Steam governing valve

A steam governing valve includes a valve body constituting a main valve together with a main valve seat formed on a casing body and having a smaller valve seat inside thereof, a valve rod movable in the valve body in an axial direction of the valve and constituting a smaller valve together with the smaller valve seat, a sleeve arranged in the casing body and guiding the valve body in an axial direction, and a pressure chamber defined by the casing body, the valve body and the sleeve. The pressure chamber communicates with an entrance chamber through a clearance provided on the sliding portions of the sleeve and valve body, and the main valve is opened by lifting the valve rod beyond the fully open position of the smaller valve. The valve body is formed on the cylindrical outer surface thereof with a plurality of axially extending grooves arranged at equal intervals in a circumferential direction. The sleeve is formed with a plurality of steam passages at positions opposite to the axially extending grooves and the pressure chamber communicates with the entrance chamber through the steam passages and the axially extending grooves when the valve body is lifted beyond a predetermined valve opening degree.

BACKGROUND OF THE INVENTION 
The present invention relates to a steam governing valve used in a steam 
turbine, and in particular, to a steam governing valve in which the 
vibration of the valve body in a large opening degree of the valve body 
can be suppressed and a stabilized motion of the valve body can be 
obtained. 
As shown in FIG. 6 a conventional steam governing valve comprises a casing 
body 1, an upper cover 2, a bush 3 secured to the upper cover 2, a valve 
rod 4 slidably fitted in the bush 3, a sleeve 7 secured to the casing body 
1, a valve body 6 slidably fitted in the sleeve 7 with a clearance 8 
interposed therebetween and forming a main valve 15, control means for 
controlling the valve rod 4, a smaller valve body 13 formed at the lower 
end portion of the valve rod 4, a smaller valve seat 14 formed on the 
valve body 6, a main valve seat 16 formed on the casing body 1, an 
entrance chamber 18 formed in the casing body 1, an inlet port 21, an 
outlet port 22, a pressure chamber 19 defined by the valve body 6, the 
sleeve 7 and the upper cover 2, and a flow passage 20 formed in the valve 
body 6. 
The valve rod 4 is formed at its lower portion with a valve rod shoulder 5, 
and the valve body 6 is formed with a projection 6a adapted to engage with 
the shoulder 5. 
The control means for controlling the valve rod 4 are composed of a 
hydraulic actuator 9, a lever 11 connected at one end thereof with a 
piston rod 10 of the hydraulic actuator 9 and at the other end thereof 
with the valve rod 4 through a pin 17 and rotatably supported at its 
middle portion by a stationary member, and a compression spring 12 always 
pressing the valve rod 4 downwards with a constant force Fs. 
A vertical motion of the piston rod 10, produced by increasing or 
decreasing the hydraulic pressure of the hydraulic actuator 9, is 
transmitted to the valve rod 4 through the lever 11. When the valve rod is 
moved upwardly, the compression spring 12 is compressed. When the lift 
amount of the valve rod 4 is smaller than the maximum lift amount l, the 
valve body 6 continues to be in close contact with the main valve seat 16, 
and the valve rod shoulder 5 is separated from the projection 6a. As a 
result, a high pressure steam flows from the entrance chamber 18 through 
the clearance 8 between the sleeve 7 and the valve body 6 into the 
pressure chamber 19, and then flows out through a gap between the valve 
rod shoulder 5 and the projection 6a and a gap between the smaller valve 
body 13 and the smaller valve seat 14, and through the flow passage 20 
towards the outlet port 22. 
When the valve rod 4 is further lifted upwardly beyond the maximum lift 
amount ( of the smaller valve, the valve rod shoulder portion 5 engages 
with the projection 6a and moves the valve body 6 upwardly. As a result, 
the valve body 6 is separated from the main valve seat 16, and the main 
valve 15 is opened to a opening degree L. In this state, the steam in the 
entrance chamber 18 flows out directly to the outlet port 22. 
FIG. 7 shows the pressure P.sub.1 at the entrance chamber 18, the pressure 
P.sub.3 at the pressure chamber 19 and the pressure P.sub.2 at the outlet 
port 22 in relation to the valve opening degree in the above-mentioned 
state of the valve. 
When the valve body 6 is moved to a position corresponding to a 
predetermined valve opening degree L, the valve rod 4 receives a force 
F.sub.P which depends on the pressure P.sub.1 in the entrance chamber 18, 
the pressure P.sub.3 in the pressure chamber 19 and the pressure P.sub.2 
at the outlet port 22. The relationship between the above-mentioned force 
F.sub.P, the force F acting on the valve rod 4 from the hydraulic actuator 
9 and the force F.sub.S from the compression spring 12 is expressed by the 
following equation: 
EQU F=F.sub.P +F.sub.S 
The compression force F.sub.S of the compression spring 12 linearly varies 
according to the change of the valve opening degree, while the force 
F.sub.P depends upon various pressures of the steam varies in a complex 
manner according to the valve opening degree. Considering the force 
F.sub.P acting on the valve rod 4, as shown in FIG. 8, the force F.sub.P 
is very small until the smaller valve body 13 is fully opened, sharply 
increases the instant when the main valve 15 starts to open, and gradually 
decreases as the valve opening degree of the main valve increases. This 
force F.sub.P is expressed in the following equation (1): 
##EQU1## 
where, P.sub.1 ; pressure in the entrance chamber 18, 
P.sub.2 ; pressure at the outlet port 22, 
P.sub.3 ; pressure at the pressure room 19, 
P.sub.a ; atmospheric pressure, 
D.sub.1 ; outside diameter of the lower end of the valve body 6 
D.sub.2 ; diameter of the outlet port 22, 
D.sub.3 ; diameter of the flow passage 20, and 
D.sub.4 ; diameter of the valve rod 4. 
In FIG. 8, in a range of the valve opening degree from zero to l, the term 
(c) is predominant in the equation (1), and the force F.sub.P is negative, 
because P.sub.a &lt;P.sub.3. 
When the valve rod shoulder 5 engages with the projection 6a and the main 
valve 15 starts to open, the terms (a), (b) and (c) are all effective in 
the equation (1), and the force F.sub.P acting on the valve rod 4 starts 
to sharply increase. When the valve opening degree further increases, the 
pressure P.sub.2 increases as shown in FIG. 7. As a result, the pressure 
differences (P.sub.1 -P.sub.2) in the term (a) of the equation (1) and 
(P.sub.3 -P.sub.2) in the term (b) decrease, and accordingly, the force 
F.sub.P acting on the valve rod 4 decreases. At a valve opening degree 
nears the full opening L.sub.o, the force F.sub.P becomes very small, 
namely regarded as F.sub.P .apprxeq.0. In other words, the engaging force 
for maintaining an engagement between the valve rod 4 and the valve body 6 
becomes very small, and the motion of the valve body 6 becomes very 
unstable in the valve axial direction (direction along the force F.sub.P), 
although it is guided by the sleeve 7. 
In a steam governing valve used near at the full opening degree L.sub.o, 
the steam flows at high speed through the main valve 15, and diffuses to 
the outlet port 22. As a result, in the downstream side of the main valve 
15, a steam flow state including severe disturbances is generated. The 
pressure variation caused by the above-mentioned flow disturbances acts on 
the valve body 6, thereby producing an abnormal vibration of the valve 
body 6 which is in an unstable condition as mentioned above. 
The characteristic of the force F.sub.P acting on the valve rod 4 of the 
prior art shown in FIG. 8 is a result of providing the smaller valve 13. 
The advantage of providing the smaller valve 13, as understood from FIGS. 
7 and 8, is that the force acting on the valve rod 4 when the main valve 
starts to open can be decreased by .DELTA.F, and accordingly, a hydraulic 
actuator having a small size and a light weight can be obtained. However, 
there is a disadvantage that the engaging force between the valve rod 4 
and the valve body 6 is small when the main valve is largely opened as 
mentioned above, and the valve body 6 is brought into an unstable 
condition. 
Japanese Patent Laid-open No. 62-147002 discloses a steam governing valve 
improved with respect to the steam flow state around the valve body when 
the main valve 15 is slightly opened. In this steam governing valve, each 
of the sleeve 7 and valve body 6 is formed with through holes extending in 
directions perpendicular to the valve axis, and these through holes 
overlap each other when the smaller valve 13 has been fully opened and the 
main valve 15 is slightly opened, thereby producing a communication 
between the entrance chamber 18 and the pressure room 19. By virtue of 
this arrangement, the steam flow rate through the flow passage 20 of the 
smaller valve 13 is increased, the mixing of the steam flow through the 
flow passage 20 with the steam flow from the main valve 15 is improved, 
and the steam flow at the outlet port 22 is stabilized, thereby decreasing 
the force of the fluid which may excite the vibration of the valve body 6. 
However, as mentioned above, the overlapping or communication between the 
through holes is obtained only in a range where the main valve opening 
degree is small, but no communication is obtained in a range where the 
main valve opening degree is near the fully open state. Therefore, the 
steam governing valve of this type has also a disadvantage that the motion 
of the valve body become unstable when the valve is moved to near the full 
open position. 
The object of the present invention is to provide a steam governing valve 
in which the vibration of the valve body is suppressed even when the valve 
body moves in the valve opening direction beyond a predetermined valve 
opening degree, and the motion of the valve body is stabilized. 
SUMMARY OF THE INVENTION 
For achieving the above-mentioned object, in a steam governing valve 
according to an embodiment of the present invention, the valve body is 
formed with a plurality of axially extending grooves on the outer 
cylindrical surface thereof at equal circumferential intervals, and the 
sleeve is formed with steam flow passages at positions opposite to the 
above-mentioned axially extending grooves for communicating the entrance 
chamber with the axially extending grooves. The steam governing valve 
functions so that, when the valve body moves beyond a predetermined valve 
opening degree, the entrance chamber and the pressure chamber communicate 
with each other through the steam flow passages of the sleeve and the 
axially extending grooves of the valve body. 
Further, in order to increase the pressure in the pressure chamber for 
stabilizing the motion of the valve body at its fully open condition, each 
of the total cross-sectional area of the plural axially extending grooves 
and the total cross-sectional area of the plural flow passages formed in 
the sleeve has a flow cross-sectional area greater than that of the 
smaller valve at its full open condition. 
For making the motion of the valve body more stable, in a steam governing 
valve according to another embodiment of the present invention, a 
plurality of compression springs are arranged above the valve body in the 
pressure chamber at equal circumferential intervals, and adapted to press 
the valve body downwardly when the valve body moves beyond a predetermined 
valve opening degree. 
When the valve rod is lifted beyond a predetermined lift amount (maximum 
gap between the smaller valve and the smaller valve seat), the valve rod 
engages with the valve body and the valve body is moved in a valve opening 
direction. When the valve body is lifted in the valve opening direction 
beyond a predetermined valve opening degree, a communication is produced 
between the entrance chamber and the pressure chamber through steam flow 
passages formed in the sleeve and axially extending grooves formed in the 
valve body. As a result, the steam in the entrance chamber flows through 
the steam flow passages formed in the sleeve and the axially extending 
grooves formed in the valve body into the pressure chamber, thereby 
increasing the pressure P.sub.3 in the pressure chamber. When the pressure 
P.sub.3 in the pressure chamber is increased, it becomes possible to 
increase a force acting on the valve rod, as understood from the equation 
(1). By increasing the force acting on the valve rod, the engaging force 
between the valve rod and the valve body is increased. Consequently, the 
vibration of the valve body can be suppressed and the motion of the valve 
body can be stabilized. 
According to a second embodiment of the present invention, in the process 
of lifting the valve rod beyond a predetermined lift amount with the valve 
rod engaging with the valve body, the force acting on the valve rod is the 
same as in the prior art, until the valve opening degree reaches a 
predetermined value. When the valve body further moves in a valve opening 
direction beyond a predetermined valve opening degree, the valve body 
compresses the compression springs arranged in the pressure room above the 
valve body. Since the compression force of the compression springs 
increases the engaging force between the valve rod and the valve body, the 
vibration of the valve body is suppressed and the motion of the valve body 
is stabilized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 show a first embodiment of the present invention, with the 
main structural feature of this embodiment is the same as in the steam 
governing valve of the prior art described by referring to FIG. 6, and 
therefore, the description relating to the same features is omitted and 
the features different from the prior art is only described. In a steam 
governing valve according to the embodiment of FIGS. 1 and 2, the valve 
body 6 is formed on its cylindrical outer surface with a plurality (four 
in the embodiment shown in FIG. 2) of axially extending grooves 23 at 
equal intervals in a circumferential direction. Each of the axially 
extending grooves is so formed that a distance L.sub.R is formed between 
the upper end of the axially extending groove and the upper end of the 
valve body 6 and the axially extending groove communicates with the 
pressure chamber 19 when the valve body 6 moves in a valve opening 
direction beyond the distance L.sub.R. 
On the other hand, the sleeve 7 is formed with through holes 24 serving as 
steam passages at positions opposite to the axially extending grooves 23. 
The total cross-sectional area of the flow passages defined by the axially 
extending plural grooves and the inner peripheral surface of the sleeve 7 
and the total cross-sectional area of the plural steam flow passages 
formed in the sleeve are both greater than that of the flow passage 20 of 
the smaller valve at its full open condition. 
A clearance 8 is provided on the sliding portions of the sleeve 7 and the 
valve body 6 extending by the distance L.sub.R. 
In the steam governing valve according to the the embodiment of FIGS. 1 and 
2, the force F.sub.P acting on the valve rod 4 is to be the same as in the 
prior art until the opening degree of the valve body 6 reaches the 
distance L.sub.R, as shown in FIG. 8. 
When the valve body 6 moves in a valve opening direction beyond a 
predetermined valve opening degree corresponding to the distance L.sub.R, 
the axially extending groove formed in the valve body 6 communicates with 
the pressure chamber 19. As a result, the high pressure steam in the 
entrance chamber 18 quickly flows through the through holes formed in the 
sleeve 7 and the grooves 23 formed in the valve body 6 into the pressure 
room 19. Since the cross-sectional area of the through holes is made 
greater than that of the axially extending grooves, the pressure loss at 
the flow passages is rather small. Therefore, the pressure P.sub.3 in the 
pressure chamber 19 is quickly increased. Based on the equation (1), the 
force F.sub.P acting on the valve rod 4 is shown in FIG. 8, where the 
force F.sub.P in case of the present invention indicated with a broken 
line is greater than the force in case of the prior art indicated with a 
solid line in a valve opening range over the opening degree L.sub.R. 
Therefore, according to the embodiment of FIGS. 1 and 2, the engaging 
force between the valve rod 4 and the valve body 6 is increased, thereby 
suppressing the vibration of the valve body 6 and stabilizing the motion 
of the same. 
The arrangements and functions of the first embodiment other than those 
described above are the same as in the prior art shown in FIG. 6. 
In the steam governing valve according to FIGS. 3 and 4, the sleeve 7 is 
formed at its lower end portion with a plurality of (four in the 
embodiment shown in the drawing) through grooves 25 of inverted U-shape at 
equal intervals in a circumferential direction. The through grooves 25 are 
arranged at positions opposite to the axially extending grooves 23 formed 
in the valve body 6, and extend by a height H from the lower end surface 
7' of the sleeve 7 so that the through grooves 25 communicate with the 
axially extending grooves 23 even when the valve body 6 is lifted to the 
maximum lift L.sub.o. 
In the steam governing valve of FIGS. 3 and 4, when the valve body 6 moves 
in a valve opening direction beyond the distance L.sub.R, the high 
pressure steam in the entrance chamber 18 flows through the through holes 
25 formed in the sleeve 7 and the axially extending grooves 23 formed in 
the valve body 6 into the pressure chamber 19. As a result, the pressure 
P.sub.3 in the pressure chamber 19 is increased, the force acting on the 
valve rod 4 is increased, and the engaging force between the valve rod 4 
and the valve body 6 is increased, thereby suppressing the vibration of 
the valve body 6 and stabilizing the motion of the same. 
In the embodiment of FIG. 5, the upper cover 2 is formed on the surface 
thereof facing to the pressure chamber 19 with a plurality of (for 
example, four) spring receiving recesses 28 arranged circumferentially at 
equal intervals. On the shoulder portion of the sleeve 7 facing to the 
pressure chamber 19, there is mounted a spring supporting plate 29. 
Between the spring receiving recesses and the spring supporting plate, a 
plurality of, for example, four compression springs 30 are arranged 
circumferentially at equal intervals. 
In a steam governing valve according to the embodiment of FIG. 5, when the 
valve body 6 moves from the full close position shown in the left half of 
FIG. 5 to a position shown in the right half of FIG. 5, where the valve 
body 6 has moved in a valve opening direction by a predetermined distance 
L.sub.R added with a distance L', the spring supporting plate 29 is lifted 
by a force from the upper surface of the valve body 6 and all of the 
compression springs 30 are simultaneously compressed, thereby producing a 
force pressing the valve body downwards. 
As a result, in the second embodiment of FIG. 5, the force acting on the 
valve rod 4 and the engaging force between the valve rod 4 and the valve 
body 6 are both increased, thereby suppressing the vibration of the valve 
body 6 and stabilizing the motion of the same. 
Further, in the embodiment of FIG. 5, the structure for supporting the 
springs 30 is not limited to that shown in the figure, but it is only 
required that the compression springs 30 are arranged in the pressure 
chamber 19 above the valve body 6, and adapted to be compressed when the 
valve body 6 moves in a valve opening direction beyond a predetermined 
valve opening degree, thereby pressing the valve body 6 downwardly.