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The quick-shut valve is the main closing mechanism between the new steam pipeline network and the turbine; in the event of an accident during operation, it can cut off the steam flowing into the turbine in the shortest possible time. The testing device can check whether the valve stem moves smoothly without affecting the normal operation of the turbine. Structure and working principle: The quick-shut valve is horizontally installed in the steam inlet chamber of the turbine cylinder. It mainly consists of a valve body, a filter screen, and a cylinder section. The quick-shut valve, also known as the main steam valve, is the primary closing mechanism between the main steam pipeline and the turbine; it enables the steam supply to the turbine to be cut off immediately in emergency situations, allowing the unit to stop quickly. Generally, quick-shut valves are installed horizontally on the side of the turbine inlet chamber. Depending on the volumetric flow rate of steam entering the turbine, a single turbine can be equipped with one or two quick-shut valves. High-power turbine quick-shut valves are also installed on the control platform. The emergency shut-off valve is closed when the turbine is shut down, while it remains fully open during turbine startup and normal operation. The valve body is primarily composed of components 7 to 13. When the quick-close valve is not yet open, fresh steam passes through the steam filter (10) to reach the chamber in front of the main valve disc (12). The valve disc is pressed tightly against the valve seat (13) by the force of the steam and the closing force of the cylinder spring (4), thereby blocking the path for fresh steam to enter the flow section of the turbine. The main valve disc is equipped with a unloading valve (11); since the control valve remains closed during the opening of the quick-close valve, as the unloading valve rises, the pressures on both sides of the main valve disc quickly reach equilibrium, thereby significantly reducing the lifting force required to open the main valve disc. During the opening of the quick-close valve or after it has been closed (with the isolation valve not closed), some steam leaks outward through the gap between the valve stem (1), the guide sleeve (9), and the steam seal sleeve (8); this leaking steam exits from interface K. When the quick-close valve is fully open, the sealing surface of the main valve disc fits tightly against that of the guide sleeve, thereby preventing steam leakage from the valve stem. The steam filters in quick-close valves are mostly made of stainless steel. The cylinder part of the quick-close valve is mainly composed of a cylinder, piston (3), spring (4), piston disc (2), and seals, etc.; the cylinder is fixed to the valve cover with bolts. To ensure the safety of cylinder installation and removal, three special long bolts are installed on the cylinder end face, with wire thread inserts at the locations where the bolts are screwed in. Note: The installation and removal of the cylinder must be carried out using long bolts and nuts to prevent injury. The cylinder section is the actuator that opens and closes the quick-close valve. When the quick-shut valve is opened by activating the two-position directional control valve of the centralized control device, the cylinder assembly carries out the following actions: Starting oil F flows to the right end of the piston (3); under the action of oil pressure, the piston is pushed against the piston disk (2) overcoming the force of the spring (4), causing the sealing surface of the piston to come into contact with that of the piston disk. After the directional control valve is activated, quick-shut oil E enters the left side of the piston disk. As oil pressure builds up on the rear side of the piston disk, the starting oil is released under the control of the directional control valve. As a result, the piston disk and the piston move together as a single unit, driven by the pressure difference between the two sides, until they are stopped by the test piston (5). Since the right end of the valve stem is connected to the piston disk, the quick-shut valve opens as the piston disk moves. The closing of the quick-shut valve is controlled by the safety system; if any component in this system triggers a quick-shut action, the pressure of the quick-shut oil is reduced. Under the force of the spring, the piston separates from the piston disc, and the quick-shut oil on the left side of the piston disc is discharged through T1. As a result, the piston disc, along with the valve stem and valve disc, is immediately pushed to the closed position. The cylinder section is also equipped with a test piston (5); together with the test valve and pressure gauge, these components form a quick-close valve testing mechanism whose purpose is to verify the reliability of the quick-close valve’s operation during the unit’s operation. The test valve is a manually operated directional valve; by operating this valve, pressure oil is allowed to enter the chamber on the right side of the test piston. Since the area of the test piston is larger than that of the regular piston, once P2 reaches a certain value, the oil pressure causes the test piston to push the regular piston, the piston disc, the valve stem, and the valve disc all in the direction of closure. The distance covered in this movement is h, and this movement does not affect the normal operation of the unit. Therefore, testing can be carried out under any load, including the rated operating conditions. P4 is the quick-shut oil pressure value during unit operation. If the test shows that P2 ≥ P1, it indicates that additional mechanical resistance has been generated on the valve stem due to salt deposits, or on moving parts such as the piston due to oil deposits, which prevents the quick-close valve from functioning properly. To ensure that the valve operates correctly, the test should be repeated several times under these conditions. If P2 remains greater than P1 even after repeated tests, maintenance should be carried out as soon as possible: the quick-close valve should be removed to identify the cause of the problem and to eliminate it. As required, the quick-close valve can be equipped with a travel switch to send corresponding signals when the valve is in the closed or fully open position. The retaining disc fixed to the valve stem serves multiple purposes: in the event that the seal of the cylinder is damaged and oil leaks out, it can prevent the oil from reaching the high-temperature areas ； Prevent the valve stem from leaking into the cylinder ； Also serves as a trigger for a travel switch.