JPS6143589B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a regulating valve for controlling the amount of steam supplied from a boiler to a steam turbine, which is a prime mover for driving a generator, in large-scale thermal and nuclear power plants.

Control valves for steam turbines operate at high temperatures and high pressures (538℃,
246Kg/cm ² ) of steam. Because steam turbines are used under such harsh conditions, abnormalities in their parts are often discovered during periodic inspections of steam turbines. The abnormalities include cracks in the valve stem connection threads, breakage of the valve stem, and abnormal wear of the valve body and valve stem connection pin. When these abnormalities are discovered, parts are replaced or valves are modified to reduce abnormal vibrations and damage to the valves, but this has not yet reached the point of eliminating instability.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A steam turbine control valve conventionally used in power plants and the like will be described below with reference to FIG.

Reference numeral 1 in FIG. 1 is a valve box, and a valve seat 2 and a valve body 3 are housed inside the valve box 1. Above valve seat 2
has a cylindrical shape, and its outer surface is fixed to the outflow end of the inlet chamber 4 formed in the valve body 1. Further, the inner surface of the valve seat 2 is formed into a tapered surface that gradually decreases in diameter from the inlet chamber 4 side toward the downstream side in a convex curved shape, and then gradually widens toward the downstream side again.

The valve body 3 has a substantially spherical surface facing the valve seat 2, and a valve stem 6 is connected to the opposite side via a pin 5. The valve stem 6 is attached so as to be able to move forward and backward through the center of a lid body 7 that closes the upper part of the inflow chamber 4. By moving the valve stem 6 forward and backward, the valve body 3 is moved along the axis of the valve seat 2. It is configured to move forward and backward in the core direction to adjust the degree of opening between the valve body 3 and the valve seat 2. Further, when the valve body 3 is fully closed, the peripheral edge of its spherical portion comes into contact with a position slightly downstream of the inflow chamber side end surface of the valve seat 2.

The inlet chamber 4 is connected to a boiler (not shown), and the downstream side of the valve seat 2 is connected to a turbine (not shown).

In this way, many steam turbine control valves having the cross-sectional shape shown in FIG. Therefore, if the valve has the characteristics shown in Figure 2, the center outlet (arrow 1) will flow from fully closed to a small opening, and the center outlet (arrow 1) will flow between a small opening and an intermediate opening. and unstable region of valve seat adhesion,
Beyond that point, the flow follows a pattern of one valve seat attachment (arrow 2) or both valve seat attachment (arrow 3). If these three types of patterns exist, the flow will be unstable in the transition region, the pressure applied to the valve wall will fluctuate, and a load will be applied repeatedly to the valve seat 2, valve body 3, etc., and this will continue for a long period of time. This results in the drawback of fatigue failure. Therefore, in order to obtain a valve that is stable over a long period of time, the present inventors firstly reduced the types of flow patterns, secondly made the width of the transition region very narrow, and thirdly, the valve body 3 and valve seat 2 Focusing on creating only stable flow patterns with no fluctuations added to the
In order to achieve these three conditions, firstly, the valve top or end face is cut flat to eliminate the pattern of one-sided valve seat attachment, and secondly, the width of the transition region is increased by cutting the valve top or straight valve seat. Extremely narrow, 3rd
found that by adopting a straight valve seat, the throat position hardly changes, so the shape after the throat on the valve side can be optimally designed. Furthermore, by opening and closing the valve, the shape of the flow path before and after the throat does not change significantly, so it is possible to maintain an almost optimal flow path shape over a wide range from fully open to nearly fully closed.
As a result, we have achieved a stable flow pattern in which no fluctuating force is always applied to the valve body 3 and valve seat 2, and have completed the present invention. The present invention has been made based on the above findings, and it is an object of the present invention to provide a regulating valve that has a shape that is easy to process and that prevents unstable flow after the valve over the entire range from fully closed to fully opened.

That is, the present invention provides a regulating valve in which the flow rate is adjusted by moving a valve body forward and backward in the axial direction of the valve seat, in which the valve body has a flat lower end surface and a recessed surface. The control valve is characterized in that the surface of the valve seat that contacts the valve body is formed into a conical slope, and curved surfaces are formed at both ends of the slope.

Hereinafter, embodiments of the regulating valve according to the present invention will be described in detail with reference to FIGS. 3 to 8. Note that the figure shows only essential parts of the present invention, and the same parts as those in FIG. In FIG. 3, the valve seat 20 has a straight part 2a and curved parts 2b and 2c.
is a conical slope with an apex angle of 50°, and the valve body is 30°.
is a hemisphere, and the area up to 10° downstream from the line tangent to the valve seat 20 is a spherical surface, and the downstream side is R/8 in the tangential direction.
It extends in a straight line (this short part has a conical shape), then bends it at a right angle toward the center of the hemisphere to form a plane 31 perpendicular to the axial direction of the valve stem 6 at a distance of about R/5. A parallel plane recess 32 is formed in the end face.

The opening and closing states of the control valve will be described with reference to FIG. 4. The two-dot chain line indicates the fully closed state of the valve, the solid line indicates the half-open state, and the dotted line indicates the fully open state. The throat position at the narrowest part of the steam passage sandwiched between the valve body 30 and the valve seat 20 moves by opening the valve body 30, but the throat position on the valve body 30 side is because the valve seat 20 is in a straight line. , is at a nearly constant position. In the case of a normal valve, as shown in FIG. 1, as the valve body 3 is opened, the throat position on the valve side moves toward the top of the valve. For this reason, in conventional control valves, the lower end surface of the valve body 3 is formed in a curved shape up to the apex of a substantially hemispherical shape, which tends to cause flow patterns such as adhesion to the valve seat on one side. Furthermore, because the outflow direction is at a wide angle, the unstable region is also wide.

5 to 7 schematically show the opening/closing diagram of the control valve in FIG. 3, and in the valve according to the present invention, the movement of the throat position on the valve side from the straight part 2a forming the conical slope is small. Furthermore, since the flow path expansion angle is small even downstream from the throat position, and the valve opens and closes in substantially the same shape regardless of the valve lift, the optimum flow path shape can be easily determined.

The flow patterns downstream of the valve in Figures 5 to 7 are indicated by arrows 21, 22, and 23, respectively. Figure 5 shows the flow pattern when the valve is slightly opened, and the valve outlet pressure is low and the valve outlet pressure is changed to the valve inlet. Since the pressure ratio before and after the valve divided by the pressure is small, the air blows out from the throat at high speed, and the jet does not adhere to the valve seat side, but instead blows out toward the center. With this flow pattern, pressure fluctuations on the valve wall surface are minute and no abnormal vibrations occur. Figure 6 shows the flow pattern when the valve opening is in the middle. At this opening, the pressure ratio before and after the valve increases, the jet velocity is medium, and both valve seats are attached, and the valve flows from the edge. is completely peeled off. This flow type is also similar to the central blowout, and pressure fluctuations on the valve wall surface are minute and no instability occurs.
Even when the valve is fully opened as shown in Fig. 7, the valve seat remains attached and does not pass through an unstable region on the way.

As described above, the regulating valve according to the present invention is a valve with very stable flow, and as shown in FIG. Therefore, there is no intermediate transition region (unstable region), there is no one-sided valve seat adhesion, and there are only two patterns: central blowout and valve seat adhesion flow.
Therefore, it is possible to provide a regulating valve suitable for a steam turbine that is stable over a wide range from fully closed to fully open.

Further, in the present invention, processing is easy because it is sufficient to simply form a recess in the lower surface of the valve body. In addition, even if the present invention is applied to a control valve for a steam turbine with a sub-valve in which a different valve is incorporated in the valve body 30, the same operation and effect as in the above embodiment can be obtained. Further, the conical apex angle of the valve seat may be selected within the range of 30° to 70°.

As detailed above, according to the present invention, the valve body 3
0 has a flat lower end surface and a recess 32 formed therein, and the surface of the valve seat 20 that contacts the valve body 30 is formed into a conical slope 2a, and curved surfaces are formed at both ends of the slope 2a. By doing so, it is possible to prevent unstable flow that occurs after the valve, and to restrict the main flow passing between the valve body and the valve seat to the center position of the valve seat, thereby reducing the fluctuation force on the valve body. The cause of vibration can be removed without any interference. Therefore, damage to the component parts and noise caused by vibration can be prevented, so there is no need to particularly improve assembly accuracy, and it is possible to provide a control valve that can reduce costs.

Note that each of the above embodiments applies the present invention to a high-pressure, large-flow control valve used in a steam turbine device, and can achieve very remarkable effects. The present invention is not limited to this, but can be widely applied to control valves in which the flow rate is adjusted by moving the valve body forward and backward relative to the valve seat in the axial direction of the valve seat.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view partially showing a conventional regulator valve, FIG. 2 is a curve diagram showing the characteristics of the valve in FIG. 1, and FIGS. For explanation purposes, Figure 3 is a schematic vertical cross-sectional view showing the state in which the valve element is in contact with the valve seat, Figure 4 shows the open/closed state of the valve element, and Figure 5 shows the flow when the valve element is slightly opened. FIG. 6 is a schematic vertical sectional view showing the flow pattern state when the valve body is in the middle, and FIG. 7 is a schematic longitudinal sectional view showing the flow pattern state when the valve body is wide open.
FIG. 8 is a curve diagram showing the characteristics of the valve. 1... Valve box, 2... Valve seat, 3... Valve body, 4...
Inflow chamber, 5... pin, 6... valve stem, 7... lid body,
8... Narrow section, 2a... Straight section, 2b, 2c...
...Curved surface portion, 20... Valve seat, 30... Valve body, 31...
...Plane, 32...Concavity.

Claims (1)

[Claims] 1. In a control valve that adjusts the flow rate by moving a valve body forward and backward in the axial direction of the valve seat, the valve body has a flat lower end surface and a recess, A control valve characterized in that the surface of the valve seat that contacts the valve body is formed into a conical slope, and curved surfaces are formed at both ends of the slope.