Valves and valve actuation – Valve head movably connected for accommodation to seat – With universal connection
Reexamination Certificate
2000-02-11
2001-10-30
Kaufman, Joseph A. (Department: 3754)
Valves and valve actuation
Valve head movably connected for accommodation to seat
With universal connection
C251S369000
Reexamination Certificate
active
06308930
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a valve according to the preamble to claim
1
for regulating flows of gas and liquid. The valve has a movable means comprising a valve member and a valve stem, at the end of which the member is arranged, for instance, with the aid of a fixed attachment. For the regulating operation, the means provides, together with the body of the valve, the valve housing, an opening area, which can be varied by moving the means in the valve housing linearly in the longitudinal direction of the stem. This movement is controlled by a bearing arrangement contained in the valve housing and intended for the valve stem, which preferably extends through the wall of the valve housing. As a rule, the bearing arrangement consists of a cylindrical portion of the valve means and a number of bearing sleeves attached to the valve housing. The movement is effected by a positioning device, which can be a hydraulic cylinder adapted to act on the valve means. The device is preferably fixed to the other end of the stem. The valve is used, for example, in power plants and the like regulating flows of water vapour and flows of hot water with high pressures and high temperatures and is installed with its valve stem in an essentially horizontal position. The invention also relates to a process for manufacturing a bearing sleeve for the regulating valve.
DESCRIPTION OF THE RELATED 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.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to provide a valve, as mentioned by way of introduction, 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.
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 surface 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 lest about 45° so as to prevent movement of the stem and obtain a sufficient contact surface. The angle should not exceed about 160°, since otherwise the clearance between the stem and the bearing will be too small. When the angle is close to 180°, a drawer effect may arise and cause locking of the stem. A suitable valve of the angle is about 70°, which is used in the preferred embodiment. The maximum diametrical dimension of the outer bearing path is suitable 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 to heat to the other part of the valve housing.
In known bearing arrangements, cyl
Bastianelli John
J. Weiss Technic Sweden AB
Jacobson & Holman PLLC
Kaufman Joseph A.
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