The shut-off valve is a device used in a fluid system to control the direction, pressure, and flow of a fluid. It is a device that allows the piping and the medium (liquid, gas, powder) in the equipment to flow or stop and control the flow rate thereof. During the construction process, the installation method of the shut-off valve will directly affect the normal operation in the future.
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The shut-off valve is designed to be low in and out, with the aim of making the flow resistance small and saving effort when opening the valve. At the same time, when the valve is closed, the gasket between the valve casing and the valve cover and the packing around the valve stem are not subjected to force, and the long-term exposure to the medium pressure and temperature can prolong the service life and reduce the probability of leakage. In addition, the valve can be replaced or added with the valve closed for maintenance.
Many people think that the stop valves are low in and out, but it is not. Under normal circumstances, the shut-off valve is low in and out, but there are some special cases where the shut-off valve is high and low:
1. High pressure shut-off valve with diameter greater than 100mm
Due to the poor sealing performance of large-diameter valves, the shut-off valve is closed in this way, and the medium pressure acts on the valve flap to increase the sealing of the valve.
2. Boiler exhaust and venting stop valve
Boiler exhaust and venting shut-off valves are only used during the boiler start-up process. The frequency of opening and closing is small, but the working fluid is often lost due to poor sealing. For this reason, some power plants have to install such shut-off valves in order to improve the tightness. High in and low out.
3. Two shut-off valves connected in series on the bypass pipe. The second shut-off valve requires “high in and low out”.
In order to ensure the tightness of the valve during an overhaul cycle, valves that are frequently opened and closed require two shut-off valves in series. For the bypass system, the installation function of the bypass is: 1 balance the front and rear pressure of the main pipeline valve, so that the opening is convenient and labor-saving, and the wear of the main pipeline valve is reduced; 2 the small flow heating pipe during the starting process; 3 the main water supply pipeline The boiler water pressure test is carried out by controlling the feed water flow rate to control the boiler boosting speed. The bypass shut-off valves according to the flow direction of the medium are the primary valve and the secondary valve respectively. When the unit is in normal operation, the primary valve and the secondary valve are closed, and both are in direct contact with the medium. In order to prevent the gasket between the valve body and the valve cover of the secondary valve and the packing around the valve stem from being affected by the medium and temperature for a long time, and the filler of the valve can be replaced during the operation, the installation direction of the secondary valve is required to be high in and low. .