WEISS JOSEF (SE)
| US4398727A | 1983-08-16 | |||
| US3100621A | 1963-08-13 |
| 1. | A regulating valve comprising a valve housing (1) and an essentially horizontally arranged, linearly movable valve means (2) for regulating a flow through the valve, the valve means comprising a stem having a cylindrical portion (22) and arranged with the cylindrical portion in a bearing path (6) contained in the valve housing, c h a r a c t e r i s e d in that the bearing path comprises on the one hand a "bed" in the base of the bearing path consisting of a depression (29) formed as a first surface consisting of a part of a cylindrical surface limited by a pair of generatrices and having a first radius (30), shown in crosssection, which corresponds to that of the cylindrical portion or just above and which is shorter than half of a maximum diametrical dimension of the bearing path and, on the other hand, a second surface arranged above the bed and bridging the first surface, and the centre angle (31) between the limiting generatrices of the first surface is between 45" and 1600. |
| 2. | A regulating valve as claimed in claim 1, c h a r a c t e r i s e d in that the second surface is a part, limited by a pair of generatrices, of a cylindrical surface with a second radius (28) which is shown in crosssection and whose centre is placed a distance above that of the first radius (30). |
| 3. | A regulating valve as claimed in claim 1 or 2, c h a r a c t e r i s e d in that the centre angle (31) between the limiting generatrices is about 70". |
| 4. | A regulating valve as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the crosssectional radius (30) of the depression exceeds that of the cylindrical portion by about 0.01 mm. |
| 5. | A process for manufacturing a regulating valve as claimed in any one of the pre ceding claims, c h a r a c t e r i s e d by first making in the valve or some part thereof, for instance, a bearing sleeve (25), in which the outer bearing path is arranged, a cylindrical basic hole in a machine tool, then translationally moving the valve or the part in its fitting in the machine tool and making a partcylindrical recess (29) which extends from the basic hole into the surrounding material. |
Prior Art A valve housing of the above-mentioned type is closed relative to the surroundings.
It accommodates two chambers with an intermediate wall having an opening. The valve member cooperates with this opening to provide the variable opening area.
An inlet duct is connected to one of the chambers. An outlet duct is connected to the other chamber. If the valve is used to regulate the effect of a steam turbine, the inlet and outlet ducts can constitute, together with the valve housing, parts of the duct of the steam turbine for supplying steam. In many cases, this duct has for practical reasons been installed with a vertical main direction. Since valves are usually formed with the valve stem extending perpendicular to the main direction of the passing flow, many valves have their valve stem in a horizontal position.
The valve stem usually has a cylindrical part, which constitutes an inner bearing path for the bearing arrangement. Known bearings have, for new or reconditioned
bearings, a cylindrical outer bearing path. The diameter thereof has a constructional overdimension in relation to the inner bearing path, which depends on the accuracy of manufacture in respect of the paths, possible differences in temperature between stem and bearing etc.
The overdimension is kept as close as possible, such that only a minimum amount of steam leaks out from the valve housing through the bearing gap formed between the bearing and the stem. This steam often has pressures which are very high and may exceed 60 atm. gauge.
Anyhow, the overdimension must be so great that the stem is positioned in a base, the diameter of which is so much greater than that of the stem that the stem engages linearly in the bearing. Since the weight of the stem, with the addition of the weights of the valve member and parts of the positioning device, thus causes high surface pressures acting on the bearing surface, wear arises. By choosing predetermined combinations of materials for the stem and the bearing, the wear can essentially be limited to the bearing, which is desirable since it is less expensive to recondition the bearing compared with the stem. It is true that moist steam penetrates between the bearing surfaces, but a supporting film which reduces the wear cannot be obtained as is the case with continuously rotating bearing arrangements.
As mentioned above, the valve is mechanically connected to the turbine by a conduit. To prevent unnecessary flow losses, one tries to keep the conduit as straight and short as possible. Vibrations of the turbine will therefore propagate to the valve housing and the bearing without much reduction. The wear caused by the great surface pressure will be increased to a considerable extent by the fact that the stem, owing to its undefined position in the base of the bearing, will move around in the base owing to the vibrations. Wear is caused by the continuous rolling of the stem on the surfaces of the bearing and motions in the base of the surface.
Moreover, fragments will be released especially from the outer bearing path owing to the choice of the combination of materials described above. This wear is increased by the fragments acting as an abrasive between the bearing surfaces.
The wear causes a growth of the gap between the upper part of the bearing and the stem. The increasing amount of steam leaking through this gap will later on necessitate reconditioning of the stem and the bearing, for instance, by grinding the stem and exchanging the bearings.
DescriPtion of the Invention Technical Problem The object of the invention is to provide a valve, as mentioned by way of introduc- tion, with improved guiding of the stem. By means of the valve, the wear in the bearing and, thus, the leakage through this bearing will be reduced to a considerable extent.
Solution This object is achieved by the valve being given the distinctive features that appear from the appended claims.
According to the invention, the bearing is arranged with a "bed" for the stem in the base of the bearing. The "bed" should give the stem a defined position in the bearing, thereby preventing as far as possible the stem from moving and rolling.
The "bed" can be a depression formed as a part, limited by generatrices, of a cylindrical surface with a cross-sectional radius corresponding to that of the stem or just above. As a result, the surface pressure between the bearing surfaces is reduced by the engagement spreading over a much larger surface. A surface engagement is then obtained instead of the linear engagement of the prior-art bearing. Since it is possible to essentially prevent the movement of the stem and to reduce the surface pressure, the bearing is subjected to much less wear in a valve according to the invention. The depth of the "bed" should be so great as to prevent movement of the stem. According to the invention, it is proposed that the depth, measured with a centre angle, shown in cross-section, between said limiting generatrices, be determined to be at least about 45" so as to prevent movement of the stem and obtain a sufficient contact surface. The angle should not exceed about 1600, since otherwise the clearance between the stem and the bearing will be too small. When the angle is close to 1800, a drawer effect may arise and cause locking of the stem. A suitable value of the angle is about 70°, which is used in the preferred embodiment. The maximum diametrical dimension of the outer bearing path is suitably the same as for prior-art bearings.
When the stem is at rest, the inner bearing surface, in bearing arrangements of the present type, will be caused by gravity to lie in the base of the outer bearing surface. Between the uppermost part of the inner bearing surface, the stem, and the outer bearing surface, the hole, a clearance is necessary, the size of which
depends on the possible differences in temperature that may arise in the bearing arrangement, soot deposits on the bearing surfaces, surface irregularities therein etc. For a predetermined use, this size of the clearance is made to be essentially proportional to the diameter-of the stem.
For a stem with a diameter of 70 mm, use is made, for valves of the type of the preferred embodiment, of a clearance of about 0.3 mm when the bearing arrangement has not been worn. The differences in temperature in the bearing arrangement may arise, for instance, as steam is supplied when starting the turbine, which means that hot steam heats the valve member and, thus, the stem much quicker and much more than the outer part of the bearing arrangement.
Furthermore the latter is kept cooler by good carrying off of heat to the other part of the valve housing.
In known bearing arrangements, cylindrical outer bearing surfaces with a diameter corresponding to that of the stem with the addition of said clearance have been chosen. The clearance has thus also been allowed to determine the radius in the base of the hole. This radius has become so much greater than that of the stem that the movement of the stem as described above and the great surface load have been obtained. According to the invention, it is therefore suggested that a lower part of the outer bearing surface, in which the stem rests, be given a radius which is smaller than half of the above-mentioned diametrical dimension, which corresponds to the diameter of the stem with the addition of a clearance as is normal in the context, usually the vertical diametrical dimension of the outer bearing path of the invention. According to the invention, the normal clearance is chosen in the same way as for known bearing arrangements.
As stated above, the base of the outer bearing path should have a radius corresponding to that of the cylindrical portion or just above. In a preferred embodiment, use has been made of an ISO tolerance with the degree h6 for the stem and the degree H7 for the base of the hole. With a stem diameter of 70 mm this means that the tolerance range is, for the radius of the stem, between about -10pm and 0 pm, and for the radius of the base of the hole, between 0 pm and 15 pm. The base then has a radius which is from that of the cylindrical portion up to 0.025 mm (10 pm + 15 pm) above that, whereas half said diametrical dimension is the radius of the cylindrical portion with half the clearance added, i.e. 0.15 mm. In this case, the radius of the base thus is between 0.125 mm (0.15 - 0.025) and 0.15
mm smaller than half the diametrical dimension. The tolerances of this dimension are not taken into consideration.
According to the invention, there is also provided a process for manufacturing the outer bearing path as suggested above. The entire valve or a part thereof which is to comprise this outer bearing path, for instance, a valve housing end wall or a bearing sleeve, is fitted in a machine tool, such as a lathe or a milling machine, whereupon a cylindrical basic hole is made. Subsequently, the part in its fitting is translationally moved in the machine, and a part-cylindrical recess is made, which extends from the basic hole into the surrounding material, for instance, the bearing sleeve. The bearing surface can be made in such a manner that the longitudinal axis of either the basic hole or the part-cylindrical recess coincides with the axis of a rotary motion of the worked object in the machine tool. A bearing sleeve is fitted, preferably with its outer surface concentric with this axis of rotation. If the axis of the recess is made to coincide with the axis of the rotary motion, the theoretically optimal guiding of the movement of the stem should, as is mostly the case, be obtained in respect of the cooperation of the valve member described above with the valve housing. In the preferred embodiment, the longitudinal axis of the basic hole is, however, made to coincide with the axis of rotation. The basic hole normally forms the surface above the hole base. It goes without saying that, alternatively, this hole can form the hole base proper.
Advantages According to the invention, simple means are achieved for reducing the wear to which the valve bearing and the stem are subjected. For, for instance, a valve corresponding to the prior-art valve of the preferred embodiment with a stem diameter of 70.0 mm, the bearing has a diameter of 70.3 mm. In the time, during which the wear has been checked, the clearance has increased from 0.3 to 0.6 mm.
The guiding of the movable element has then become impaired, such that the valve has become more sensitive to vibrations and the flow of the leaking steam has become so great that it has been considered necessary to recondition the bearings and the stem.
According to the invention, the shape of the hole, apart from the lower part, the "bed", is not bound as long as there is sufficient clearance. For the preferred embodiment, use is made of a part-cylindrical shape of the hole also above the mentioned generatrices with a centre angle of 70" This shape of the hole thus has
generatrices which are shared by the "bed" and has such a radius that the vertical diameter of the hole corresponds to said maximum diametrical distance. From experience it is known that during said time the clearance will increase, owing to wear, from 0.3 to 0.4 mm only, which implies that the reconditioning of the bearing arrangement is not necessary with the same frequency. A further advantage is that the service life of the entire valve is extended since the valve is less sensitive to vibrations and the cost of steam leakage is reduced.
Description of Figures A preferred embodiment will now be described in more detail with reference to the accompanying Figures, the reference numerals of which designate equivalent parts.
Fig. 1 is a longitudinal section of an inventive valve for regulating and closing a steam flow to a steam turbine.
Fig. 2 is a sectional view ll-ll from Fig. 1 through the bearing of the valve stem and the surrounding part of the valve housing.
Preferred Embodiment For the sake of ciarity, the valve is shown in a simplified embodiment. It is used to control the effect of a steam turbine in a power plant and is arranged adjacent to the turbine. The valve has as main parts a valve housing 1 and a movable horizontal valve means 2, which is actuatable by a positioning device 3. This device can form a unit together with the valve. The movable valve means is adapted to form, together with the valve housing, an area 4 through which the steam must pass. The size of this area is varied by linearly moving the valve means in directions 5 coinciding with the longitudinal axis of the means, the means being guided by a bearing 6 which extends through the valve housing, and being handled by the positioning device arranged outside the valve housing.
The valve housing, which serves as a body and a duct closed to the surroundings, consists essentially of a valve chest 7 and a valve housing end wall 8 fitted with the bearing 6. The end wall is fixed, by means of a flange 9 coaxial with the bearing, to the valve chest with the aid of bolts 10. The bolts are inserted in through flange holes 11 and screwed into threaded holes 12 of the valve chest, uniformly distributed around the flange.
The valve chest, which is the main part of the valve housing, is like the valve housing end wall designed as a shell of cast steel. The shell 13 of the valve chest forms walls for an inlet chamber 14 and an outlet chamber 15. A wall 16 shared by the chambers has an opening formed as the hole of a rotationally symmetrical nozzle tube 17 which is coaxial with the bearing 6. The nozzle tube extends a distance into the inlet chamber as well as the outlet chamber. That part of the nozzle tube which extends into the inlet chamber is terminated with a slightly rounded, inner annular edge 18, which is that part of the valve housing which cooperates with the movable valve means 2 for regulating the flow of steam. The shell of the valve chest also forms an inlet tube 19 and an outlet tube 20. These vertically arranged tubes are connected to the inlet chamber 14 and the outlet chamber 15, respectively. The latter tube is directly connected with the steam intake pipe of the turbine.
The rotationally symmetrical movable valve means 2 comprises essentially a valve member 21 and a cylindrical valve stem 22, at one end of which the valve member is fixed. The valve member is formed as a cylinder whose outer terminal edge is bevelled to form a truncated conical surface 23, which is that part of the movable valve means which cooperates with the annular edge 18 of the nozzle. The valve means can be moved linearly between the end positions of the valve member, which are indicated in the drawing.
The other end of the valve stem is connected to the positioning device 3. This can be an electric motor with a gear wheel meshing with a gear rack which constitutes an extension of the valve stem. In the preferred embodiment, the device, however, is a hydraulic driving cylinder, whose driving piston is attached to the valve stem.
The driving cylinder is fixed to the valve housing by means of a holder (not shown).
The shell of the valve housing end wall 8 is formed as a cup which accommodates the valve member. At the edge of the cup, the flange 9 is connected. From the bottom of the cup, the end wall shell projects in a tubular manner to form a mounting 24 for a pair of bearing sleeves 25, which are used as bearings and which are inserted with a press fit into the mounting.
With a view to preventing steam from leaking into the turbine hall, the bearing is formed with a suction space 26 for leaking steam. The space, which is placed between the two bearing sleeves, is connected, by the intermediary of a duct in a suction tube 27, to a system for the power plant's recovery of leaking steam.
The bearing path of each bearing sleeve is made by turning in a lathe in two steps.
For the preferred embodiment with a stem diameter of 70.0 mm, first a hole 28 with R = 35.1 mm is turned, which is concentric with the outer surface of the sleeve.
Then the sleeve is given an eccentricity of such an extent in its fitting in the lathe that a longitudinal depression 29 of 0.03 mm, which is symmetrical with a vertical plane, is obtained at the lowermost part of the bearing path, when turning with a radius 30, which exceeds the radius of the stem by about 0.01 mm. A "bed" is then obtained, which has a centre angle 31 of about 70".
In the preferred embodiment, a cylindrical valve stem 22 is shown, which cooperates with a pair of bearing sleeves 25 with equally large holes. However, the stem could be stepped with at least two concentric subsequent cylinders with different diameters, in which case the bearing sleeves would have holes of corresponding sizes according to the invention. The embodiment also shows a valve with a simple function. With a view to securing the possibility of quickly stopping the flow of steam to the turbine, for instance, in case of disturbance in the current supply of the generator, this kind of valves is in many cases fitted with a special movable valve means for this function. Also this means is then suitably arranged according to the invention.