self-alignment of the
Stem (4) during the compression and de-compression of the spring to the center of the
disc which further aids in positive sealing around the Seat (2).

In another feature of the current embodiment, the Spring Assembly (22) as
detailed in FIG-5 is designed with specialities as mentioned below.
(i) Two springs arranged in series (25)
(ii) Spring guide (26)
(iii) Pre-compression bolts and nuts with washers (27)
(iv) Spring Bottom Washer (28)
(v) Stopper plate with screws and washers (29)
(vi) Spring Top Washer (30)
Two springs (25) are designed such that the spring rate of 27.488 kgf/mm for
each spring required for the load acting on the disc (3 of FIG-2) and the required stroke
of the valve is distributed between two springs and the device meets the required set
pressure. This arrangement of two springs in series is having the advantage of
economically manufacturing the springs with commercially available raw materials.
The spring guide (26) is designed such that this fits into the above two springs
and hence used for guiding, connection of the two springs and aids in transmission of
load between the two springs. This also avoids buckling of the springs.

The Pre-compression bolts and nuts with washers (27) are designed such that
the springs can be compressed by tightening the bolts and nuts. This arrangement will
reduce the span of movement of the spring adjuster (10 of FIG-2) to achieve the
required set pressure. This arrangement will also help in limiting the size of the bonnet.
Since this arrangement converts the springs as an assembly where the spring assembly
as a whole can be removed during maintenance activity hence ensuring safety for
maintenance. Holes are drilled in the heads of the pre-compression bolts to insert a
stainless steel wire thus avoiding rotation of the bolts due to vibration during assembly,
transportation and operation.
The Spring Bottom Washer (28) is designed with slots to suit the Pre-
Compression Nut, such that their rotation is arrested, also it is designed with a tapered
face to complement the spherical face of stem for self-alignment of the spring.
The Stopper Plate with screws and washers (29) is designed such that it is
screwed to the bottom spring washer (iv of FIG-5) which avoids the pre-compression
nuts from falling down and disturb the alignment of the stem.
The Spring Top Washer (30) is designed such that a hard faced layer with a
taper to complement the spherical profile of the spring adjuster (10 of FIG-2) helps to
avoid erosion and ensure smooth rotation of the spring adjuster (10 of FIG-2).

In another feature of the current embodiment, Spring Adjuster (10 of FIG-2) is
designed such that it is capable of taking the load transmitted by the spring assembly
by mating through a thread in the Bonnet Bush (17 of FIG-2) and the spherical portion
ensures smooth rotation of the spring adjuster (10 of FIG-2) over the Spring Top
Washer (5 of FIG-2). This along with Locknut (11 of FIG-2) helps in setting the required
set pressure by compressing the spring due to its rotation and maintaining the spring
compression.
In another feature of the current embodiment, Bonnet Bush (17 of FIG-2) is such
that it provides a minimum required thread engagement for taking the load transmitted
by the spring assembly during operation.
In another feature of the current embodiment, Cap (13 of FIG-2) is designed
with a through hole in which a threaded Plug (14 of FIG-2) is provided which helps in
detection of availability of pressure inside the device just by loosening the Plug (14 of
FIG-2) which in turn avoids the pain of loosening the NUTS (16 of FIG-2) and also
ensuring the safety of the maintenance personnel. This cap is also designed such that it
acts as a lift stop for arresting the span of opening of the device which in turn avoids
failure of the spring.
In another feature of the current embodiment, Stainless steel Ring joint gaskets
(12 and 24 of FIG-2) are used in this device between Body (1 of FIG-2) – Bonnet (7 of

FIG-2) and Bonnet (7 of FIG-2) – Cap (13 of FIG-2) bolted flange joints to ensure
positive sealing against internal pressure and avoiding corrosion of the gaskets which
can be caused due to contact of medium.
The embodiment of the present subject matter has been manufactured for a size
16”, pressure class rating 2000SPL and Set pressure range to suit the project
requirement and the same has been tested at our factory as per the test data provided
below.

Although embodiments for the present subject matter have been described in
language specific to structural features, it is to be understood that the present subject
matter is not necessarily limited to the specific features described. Rather, the specific
features and methods are disclosed as embodiments for the present subject matter.
Numerous modifications and adaptations of the system or device of the present
invention will be apparent to those skilled in art and thus it is intended by the appended
claims to cover all such modification and adaptations which fall within the scope of the
present invention.

WE CLAIM
1. A mechanically actuated device to maintain flow of water into steam generator
through a bypass line, the said device comprising;
a movable disc (3) for allowing and arresting the flow of water; the said disc
having a conical nose like structure on the inlet and outlet side of the device with
plurality of pressure balancing holes;
a stem (4) capable of moving upwards and downwards;
a body (1);
a disc guide (23) for guiding the disc (3) to avoid tilting of the disc (3);
a spring assembly (22),
the said spring assembly comprising;
two springs arranged in series (25);
a spring guide (26);
a plurality of pre-compression bolts and nuts (19) with washers for compressing
the springs and for reducing the span of movement of the spring adjuster (10) to
achieve the required set pressure;
a spring bottom washer (6);
a stopper plate with screws and washer (20) screwed to the bottom spring
washer (6) for restricting the said nut (19) to fall down;

a spring top washer (5);
a spring adjuster (10) for setting the set pressure of the device, guiding the stem
(4) and for ensuring self alignment of the stem during compression and decompression
of the spring to the centre of the disc;
a lock nut (11) for arresting the rotation of the spring adjuster (10) after the set
pressure is set;
a threaded bonnet bush (17) for guiding the spring adjuster (10) ensuring its
smooth rotation over the spring top washer (5);
a cap (13) disposed on the top of the bonnet (7);
a plug (14);
a plurality of stainless steel ring joint gaskets disposed in the device between
body (1) and bonnet (7) and bonnet (7) and cap (13) for ensuring positive sealing
against internal pressure;
Characterized in that,
two springs (25) disposed in series configured with a spring rate required for the
load acting on the disc (3) during operation and for making the device to meet the
required set pressure wherein the spring guide (26) disposed for guiding the springs
and transmission of load between springs and avoiding buckling of the springs wherein
the spring bottom washer (6) having slots to suit the pre-compression nut to arrest
their rotation configured with a tapered face to complement the spherical face of stem

for self-alignment of the spring assembly (22) wherein the spring top washer (5) having
a hard faced layer with a taper to complement the spherical profile of the spring
adjuster (10) ensuring its smooth rotation wherein, a welded metallic seat ring (2) with
hard facing and machined tapered seat arrangement is provided for positive sealing by
self alignment of the disc (3),
wherein the disc (3, C) is configured with a conical nose on the inlet side for
controlling linear flow of water parallel to the tapered seat (2) and for maximizing the
flowrate across the seat in a short span of opening during upward movement of the
disc (3) and stem (4), when the springs (25) are set at set pressure, wherein the
conical nose on the outlet side of the device configured to match spherical nose of the
stem (4, B) for realignment of the stem force to the centre of the disc and for arresting
the flow of water when the disc (3, C) and the stem moves downward making a
positive sealing around the seat (2, A) as the spring falls below the set pressure,
wherein the cap (13) having a through hole in which a threaded plug (14) is provided
for detecting availability of pressure inside the device by loosening the plug (14), the
said cap acts as a lift stop for arresting the span of opening of the device to avoid
failure of the springs (25).
2. The device as claimed in claim 1, wherein the stem (4) is configured with
spherical seat to complement the tapered profile in the spring bottom washer (6) and

the length of the stem is such maintained that the stem (4) is guided inside the spring
adjuster (10) for maintaining self-alignment of the stem (4) during compression and de-
compression of the spring and for creating a positive sealing around the seat.
3. The device as claimed in claim 1, wherein the spring rate of each spring is
maintained at 27.488 kgf/mm.
4. The device as claimed in claim 1, wherein the set pressure for the device to act
is maintained at 7.5 kgf/cm2.