The role and type of water turbine inlet valve In the water turbine inlet system, according to the needs of the operation and maintenance of the hydropower station, corresponding gates or valves should be installed at different positions. Such as the working gate and overhaul gate of the water inlet, the valve in front of the turbine volute and the tail water gate. The valve usually installed in front of the turbine volute is called the inlet valve (also called the main valve). Gates and valves are used to control water passage openings in water structures. It is used to safely adjust the upstream and downstream water level or flow for power generation, drainage, sand discharge, ship passing, wood passing and other floating objects. General gates and valves are mainly composed of the following parts: (1) Active part; it is a water blocking body that closes the orifice and can open the orifice. (2) Buried part: it is a small component fixed in the underwater building, which plays a role of bearing. (3) Opening and closing machinery: control equipment for operating gates and valve movable parts. 1. The role of the water turbine inlet valve (1) Provide safe working conditions for unit maintenance. When the power station uses a main water pipe to simultaneously supply several units for power generation. A water inlet valve must be installed in front of each unit, so that when a unit is overhauled, closing the water inlet valve of the unit will not affect the normal operation of other units. (2) Reduce the water leakage of the unit and shorten the time required for restarting during shutdown. When the unit is shut down, the guide vanes of the turbine cannot be closed tightly, and there is always a certain amount of water leakage, especially after a period of operation, due to cavitation and wear at the guide vane gap, the guide vane gap becomes larger and the water leakage Increase. Generally, the water leakage when the guide vanes are fully closed is 2% to 3% of the maximum flow rate of the turbine: severely, it can even reach 5%, causing a large loss of water energy. Therefore, the wood inlet valve should be closed when the unit is shut down for a long time. Can greatly reduce the amount of water leakage. The unit shuts down for a short time, and the inlet gate is generally not closed. Because the water in the pressurized water pipe is released and the unit needs to be refilled when it is put into operation again, it not only prolongs the start-up time of the unit, but also prevents the unit from maintaining standby status at any time, and loses the flexibility and quick mobility of the hydropower station. The installation of water inlet valve in Tuan here has a more obvious effect on the hydropower station with Dinggao head and long pressure diversion pipeline. (3) To prevent the runaway accident of the unit, the expanded water inlet valve can be used as a backup protection for the overspeed of the unit. When the unit loses load and the governor fails again and cannot be closed, the guide vane is out of control. At this time, the water inlet valve should be closed and cut off urgently. Water flow prevents the unit's escape time from exceeding the allowable value and avoids the expansion of accidents. 2. Technical requirements for the inlet valve (1) Easy to operate, small in size and light in weight; (2) There should be a tight water stop device. Reduce water leakage to facilitate maintenance work on parts behind the valve. (3) The structure and strength of the valve and its operating mechanism should meet the requirements of long distance travel. In the event of an accident, it can be quickly closed under a certain hydrodynamic pressure. The closing time should meet the requirements of the allowable duration of the runaway speed of the generator and the allowable water hammer pressure value of the pressure pipeline,’ generally 1~3min. If high-pressure oil is used from the transmission valve, it can be closed in an emergency within 30~50s. The inlet valve is only used for overhauling the unit. The opening and closing time is determined by the operation plan, generally 2~5min (acting in still water). The inlet valve usually has only two situations, fully open and fully closed, and cannot be partially opened to adjust the flow, so as to avoid excessive hydraulic loss and affect the stability of water flow. The water inlet valve is not allowed to be opened under dynamic water conditions, because this requires a greater operating torque. 3. The installation conditions of the inlet valve The inlet valve is expensive, and the installation of the inlet valve will increase the civil investment and equipment installation and operation costs. Therefore, the installation of the inlet valve should be carried out under the following conditions: (1) When a single inlet When the water main pipe supplies water for several turbines, a metering inlet valve should be installed in front of the radio turbine. (2) For unit water pipes with a water head greater than 120m. Consider setting up an inlet valve. Because the pressure pipe of high-head diversion power station is longer, the water filling time is long; in addition, the higher the water head of the hydropower station, the more serious the water leakage of the guide vanes, so the energy loss is higher. Two valves can also be installed in high-head power stations. -One is installed at the beginning of the penstock, and the other is installed in front of the turbine, as protection facilities for the penstock and the unit. (3) For unit water pipes with a maximum water head of less than 120m and shorter lengths, such as behind-dam hydropower stations, fast gates are generally installed. 4. Types and selection of inlet valves The inlet valves widely used in hydropower stations are butterfly valves, gate valve
s and ball valves. The performance comparison of butterfly valve and ball valve is shown in Table 10-1. (1) Gate valve: often used in occasions with a pipe diameter of 0.5m or less (2) Butterfly valve (sometimes referred to as 'butterfly valve'): Butterfly valve is widely used for water heads below 200m. It has small size, short opening and closing time, and small operating force. Advantages such as cheap price. (3) Ball valve: suitable for high water head, it has the advantages of low flow resistance when fully opened, good sealing performance when fully closed, and water leakage. Table 10-1 Comparison items of butterfly valve and ball valve Application head range of butterfly valve ball valve (m)u003c200≥200 The valve diameter is greater than the diameter of the inlet pipe equal to the diameter of the inlet pipe. The head loss is small, close to zero, and the amount of water leakage is small. Small structure size structure Simpler, smaller size, more complicated structure, larger size. Auxiliary equipment installation of expansion joints, air valves, bypass valves Installation expansion joints, air valves, bypass valves, unloading valves Note: The applied water head does not include water hammer rise Pressure. The application head of the ball valve has reached 950m abroad, the maximum diameter is 3.4m, and the maximum diameter of the butterfly valve is 8.23m.
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