JPS5834717B2 - steam stop valve - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a steam stop valve for a steam turbine, for example for driving a high-pressure feed water pump in a nuclear power plant.

Background of the Invention In BWR nuclear power plants, when water supply control becomes poor due to a failure in the reactor water supply system, or small-scale damage occurs to the reactor cooling system piping, etc., the reactor water level drops due to a decrease in cooling water. Then, there is a high-pressure water injection system that detects this and supplies cooling water to the reactor.

This high-pressure water injection system uses steam generated in the nuclear reactor to drive a steam turbine, rotates a water supply pump directly connected to the steam turbine, and supplies water to the reactor.

A steam stop valve is installed between the nuclear reactor and the driving turbine.

As shown in FIG. 1, the steam stop valve includes a valve box 1, an upper lid 2, an inlet chamber 3 formed in the valve box 1, and a valve seat 4.
and an outlet chamber 5, a balance chamber γ surrounded by a cylindrical case 6 attached to the upper lid 2 above the valve seat 4, and a pressure passage 9; and a valve housed in the balance chamber γ. It includes a disk 8, a pilot valve 11 and a valve rod 12 provided therein, and a hydraulic cylinder 13 for controlling the valve.

The valve disc 8 is connected to a hydraulic cylinder 13 via a pilot valve 11 and its valve stem 12, and is opened and closed by supplying and discharging control oil Q to the hydraulic cylinder 13. During its opening operation, a turbine (not shown) is driven.

Note that the pilot valve 11 and the hydraulic cylinders 13 and 1
constitutes an actuator of the valve disk 8, which is a valve body.

The driving force of the hydraulic cylinder 13 is not sufficient to open the valve at once against the steam pressure pressurized upstream of the valve disk 8.

For this reason, a pilot valve 11 is built into the valve disk 8, and when the valve is opened, the pilot valve 11 is first opened by a hydraulic cylinder 13.

This eliminates the differential pressure across the valve disc 8, and the valve disc 8 can be easily opened using the hydraulic cylinder 13.

The outer periphery of this valve disk 8 is surrounded by a case 6 in order to prevent vibrations such as dynamic pressure caused by steam flow and swirling flow.

The pressure in the balance chamber T surrounded by the case 6 is
Steam S' flowing in through the gap 10 between the inner periphery of the case 6 and the outer periphery of the valve disk 8 equalizes the pressure in the inlet chamber 3 on the upstream side.

However, when the pilot valve 11 opens during the valve opening operation, the steam in the balance chamber T is released to the downstream side.

At this time, a difference occurs between the amount of steam supplied from the gap 10 into the balance chamber 1 and the amount of steam released from the balance chamber 7 via the pilot valve 11, resulting in a change in pressure distribution.

If the amount of steam released via the pilot valve 11 is greater than the amount of steam supplied into the balance chamber T, the pressure inside the balance chamber 7 will be lower than the pressure in the inlet chamber 3.

This causes the valve disc 8 to be lifted from below and suddenly open beyond the control range of the valve.

If the valve suddenly opens beyond its control range, a large amount of steam will flow into the turbine, causing the turbine to trip due to an increase in rotational speed.

In order to prevent such a phenomenon, the conventional stop valve allows the steam on the upstream side of the valve, that is, the inlet chamber 3 side, to bypass the gap 10 between the inner periphery of the case 6 and the outer periphery of the valve disk 8, and transfers the steam to the balance chamber T. A steam passage 15 for directly supplying steam is provided within the steam passage 15, and a throttle area adjustment screw 16 for adjusting the amount of steam supplied is inserted into the steam passage 15.

In FIG. 1, reference numeral 1γ indicates a blind plug, 18 indicates a drain pipe on the upstream side of the valve, and D indicates a drain on the upstream side of the valve.

However, with the throttle area adjustment screw 16, it is difficult to finely adjust the opening area of the bypass steam supply amount, and furthermore, this adjustment is impossible because steam leaks from the threaded portion during operation. It has drawbacks such as low reliability due to repeated adjustment, that is, adjustment by trial and error.

Furthermore, the gap 10 between the case 6 and the valve disk 8 tends to increase over time due to wear during use;
The configuration shown in the figure had the disadvantage of poor workability, as the operation had to be stopped to make adjustments.

OBJECTS OF THE INVENTION An object of the present invention is to provide a steam stop valve that can finely adjust the pressure in a balance chamber at any time during operation of a turbine, etc., in order to eliminate the above-mentioned drawbacks.

Summary of the Invention The present invention is characterized in that the steam inlet chamber side and the balance chamber side in the valve box are communicated through a bypass pipe provided outside the stop valve, and a flow rate adjustment valve is provided in the bypass pipe. With this configuration, the above objective could be achieved reliably.

Examples of the invention Hereinafter, the present invention will be explained based on the drawings.

FIG. 2 shows an embodiment of the present invention suitable for a steam stop valve of a steam turbine for driving a high-pressure feed water pump in a BWR nuclear power plant.

In FIG. 2, the same parts as in FIG. 1 are designated by the same reference numerals.

The present invention provides a bypass pipe 20 in which the steam inlet chamber 3 side and the balance chamber T side in the valve box 1 are provided outside the stop valve.
A flow rate control valve 22 is provided in the bypass pipe 20.

The steam inlet chamber 3 side of the bypass pipe 20 is connected via a T piece 19 attached to the valve upstream side drain pipe 18, and the balance chamber T side is connected via a through hole 21 formed in the upper lid 1. has been done.

The flow control valve 22 is preferably a needle valve.

Further, the opening degree of the flow rate regulating valve 22 may be adjusted manually or by remote control using electricity, fluid pressure, or the like.

Next, the operation of the control system of the above embodiment will be explained in relation to the operation of the stop valve.

In other words, during normal operation of the BWR nuclear power plant,
Since the hydraulic cylinder 13 is not supplied with control oil Q, the valve disc 8 and the pilot valve 11 are closed, and the steam S fills the inlet chamber 3 and the balance chamber 1.

If damage occurs to the reactor cooling system piping and the cooling water decreases, causing the water level in the reactor to drop, a control signal that detects this will supply control pressure oil Q to the hydraulic cylinder 13, and the valve rod The pilot valve 11 is operated upward via the valve 12.

Thereby, the steam in the balance chamber γ passes through the steam passage 9 provided in the valve disk 8 and is discharged into the steam outlet chamber 5.

As a result, the pressure inside the balance chamber γ begins to decrease, but steam is supplied into the balance chamber γ from the steam inlet chamber 3 side through the valve upstream drain pipe 18, the bypass pipe 20, the flow rate control valve 22, and the through hole 21. be done.

Since the amount of steam flowing into the balance chamber γ through the space @ 10 and the flow rate adjustment valve 22 is smaller than the amount flowing out from the balance chamber 1 to the outlet chamber 5 through the steam passage 9 and the pilot valve 11, The pressure in the balance chamber γ is slightly lower than the pressure in the inlet chamber 3, relieving the pressure that was pressing the valve disk 10 downward (this pressure is caused by the pressure difference between above and downstream of the valve seat 4). Therefore, when the valve stem 12 is displaced upward, the upper end of the pilot valve 11 is displaced upward together with the valve disk 8, thereby opening the steam stop valve.

Since the opening speed of the valve disk 8 is determined by the upward movement speed of the valve stem 12, it can be controlled by changing the signal of the pressure oil Q supplied to the hydraulic cylinder 13.

If the amount of leaked steam passing through the gap 10 changes over time, the pressure inside the balance chamber 7 can be adjusted by reducing the opening degree of the regulating valve 22, so that the opening characteristics of the stop valve against changes over time can be adjusted. Adjustments can be made easily.

Moreover, since no leakage of steam occurs due to the adjustment, the pressure inside the balance chamber γ can be adjusted at any time even during operation.

In the present invention, the specific structure of each part is not limited to the illustrated embodiment, and may be any structure as long as it can achieve the intended purpose operation.

As described in detail, according to the present invention, the pressure in the balance chamber can be adjusted at any time even during operation of a turbine or the like.

Further, since the adjustment work can be performed while the turbine is operating, even if the opening characteristic of the stop valve changes over time, it can be easily corrected to the desired characteristic.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a conventional steam stop valve, and FIG. 2 is a sectional view of a steam stop valve according to the present invention. 1... Valve box of stop valve, 2... Upper cover, 3
...Steam inlet chamber, 4...Valve seat, 5.
... Steam outlet chamber, 1 ... Balance chamber, 8 ... Valve disk, 10 ... Inner peripheral surface of balance chamber case and outer periphery of valve disk. Gap between surfaces, 11...Pilot valve, 13...
...Hydraulic cylinder for valve control, 18...Drain piping on the upstream side of the valve, S...Steam 1, Q...
・Pressure oil supplied to and discharged from the hydraulic cylinder, 2o...
... Bypass pipe, 21 ... Through hole formed in the upper lid, 22 ... Flow rate control valve.

Claims (1)

[Claims] 1 A valve box 1 having an inlet chamber 3 on the upstream side of the valve seat 4 and an outlet chamber 5 on the downstream side, and a cylindrical valve disk provided inside the inlet chamber 3 at a position facing the valve seat 4. a sliding case 6; a balance chamber 1 formed by the valve case 6 and the valve disk 8; a balance chamber 1 provided within the valve disk and communicating the balance chamber and the outlet chamber;
A bypass pipe 2 having a pilot valve 11 to shut off and an actuator driving the pilot valve, in which the balance chamber and the inlet chamber are provided outside the valve box.
1. A steam stop valve, characterized in that the bypass pipe is connected to the steam stop valve at 0 and is provided with a flow control valve 22 in the bypass pipe.