CA1100120A - Steam stop valve assembly with internal bypass valves - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A steam stop valve assembly with internal bypass valves for use in controlling the steam supply to a steam turbine. The steam stop valve assembly has a main valve in which formed are a plurality of bypass passages extending in the axial direction of the valve spindle. Steam inlets communicating with respective bypass steam passages are formed in the peripheral wall of the main valve. A
retainer member having an inwardly directed recess is attached to the top of the main valve. Between the retainer member and the main valve, disposed is an intermediate member provided at its top surface with a projection which is loosely and slidably received by the recess of the retainer member. The intermediate member is provided with bypass valves adapted for opening and closing corresponding bypass steam passages.

Description

BACKGROUND OF THE INVENTION
The present invention relates to a steam stop valve assembly with internal bypass valves adapted for use in controlling the flow of main steam to a steam turbine and, more particularly, to a steam stop valve assembly of the kind described and constructed to have a superior erosion resistance.
A typical conventional steam stop valve assembly of this kind has, as disclosed in the specification of United States Patent No. 3,141,476, a main valve having a bypass passage therein and a bypass valve connected to a valve spindle, the bypass valve being slidably movable ~n the main valve so as to open and close the bypass passage. The bypass passage and the bypass valve are provlded for allowing a small amount of steam to flow into the turbine9 prior to the supply of the main steam, in order to prevent the thermal stress in the turbine from becoming excessively large in the startup of the turbine.
In this type of steam stop valve assembly, the steam ~2~ passage defined between the main valve and the bypass valve is extremely small in cross-section and is directed to the valve spiodle. Therefore, the steam flowing through this passage impinges upon the valve spindle, as a jetting flow Oe a high f10wing vs10city. ~s a rssu1t, the vs1vs spiDd1s . .

: :

- . . : . . - : :
.
, ,~
.

is attacke~ and eroded by fine solid particles which are usually suspended ln the steam. In the steam stop valve assembly o~ the kind described, therefore, the valve spindle and its bush are padded with a hard material by a build-up welding, sa as to avoid the erosion of the valve spindle.
This countermeasure, however, is not effective enough to check the erosion of the valve spindle. As a result, additional padding is required at each time of the periodical inspection of the turbine.
As an alternative measure for preventing the erosion of the valve spindle, such a steam stop valve assembly has been proposed as having a skirt provided beneath the bypass valve so as to overlie the valve spindle, the surface of the skirt being padded with hard material by a build-up welding. In this type of steam stop valve assembly, the skirt is inconveniently struck and eroded by the jetting flow of the steam flowing through the restricted steam passage formed between the skirt and the main valve~ although the valve spindle is protected against the corrosion. This erosion of the sklrt can never be avoided, even by the coating of the skirt with the hard material. In the worst case, the skirt is scooped and the fraction or fragment is dangerously conveyed into the turbine, ~o cause a serious damage in the latter.

, ,... . .. - , .

- .: .. : .
,. , : .:
: : . .
, . . , .:
- .

-SUMMARY OF THE INVENTION
It is therefore an object of the invention to providea steam stop valve assembly with internal bypass valves, constructed to have a superior resistance of the valve portion to erosion.
It is another ob~ect of the invention to provide a steam stop valve assembly with internal bypass valvesS
constructed to have a superior resistance of the valve spindle to erosion.
/~ To these ends, according to the invention, there is provided a steam stop valve assembly with internal bypass valves, characterized by comprising a ~ain valve, a valve spindle, a plurality of bypass passages formed irl the main valve and extending in the axial direction of the valve spindle, a retainer member secured to the top portion of the main valve, an intermediate member connected to the valve spindle and disposed between the retainer member and the main valve slidably in the vertical direction, and bypass valves attached to the intermediate member and adapted J~ to open and close respective bypass passages.
These and other objects, as well as advantageous features of the invention will become more clear from the following description of the preferred embodiments taken in conjunction with ~he accompanylng drawings.

'~ :

: .
. , ' : , ' - ' ' '. ' ', ' ' ' . ~ . .

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. l is a sectional view of a steam stop valve assembly with o~ internal bypass valves, constructed in accordance with an embodiment of the invention, Fig, 2 is a sectional view taken along the line II-II
of Fig. l, Fig, 3 i8 a sectional view taken along the line III-I~I
of Fig. l, Fig. 4 is an enlarged view of a bypass valve incorpor~te~
/C~ in the steam stop valve assembly as shown in Fig. l, Fig. 5 is a sectional view of a steam stop valve assembly with ~ internal bypass valve~ constructed in accordance with another embodiment of the invention, Fig. 6 is an enlarged view of a bypass valve incorporated in the steam stop valve assembly as shown in Fig. 5, Fig. 7 is a sectional view taken along the line VII-VII
of Fig. 5, Fig. 8 is an illustration e2planatory of the state of the flow of steam into the steam stop valve assembly, Fig. 9 is a sectional view of a part of the steam stop valve assembly as shown in Fig. 5, showing particulaFly the ` portion for receiving a spring, and Fig. lO is a sectlonal view of a part of a steam stop valve with ~ internal bypass valve~ constructed in accordance wi~h a further embodlmerit of the invention, showing parti-cularly a by~a~s va1ve incorporated.

:

.. , .. , . . . , :. ' ~: :
:

.

DESCRI~TION OF THE PREFERRED EMBODIMENTS
Hereinafter, the invention will be fully described through its preferred Eorms, with reference to the accompanying drawings.
Referring first to Figs. 1 to 3 showing a steam stop valve assembly constructed in accordance with a first embodiment of the invention, a main valve 16 has three bypass steam passages 22 formed therein. These bypass steam passages 22 extend in the axial direction of a valve spindle 17, and are disposed at 120 intervals around the latter. A cap member 14 is fixed to the top of ~he main valve 16, by means of a bolt 31. An intermediate disc 21 screwed to the end of the valve spindle 17 i6 slidably fitted in the cap 14. The intermediate disc~
is provided at its periphery with three arms 21a which extend radially outwardly to overlie respective bypass steam passages.
The intermediate disc 21 is further provided at its lower portion with a protrusion 18 capable oE contacting the top portion of the main valve 16. The arms 21a are received by notches 34 which are formed in the cap 14, so as to prevent the intermediate disc 21 from being rotated. The protrusion 18 has a convexed spherical contacting surface 18a which is adapted to make a spherical surface contact with a concaved spherical contact surface lla formed on the~top of the main valve 16.
dach a Z~a ls provided ~lth a bore 36 for recelvlng . , . , ~
~ . , , ' ;

a cylindrical bypass valve 37 adapted for opening and closing corresponding bypass passage 22. The bypass valve 37 has an outside diameter somewhat smaller than the inside diameter of the bore 36, so that a slight gap may be formed between the wall of the bore 36 and the bypass valve 37 received by the latter. Each bypass valve 37 loosely received by the bore 36 is connected to corresponding arm 21 by means of a pin 23. This pin 23 has an outside diameter somewhat smaller than the inside diameter of a pin-receiving /0 bore formed in corresponding bypass valve 37. Therefore, the bypass valve 37 is allowed to contact at its lower spherical surface 37a with a valve seat portion 16a in a sealing manner, when it is in the closing position.
At the same time, a slight gap ~ is formed between the shoulder portion of each bypass valve 37 and the associated arm 21a of the intermediate disc. Steam inlets 35 open in the main valve 16, and are in communication wlth respective bypass steam passages 22.
In operation of the steam stop valve of this embodlment, as the v~lve spindle 17 is lifted by a hydraulic mechanism (not shown), the valve spindle 17 comes into contact with the bottom 21b of a threaded bore 21b of the intermediate disc 21.
As the valve :pindle 17 is further raised, thé intermediate disc 21 comes to move upward together with ~he valve spindle 17, so that the arms 21a of the intermediate disc 21 come .

.

~ ,, ~ . .

- : , . . .
-: :. . , , : : :
., .
.. , . :. . . . . .
.- ~ . .
, .. . .

into contact with the shoulders of the bypass valves 37, so as to llft the bypass valves, thereby to open the bypass passages 22. Then, as the valve spindle 17 is further raised, the tops of the bypass valves 37 are brought into contact with the cap 14, and lift up the cap 14. As a result, the main valve 16 to which the cap 14 is fixed is moved upward to open the main steam passage of the steam stop valve.
~ hen the bypass steam passages 22 have been slightly opened by the bypass valves 37, the steam coming through the steam inlets 35 is made to flow along the entire peripheries of the bypass valves 37.
Consequently, the jetting flow of the steam is uniformly distributed over the entire periphery of each valve seat 16a and is introduced into corresponding bypass steam passage 22 through the gap between the valve seat 16a and the bypass valve 37, as shown in Fig. 4. At the same time, the solid particles suspended by the steam, if any, collide with the jetting streams of the steam as shown C~ by full lines 46, so that the kinetic energies possessed by these particles are conveniently nullified and extinguished.
As a result, these particles are prevented from impinging upon the wall of the bypass passage 22, and the erosion is avoided accordlngly. The valve splndle 17 is also protected a8aiDst eroslon, because it is isolated from the bypass ~ 7 ~
/

:` ~

': ' , ~ , :
.
:

- ., ' ~ '; ,' ~ ' :

' steam passages 22.
When the valve is fully closed, the protrusion 18 of the intermediate disc 21 is kept in contact with the head lla of the main valve 16, so as to function as a stopper, so that no impact is imparted to the bypass valves 37 nor to the pins 23. In addition, the leak of steam along the valve spindle 17 is fairly avoided thanks to the provision of the gap between the shoulder 37 of the bypass valve 37 and the arm 21a of the intermediate disc 21.
In order to ensur~ a sufficient erosion resistance of the bypass steam passage, as well as the seal performed by the bypass valves 37 during the clo~ing thereof, it is recommended to pad the touching surface of each bypass valve 37 and the upper part of the wall of each bypass steam passage 22 with stellite or the like hard material as at 44~45.
It is also to be noted that, since the cap 14 of the main valve 16 is closed at its upper end, the guide portlon of the intermediate disc 21 is insulated from the foreign matters, so that the unfavourable stlcking of the valve stick 17 is O fairly avoided.
It will be seen that the erosion of the valve spindle and other essential parts during the bypassing of the steam is completely eliminated in the steam stop valve assembly of this embodiment.

.
:
- .. . : .
. ' -- . .,: , . : . , : .
-: . . .. : ' .
- : . -' ~ - . :
- . ... . : .
.
,. ,~ .

Figs, 5 to 9 in combination show a steam stop valve assembly constructed in accordance with another embodiment of the invention. In these Figures, same reference numerals are used to denote the same member or parts as those of Figs. 1 to 4, and explanation of these members or parts is omitted here. A reference numeral 39 denotes a rod-like projection proJecting downwardly from the lower end of each bypass valve 37 and having a circular cross-section. The diameter of this projection 39 is smaller than the inside / diameter of the bypass passage 22, so that a throat 40 for the steam passing therethrough is forrned between the outer periphery of the projection and the inner perlphery of corresponding bypass passage 22.
A pillar-like projection 41 is formed at the center of the upper surface of each bypass valve 37, so as to extend upwardly therefrom. The projection 41 is movably received by a hole 42 which is formed in the cap 14 at portion thereof where each notch 34 is formed. In each hole 42, disposed is a spring 24 adapted to bias the bypass ac~ valve 37 downwardly.
At the same time, as shown in Fig. 7 7 each steam inlet 35 has side walls 35b ahich are so curved that the distance g between the outer peripheral surface of each bypass valve 37 and each side wall 3Sb is gradually reduced toward the center of the steam stop valve assembly.

.
~ 9 ~

' .~ ' . ' .
.

The steam stop valve assembly of thls embodiment operates in the following manner. As the valve spindle 17 is raised slightly by a driving mechanism which is not shown, the upper end of the valve spindle 17 comes into contact with the inner bottom surface (surface Y) of the intermediate disc 21. A further upward movement of the valve spindle 17 causes the intermediate disc 21 to move upward, so that shoulders 36a of bores 36 formed in respective arms 21a of the intermediate disc 21 are brough~ into contact with the collars 37b of corresponding bypass valves 37, as shown in Fig. 6. Consequently, the bypass valves are lifted over-coming the depressing forces of the springs 24. While the lift of the valve spindle 17 is still small, the lower end peripheral surface of each bypass valve slightly clears the associated valve seat 16a, so that the steam is al]owed to flow into corresponding bypass passage 22 through the gap between the valve seat 16a and the bypass valve 37, as illustrated in Fig. 6. In this connection, it is to be noted that the steam or particles flowing through the gap into the bypass passage 22 is forcsd by the downward projection 39 at the lower end of the bypass valve 37 to flow downwardly in the axial direction of the paasage 22, as shown by full lines 43. Thus, no flow of steam and fine solid pareicles which would cross the bypass passage as shown by a broken line ~2 does take place. At the same time, .; : .
.,1 -~ ~ ' ' . : :.,:

. . . . ~ . - : , .' . . .'' ' ..
-:

. :
,

2~3 the kinetic energy of the jetting flow is conveniently attenuated and extinguished. For these reasons, the solid particles suspended by the steam are prevented from impinging upon the walls 22a of the bypass passages 22, and, accordingly, the walls 22a are protected Erom the erosion.
In order to ensure a sufficient resistance of the bypass steam passages 22 to erosion, as well as a good seal performed by tbe bypass valves during closing of the latter, it is recommended to pad the touching surface and the outer surface of the projection 39 of each bypass valve 37, as well as the upper part of the wall of each bypass steam passage 22, with stellite or the like hard materlal as at 47,48.
It is also to be noted that, since the side walls 35b of the steam inlets 35 are curved to have a surface R of a semiclrcular cross-section as shown in Fig. 8, the steam a flows along the surface R when the bypass valve is kept slightly opened and, therefore, is uniformly distributed over the entire periphery of the bypass valve 37 before it flows into the bypass passage 22. Consequently, the jetting fIows of steam in a common bypass steam passage 22 are made to collide with one another, so as to nullify their kinetic energies, thereby to enhance the effect of prevention of the erosion.
Further, the following advantage is derived from the use of the springs 24 for biasing the bypass valves 37.

. . :
' . . ~ ' .. : . . . .:
, .. ' . , .
. . .

Namely, in the course of opening of the bypass valves, each bypass valve 37 is lifted while the collar 37b thereof is pressed against the shoulder 36a of corresponding arm 21a of the intermediate disc 21. Consequently, ~mfavourable vibration caused by the steam of high pressure and tempera-ture is suppressed, and the wear down of the bypass valves attributable to the vibration is conveniently avoided.
The depression fo~ce exerted by each spring 27 on each bypass valves 37 ensures also a perfect seal against the leak of steam, in the closed state of the bypass valves.
Referring now to Fig. 10 showing still another embodiment of the invention, each bypass passage 22 is designed and constructed as a divergent passage 44 having a diameter which increases gradually toward the downstream or outlet side enc of the passa~e. It will be understood that this form of passa~e further decrease of the chance of direct attack on the lnner wall 44 of the bYpass passa~e 44 bY the jettin~ flow of steam and fine solid particles, so as to further enhance the effect of prevention of erosion.
As has been described, in the steam stop valve assembly of this embodiment, the kinetic energies possessed by the steam and~suspended fine solid particles flowing into each bypass passage through ehe gap between ~he bypass valve and associated valve seat are~nullified and extinguished due to the mutual collision of flows of steam and particles, so that ' `

.- , ' - . ' - - ., .. : ~. . - ,. ,, ': ' ' ~. . . -.

- . . .. .

the solid particles are prevented from directly impinging upon the inner wall of the bypass passage. Consequently, the inner walls of the bypass passages are fairly protected against the erosion which may, for otherwise, be caused by the att~ck by these solid particles.
This remarkable effect of prevention of erosion is further enhanced by adopting curved side walls of steam inlets, as in the previously described embodiment, or a diverging form of the bypass passage. Further, a perfect ~j seal against the steam in the closed state of the bypass valves is ensured by the use of springs for biaslng the bypass valves. This in turn prevents the erosion of the bypass steam passage which may be caused, even in the fully closed state of the bypass valves~ by a leak of the steam.
In the described embodiment, only the side walls 35b of the steam inlet formed in the main valve 16 are curved.
It is possible, however~ to form the side walls in the cap 14 also at a corresponding curvature, although it is preferred to form curved side walls only in the main valve 16, because the provision of curved side walls in the cap in combination with the notches 34 renders the construction of the cap impractically complicated.
~ rom the foreeoing description7 it will be understood that the present invention provides a steam stop valve assembly with an lDternal bypass valves constructed to protect the valve portion against erosion.
` ~ ' ': ~ ,', ', ,: .

Claims (9)

What is Claimed is:

1. A steam stop valve assembly with internal bypass valves comprising: a main valve; a plurality of bypass passages formed in said main valve and extending in the axial direction of the valve spindle; steam inlets formed in the periphery of said main valve and communicating with respective bypass steam passages;
a retainer member attached to the top portion of said main valve; an intermediate member disposed between said retainer member and said main valve movably up and down relatively to said retainer member and connected to said valve spindle;
and a plurality of bypass valves mounted in said intermediate member and adapted to open and close corresponding bypass passages.

2. A steam stop valve assembly with internal bypass valves as claimed in claim 1, wherein each bypass valve has a projection extending downwardly from the bottom thereof.

3. A steam stop valve assembly with internal bypass valves as claimed in claim 1, wherein the side walls of each steam inlet formed in said main valve are so curved that the distance between the surface of said bypass valve and each side wall is gradually reduced toward the axis of said valve spindle.

4. A steam stop valve assembly with internal bypass valves as claimed in claim 1, wherein said intermediate member is provided with arms extending radially outwardly therefrom, said bypass valves being mounted in said arms.

5. A steam stop valve assembly with internal bypass valves as claimed in claim 1, wherein the wall of said retainer member facing said intermediate member is provided with a recess, while said intermediate member is provided at its top surface with a projection slidably received by said recess of said retainer member.

6. A steam stop valve assembly with internal bypass valves as claimed in claim 1, characterized by further comprising resilient members disposed between said bypass valves and said retainer member, said resilient members being adapted to bias corresponding bypass valves toward said bypass passages.

7. A steam stop valve assembly with internal bypass passages as claimed in claim 1, wherein each bypass passage has a divergent form.

8. A steam stop valve assembly with internal bypass valves as claimed in claim 1, wherein the portion of each bypass valve around the lower end which contacts in the closed state of said bypass valve with the valve seat formed at the upstream end of said bypass passage is coated or padded with a hard material.

9. A steam stop valve assembly with internal bypass valves as claimed in claim 2, wherein the portion of each bypass valve around the lower end which contacts in the closed state of said bypass valve with the valve seat formed at the upstream end of said bypass passage and said projection extending down-wardly from the bottom of said bypass valve are coated or padded with a hard material.