Butterfly valve with low noise

Details Butterfly valve with low noise Butterfly valve with low noise

2000-12-18

2002-01-15

Shaver, Kevin (Department: 3754)

Valves and valve actuation

Rotary valves

Butterfly

Reexamination Certificate

active

06338468

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a butterfly valve that is a kind of industrial valves used for the control of flow rate and pressure of liquid. In particular, the invention relates to a butterfly valve that can reduce the cavitation noise likely to occur in a small valve opening.
BACKGROUND ART
In a conventional butterfly valve, as shown in
FIG. 1
, a flow rate of the valve increases in a narrowed portion or a narrow area at an orifice side and a pressure around the valve lowers. The lowering of the pressure quickly increases the volume of each of fine air bubbles (bubble nuclei) contained in the liquid thereby generating cavitation bubbles. After liquid passes through the narrow area within the valve, the velocity of the flow decreases and recovers. Therefore, cavitation bubbles collapse in the downstream of the valve.
When the cavtation air bubbles grow from the air bubble nuclei around the valve, the peripheral pressure varies according to the contraction movement of the air bubbles, and this movement causes a tremendous noise. Further, the collapse of cavitation bubbles causes an impact pressure and the so-called cavitation phenomenon occurs that gives damages to the valve or piping arrangements by noise or vibrations.
Furthermore, the butterfly valve used for control aims originally at adjusting the flow rate or pressure by throttling the valve opening, and to achieve the object there is current no alternative but to use the butterfly valve while keeping patience on a cavitation accompanied by noise.
In light of the above present status there have been so far proposed butterfly valves for controlling a noise and cavitation to be produced from valve bodies.
FIGS. 2A and 2B
show one example (see Japanese Patent Unexamined Publication No. 57-157866) of such a butterfly valve. The reference numeral
1
designates a valve disc which is disposed within a valve casing
2
and is pivotally supported by a valve rod
3
orthogonally crossing at the centre axis of the valve casing
2
. The valve disc
1
is shown in the fully closed state in the drawing. The valve disc
1
is provided with a valve disc
1
a
in an angled form, being vertical to the valve rod
3
. The peripheral surface of the valve disc
1
a
is cooperated with the inner surface
2
a
of the valve casing
2
to form a sealing surface which is shown with dotted line
1
b
in the drawing. The centre axis
1
c
of the sealing surface
1
b
passes through bores
4
provided on the valve disc
1
for receiving the valve rod
3
. The centre axis
1
c
is inclined making an angle of about 15° to 20° relative to an axis
2
b
vertical to the inner surface
2
a
of the valve casing
2
.
The valve disc
1
a
is intended to be in close contact with the inner surface or bore
2
a
of the valve casing
2
of the butterfly valve and is in such configuration that two semi-circular wall portions make an angled form as described above. Over one semi-circumference of the valve disc
1
a
are provided comb-teeth shape projections
5
at the flow-in side so that they are integrally projected in the flow-in direction (shown with thick arrow mark F
1
) at use. The other semi-circumference are provided with comb-teeth-shape projections
6
at the flow-out side which are integrally projected in the flow-out direction of the fluid i.e. in the reverse direction to the comb-teeth-shape projections
5
at the flow-in side. Both the comb-teeth-shape projections
5
and
6
are formed so as to be approximately in parallel with the inner surface
2
a
of the valve casing
2
, and have tip ends formed so as to be positioned with the surface vertical to the inner surface
2
a
of the valve casing
2
. Further, each of the comb-teeth-shaped projections
5
and
6
is formed to become gradually shorter towards bosses
7
each of which is positioned at the centre axis and into which the bores
4
are formed.
In the operation of the illustrated valve, if the valve disc
1
is rotated clockwise as shown with an arrow F
2
from the fully closed state shown in
FIG. 2A
, the flow rate varies with the valve opening. At that time, the fluid passes through a nozzle side area and an orifice side area. The orifice side area is an opening portion delimited by the inner surface
2
a
of the valve casing
2
and the peripheral portion of the valve disc
1
positioned in the downstream side of the valve rod
3
. The nozzle side area is an opening portion delimited likewise by the inner surface
2
a
of the valve casing
2
and the peripheral portion of the valve disc
1
positioned in the upstream of valve rod
3
. The fluid flow passing through the nozzle side area and the orifice side area changes to fine jet streams by trapezoidal (in section) passages
8
, as shown in
FIG. 2B
, formed between the plural respective comb-teeth-shaped projections
5
and
6
. Consequently, the cavitation generated in the downstream side of the valve body
1
is dispersed to suppress the growth of the cavitation. In
FIG. 2B
the reference numeral
9
denotes inlets.
FIGS. 3A and 3B
show another example of a conventional butterfly valve with a cavitation control function (see Japanese Patent No. 2536329). In a valve casing
11
a valve disc
12
is rotatably supported by valve rods
13
which are mounted on its two sides. When the valve disc
12
rotates from its closed state towards its opening, one semi-circumferential portion
12
A of the valve body
12
moves towards the upstream side while the other semi-circumferential portion
12
B moves towards the downstream side. In the surface near the outer periphery in the downstream side of the semi-circumferential portion
12
A there are continuously projected approximately equally thicked ribs
14
over the whole semi-circle connecting the two supports
15
of a valve rod
13
. Then, the respective ribs
14
are provided with a plurality of through bores
16
which inverse-radially converge being directed towards the surface centre axis
12
C of the valve disc
12
.
FIGS. 4A and 4B
show still another example of a conventional eccentric butterfly valve (see Japanese Patent Publication No. 52-33330). The butterfly valve comprises a valve casing including a casing body
21
and a casing flange
22
. A valve disc
23
is supported by a valve rod or biassed trunnion
24
attached to the casing body
21
in a position offset from the disc
23
. The valve seat portion of the eccentric butterfly valve is provided with a resilient seating ring
25
in such a manner that the ring may be embedded in an inner wall recess
26
of the casing body
21
.
The casing body
21
is provided with recesses
21
a
and
21
b
in the downstream side of the valve seat. As illustrated in
FIG. 4B
, the recesses
21
a
and
21
b
are formed to have a maximum depth in the intermediate position between bearing portions at both the sides of the biassed trunnion
24
and zero depth in the bearing portions at both the sides.
Then, it is arranged that at the rotation of the valve disc
23
the sectional area in the flow route takes place in almost the same proportion. herefore, the fluid torque applied to the disc
23
is reduced compared with a torque generated during the releasing motion of the valve in case the disc is vertically disposed relative to a cylindrical bore.
With the butterfly valves illustrated in
FIGS. 2A
,
2
B,
3
A and
3
B, in the body casing or valve body side there are provided projections or grooves for defining fluid flow passages, or holes or additional elements which shut out the fluid flow line, thereby separating the flow of the fluid. Therefore, there is reduced the difference in velocity between a narrowed portion where a fluid flows at a high velocity and a low velocity flow portion where a fluid flows at a low velocity, and the cavitaton and thus the noise are controlled or suppressed.
However, such butterfly valves of the known structure have common problems as described below.
(i) The flow route is finely separated by a plurality of through bores which inverse-radially converge, the bores being provided in

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