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Crane valves are an important component of the safety system for thermal power plant units. They are critical safety devices that ensure the safe operation of extraction steam units and prevent turbine overspeed accidents caused by steam backflow in the extraction steam piping. To this end, Article 8110 of the "Twenty-Five Key Requirements for Preventing Major Accidents in Power Production," issued by the State Power Corporation of China, specifically emphasizes that "the adjustable extraction steam check valves in extraction steam units must be tight, with reliable interlock action, and extraction steam stop valves capable of rapid closure must be installed to prevent overspeed caused by extraction steam backflow." Currently, the safety measure adopted by extraction steam units to prevent overspeed due to steam backflow is the installation of check valves on the extraction steam piping. However, existing extraction steam check valves suffer from slow closing response, inadequate sealing, poor reliability, and an inability to effectively prevent steam backflow. These deficiencies have previously caused several major accidents involving severe overspeed due to steam backflow, posing significant risks to safe production. Therefore, it is highly necessary to install a new type of faster-acting, safer, and more reliable quick-closing valve on this pipeline to effectively prevent such accidents and substantially improve the safety performance of the unit.

Crane Valve Structure

It consists of four parts: hydraulic actuator, mechanical conversion mechanism, triple-offset butterfly valve, and electrical control system. 1) Hydraulic Actuator The hydraulic actuator consists of an integrated hydraulic control system, including a power oil source, accumulator, control valve block, and hydraulic cylinder. The output of the actuator's hydraulic cylinder is linear motion. The cylinder piston is connected to the rack of the mechanical conversion mechanism via threads. 2) Mechanical Conversion Mechanism The mechanical conversion mechanism consists of a rack and a gear transmission mechanism. It converts the linear output of the hydraulic cylinder into angular output. The mechanical conversion mechanism is connected to the valve body via a flange. Its gears are directly connected to the drive of the butterfly valve, driving the valve disc to perform various actions, thereby enabling the actuator to control the butterfly valve and achieve functions such as quick closing. 3) Valve The valve offers excellent tightness, zero leakage, no sticking, long service life, and low torque. To ensure the safety and reliability of valve operation, the valve paired with the electro-hydraulic control quick-shutoff device should be a high-quality triple-offset metal-sealed butterfly valve. Various imported and domestic valves are available. 4) Electrical Control System The electrical control part consists of an operation unit, controller, and display and alarm unit. The operation unit supports automatic, manual, remote, and local operation modes. In automatic mode, it receives protection signals such as turbine main steam valve closure or oil circuit breaker tripping to implement quick valve closing. Manual remote operation can be performed from the control room to implement quick closing, normal opening and closing, and valve activity tests. A manual local operation mode with the same functions as manual remote operation is provided to facilitate adjustment tests and emergency handling in accident situations. The controller receives information from the operation unit, performs logical judgments, outputs function commands, and controls solenoid valves to achieve various control functions. The solenoid valves are normally de-energized and operate when energized. The controller also receives system oil pressure signals to control the start and stop of the oil pump, maintaining constant pressure in the oil system. The display and alarm unit provides status indications for valve "Open," "Close," "Activity Test," and "Quick Close." It also monitors and alarms for faults such as low oil system pressure, low oil tank level, low accumulator gas pressure, and motor overheating.

Crane Valve Functions

1) Slow Opening/Closing When the PLC receives a slow opening/closing signal, it sends pulse commands to the stepper motor, causing the motor to rotate in the corresponding direction. This inputs high-pressure oil into the right or left side of the double-acting cylinder, driving the gears and valve to move in the opening or closing direction. Upon receiving signals for the fully open or fully closed positions, the PLC continues to send commands for a period to ensure the valve reaches the fully open or fully closed position. 2) Position Holding When the PLC does not receive any commands, the motor, pump, and gears do not move. Since the hydraulic components in the equipment are leak-free, the valve maintains its position in this state. 3) Quick Closing When the PLC receives a quick-close signal, it energizes the quick-close solenoid valve. The two chambers of the double-acting cylinder communicate to release oil pressure. Under the action of the quick-close spring, the valve rapidly moves to the fully closed position. 4) Buffering To reduce impact during the quick-closing process, variable throttling buffering is added to the double-acting cylinder when the valve closes to 10% of its travel. 5) Status Display and Alarm Displays working statuses such as valve "Open," "Close," and "Quick Close." It also monitors and alarms for faults such as "Actuator Error" and "Valve Switching Time Too Long." Working Principle: The electro-hydraulic control quick-shutoff valve consists of an electrical control device, actuator, and valve. Control signals output control commands through the controller, and the hydraulic actuator drives the valve action to achieve various control functions.

Crane Valve Working Principle

The electro-hydraulic control quick-shutoff valve consists of an electrical control device, actuator, and valve. Control signals output control commands through the controller, and the hydraulic actuator drives the valve action to achieve various control functions.

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