FIELD OF INVENTION
The invention relates to Butterfly valves used in hydro electric projects. More
particularly this invention relates to a guard designed to protect butterfly valve
seals against silt erosion.
BACKGROUND OF THE INVENTION
A butterfly valve is a shut-off device upstream of a turbine or upstream of a
main inlet valve to turbine. A butterfly valve serves the following functions:
1. As an isolating device for carrying out maintenance of either the turbine when
used as a main inlet valve or of the main inlet valve when used as a penstock
valve.
2. As an emergency closing device to shut off water to turbine in the event of
failure of water regulating mechanism when used as a main inlet valve.
3. As an emergency closing device to shut off water in the event of bursting of
penstock or failure of main inlet valve.
A butterfly valve consists of a door (4) as shown in fig.1 with a rubber seal (1)
clamped on to it at its periphery on disc (4a). For closing of the butterfly valve

the door is turned so as to make the disc (4a) vertical i.e. perpendicular to flow.
In this closed position the rubber seal (1) presses against a stainless steel seat
(3) in the valve body (2) and seals the upstream water.
For opening the butterfly valve the door (4) is turned through 90° to make the
disc (4a) parallel to the flow, as shown in fig.2.
When the rubber seal (1) gets worn-out or becomes ineffective the water
conductor upstream and downstream of the valve is dewatered and the rubber
seal is replaced. This process of dewatering the water conductor system and
replacement of rubber seal takes lot of time which leads to generation loss.
To minimize the shutdown time and the generation loss the next generation
butterfly valves have been provided with maintenance seal (5), as shown in fig.3.
The intended purpose of the maintenance seal (5) was to avoid dewatering of
water conductor system upstream of the valve. However in silt laden water the
maintenance seal (5) though intended only for occasional use did not prove to be
effective when really put to use.
Root cause analysis revealed that both the main seal and maintenance seal
which are fixed on the door get damaged by impingement of the hard sand
particles. The sealing surfaces get damaged and the valve leaks profusely when

closed. So, there exists a need to find protective means to guard the seals (1)
and (5) from silt erosion. Accordingly, this invention is about providing protection
to the seals (1) and (5) fixed on door against the impingement of sand particles
in order to prolong the life of the seals and minimize the generation loss.
In the prior designs of butterfly valves with lattice type doors either of single disc
type or double disc type there was no protection guard against silt erosion. The
silt (sand) particles in flowing water impinge on the rubber seal fixed on the
butterfly valve door and sealing surfaces of the rubber seal gets damaged.
Butterfly valves with such damaged seals leak badly when closed for either
emergency or maintenance.
Since the maintenance seal (5) which is also of rubber gets eroded in this portion
facing flow, leaks profusely when applied for replacing main seal.
OBJECTS OF THE INVENTION
Therefore it is an object of the invention to propose a guard for single disc and
two guards for double disc for butterfly valve seals of hydel projects for
protection against silt erosion which can bear the impingements of hard sand
particles.

Another object of the invention is to propose a guard for single disc and two
guards for double disc for butterfly valve seals of hydel projects for protection
against silt erosion which is capable of deflecting and diverting the flow and thus
preventing the rubber seals from hitting by the sand particles.
A further object of the invention is to propose a guard for single disc and two
guards for double disc for butterfly valve seals of hydel projects for protection
against silt erosion which is capable of minimizing the flow disturbance by
providing guidance instead of allowing water to hit on a blunt edge of butterfly
valve door.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - shows general arrangement of lattice type, single disc butterfly valve of
prior art in closed position.
Fig.2 - shows general arrangement of lattice type, single disc butterfly valve of
prior art in open position.
Fig.3 - shows general arrangement of lattice type, double disc butterfly valve
with maintenance seal of prior art in closed position.
Fig .4 - shows general arrangement of lattice type, double disc butterfly valve
with maintenance seal of prior art in open position.

Fig.5 - shows enlarged view of butterfly valve door seal in open and closed
positions of prior art.
Fig.6 - shows enlarged view of butterfly valve door seal damaged by silt erosion
in open and closed positions of prior art.
Fig.7 - shows guard for lattice type single disc butterfly for protection of seal
against silt erosion according to present invention.
Fig.8 - shows guard for lattice type double disc butterfly for protection of seal
against silt erosion according to present invention.
Fig.9 - shows enlarged view of the designs of guard of present invention.
Fig. 10- shows enlarged plan view of the design of guard of present invention
List of items as shown in the drawings
1. Butterfly valve rubber seal
2. Butterfly valve body
3. Stainless steel seat in body
4. Butterfly valve door
4a. Disc of butterfly valve door facing downstream
4b. Disc of butterfly valve door facing upstream
5. Maintenance seal on door
6. Flow guides
7. Steel bar nose
8. Seal clamping ring

9. Nut
10. Stud
11. Valve inlet pipe
12.Stiffener inside flow guard
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
In butterfly valves used in hydel projects, the portion of rubber seals (1,5) fixed
on the door and facing upstream get eroded due to Impingement of hard silt
particles. The guard for protection of these seals comprising of a steel bar and
steel flow guides welded inside the inlet pipe upstream of the valve door that
gives necessary protection against silt erosion. By this guard the life of seals
would be prolonged. The number of shutdowns required for replacement of seals
would be reduced thus minimizing the generation loss.
The rubber seals (1) fixed on the door of butterfly valves of hydel projects get
damaged by silt particles in the flowing water.
In order to reduce the downtime required to dewater the upstream water
conductor for replacement of the rubber seal (1) on disc (4a) of door (4),
maintenance seals (5) as shown in fig.3, were provided on disc (4b) on the next

generation of butterfly valve. However since the maintenance seal (5) seat Is
also in the flow passage it gets damaged and Is not really effective when used
for replacement of main seals.
Thus in order to protect the seals (1) and (5) fixed on butterfly valve door discs
(4a) and (4b) from damage by silt erosion, this invention proposes a protection
guard.
As shown in fig. 10, the protection guard (P) comprises of a steel bar nose (7)
welded upstream of the valve disc inside the valve inlet pipe (11), This steel bar
(7) bears the initial impingement of the silt particle In the flow In front of the
rubber seal on door.
As shown in fig.9, to this steel bar (7) are welded steel flow guide (6) on either
side that is on top and bottom side inside the valve inlet pipe (11). These flow
guides (6) further guide the silt particles deflected by the steel bar (7) away from
the rubber seal (1). Between the flow guides a stlffener (12) Is welded to give
additional rigidity and strength to the protection guard.
As shown in fig.8, in a double disc type lattice door With two rubber seals (1) and
(5) on the door namely the working seal and the maintenance seal two

protection guards (P) are welded in front of the seals (1) and (5) in the inlet pipe
(11).
The steel bar (7) welded inside of valve inlet pipe (11) bears the impingements
of hard sand particles. A plurality of flow guides (6) welded to the steel bar (7)
on the inside of inlet pipe further divert and guide the sand particles deflected by
the steel bar thus preventing them from hitting the rubber seals fixed on the
door and preventing damage. The bar (7) with flow guides (6) minimizes the
flow disturbance which would have otherwise been there on hitting the blunt
edges of valve disc.

WE CLAIM
1. A guard (P) for butterfly valve seals of hydel projects for protection
against silt erosion comprising:
a steel bar (7) welded with a plurality of steel flaw guides (6) on top and
bottom side inside the valve inlet pipe (11);
a stiffener (12) welded between the flow guides (6) for providing
additional rigidity and strength to the protection guard (P); characterised
in that the steel bar (7) bears the impingement of hard sand particles
wherein a plurality of flow guides (6) further divert and guide the sand
particles deflected by the steel bar (7).
2. A guard (P) as claimed in claim 1, wherein one single guard is provided
for a single disc type door of the valve with one seal (1 ).
3. A guard (P) as claimed in claim 1,wherein two guards are provided for a
double size type door of the valve with two seals (1,5).

A guard (P) to protect the seal/seals fixed on butterfly valve door disc/discs (4a and 4b) from damage by silt erosion consists of a steel bar (7) welded with steel flow guides (6) on top and bottom side inside valve inlet pipe (11). A stiffener (12) is welded between the flow guides (6) for providing rigidity and strength to the guard (P). The steel bar (7) bears the impingement of hard sand particles when the flow guides (6) further divert and guide the sand particles deflected by the steel bar preventing them from hitting the rubber seals (1,5).