JPH0621667B2 - Control valve - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control valve used in a nuclear power plant, a thermal power plant, etc., and in particular, it is installed in a pipe from a turbine to a condenser and has a high pressure upstream. The present invention relates to a structure for preventing damage to a valve seat portion due to erosion or flushing due to a seat leak of a control valve that has a low differential pressure condition on the downstream side.

[Conventional technology]

A control valve used for high differential pressure is disclosed in Japanese Patent Laid-Open No. 60-1468.
As disclosed in Japanese Unexamined Patent Publication No. 0, there is one in which a skirt of a perforated plate is installed for noise prevention due to cavitation or the like. This conventional skirt also serves as a countermeasure against cavitation and flashing, and the skirt itself may be damaged, so it was supposed to be inspected and replaced at the time of regular inspection.

[Problems to be solved by the invention]

As shown in FIG. 4, a heater drain system is installed in a nuclear power plant or a thermal power plant in order to recover the drainage of the used steam. The drain passes through the first, second and third feed water heaters and is finally collected in the condenser. The water level of each feed water heater is controlled by a control valve installed between them. The excess drain is collected through the line that goes from each line to the condenser. The control valve installed on the line that goes to this condenser is normally in a fully closed state and opens only in an emergency (when there is a lot of drain).

An example of this control valve is shown in FIG. 5A. This control valve comprises a valve box 1, a cage 2, a valve lid 3, a valve rod 4, a valve body 5 and a seat ring 6, and the valve body 5 moves up and down in the cage 2 and is in contact with the seat ring 6. It is fully closed. However, since the control valve prioritizes the flow rate control function, a certain amount of seat leak is allowed even when fully closed. Therefore, the control valve installed on the line going to the condenser and used as the stop valve has the following problems.

A. At the time of fully closed use, the fluid leaked from the valve seat portion is flushed at the outlet of the valve seat portion due to the negative pressure on the outlet side (see FIG. 5B), so that the seat ring 6 is eroded. There is a case that causes. The present situation is that the seat ring 6 of the control valve is replaced at every regular inspection.

B. When there is a large amount of drainage during the plant startup test, use this control valve at an intermediate opening. The flow entering from each hole of the cage 2 is concentrated in the center of the cage 2, and the bottom of the valve box collides at high speed with the flow of flush, and there is a possibility that the bottom may be damaged (face, skin). (Fig. 6).

C. If there is a rising part downstream of this control valve, a drain pool will be created there. In this situation, when high-temperature steam flows from the upstream side, the drain suddenly expands thermally and the piping may cause hammering.

The above-mentioned phenomenon is caused by the negative pressure on the valve outlet side (downstream) and the high differential pressure condition with the upstream side as shown in FIGS. 5B and 7A. It is considered that a high-speed flush flow occurs as shown in Fig. 7B, which causes erosion of the seat ring and damage to the bottom of the valve box.

An object of the present invention is to provide a control valve capable of relaxing a high differential pressure condition between an upstream side and a downstream side, suppressing a high-speed flush flow, and preventing damages to an erosion of a seat ring and a bottom of a valve box.

[Means for solving problems]

In order to achieve the above object, the present invention provides a control valve of a two-stage depressurization method, instead of the conventional method of immediately reducing the pressure at the valve seat outlet to a negative pressure.

Specifically, a baffle that narrows the outlet flow path inside the valve box on the downstream side of the control valve and keeps pressure is provided so as to hang from the valve box ceiling.

[Action]

This structure has a function of temporarily confining the flush flow flowing out from the valve seat portion and then flowing it downstream. Therefore, the pressure change in the valve seat portion is alleviated, the differential pressure between the valve seat portion and the downstream side becomes relatively small, and the erosion of the valve seat surface seat and the damage of the valve box bottom portion due to flushing can be prevented.

When part of the floor surface of the valve box is raised to form the baffle, or when a normal orifice is used, drainage can be formed on the downstream side of the valve, and the hammering occurs when the flush flow passes through. Occurs, which is not preferable.

Therefore, from the ceiling of the valve box, a baffle in the shape of an arc or the like, which becomes the resistance of the flow path, is formed.

These baffles increase the internal pressure of the valve, increase the pressure of the fluid discharged from the valve seat portion, reduce at least a part of the fluid once turned into a gas, and reduce the velocity of the fluid, The above object will be achieved. An example thereof is shown in FIGS. 7C and 7D.

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings. The parts corresponding to those of the conventional example shown in FIGS. 5 and 6 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a vertical sectional view and a partial side view showing an embodiment of a control valve according to the present invention. The present embodiment is different from the conventional example in that an arcuate baffle 7 that narrows the outlet flow passage and keeps pressure is provided in the downstream side of the valve box 1 so as to be suspended from the valve box ceiling. The baffle 7 can be simultaneously formed by a mold when the valve box 1 is made.

The fluid flowing into the control valve of the present embodiment having such a structure from the valve inlet side is formed when passing through the narrow valve seat portion formed by the cage 2 and the valve body 5, and temporarily becomes equal to or lower than the saturated vapor pressure. Become. However, since the baffle 7 is provided, the pressure in the valve seat outlet space increases as compared to the conventional case, and the pressure becomes equal to or higher than the saturated vapor pressure. As a result, at least a part of the gas once turned into water again, and the flow velocity at the valve seat outlet is significantly reduced as compared with the conventional case. Therefore, erosion of the seat ring and damage to the bottom of the valve box (face and skin) do not occur.

The shape of the baffle 7 is not limited to the arcuate shape shown in FIG. 1, and it is sufficient if the baffle 7 hangs down from the valve box ceiling side as much as possible to resist the fluid. Therefore, the shape of the baffle 7B shown in FIG. Can also be

As shown in the application example of FIG. 3, even if the baffle 7C is formed on the upstream side of the valve box, some effect can be obtained in the sense that the inflowing fluid pressure is relaxed.

〔The invention's effect〕

 According to the present invention, the following effects can be obtained.

(1) The flushing state at the valve seat outlet is eliminated, and seat ring erosion due to valve seat leakage can be greatly reduced. The baffle is not damaged.

(2) The flow velocity can be reduced even for concentrated flux when the valve is used in the middle, and the possibility of damaging the valve bottom can be reduced.

(3) Since the valve outlet baffle is hung from the ceiling,
No drainage pool is formed and problems such as hammering do not occur.

[Brief description of drawings]

FIG. 1 is a view showing an embodiment of a control valve according to the present invention, and FIG.
FIG. 4 is a diagram showing another embodiment, FIG. 3 is a diagram showing an application example of the present invention, FIG. 4 is a system diagram showing an example of a heater drain system including a control valve, which is a target of the present invention, and FIG. Is a view showing a conventional control valve, FIG. 6 is a view showing a damage phenomenon of a valve box bottom portion of FIG. 5 conventional example, and FIG. 7 is a comparison of pressure and flow velocity in the control valve of the conventional example and the present invention. FIG. 1 ... Valve box, 2 ... Casing, 3 ... Valve lid, 4 ...
Valve rod, 5 ... Valve body, 6 ... Seat ring, 7, 7B, 7
C ... Butful.

Claims (1)

[Claims] 1. A control valve installed in a pipe from a turbine to a condenser and having a high differential pressure condition of high pressure upstream and low pressure downstream, wherein an outlet flow passage inside the downstream valve box is narrowed to keep pressure. A control valve characterized in that a baffle that allows it to be hung down is provided from the ceiling of the valve box.