What is a quick closing valve

What is a quick closing valve?

Quick closing valve, also known as the main steam valve, is the main closing mechanism between the main steam pipeline and the steam turbine. In case of emergency, the steam inlet of the steam turbine is cut off to make the unit shut down quickly, so as to achieve the purpose of protecting the unit.
The quick closing valve consists of valve body and oil cylinder. In the process of operation, the quick closing valve keeps open through quick closing oil to overcome the resistance of spring. When the quick closing oil loses pressure, under the force of the spring, the piston disc and the piston in the oil cylinder will be separated, and the quick closing oil is connected with the oil discharge port, so that the quick closing oil will be discharged instantly, and the piston disc, the valve stem and the main valve disc will be pushed to the closed position.

Structure and working principle of quick closing valve

The quick closing valve is horizontally installed on the steam inlet chamber of steam turbine cylinder, which is mainly composed of valve body, filter screen and oil cylinder.
The quick closing valve, also known as the main steam valve, is the main closing mechanism between the main steam pipeline and the steam turbine. In case of emergency, it can immediately cut off the steam inlet of the steam turbine and make the unit shut down quickly.
Generally, the quick closing valve is horizontally assembled on the side of the steam turbine inlet chamber. One or two quick closing valves can be equipped for a steam turbine according to the different inlet volume flow of the steam turbine. There are also high-power steam turbine quick closing valves installed on the operating platform.
The quick closing valve is closed when the turbine is shut down, and it is fully open during the start-up and normal operation of the turbine.
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The valve body is mainly composed of parts 7-13. When the quick closing valve is finally opened, the fresh steam flows through the steam filter screen (10) to the chamber in front of the main valve disc (12). The valve disc is tightly pressed on the valve seat (13) under the action of steam force and the closing force of the cylinder spring (4), and the passage of the fresh steam into the flow passage of the steam turbine is cut off. The main valve disc is equipped with an unloading valve (11). Because the valve is closed during the opening process of the quick closing valve, the pressure of the main valve disc tends to be balanced quickly with the increase of the unloading valve, so that the lifting force of the main valve disc can be greatly reduced.
During the opening process of the quick closing valve or after the quick closing valve is closed (the isolation valve is not closed), a part of steam leaks outward along the gap between the valve stem (1), the guide sleeve (9) and the steam seal sleeve (8), and the leakage steam is led out from the interface K. When the quick closing valve is fully opened, the sealing surface of the main valve disc and the guide sleeve closely fits, and the steam leakage of the valve stem is blocked.
The steam filter screen in the quick closing valve is mostly made of stainless steel.
The oil cylinder part of the quick closing valve is mainly composed of oil cylinder, piston (3), spring (4), piston plate (2) and seals. The oil cylinder is fixed on the valve cover with bolts. Based on the safety of assembling and disassembling the oil cylinder, three special long bolts are installed on the end face of the oil cylinder, and a steel wire thread sleeve is installed at the screw in position of the bolt. Attention: long bolts and nuts must be used to assemble and disassemble the oil cylinder to avoid personal injury.
The cylinder part is the actuator for the quick closing valve to open and close. When the quick closing valve is opened by starting the two position directional valve of the centralized control device, the oil cylinder part has the following actions: the starting oil f flows to the right end of the piston (3), the piston is pressed to the piston disc (2) under the action of oil pressure to overcome the force of the spring (4), so that the piston contacts with the sealing surface of the piston disc. After opening the directional valve, the quick closing oil e flows to the left side of the piston disc, and the quick closing oil flows with the piston disc With the establishment of the pressure, the starting oil is discharged under the control of the directional valve, so the piston disc and the piston are as an integral component. Under the action of the oil pressure difference on both sides, they continue to move to the right until the tested piston (5) is limited. Because the right end of the valve stem is connected with the piston disc, the quick closing valve will open when the piston disc moves.
The closing of the quick closing valve is controlled by the security system. If the quick closing action occurs in any link of the security system, the quick closing oil will lose pressure. Under the action of the spring force, the piston and the piston disc will be separated, the quick closing oil on the left side of the piston disc will be discharged from T1, and the piston disc, together with the valve stem and valve disc will be immediately pushed to the closed position.
The oil cylinder is also equipped with a test piston (5), which is composed of a test piston, a test valve and a pressure gauge. Its function is to check the reliability of the quick closing valve during the operation of the unit.
The test valve is a manual directional valve. By operating the test valve, the pressure oil enters the right end chamber of the test piston. Because the area of the test piston is larger than that of the piston, when P2 reaches a certain value, under the action of oil pressure, the test piston pushes the piston, piston disc, valve stem and valve disc to move to the closing direction at the same time. The stroke is h. This stroke will not affect the normal operation of the unit, so the test valve is safe The test can be carried out under any load including rated condition.
P4 is the quick closing oil pressure value when the unit is running.
If P2 ≥ P1 is measured in the test, it indicates that there is additional movement resistance due to salt scale on the valve stem or oil scale deposition on the piston and other movable parts, resulting in abnormal action of the quick closing valve. In order to make the quick closing valve operate normally, the test should be repeated for many times. If P2 > P1 is still detected in the end, the maintenance should be arranged as soon as possible, and the quick closing valve should be removed to find out the cause and eliminate the fault.
According to the need, the quick closing valve can be equipped with a travel switch, which is used to send corresponding signals at the closed and fully open positions of the valve.
The baffle plate fixed on the valve rod has many functions: in case the seal of the oil cylinder is damaged, it can stop the oil from spraying to the high temperature part; it can prevent the valve rod from leaking to the oil cylinder; it can also be used as the trigger of the travel switch.

Control system

Hydraulic system to control the opening and closing of quick closing valve. The control valve is controlled by the hydraulic control system. A spring is attached to the upper end of the control valve. When the control valve is closed, the spring is in an extended state under the action of oil pressure. When the command to open the valve is received, the pressure in the hydraulic chamber disappears instantaneously, the oil pressure is unloaded, and the control valve moves upward under the action of spring force to remove the hydraulic oil in the hydraulic chamber and open the control valve. When the control valve needs to be closed, hydraulic oil is injected into the hydraulic cavity. Then the control valve moves downward under the joint action of hydraulic oil and spring force until the valve port is closed. In addition to the hydraulic control valve, the control part also has the manual wheel control part. When the hydraulic control valve fails and the quick closing valve needs to be closed, the quick closing valve needs to be closed manually.

Drive actuator

The driving part includes power source and hydraulic actuator. The hydraulic medium is oil. The oil cylinder, oil pump and accumulator constitute an independent closed power oil source system. The oil pump provides hydraulic power, and the hydraulic actuator is composed of cylinder, piston, valve head, stem and other main parts, as well as the guiding and sealing devices, which are connected to form a moving whole. Through the up and down movement of the piston, the movement of the valve head and the valve stem is driven to realize the opening and closing of the quick closing valve.
Figure 2 is a three-dimensional solid diagram of the piston. As shown in the figure, the piston is an annular structure, which is connected by the middle hole, the valve stem and other parts. The circumferential annular groove is used to place the sealing parts. Piston plays an important role in the operation of quick closing valve, which transforms the potential energy of oil pressure and spring force into the kinetic energy of actuator. So as to realize the quick closing of the quick closing valve.

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Figure 2 three dimensional solid diagram of piston
The valve head and stem will be subject to great impact force in the process of quick closing, so there are high requirements for the structure and material properties of the valve head and stem, so as to ensure that the quick closing valve can meet the use requirements when it is closed quickly.

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Fig. 3 three dimensional solid diagram of hydraulic cylinder
The lower side of the transmission mechanism is the oil cylinder, and there is a piston between the transmission mechanism and the oil cylinder. The power oil source system is integrated into a hydraulic oil station. Under normal conditions, the oil pump supplies oil to the system to maintain the rated pressure of the system, and the valve’s position keeping function is realized through the locking of the control valve. Under the working condition, the hydraulic actuator is controlled by the hydraulic valve, and relies on the system to control the oil pressure and release the energy stored in the accumulator, so as to implement the quick closing and normal opening and closing. In the process of rapid closing of the valve, when it is close to the fully closed position, it will slow down and close to prevent the sealing surface from being impacted.
When the quick closing valve is opened, the hydraulic oil works on the piston, and the spring at the bottom accumulates energy. When the quick closing valve needs to be closed, the spring releases energy to work on the piston, driving the valve head and stem to move, so that the quick closing valve can be closed quickly. Cylinder block is one of the main parts of quick closing valve mechanism, which has large volume and weight, many oil passage holes and grooves, and requires high machining accuracy. Its air tightness directly determines whether the quick closing valve mechanism can run smoothly and effectively. Its mechanism is shown in Figure 3.

Working principle editor

When the ship is sailing, the oil inlet is opened and the oil outlet is closed. The hydraulic oil enters from the oil inlet. Under the action of the hydraulic oil, the piston moves downward, and the bottom spring is compressed until the specified position. The quick closing valve is fully opened. At this time, the hydraulic pressure in the working chamber is balanced with the spring force at the bottom of the piston.
When the ship needs to reverse navigation, the control valve receives the command of closing the quick closing valve. The control valve moves up rapidly under the action of the top spring force for a very short time. The oil outlet can be ignored. The liquid pressure in the working chamber disappears instantly. The piston moves up rapidly under the action of the bottom spring force and the inertial resistance of the liquid flow. The hydraulic oil in the oil chamber is discharged from the oil outlet to the oil tank Now close the valve quickly.

Source: China Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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