The quick shut-off valve is an important part of the safety system of the thermal power plant unit. It is an important safety equipment to ensure the safe operation of the extraction unit and prevent the steam turbine from over-speeding caused by the steam backflow of the extraction pipeline.
Electro-hydraulic control quick shut-off valve structure and principle
It consists of four parts: hydraulic actuator, mechanical conversion mechanism, triple eccentric butterfly valve and electrical control system.
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1, hydraulic actuator
The hydraulic actuator consists of an integrated hydraulic control system, consisting of a power oil source, an accumulator, a control valve block, a cylinder, etc. The hydraulic cylinder output of the actuator is a straight stroke, and the cylinder piston and the rack of the mechanical conversion mechanism are screwed together.
2, mechanical conversion mechanism
The mechanical conversion mechanism is composed of a rack and a gear transmission mechanism, which converts the straight stroke output of the hydraulic cylinder into a angular stroke output. The mechanical conversion mechanism is connected to the valve body through the flange, and the gear inside is directly connected with the driving of the butterfly valve, and the butterfly valve plate is driven to perform various actions, thereby realizing the control of the actuator to the butterfly valve, and completing various action functions such as quick closing.
3, the valve
The valve has good tightness, zero leakage, no jam, long life and low torque. In order to ensure the safety and reliability of the valve operation, the valve matched with the electro-hydraulic control quick shut-off device should be made of high-quality three-eccentric metal sealing butterfly valve. A variety of imported and domestic valves are available.
4, electrical control system
The electrical control section consists of an operating unit, a controller, a display and an alarm unit.
The operating unit has automatic, manual, remote and local operation. In the automatic mode, the protection signal of the steam turbine main valve closing or oil switch tripping is accepted, and the valve is quickly closed; the manual remote operation can be performed in the control room, and the valve can be quickly closed, normally opened and closed, and the valve activity test is performed. ; Manual local operation with the same functions as manual remote operation, to facilitate adjustment of the test and emergency handling in the event of an accident.
The controller accepts the operation unit information, performs logical judgment, outputs function commands, controls the solenoid valve, and realizes various function control. The solenoid valve is normally de-energized and energized. The controller also accepts the system oil pressure signal to control the start and stop of the oil pump to keep the oil system running at constant pressure.
The display and alarm unit is equipped with: valve open, close, activity test, quick off and other working status display; oil system low oil pressure, low fuel tank oil level, low accumulator air pressure, motor overheating and other fault alarms.
Working principle: Electro-hydraulic control quick shut-off valve is composed of electrical control device, actuator and valve, and the structural principle. The control signal outputs a control command through the controller, and the hydraulic actuator drives the valve to realize various control functions. 
A new type of spring quick shut-off valve
The quick shut-off valve (quick shut-off valve) is an important part of the safety system of the steam turbine unit of the power plant. It is an important safety device to ensure the safe operation of the steam turbine unit and prevent the steam turbine from over-current causing the super-speed accident of the steam turbine. At present, the safety measure adopted by the extraction unit to prevent the over-speed of the extraction is to install the check valve on the extraction pipe. However, the currently applied extraction check valve has a slow response and is not tight enough to prevent the extraction. The backflow of defects, there have been major accidents in the organic group.
The spring quick closing valve is a new type of integrated electro-hydraulic control quick-closing valve developed for the above problems. It uses spring as the fast-closing power and adopts advanced electro-hydraulic control technology for automatic control. The valve and its drive control mechanism are self-control. Integral, no external control oil source is required, and integrated and modular design is adopted.
Structure and working principle
The spring quick closing valve consists of a hydraulic actuator, a mechanical switching mechanism, a valve and an electrical control box (Fig. 1).
(1) Hydraulic actuator
The hydraulic actuator includes a REXA power unit, a double-acting cylinder, a quick-acting solenoid valve, and a proximity switch assembly for detecting the extreme position of the double-acting cylinder rod. These components are organically integrated using an integrated, modular design that is compact and has no external oil and oil lines. The hydraulic actuator is a closed actuator (ie, the fuel tank is closed), thus overcoming the shortcomings of the conventional open hydraulic actuator that must ensure that the fuel tank is vertically upward, meeting the requirements of any valve shaft installation direction.
(2) Mechanical conversion mechanism
The mechanical conversion mechanism consists of a rack and pinion mechanism that converts the linear output of the double-acting cylinder into a angular output. One end of the rack is connected to the piston rod of the double-acting cylinder, and the other end is connected to the quick-closing spring assembly. The mechanical conversion mechanism is connected with the valve through the flange, and the gear inside is directly connected with the drive shaft of the valve, and the valve plate is driven to perform various actions, thereby realizing the control of the valve by the hydraulic actuator, completing various action functions such as quick closing. .
In order to ensure the safety and reliability of the valve operation, the valve of the quick closing valve adopts a triple eccentric metal sealing butterfly valve with strictness, zero leakage, no jam, long life and small torque. Plate, valve shaft and other components, which is mainly composed of valve body and butterfly.
(4) Electrical control box
The electrical control box includes operation display, sensing drive, programmable logic control unit (PLC) and cabinet. It can complete all operations on site, as well as protection signals such as remote operation of the control room and shutdown of the main steam valve of the turbine. Linked automatic fast closing can be practiced. When the electrical control box receives an instruction to slowly open or close the valve, it issues an instruction to cause the stepping motor on the REXA power unit 1 to drive the oil pump forward and reverse, thereby outputting high pressure oil to the right or left chamber of the double acting cylinder 2, Push the mechanical switching mechanism to achieve slow opening and closing of the valve. When the quick closing command is received, the quick closing solenoid valve 3 is energized, and the two cylinders of the cylinder communicate the oil discharge pressure, and the valve is quickly closed under the action of the quick closing spring 5.
In the event of an electrical control box failure, the valve can be slowly closed by hand turning the handwheel on the hydraulic actuator motor. In addition, the bypass valve on the hydraulic actuator can be opened, allowing the quick-closing valve to close faster in the event of a power failure.
Main functions and performance indicators
(1) Slow switch
When the PLC receives the slow switching signal, it sends a pulse command to the stepping motor to make the motor run in the corresponding direction, and input the high pressure oil to the right or left side of the double acting cylinder, thereby driving the gear and the valve toward the opening direction or When the signal is turned off, the PLC will continue to issue commands for a period of time to ensure that the valve reaches the fully open and fully closed positions after receiving the signal of the fully open or fully closed position.
When the PLC does not receive any commands, the motor, pump and gear do not move. Since the hydraulic components in the equipment are non-leakage components, the valve is in this state.
(3) Quick shutdown
When the PLC receives the fast closing signal, the PLC energizes the fast closing solenoid valve, and the double acting cylinder communicates with the oil pressure. Under the action of the quick closing spring, the valve quickly moves to the fully closed position.
In order to reduce the impact of the valve during the closing process, a variable throttle buffer is added to the double-acting cylinder when the valve is closed to 10% of the stroke.
5) Status display and alarm
Display the working status of the valve open, close, fast shut, and monitor and alarm the faults such as driver error and switch valve time is too long. The main performance indicators of the quick closing valve are as follows:
(1) The full opening and closing time of the valve is 45s.
(2) The valve full stroke fast closing time is less than 0.8s.