FIELD OF THE INVENTION
This invention generally relates to butterfly valves used in hydroelectric and lift irrigation
systems. In particular, this invention is an arrangement of flexible metallic maintenance
seal on single disc butterfly valves so that the main rubber seal can be of rubber and may
be replaced easily sans dewatering the upstream pipe of the valve.
BACKGROUND OF THE INVENTION
A butterfly valve is an emergency shut-off / maintenance device installed for any of the
following applications:
a) When used as a main inlet valve, it acts as an emergency closing device to shut-off
water to a turbine in the event of failure of the turbine water regulating mechanism.
b) When used as a main inlet valve it can be closed in conjunction with draft tube gates
for carrying out maintenance of underwater parts of turbine after dewatering.
c) When used as a penstock guard valve, it acts as an emergency closure device to cut-off
water in the event of failure of penstock either due to earthquake/landslides or due to
bombardment by enemy. It is also used in emergency when both the water regulating
mechanism of a turbine and the main inlet valve to shut off water to the turbine fails.
d) When used as a penstock guard valve, it operates an isolating device for carrying out
maintenance of the main inlet valve in a power house.

e) For high head reversible pump turbine installations with a long tail race tunnel and deep
submergence, the emergency shut-off valve is installed in a draft tube, and can be closed
in conjunction with the main inlet valve (spherical valve) for dewatering and carrying out
inspection and repair of underwater components.
Conventionally, the butterfly valves comprise only one seal of rubber fixed on the door,
and when the door was turned by 90 degrees from its full open position, the seal is
pressed against a stainless seat in the valve body. But since the rubber seal is fixed on the
door, it rests in the flow passage and gets eroded by the silt particles in the flowing water.
Replacement of this seal, needs dewatering of an upstream water conductor system,
which is time consuming and leads to heavy generation loss of turbine generating sets due
to long shutdown. To reduce this downtime for replacement of the main seal of rubber, the
butterfly valves with different types of maintenance seals are available in the art. Salient
features of some of the prior art seals are described in the ensuing portions.
As shown in figure 1, a butterfly valve consists of a body(l) in which rotates a door(14)
with a rubber seal fixed on a downstream disc (4) as service seal (5) and a metallic sealing
(12) on an upstream disc (13). This arrangement of metallic maintenance seal (12) on the
upstream disc (13) has many lacunas. Firstly this prior art calls for one additional disc to
accommodate the metallic maintenance seal (12) arrangement which exhibits higher flow
losses. Secondly, on account of additional disc, this known arrangement increases the cost
of the valve. Thirdly, in this known design, there are two components which take part in
the sealing . One is a moveable cylindrical component (8) and other is a metallic
maintenance seal (12)mounted on disc. When the door under pressure gets deflected
towards downstream, perfect sealing in trunnion (16) zone take place due to desired line
contact of the moveable component (8) on the other hand, perpendicular to the trunnion,
the sealing goes out of plane due to deflection and a crescent gap is created at the top and

bottom discs leading to a profuse leakage from the upstream disc (13). Fourthly, to cater
for this leakage problem, a variable tightening arrangement having disc springs (15) is
used which requires skilled operator and huge time for tightening to arrest the leakage
substantially.
As shown in fig 2, another sealing arrangement is known where a Butterfly valve door (14)
having two discs houses including two rubber sealing elements, one each on upstream
disc (13) and downstream disc (4). In this design the metallic seal of upstream disc (13)
was replaced with a rubber sealing element (7) to cater for tight sealing and eliminate
tedious variable tightening arrangement of prior art of figure 1. However this design has
two drawbacks. First this design also has double disc configuration like prior art of figure
1, and subjected to more flow losses & escalates the cost of the valve. Secondly it has a
major drawback of erosion of rubber sealing element (7) clamped on the upstream disc
(13).
Figure 3 shows another known sealing arrangement for butterfly valves. This design
involves a main sealing (5) and. a maintenance sealing (7) on downstream side and
eliminates the additional upstream disc (13) for the provision of maintenance sealing.
Although this design addresses the issue of flow loss of prior art shown in figures 1 and 2,
but it has its own drawbacks. Firstly in this design maintenance seal is of rubber element
(7) like that of figure 2, which is subjected to erosion and becomes defunct easily.
Secondly, this design also requires variable tightening adjustment for the maintenance
seal (7).

OBJECTS OF THE INVENTION
It is therefore, an object of the invention to propose a flexible metallic maintenance seal
(12) on single disc butterfly valves which has a prolonged life against silt erosion.
Another object of the invention is to propose a flexible metallic maintenance seal (12) on
single disc butterfly valves which facilitates easy replacement of the main rubber seal (5)
without dewatering the upstream water conductor system.
A still another object of the invention is to propose a flexible metallic maintenance seal
(12) on single disc butterfly valves, which accommodates both the maintenance seal and
main rubber seal on a single disc thus minimizing the flow losses.
A further object of the invention is to propose a flexible metallic maintenance seal (12) on
single disc butterfly valves, which enables both the valve seal and valve seat to absorb
deflection of the door including the valve body to achieve a better sealing.
SUMMARY OF THE INVENTION
In order to reduce flow loss due to down time associated with dewatering of upstream
water conductor system, an additional disc on the upstream side to accommodate either
a rubber maintenance seal (7) or a stainless steel maintenance seal (12), is provided in
prior art butterfly valves. The additional disc introduced losses, minimized the flow
however problems on the upstream stainless steel seal (12) was noticed relating to sealing
performance. Another prior art design of butterfly valve with a single disc had a rubber
maintenance seal (7) of "J" type profile housed in a downstream flange (17) of the valve

body. This design had a better sealing performance but suffered from the drawback of
erosion of the seal being made of rubber. The present inventors noted that a flexible
sealing device for single disc butterfly valves with metallic maintenance seal (12) can be
designed to reduce the flow losses, improve sealing performance and enhance life of the
seals operating in silt laden waters.
Accordingly, the present invention provides a single disc butterfly valve with metallic
(stainless steel) maintenance seal. This design has a movable stainless seat ring housed
in a downstream flange of the butterfly valve, to be moved towards the door by water /oil
pressure when the metallic maintenance seal is to be engaged for replacement of the
main rubber seal. The movable seat ring has a thin flexible lip at the front end which
makes contact with the stainless steel seal fixed on the door. The stainless seal fixed on
the door is a thin hollow structure filled up by hollow rubber / polyurethane extrusion. This
hollow extrusion prevents filling up of the cavity by silt/mud so that flexing of seal which
is important is not hindered. As compared to rigid sealing systems of prior art, flexing of
both the movable seat as well as the maintenance seal by the inventive sealing device
helps in absorbing the deflections of door and body and achieve a better sealing.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1: Prior art-1 Double disc butterfly valve with metallic maintenance seal
Figure 2: Details of double disc butterfly valve of figure 1.
Figure 3: Double disc butterfly valve with rubber maintenance seal according to prior art.
Figure 4: Details of the seal of figure 3.
Figure 5: Single disc butterfly valve with rubber maintenance seal according to prior art.
Figure 6: Details of the sealing arrangement of figure 5.
Figure 7: Single disc butterfly valve with stainless steel maintenance seal according to the
present invention.

Figure 8: Details of engaged position of the maintenance seal of figure 7.
Figure 9: Details of disengaged position of the maintenance seal of figure 7.
List of Items
I.BF Valve Body
2.Seat Carrier Ring
3.Dismantling Ring
4.Downstream Disc of BFV Door
5.Service Seal of Rubber
6.Clamping Ring
7.Maintenance Seal of Rubber
8.Sliding Ring/Movable seat ring
9.Sealing Flange
lO.Spacer Ring
Il.Service seal of Metal
12.Maintenance seal of Metal
13.Upstream Disc of BFV Door
14. BFV Door
15.Disc Spring
16.Trunnion
17.Downstream Flange of Body
18.Hollow rubber /Polyurethane
19. Round Nuts
20. Rib
21.Studs
22.0 ring

DETAILED DESCRIPTION OF THE INVENTION
This inventive design consists of a movable stainless steel seat (8) with flexible sealing lip
which is moved forward by fluid pressure for engaging. In this design the single disc of the
butterfly valve houses two seals. One seal of rubber acts as service seal (5) while other
one fixed behind the service seal is a metallic seal acts as maintenance seal (12). Movable
stainless steel seat ring (8) when advanced towards upstream gets engaged with metallic
maintenance seal (12) clamped on disc (4) .Movable stainless steel seat (8) has an
integral/in-built flexible sealing lip which provides the effective sealing along the periphery
and cater for variable deflection of door(14) and body(l) which is a lacuna in prior art-1 &
3,Metallic maintenance seal(12) housed on disc (4) behind the service seal(5) is of hollow
construction. It is clamped on disc using studs (21) & round nuts (19) fixed in counter
bores. Hollow construction of maintenance seal (12) allows it to flex according to variable
deflection pattern of door (14) and body (1). In order to maintain this flexing feature of
maintenance seal (12), hollow space of seal is filled up by a hollow rubber or polyurethane
(18) of suitable cross section. Putting a hollow rubber or polyurethane into the hollow
space of maintenance seal also prevents the hollow space of the stainless seal (12) from
getting filled up by mud/silt and hampering flexing which is an important requirement for
satisfactory performance of seal. Movable stainless steel seat (8) is strengthen by ribs (20)
to maintain its rigidity during handling and its controlled flexing when door and body get
deflected and sealing takes place.Maintenace seal (12) is of such a construction that its
hollow shape allows it to flex according to deflection pattern and provides better sealing.
At the same time, this peculiar shape also acts as a guard against the silt present in flowing
water. Since this design does not require any additional disc to accommodate
maintenance seal (12) rather has an inventive arrangement to put the maintenance seal
along with service seal (5) on the single disc; which makes this design more economical
and free from flow losses associated with additional disc. This invention also eradicates the

problem of erosion of seal like prior art 2&3 wherein maintenance seal is of rubber (7)
whereas in this design maintenance seal is of metal. This design also provides a circular'O'
ring (22) on disc to avoid any residual possibility of leakage through the clearance holes
given for clamping.

WE CLAIM :
1. A flexible metallic maintenance seal for single disc butterfly valves.; comprising:
- a movable stainless steel seat (8) with seals housed in a downstream flange (17) of the
valve body (1), such that the seat (8) can be moved forward by fluid pressure (water
/oil) towards a maintenance seal (12), for engaging the maintenance seal (12) as well
as replacing a main rubber seal (5); and
- a main rubber seal (5) disposed behind the maintenance seal (12), wherein the
movable stainless steel seat (8) comprising a flexible sealing lip at a front end to seat
against the maintenance seal (12) fixed on the disc (4) of the door (14), the flexing of
the seal absorbing the varying deformation pattern of the valve body (1) and door (14)
along the sealing periphery, wherein the flexing of the front sealing lip is restricted by
ribs welded on the movable seat (8), wherein the maintenance seal (12) is fixed on the
disc (4) of the door (14) behind the main seal (5) by round nuts (19) in counter bored
holes of the maintenance seal (12), and wherein the maintenance seal is made hollow
so that it can flex to absorb variation of deformation pattern of the door (14) and the
body (1) along the sealing periphery.
2. The device as claimed in claim 1, wherein the hollow space of the maintenance seal
(12) is filled up by a hollow rubber or polyurethane extruded seal (18), to prevent the
hollow space of the stainless seal (12) from getting filled up by mud /silt and allows
flexing which is the required technical parameter to achieve better sealing.

ABSTRACT

The invention relates to a flexible metallic maintenance seal for single disc butterfly
valves.; comprising: a movable stainless steel seat (8) with seals housed in a
downstream flange (17) of the valve body, such that the seat (8) can be moved
forward by fluid pressure (water /oil) towards a maintenance seal (12), for engaging
the maintenance seal (12) as well as replacing a main rubber seal (5); and a main
rubber seal (5) disposed behind the maintenance seal (12), wherein the movable
stainless steel seat (8) comprising a flexible sealing lip at a front end to seat against the
maintenance seal (12) fixed on the disc (4) of the door (14), the flexing of the seal
absorbing the varying deformation pattern of the valve body (1) and door (14) along
the sealing periphery, wherein the flexing of the front sealing lip is restricted by ribs
welded on the movable seat (8), wherein the maintenance seal (12) is fixed on the disc
(4) of the door (14) behind the main seal (5) by round nuts (19) in counter bored holes
of the maintenance seal (12), and wherein the maintenance seal is made hollow so
that it can be correspondingly flexed to absorb variation in the deformation pattern of
the door (14) and the body (1) along the sealing periphery.