Arrangement at a shaft seal

An arrangement at rotating shafts with a wheel fixedly mounted to the shaft, which wheel rotates in a housing surrounding the wheel, an essentially pipe-shaped element surrounding the shaft, an with essentially axially sealing surface provided sealing device between the pipe-shaped element and the wheel and a passage in the housing for the shaft with a sealing device, which seals against the pipe-shaped element. There is mounted a fastening device on the shaft for axial displacement of the pipe-shaped element in order to cause a sealing effect by means of the sealing device between the pipe-shaped element and the wheel. The fastening device is fixed in sealing position by a locking device.

BACKGROUND OF THE INVENTION 
The present invention relates to an arrangement at rotating shafts, which 
comprises a wheel fixedly mounted to the shaft, which wheel rotates in a 
housing surrounding the wheel, an essentially pipe-shaped element 
surrounding the shaft, and with essentially axially sealing surfaces 
provided sealing device between the pipe-shaped element and the wheel and 
a passage in the housing for the shaft with a sealing device, which seals 
against the pipe-shaped element. 
Sealing arrangements of the kind described above are used on several 
various kinds of machines. An especially important field of use is fans 
and pumps of the centrifugal type. 
The invention has been found to be especially valuable in those cases, when 
a pump impeller is mounted on a conical shaft end. This is because it has 
been found at the machining of the centre hole for the shaft end, that a 
very small difference in machining depth makes a great difference in the 
axial position of the pump impeller, when it is mounted. Previously known 
pumps of this type comprise a pipe-shaped element in the shape of a wear 
or shaft sleeve surrounding the pump shaft and a stuffing box mounted on 
the pump housing, which seals against the outside of the wear sleeve. In 
order not to get leakage between the wear sleeve and the shaft, there is 
also at this place required a sealing arrangement, which suitably is 
placed between the end surface of the wear sleeve and the pump impeller. 
This seal usually is a ring of resilient material placed in a slot between 
the sleeve and the pump impeller. 
However, it has been found that in those cases when the distance between 
the end surface on the wear sleeve and the pump impeller varies within 
rather wide limits, so will such a resilient ring not always give 
satisfactory sealing effect. This is because a ring, which is so soft, 
that it is always compressed at mounting of the wheel, cannot give a 
perfect seal at high pressure differences if said slot is wide. If a 
sealing ring made of harder material is used, one cannot be sure, that the 
pump impeller has been mounted solidly abutting against the shaft end and 
not against the sealing ring. More narrow size tolerances for the pump 
impeller would on the other side cause great costs because of an increased 
number of cessations during machining. The use of sealing rings of 
different widths will certainly cause errors at the mounting because the 
right size of sealing ring is not used. 
It is previously known to arrange a threaded portion on a pump shaft for 
tightening a nut or a threaded shaft sleeve. This embodiment has several 
disadvantages. Should any damage occur to the thread, this will cause 
substantial spare part costs, because the entire shaft must be replaced. 
When the threaded portion is repaired, for instance rethreading or 
loosening of a nut, which is stuck by rust, the entire pump must be 
dismantled and the shaft removed from the bearing housing. In both cases, 
there may also be great down-time costs because of lost production. The 
thread itself constitutes an indication of fracture, which may cause 
fatigue failure of the shaft. The thread itself is not protected and may 
easily be damaged during storage and transport. Such an arrangement with a 
threaded shaft cannot be installed in an existing pump without a great 
interference in the pump and exchange of the shaft. 
OBJECTS AND SUMMARY OF THE INVENTION 
The object of the present invention is to provide a seal between a wheel 
fixedly mounted on a shaft and an essentially pipe-shaped element 
surrounding the shaft. Especially the invention relates to an arrangement, 
which can give a perfect seal independently of how far in on the shaft the 
wheel is mounted. 
Further object of the invention are to provide a fastening device, which is 
detachably mounted on the shaft, can be installed at an existing machine, 
is easy to install and dismantle as well as is cheap to produce and 
maintain. 
In order to achieve this the invention is primarily characterized in, that 
a detachable fastening device is mounted on the shaft for axial 
displacement of the pipe-shaped element in order to cause a sealing effect 
by means of the sealing device between the pipe-shaped element and the 
wheel, the fastening device comprising an axially stationary part and an 
axially moveable part, whereat the axially stationary part is abutting 
against a shoulder on the shaft, directly or through an intermediate 
element or elements. 
Fastening devices of the kind mentioned above may be made in various ways, 
for instance hydraulic piston devices, wedge devices or one or more 
spreader screws arranged at the outside of the shaft, which force the 
pipe-shaped element against the wheel. However, it has been found to be 
especially favourable to use a screwing device comprising an axially 
stationary and an axially moveable part, whereat the thread of the 
screwing device surrounds the shaft. This provides a cheap design, which 
is protected from damage from the outside and from dirt which may damage 
the threaded surface. The protruding part of the thread is suitably 
covered by a protection ring. In a preferred embodiment the axially 
stationary part is provided with an outside thread and is secured to the 
shaft with the aid of a locking screw. 
In an alternative embodiment the stationary part has an inside thread and 
the moveable part is pipe-shaped and surrounds the shaft. 
In a special embodiment, the screwing device comprises screw surfaces on 
the end surface of at least one of the parts with at least one entrance. 
In order to get more symmetric fastening forces, the screwing device 
should suitably comprise two or more symmetrically arranged entrances. At 
one of the parts it is possible, that the material in the part continues 
all the way out to the outer end of the thread on its outside or inside, 
in order to give increased strength. This embodiment may for instance be 
used in the case when the pipe-shaped element itself is provided with a 
screw surface, and thus at the same time comprises the moveable part of 
the screwing device. The pipe shaped element may, of course, also be 
provided with an outside or inside thread. 
In order to fix the stationary part of the fastening device in an axial 
direction, it is suitably arranged to abut directly or through 
intermediate elements against a shoulder on the shaft. 
In a specially advantageous embodiment the screwing device is replacing the 
slinger ring, which usually is arranged to protect the bearing device of 
the shaft on the side facing the wheel. By suitably chosen dimensions of 
the screwing device, one does not need to change the dimensions of the 
shaft and other parts, and may even exchange the slinger ring on already 
existing machines for a screwing device according to the invention. 
In order to fix the fastening device in sealing position it should be 
provided with some kind of locking device. This locking device may for 
instance be screws, which are tightened against the shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a pump with an arrangement according to the invention 
comprising a pump frame 1, longitudinal frame plates 2, 3, a base plate 4 
and transversal frame plates 5, 6, 7, with seats for a bearing housing 8 
with a pump shaft 9 and a pump housing 10 with an inlet portion 11. On the 
pump housing is mounted a shaft sealing housing 12 in the shape of a 
stuffing box, which seals against a pipe-shaped element or shaft sleeve 13 
surrounding the shaft. The pump housing and adhering components and its 
wear lining are mounted with the aid of bolts. On the pump shaft 9 is 
mounted a pump impeller 14 on a conical shaft end with the aid of a 
retaining washer 15 and a bolt 16 covered by a cover 17. In order to 
achieve a seal between the pipe-shaped element 13 and the pump impeller 14 
there is arranged a sealing washer 18, which is forced against the pump 
impeller 14 by a screwing device 19 situated on the other side of the 
pipe-shaped element. 
The sealing washer and the screwing device are more evident from FIG. 2, 
which shows a detail of a pump shaft between the pump impeller and the end 
of the bearing housing 8 facing the pump wheel. Here it is evident, how 
the sealing washer 18 has a metallic contact with the iron frame 20 of the 
pump impeller 14, while a rib 21 is pressed into the wear rubber cover 22 
of the pump impeller. In a bevel in the shaft sleeve 13, there is an 
O-ring 23 squeezed into the interspace towards the shaft 9 and the sealing 
washer 18. At the outside of the shaft sleeve there are another two 
O-rings 24 fitted in grooves in an extension of the sealing washer 18 
surrounding the shaft sleeve. At the opposite side of the shaft sleeve 
there is a screwing device 19, which forces the shaft sleeve against the 
sealing washer 18, such that a seal is achieved against the pump impeller 
14. The screwing device 19 comprises of an axially moveable screw ring 25 
with outside thread, an axially stationary screw ring 26 with inside 
thread and a protection ring 27, which covers the protruding end of the 
thread. In order to prevent the screwing device from loosening, both the 
stationary and the moveable screw ring are provided with locking devices 
in the shape of one or more lock screws 28, 29. The screwing device 19 at 
the same time serves as a slinger ring in relation to a cover 30 for the 
bearing housing. The stationary screw ring 26 is through a bearing 31 and 
a spacer ring 32 abutting against a shoulder 33 on the shaft 9. 
At the mounting of the pump impeller the moveable screw ring 25 is screwed 
to its innermost position in the stationary screw ring 26. The shaft 
sleeve 13 is pushed onto the shaft to an inner position abutting against a 
shoulder 34 and the sealing washer 18 with its O-rings are pushed after. 
The pump impeller 14 is now mounted, whereupon the sealing washer 18 is 
pressed against the pump impeller by screwing out the screw ring 25, such 
that the shaft sleeve 13 is pushed outwards. In order to make it possible 
to screw with enough torque, the screw rings are suitable provided with 
notches for so-called SKF-keys or shaped with attachments for other tools. 
Finally, the screw rings are fixed in position on the shaft by tightening 
the lock screws 28, 29 against the shaft 9. 
FIG. 3 shows another embodiment of the invention with a screwing device 19A 
comprising an axially stationary screw ring 35 with outside thread and an 
axially moveable screw ring 36 inside thread and a protection ring 37. A 
device according to this embodiment offers the advantage, that the free 
thread surface is better protected against damage. In the figure 
corresponding details have been given the same designation as in FIG. 2. 
FIG. 4 shows a device according to the invention where the pipe shaped 
element is designed with a screw surface at its end surface. In the figure 
corresponding parts have been given the same designations as in the 
previous figures. The screwing device here comprises a modified slinger 
ring 38 with a screw surface-shaped end surface facing the pump impeller. 
The shaft sleeve 39 has a screw surface-shaped end surface 40, which is 
engaging the end surface of the slinger ring 38. For tightening of the 
shaft sleeve 39, such that the sealing washer 18 is pressed against the 
pump impeller, there is a notch 41 for a so-called SKF-key. The shaft 
sleeve is prevented from loosening by the lock screw 42. The thread 
surfaces are also covered by a protection ring 43. 
The invention is not limited to the examples and embodiments described 
here, but may be varied within the limits of the following patent claims.