JPS5844909B2 - steam control valve - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a steam control valve used, for example, in a thermal power plant, etc., and the present invention relates to a steam control valve used, for example, in a thermal power plant, etc. This invention relates to an improvement in a steam control valve that allows the flow to flow.

[Prior art]

Conventionally, this type of valve has a subcritical pressure or a supercritical pressure that reduces the pressure to approximately 80 kg/i or more when the steam pressure is approximately 170 kg/- or more and the flow rate is 300 to 600 bottles/see passing through the valve. Because we are handling steam, if the flow of steam is unstable when the valve is opened, an accident may occur with the valve components.

FIG. 1 schematically shows a conventional steam control valve, and reference numeral 1 indicates a valve casing, and a main valve body 2 is housed in the valve casing 1, and this main valve body 2 is fitted with a sleeve. 3 so that it can slide freely.

Further, a sub-valve body 5 is housed within the main valve body 2 and is integrally connected to a valve stem 4 , and the valve stem 4 is connected to the crosshead 7 through a threaded joint 8 .

In the steam control valve having the above structure, when the lever 9 is first moved in the direction of the arrow at startup, the sub-valve body 5 moves upward accordingly.

Then, the steam S passing through the inlet 10 enters the chamber 11 through the gap C between the sleeve 3 and the main valve body 2, and from there flows through the opening 12 of the main valve body 2 to a steam turbine (not shown). ing.

In this way, the steam S that has passed through the valve warms up the steam turbine sufficiently, and then the main valve body 2 moves upwards, so that the entire amount of steam S flows to the steam turbine and reaches the rated load. reach.

FIG. 2 schematically shows a type of steam control valve that does not have a sub-valve body, and the connection between the valve body 20 and the valve stem 21 is as follows:
It is connected through pin 23.

The other components have almost the same configuration as the embodiment shown in the first figure.

[Analysis of problems in the prior art and their causes] By the way, the steam control valves shown in FIGS. 1 and 2 above both have the following characteristics:
When the valve opens, the steam flow is high speed (subsonic or supersonic)
, passing through the main valve body or the opening between the valve body and the valve seat, the steam impact of this high-speed flow applies extremely severe vibrations to the main valve body or the valve body in the transverse and vertical directions, causing the valve to vibrate violently. Threaded or pinned connections on the rod can be damaged.

This problem is thought to be caused by the following reasons.

The cause of this will be explained below.

(See Figure 2). That is, in the same figure, when the valve is slightly opened,
The steam passing through the opening between the valve body 20 and the valve seat 24 has an extremely high pressure difference between the inlet and the outlet of the valve body, so the steam flows as a free jet along the streamline a, and a stable flow is obtained.

However, as the lift (valve opening degree) of the valve body 20 increases, the pressure difference between its inlet and outlet decreases, and the flow velocity decreases, the steam adheres to the valve seat 24 side and flows along the flowing streamline b'. Or, they may adhere to the valve body 20 side and become flowing streamlines, which are repeated alternately, causing turbulent flow.

Furthermore, as the lift of the valve body 20 is increased, the above-mentioned phenomenon subsides, and a stable flow C is obtained.

FIG. 3 shows the valve opening characteristic showing the relationship between the lift of the valve body and the valve outlet pressure/valve inlet pressure shown in FIG.
C corresponds to the streamline asC and is a stable flow.

However, as mentioned above, in region B, flow occurs with streamlines attached to the valve body side, flow lines b' adhere to the valve seat side, and these are repeated instantaneously, resulting in unstable flow. ing.

To explain this cause in more detail, generally speaking, in this type of valve used for subsonic or supersonic speeds, when the valve is slightly opened, the pressure difference between the inlet and the outlet of the valve body is approximately 17 kg//d or more. Since the inertia of the streamlines is extremely high, the flow is straight and stable.

However, as the valve opening increases and enters the above-mentioned region B, the pressure difference between the inlet and outlet of the valve element decreases, and the fluid that has been flowing while adhering to the valve element or valve seat is reduced. A pressure change occurs between the wall surface and the boundary layer surface, and this pressure change causes boundary layer separation.

This boundary layer separation is thought to cause the fluid to alternately flow along the valve body side and the valve seat side, resulting in unstable flow.

The fluid flow shown in FIGS. 4 and 5 is an experimental verification of the boundary layer separation phenomenon described above.

In these experiments, the valve opening was kept constant, the fluid pressure on the valve body inlet side was kept constant, and the fluid pressure on the valve body outlet side was gradually lowered by throttling operation of a regulating valve (not shown). .

That is, step I shown in FIG. 4 is when the difference between the pressure on the valve body inlet side and the pressure on the valve body outlet side is extremely low,
The fluid flows while adhering to the valve seat side.

However, if you keep the valve opening constant and gradually lower the pressure on the outlet side of the valve body and increase the pressure difference, the state from the left half of step ■ to the right half of step ■ will change. In other words, the fluid on the valve seat side causes separation and adheres to the valve body.

Furthermore, when the pressure difference is increased, as shown in step
Repeated adhesion creates vibrations and extremely unstable flow.

If the pressure on the outlet side of the valve body is further lowered from the unstable flow state, the fluid becomes a free jet flow and a stable flow is obtained as in step (3).

The above-mentioned phenomenon occurs due to the following relationship (R>r is actually used in this type of valve), where R is the curvature of the valve body and r is the curvature of the valve seat. Considering this, we fabricated a valve body that satisfied the following relationship and attempted an experiment.

The curvature of the valve body according to this experiment is R = 0.65D
The curvature of the o s valve seat is r = 0.73 Do.

Here, Do is the diameter of the valve seat at the point of contact between the valve body and the valve seat.

FIG. 5 shows the flow of fluid due to the valve configuration described above, and step (2) was exactly the same as step I shown in FIG.

However, when the pressure on the outlet side of the valve body is gradually lowered, the same phenomenon as step ■ shown in Figure 4 occurs in step ■.
Up to this step (2), the fluid was still flowing while adhering to one side of the valve seat.

Furthermore, when the pressure on the outlet side of the valve body was lowered, step

When the pressure was lowered more than the above, the fluid became a free jet as in step M, which corresponded to step (3) in the fourth diagram.

By the way, from the results of each step shown in Figure 5, r >
It has been found that a valve body that satisfies the relationship R has a relatively strong tendency for fluid to flow while adhering to the valve seat.

This tendency is considered to make it easier to obtain a stable flow than when the fluid flows while adhering to the valve body side.

[Purpose of the invention]

Therefore, the present invention aims to prevent the occurrence of the above-mentioned unstable phenomenon in this type of valve by preventing the flow from separating from the valve seat side mainly in the intermediate lift region where the flow pattern changes. This is a technical issue.

[Structure 1 of the Invention The technical means taken to solve the above technical problem are as follows.

(1) The curvature r of the seat surface of the valve seat is set to 06 times or more the seat surface diameter Do of the valve body that comes into contact with this seat surface, and (2) the curvature R of the hemispherical surface of the valve body is set to the seat surface of the valve body. (3) A concave portion is cut at the lower end of the valve body, and the edge portions provided at both ends of the concave portion are set so that the valve body is in the intermediate lift region. When the flow line adheres to the valve body and flows, it should be installed upstream of the point where the flow line separates.

The above technical means works as follows.

When the steam control valve gradually begins to open, at this initial stage of opening, steam adheres to the valve seat side in a stable state and flows as shown in the step shown in FIG.

Furthermore, as the valve list is raised and the valve body enters the intermediate lift region, in prior art valves the velocity of fluid through the passage between the valve body and the valve seat gradually decreases, which causes the valve seat wall to A pressure change occurred between the valve and the boundary layer surface, which penetrated the boundary layer separation, resulting in a flow pattern that alternated between flow adhering to the valve seat and flow adhering to the valve body. .

However, in the present invention, the curvature of the seat surface of the valve seat is the curvature of the hemispherical surface of the valve body, and the edge portions provided at both ends of the concave portion at the lower end of the valve body are such that the fluid that adheres to the valve body and flows is separated. Since the flow line is provided upstream of the point where the separation point occurs, the streamline separates from the surface of the valve body upstream of the separation point.

Therefore, even if the valve body is in the intermediate lift region, the force that attracts the flow toward the valve body is always smaller than the force that attracts the flow toward the valve seat, and the fluid always flows while firmly adhering to the valve seat as in step XXI. .

In other words, the steam flow is prevented from repeatedly moving toward the valve body and toward the valve seat.

[Special effects of the invention]

The above-mentioned oscillation of the steam flow in the unstable region can be prevented by always adhering the steam flow to the valve body side in the unstable region of the steam flow. Because it can be attached to the valve seat side, the valve seat is a fixed part, so the flow itself is more stable than if it is attached to the valve body side. Continuing the pattern as it is, step XXI, XXII in a stable state
It has the unique effect of transitioning to

[Actual case of invention]

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

In FIG. 6, reference numeral 60 indicates a valve casing, which forms a steam chamber 61, and a valve seat 62 having a throttle shape is fixed to the outflow end of the valve casing 60.

Further, the valve seat 62 has a constricted shape at the outflow end, but the downstream side thereof is formed to gradually widen while having a smooth curve.

A valve body 63 is provided opposite to the valve seat 62, and a valve rod 65 is connected to the valve body 63 through a pin 64.

Further, the valve stem 65 is mounted on a shaft so as to move up and down through a sleeve 66, and by moving the valve stem 65 up and down, the opening degree between the valve body 63 and the valve seat 62 can be adjusted. ing.

Therefore, the valve body 63 has a curvature R from the base point O of the axis, a valve seat diameter Do based on the contact point P between the valve body 63 and the valve seat 62, and the valve seat 62 at the contact point P. The curvature of r
Then, the curvature R of the valve body 63 and the curvature r of the valve seat 62 are
determined respectively.

These numerical ranges are the most preferable application ranges determined through experiments, and fluid flows outside these numerical ranges will cause boundary layer separation as in the past, making it impossible to obtain a stable flow area. has been confirmed.

On the other hand, the valve body 63 has an edge portion 67 located relatively downstream from the contact point P and upstream of the point where fluid separation occurs, and extends inward from the apex of the edge portion 67. The notch is cut over a range of angle θ, and a flat concave portion 68 is formed.

According to the above specific example, it has been confirmed that the fluid flows reliably along the valve seat side even in the middle region of the valve list (see Figure 7). Boundary layer separation with alternating adhesion to body 63 and valve seat 62 is eliminated.

[Brief explanation of the drawing]

Figures 1 and 2 are partially cutaway cross-sectional views showing the main structure of a conventional steam control valve, Figure 3 is a graph showing the valve opening characteristics of a conventional steam control valve, and Figure 4 is a conventional steam control valve. This is a schematic diagram showing the flow pattern of a steam control valve in which the curvature of the valve body is larger than the curvature of the valve seat. FIG. 6 is a schematic longitudinal sectional view showing an actual case of the steam regulating valve according to the present invention; FIG. 7 is a schematic diagram showing the flow pattern of the steam regulating valve according to the present invention. be. 60... Valve casing, 61... Steam chamber, 62... Valve seat, 63... Valve body, 6
5... Valve stem, R... Valve body curvature, r.
...Valve seat curvature, Do...Valve seat diameter.

Claims (1)

[Scope of Claims] 1. A valve body that is formed into a spherical curved surface and has edge portions on both end faces of a concave portion cut into the lower end of this curved surface, and a valve body that gradually moves downstream from the position where the valve body contacts. In a steam control valve, the curvature of the valve body is R1, and the valve seat is provided with a valve seat having a spherical curved surface so as to widen to a spherical surface.
When the curvature of the valve seat is r, and the valve seat diameter at the point of contact between the valve body and the valve seat is Do, the curvature of the valve body and the valve seat is as follows, and the edge part of the valve body is 1. A steam control valve, characterized in that it is provided upstream of a point at which boundary layer separation occurs when fluid is in an intermediate lift region.