Apparatus and process for repair of large butterfly valves

A repair of a butterfly valve having metal seat includes de-watering of the valve, and movement of the disc to the open position. As in the prior art, the extant (usually brass) valve seat is machine in situ and capped with a stainless steel substitute seat having relatively low slope in the range of 10.degree. to 20.degree. with respect to the closing valve disc. The valve disc edge and valve disc edge caps are removed. A new valve flap seal clamp and relatively hard rubber seal (in the range of 70.+-.5 shore) is inserted. The new valve seal edge clamp has a profile to completely capture the inserted rubber valve seal edge and assure that all elastic extrusion occurs only to and toward the refurbished valve seat. This elastic extrusion necks down and decreases in cross-section toward the edge of the disc of the valve. When the clamp is compressed, the elastic section of the rubber valve seal is extruded to extend to and toward the valve seat. This extension by extrusion occurs along an axis, which axis is at an obtuse angle with respect to the refurbished seat on the high-pressure side of the valve disc.

This invention relates to the repair of large butterfly valves. More 
specifically, an apparatus and process is disclosed in which metal seats 
and metal flap edges (usually made of brass) are replaced with a 
combination of a stainless steel valve seat and a compressed rubber flap 
edge to provide a new and improved seal. 
BACKGROUND OF THE INVENTION 
I have effected the repair of a 12-foot diameter butterfly valve having a 
brass seat and a brass disc edge. This valve resided in a hydroelectric 
facility of the Tennessee Valley Authority (TVA) and operated at what I 
considered to be a relatively low pressure--under 150 psi. This one repair 
is relevant prior art of which I am aware that is pertinent to this 
invention. 
In this prior art repair, the following procedures were followed: 
First, the valve was de-watered and moved to the open position. 
Second, the valve seat attached to the valve body was machined down. A 
stainless steel seat was placed over the machined down seat and bolted 
into place. By leaving the old machined down seat in place and bolting 
either to the machined down portion of the seat, the valve body or both, a 
repair simplification occurred. 
Third, the metal disc edge was removed from the valve disc. 
Fourth, a rubber seal was substituted for the removed metal seat. 
Finally, the valve was rotated to the closed position. Thereafter, the 
clamping of the rubber was used to effect excursion of the rubber to come 
into contact with the newly refurbished valve seat. 
This repair worked. However, the reader must understand that this valve 
operated in what I denominate to be the low-pressure range. Further, the 
valve was of a dimension that the blue prints of the valve and the actual 
dimensions of the valve tracked fairly closely. 
In what immediately follows, I describe the problem environment of this 
invention; this invention is applied to large high-pressure valves. In 
making this description I will set forth-certain difficulties. The reader 
is to understand that invention can reside in identifying the problem to 
be solved as well as the solution to the problem, once it is known. 
Before describing in detail this improved repair technique, the reader 
should understand that the valves on which the new repair technique is 
proposed are extremely large. For example, one valve is 138 inches in 
diameter or 11 feet 6 inches in diameter. I also should make the point 
that flap valves in hydroelectric facilities are old and come from a time 
in engineering practices that are out of step with current accepted 
techniques and records. For example, most of these valves are at least 
over 30 years old and many on the order of 40 years and older. At the time 
of construction of these large valves, "blue prints" acted more as a guide 
than as a rigid design constraint to the valves. As a consequence, when 
such valves are repaired, reference to the drawings of the valves give the 
repairing engineer a rough idea of valve dimensions--but that is all. 
Actual valve dimensions vary widely from prints of record. For example, 
although the prints often indicate that the valve seats and valve seals 
are round, they frequently depart from what is the modern definition of 
the term "round." Therefore, repair techniques must be ready to 
accommodate unexpected dimensional excursion. 
Trying to transfer my valve repair technique to large high-pressure valves 
left many short-comings. 
First, I understood that my prior technique was not suitable pressures in 
excess of 150 psi. I had to locate a disc edge design with an elastic 
extrudable seal edge that could be relied upon not to elastically deform 
and then leak in high-pressure environments, such as 150 to 600 psi. 
Second, the clamping of the rubber at the edge of the valve flap of the 
prior art design was inadequate. Such clamping was not central to the mass 
of the rubber edge inserted to the valve. As the present design eventually 
developed, finite element analysis gave the realization that clamping of 
the newly substituted valve seat would cause a non-symmetrical elastic 
extrusion of the rubber. This non-symmetrical extrusion of the rubber 
advanced extruded rubber having bending resistance less than the contained 
pressure. Such bending resistance less than the contained rubber would 
lead to leakage in the finished valve. 
Third, while it at first seem logical to provide an increased mass of 
elastically extruded rubber for resistance of high pressure, it turned out 
that the elastic extrusion of rubber required instead a decreased mass of 
compressed elastically extruded rubber at the valve seat contacting 
portion of the flap. 
Finally, in the originally fabricated edge of the valve seat, the edge 
protruded normally outward of the valve seat. As will hereafter become 
apparent, the extruded edge of the seat has angularity with respect to the 
seat edge. Specifically, the elastically extruded portion of the disc edge 
is inclined to and toward the high-pressure portion of the valve disc. 
This inclination gives the extruded portion of the valve flap an "over 
center" seating. For the seal produced by this invention to fail, the 
elastically extruded portion of the valve disc edge must compress with 
respect to the valve seat. Further, and during such compression with the 
valve seat, the elastically extruded portion of the valve seat must deform 
in a manner, which is "over-center." Thus, resistance of leakage at high 
pressure is enhanced by the disclosure of the disc edge design here set 
forth. 
SUMMARY OF THE INVENTION 
A repair of a butterfly valve having metal seat includes de-watering of the 
valve, and movement of the disc to the open position. As in the prior art, 
the extant (usually brass) valve seat is machine in situ and capped with a 
stainless steel substitute seat having relatively low slope in the range 
of 100 to 200 with respect to the closing valve disc. The valve disc edge 
and valve disc edge caps are removed. A new valve disc edge clamp and 
relatively hard rubber seal (in the range of 70.+-.5 shore) is inserted. 
The new valve disc edge clamp has a profile to completely capture the 
inserted rubber valve seal edge and assure that all elastic extrusion 
occurs only to and toward the refurbished valve seat. This elastic 
extrusion necks down and decreases in cross-section toward the edge of the 
seal of the valve. When the clamp is compressed, the elastic section of 
the rubber valve seal is extruded to extend to and toward the valve seat. 
This extension by extrusion occurs along an axis, which axis is at an 
obtuse angle with respect to the refurbished seat on the high-pressure 
side of the valve disc. This elastic extrusion has two features, which 
resist leakage between the valve disc edge and refurbished seat. First, 
and before the valve seal edge can be elastically deformed to move beyond 
the edge of the seat to a position where it can leak, it must be forced 
under increased pressure onto the valve seat. This forced movement occurs 
first towards a position of being normal with respect to the valve seat, 
it being realized that during such movement the pressure of seal edge 
contact to the seat will increase. Second, because of the decreasing 
section of the rubber valve seal edge as it is compressed away from the 
clamp, the rubber of the valve seal edge must be elastically compressed. 
As both the compression phenomena and the over center phenomena resist 
high-pressure leakage of the elastically extruded valve edge seal with 
respect to the refurbished seat, a seal valve edge repair having 
resistance to high pressures in the range of 150 to 600 psi results. 
In the normal case, size does not matter in assessing patentability. The 
reader will appreciate that here size is a major consideration. 
Specifically, given the large area of the valve disc, and the use of a 
substituted rubber seal edge for the originally designed valve seal edge, 
careful selection of edge design is required to prevent elastic 
deformation with subsequent leakage at the valve seal edge.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
Referring to FIG. 1A, a prior butterfly flap valve V, which is to be 
repaired is shown in front elevation section. Valve housing H is shown 
with pivot P extending across valve housing H. Pivot P has valve seal F 
attached. 
Referring to FIG. 1B, valve disc F is shown in the closed position with 
valve disc F pivoted to extend across valve body H. In this disposition, 
and as shown in FIG. 2 in the original design, seat S mated with valve 
seal edge E'. Specifically, seat edge slope 16 is imparted an angularity 
with respect valve seat edge slope 14. When valve disc F turns on trunnion 
P with valve seal edge E' moving in the direction of opening O, opening of 
butterfly valve V occurred. Conversely, when valve disc F turns on 
trunnion P with valve seal edge E' moving against the direction of opening 
O, closing of butterfly valve V occurs. 
At this point two comments need to be made. First, this particular 
butterfly valve V is huge. It is 11 feet 6 inches in diameter. Second, 
this valve is a survivor from a different era. Specifically, butterfly 
valve V was made by the Baldwin, Lima, Hamilton Company, the famous maker 
of locomotives and other heavy machinery. Manufacture of this valve 
occurred around 1967. In such valves, seat S and valve seal edge E' were 
made of brass. Most importantly, such valves were essentially fitted for 
closure by hand. In actual fact, the "blue prints" of such valves are 
merely guides as to what one might expect in the field. Further, time, and 
installation sites have caused such valves to change configuration. 
Further, just a moments reflection will leave the reader with the 
impression that such valves are simply too large to move. They are 
frequently placed at their sites in such a way that movement is either not 
practical or impossible. 
After about forty years of service, seat S at seat edge slope 16 and valve 
seal edge E' at valve flap edge slope 14 start to leak. Further, the 
reader will remember that the repair which is the subject of this 
disclosure is aimed at pressures between 150 psi and 600 psi. At these 
high pressures, small discrepancies in seat S and valve seal edge E' cause 
large quantities of water to leak through flap valve V. 
The location of these-flap valves V is typically upstream of turbines. 
Butterfly valve V are only occasionally shut for turbine repair. And where 
large volumes of water leak upon valve closure, turbine repair is 
impossible. 
There is an additional constraint in which the repair of butterfly valve V 
resides. With large turbines, the time such turbines are off lines 
correlates to revenue loss. And where the butterfly valve V upstream of 
the turbine is being repaired, the entire system for providing water to 
the turbine must be de-watered. This being the case, time is of the 
essence. Clearly a repair procedure must be adopted which is fast and 
reliable. 
Having said this much, attention will now be devoted to the prior art 
aspects of this repair. 
First, butterfly valve V is de-watered and has valve disc F on trunnion P 
moved to the open position. 
Second, and with reference to prior art FIG. 2 and FIG. 4, brass seat S is 
machined down to seat profile 18 shown in FIG. 4. Thereafter, stainless 
steel seat surface is introduced over the top of seat S. Fastening occurs 
directly to the remaining metal of seat S and even into valve housing H of 
stainless steel seat surface 20 by countersunk bolt apertures 22 held by 
countersunk bolts 24. 
It will be understood that stainless steel seat surface 20 is provided with 
a beveled surface. This surface is angled from 20 degrees adjacent the 
edges to 10 degrees adjacent the center. Further, stainless steel seat 
surface 20 is designed to be reversible. That is to say, valve flap edge E 
can approach stainless steel seat surface 20 from either direction and 
effect a seal. 
Stopping at this juncture, this is the end of the prior art. In what 
follows, I describe the new functions of this disclosure. 
Referring to FIG. 3, elastic flap edge 30 is shown in an elastically 
uncompressed and unextruded shape. This member is made from hard rubber in 
the range of 70.+-.5 shore. Such rubber can be obtained from the American 
Rubber Company of Walnut Creek, Calif. under the designation V173072 
Acrylonitrile Butadiene NBR Shore A 70.+-.5. 
Several observations can be made about elastic seal edge 30. First it has 
rounded edge 32. Rounded edge 32 forms the seating surface on the edge of 
valve seat F. 
Second, it will be seen that elastic seal edge 30 is provided with beveled 
section 33 adjacent rounded edge 32, beveled section 33 is only on one 
side of elastic seal edge 30. As will later become apparent, this provides 
for elastic compression and extrusion along angled vector 35 when clamping 
occurs. 
Third, it is required that elastic extrusion occur away from valve disc F 
and 20 toward seat S. This being the case, inner rubber surface 34 must be 
limited in its ability to elastically extrude away from the edge of valve 
disc F. 
Fourth, elastic compression and extrusion occurs between high pressure 
surface side 36 and low pressure and beveled surface side 38. It is also 
to be understood that beveled section 33 is equally compressed due to the 
shape of the introduced clamp. 
Some important statements can be made about rounded edge 32 and angled 
vector 35. Angled vector 35 is the bisected angle of beveled section 33 
and high pressure surface side 36. It is inclined about 10 degrees from 
the plane of valve disc F. 
Thus, and when elastically compressed and elastically extruded by a clamp, 
elastic seal edge 30 expands rounded edge 32 in the direction of angled 
vector 35. 
Further, the rubber of elastic seal edge 30 is elastically compressed and 
elastically extruded at rounded edge 32. Thus, the compression makes 
elastic flap edge 30 at rounded edge 32 harder. Although the total 
available cross-section of elastic seal edge 30 decreases, the elastic 
compression and elastic extrusion is sufficient to make a seal. 
Finally, it will be remembered that high pressure surface side 36 of 
elastic seal edge 30 encounters considerable hydraulic pressure. This 
pressure will urge rounded edge 32 of elastic seal edge 30 to rotate 
counter clockwise from the position illustrated in FIG. 3. By elastically 
compressing and elastically extruding rounded edge 32 in the direction of 
angled vector 35, this pressure will urge rounded edge 32 into tighter 
contact with stainless steel seat surface 20. In fact, for leakage to 
occur, rounded edge 32 of elastic seal edge 30 will have to rotate past 
stainless steel seat surface 20. Presuming that sufficient elastic 
compression and elastic extrusion has occurred, such motion will not 
occur. 
Having described elastic seal edge 30 in detail, its complimentary clamp C 
will be set forth with respect to FIG. 4. 
First, clamp C includes seal expansion limiting surface 40. This prevents 
elastic seal edge 30 from elastically expanding and elastically extruding 
to and toward the central portion of valve disc F. The only elastic 
expansion and elastic extrusion that is permitted of elastic seal edge 30 
is to and toward the edge of valve disc F. 
Second, clamp C is provided with through bolt B. This through stud B is 
concentric of high pressure surface side 36 and causes uniform elastic 
compression and elastic extrusion of rounded edge 32 of elastic seal edge 
30 along angled vector 35. If this were not located concentrically of 
elastic seal edge 30, elastic compression and elastic extrusion would not 
occur with uniformity; the desired sealing effect would be lost. 
Third, clamp C will be observed to have necked down portion 44 mating to 
beveled section 33. This section of clamp C is vital in providing the 
desired elastic compression and elastic extrusion of rounded edge 32 
toward stainless steel seat surface 20. 
Fourth, and referring to FIG. 5, clamp sections C1, C2, and C3 can all be 
seen. These respective clamp sections occupy segments of the total 
periphery of valve flap F. Additionally, and to prevent rotation of 
through stud B, stainless lock strips 46 are bent upward to lock the nuts 
of the through studs in place, once tightening has occurred. 
Having set forth the total parameters of elastic seal edge 30 and clamp C, 
operation can now be described. Presuming that complete replacement with 
stainless steel seat surface 20 and elastic seal edge 30 has occurred, 
valve disc F is moved to the closed position. Thereafter, tightening of 
through studs B occurs until rounded edge 32 elastically compresses and 
elastically extrudes along angled vector 35 into contact with stainless 
steel seat surface 20. This is usually done visually. 
Thereafter, hydraulic pressure is introduced to high pressure surface side 
36 of elastic seal edge 30 and valve disc F itself. Further compression of 
through bolts B occurs until leakage ceases or is maintained at an 
acceptable rate. 
Finally, stainless lock strips 46 are bent upward to prevent through stud 
and nut B rotation and the repair is complete. 
The reader will understand that the shape of elastic seal edge 30 at 
rounded edge 32 is some what counter intuitive. Even through high pressure 
is encountered--and one would normally want elastic seal edge 30 to be 
thicker where the high pressure is encountered at stainless steel seat 
surface 20, I have found that "necking down" of elastic seal edge 30 is 
required at this point. Further, I have observed that elastic seal edge 30 
at rounded edge 32 both elastically compresses and elastically extrudes 
under the action of clamp C. Thus, rounded edge 32 as it advances along 
angled vector 35 is both hard and compressed so that its interaction with 
stainless steel seat surface 20 is sufficient to resist the hydraulic 
pressure encountered.