Rotary shaft water seal device in hydraulic machine

A rotary shaft seal device in a hydraulic machine. With the water seal segments in the conventional water seal device, a gap tends to be generated between the inner peripheral surface of the segment packing and the outer peripheral surface of a liner of the rotary shaft due to the wear during use and progressively developed. The present invention contemplates to minimize the gaps between the adjacent segments and guide members interposed between the adjacent segments are solidly secured, whereby the flow rate of water leakage through the segments is reduced and the segments themselves are improved in mechanical strength, so that the segments can be reduced in size and the water seal device itself can be rendered compact in size.

BACKGROUND OF THE INVENTION 
This invention relates to a water seal device for a rotary shaft in a 
hydraulic machine, such as a water seal device for a rotary shaft suitable 
for use in a large-sized hydraulic machine, for example, a turbine for a 
hydraulic power plant, and more particularly to a shaft seal to seal water 
on the outer peripheral surface of a rotary shaft by solid packing. 
FIG. 1 shows the hydraulic power plant in common use. The power plant of 
this type comprises: a runner 1 to convert a potential energy of water 
into a kinetic energy; a generator to convert the kinetic energy of the 
runner into an electric energy; a main shaft 3 connecting the runner to 
the generator; a casing 4 to uniformly introduce water, which has passed 
through a hydraulic steel piping from an upper reservoir, to the entire 
periphery of the runner; guide vanes 5 to adjust a flow rate of the water 
thus introduced; an upper and lower covers 6 and 7 to cover the top and 
bottom of the runner; a draft pipe 8 and a tube 9 for leading the water, 
which has left the runner to a lower reservoir. In the power plant of the 
type described, in order to prevent water under pressure in a housing 
chamber of the runner to be blown out along the outer periphery of the 
main shaft 3, there is provided a rotary shaft water seal device 10 around 
the main shaft 3 in the upper cover 6. 
FIGS. 2 through 5 show the conventional rotary shaft water seal device of 
the type described. This device includes two carbon packings 12, 13 and a 
resin packing 14, each of which consists of a plurality of circular 
arcuate segments (all of which are solid packings), and these solid 
packings are received in an arrangement of three stages in an annular 
packing box solidly secures to the upper cover 6 at the outer periphery of 
a liner 3A of the main shaft 3. The packing box 11 is provided therein 
with support surface portions 11A, 11B and 11C which are disposed in three 
stages in the vertical direction, respectively. The resin packing 14 is 
mounted on the lower support surface portion 11A, one of the carbon 
packings 13 on the middle stage support surface portion 11B, and the other 
of the carbon packings 12 on the upper support surface portion 11C, 
respectively. The upper surface of the carbon packing 12 is blocked by a 
cover portion 11D of the packing box 11. 
The inner peripheral surfaces of the solid packings 12, 13 and 14 are in 
sliding contact with the outer peripheral surfaces of the liner 3A of the 
main shaft 3 and pressed against the liner 3A of the main shaft 3 by a 
spring 15 wound around the outer periphery of the respective packings. 
Description will now be given of the arrangement of the solid packing in 
conjunction with an example of the carbon packing 12 mounted on the upper 
stage. This packing is of such an arrangement in which a plurality of 
circular arcuate segments 12A are annularly arranged with a slight gap G 
being held between the adjacent segments. The segments 12A is each 
provided in a guide groove 17 formed at an intermediate portion between 
the adjacent segments 12A with a guide member 16 to guide the segment to 
be displaced in the radial direction of the rotary shaft and prevent the 
segment to be displaced in the circumferential direction. Each of the 
guide members 16 is solidly secured to the support surface 11C of the 
packing box by means of a set-screw. 
Description will now be given of the reasons for adopting such a 
construction that the aforesaid gap G is taken and the segments are 
permitted to be displaced in the circumferential direction. The inner 
peripheral surfaces of the segments 12A are worn due to sliding contact 
with the liner 3A of the main shaft 3. Assumption is made that the 
segments are solidly secured to one another in an annular state with the 
adjacent segments being abutted against each other. Due to the wear on the 
inner peripheral surfaces the segments, a gap is generated between the 
inner peripheral surface of the packing and the outer peripheral surface 
of the liner and progressively developed. In order to prevent the 
development of this gap, the packing should be decreased in diameter, 
following the extent of wear. The above-described arrangement has been 
adopted to secure this decrease in diameter of the packing. 
SUMMARY OF THE INVENTION 
However, the conventional rotary shaft water seal device as described above 
presents the disadvantage that the flow rate of water leakage through the 
aforesaid gaps G is decreased from the following reasons. 
The guide member to permit the segment to be displaced only in the 
circumferential direction is solidly secured to the packing box through 
the setscrew. However, because the center alignment is difficult to effect 
in a threading work, an error tends to occur in installing the guide 
member into the box. To absorb the error, a slight clearance is set on the 
sliding surfaces of the guide member and the guide groove. Due to the 
presence of this clearance, the values of displacement of the segments in 
the circumferential direction are increased to reach .+-.0.5 to 1.0 mm. 
When these values of displacement of the segments in the circumferential 
direction are large, there occurs a possibility of damages at the end 
portions of the adjacent segments due to the abutment against each other. 
In order to eliminate this possibility, it becomes necessary to set a 
sizable gap G between the segments. This gap G has heretofore been 
determined to from appox. 2 to 5 mm. The flow rate of water leakage 
through the gaps G should necessarily be increased with the increase in 
the size of the gap G. 
Here, the following is the total flow rate Q in the rotary shaft water seal 
device with the abovedescribed arrangement in an equation. 
##EQU1## 
where Q.sub.1 is the flow rate through the gaps G, Q.sub.2 a flow rate of 
water leakage through the sliding surfaces of the packing and the shaft 
liner, A an area of the water leaking portions of the gaps G, k.sub.1 and 
k.sub.2 constants of proportionality, B dimension values of the sliding 
surfaces, and P.sub.0 is a back pressure led and applied to the rear 
surface of the segment. 
The flow rate of water leakage Q.sub.1 is proportional to the area A of the 
water leaking portions of the gaps and the square root of the back 
pressure P.sub.0, and hence, the flow rate of water leakage Q.sub.1 is 
increased with the increase in the dimensions of the gaps. 
In addition, the flow rate of water leakage Q.sub.2 is proportional to the 
dimension values of the sliding surfaces B and the back pressure P.sub.0, 
and hence, the ratio between Q.sub.1 and Q.sub.2 is different due to the 
back pressure. However, it is 1:2 under the normal water pressure during 
use. 
The present invention has as its object the provision of a rotary shaft 
water seal device in a hydraulic machine, capable of controlling the flow 
rate of water leakage through the gaps. 
According to the present invention, the guide members to guide the packing 
segments to be displaced in the radial direction are solidly secured to 
the packing box, whereby the installation error is reduced to a value as 
small as possible, so that the gap G can be controlled by a value as small 
as possible.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Description will hereunder be given of one embodiment of the present 
invention with reference to the drawings. FIGS. 6 and 7 show one 
embodiment of the rotary shaft water seal device according to the present 
invention, illustrating the portions of the adjacent packing segments 
abutted against each other, which constitute the essential portions of the 
embodiment. 
In FIGS. 6 and 7, the abutting end portions of the adjacent segments 12A 
and 12A are inclinedly cut away in such a manner that the abutting end 
portions are progressively flared in the radially outward direction. A 
vacant space at these inclined end faces substantially forms a guide space 
20. The portion of this space 20 in contact with the main shaft liner 3A 
is open and forms a gap G. A substantially wedge-shaped guide member 21 
formed in a shape similar to this shape 20 is received in this space 20 in 
a manner to be rested on the support surface portion 11A of the packing 
box 11. The opposite inclined surface portions of this guide member 21 are 
abutted against the inclined surface portions of the space 20. The guide 
member 21, upon being accurately positioned by means of a gange or the 
like, is solidly secured to the support surface portion 11A through a 
welded portion 19 formed at a circular arcuate peripheral portion of the 
guide member 21 by a billet welding means or the like. 
As described above, the guide member 21 is welded onto the support surface 
portion 11C, whereby little installation error thereof is developed. In 
consequence, the gap G can be minimized in dimensions, so that the flow 
rate of water leakage through the gaps G may be reduced. 
Furthermore, the present embodiment can offer the following advantages in 
addition to the advantage of controlling the gap G in dimensions. 
The surfaces of the guide member 21 and of the segments 12A, 12A, which are 
brought into sliding contact with one another, are inclined, whereby the 
segments 12A and 12A can be smoothly displaced in the radial direction. In 
passing, a tapered angle .theta. formed by the both inclined surfaces is 
indicated by .theta.=360/n, where n is the number of segments, i.e., the 
number of division of the packing. In addition, the length of the guide 
member 21 in the radial direction is smaller than the width of the semgent 
in the radial direction. The reason for this is to avoid that the side 
surfaces of the guide member 21 press against the spring 15 due to the 
worn segments 12A, whereby the spring 15 cannot apply the biasing force to 
the segments. 
The guide member 21 fills up the space 20 formed at the outside of the gap 
G, whereby this guide member 21 functions as a fluid friction against the 
water leakage from the gap G to the space 20, so that the back pressure 
P.sub.0 can be reduced. 
Further, the guide member 21 is provided at the sides of the segments, 
whereby need for forming a guide groove in the segment can be eliminated, 
so that the segment itself can be increased in the mechanical strength. 
The segment, being improved in the mechanical strength, can be formed 
thin, so that the number of grooves 22 for cooling, which are formed on 
the inner peripheral surace of the packing can be reduced from two to one. 
Furthermore, in the above-described embodiment, description has been given 
of one of the carbon packing 12, however, same is true of the other carbon 
packing 13 and the resin packing 14. Additionally, the present invention 
is applicable to solid packings other than the packing made of carbon and 
resin, and satisfactorily applicable as a rotary shaft water seal device 
for the hydraulic machine other than the hydraulic power plant. 
Further, in the above-described embodiment, description has been given of 
the case where the guide members are welded, however, the guide members 
may be solidly secured by use of a bonding agent. 
As has been described hereinabove, according to the present invention, the 
flow rate of water leakage through the gaps can be reduced.