Rising Stem Gate Valve vs Non Rising Stem Gate Valve
Aug 02,2022Read More
Globe valve, also known as cut-off valve, is a kind of forced-sealing valve, which is a kind of cut-off valve. According to the connection method, it is divided into three types: flange connection, thread connection and welding connection.
The flow direction of the globe valve is always from top to bottom, so there is directionality during installation. The movement form of the valve stem is a lifting and rotating rod type, which can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. Therefore, this type of shut-off globe valve is very suitable for shut-off or regulation and throttling. Because the valve stem of this type of valve has a relatively short opening or closing stroke, and has a very reliable shut-off function, and because the change of the valve seat port is proportional to the stroke of the valve disc, it is very suitable for flow regulation.
The industrial globe valve is designed with low in and high out, the purpose is to make the flow resistance small and save effort when opening the valve. At the same time, when the valve is closed, the gasket between the valve shell and the valve cover and the packing around the valve stem are not stressed, so that they will not be affected by the medium pressure and temperature for a long time, which can prolong the service life and reduce the probability of leakage. In addition, the packing can be replaced or added when the valve is closed, which is convenient for maintenance.
Many people think that the globe valve is low in and high out, but this is not the case. In general, the globe valve is low in and high out, but there are some special cases where the globe valve is high in and low out.
1. High pressure globe valve with diameter greater than 100mm
Due to the poor sealing performance of large-diameter valves, when the globe valve is closed by this method, the medium pressure acts on the top of the valve disc to increase the sealing performance of the valve.
2. Two shut-off valves in series on the bypass pipeline, the second shut-off valve requires "high in and low out"
In order to ensure the tightness of the valve within a maintenance cycle, the valve that is frequently opened and closed requires the installation of two shut-off valves in series. For the bypass system, the functions of this bypass are: to 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; during the start-up process, the small flow warms the pipe; On the main water supply pipeline, control the water flow rate to control the pressure rise speed of the boiler to carry out the boiler water pressure test. According to the flow direction of the medium, the bypass shut-off valve is a primary valve and a secondary valve. The primary valve and the secondary valve are closed when the unit is in normal operation, and both are in direct contact with the medium. In order to prevent the gasket between the valve casing 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 packing of the valve can be replaced during operation, the required installation direction of the secondary valve is "high in and low out".
3. Boiler exhaust and vent shut-off valve
Boiler exhaust and vent shut-off valves are only used in the process of boiler startup and water supply. The frequency of opening and closing is small, but losses are often caused due to poor sealing. For this reason, some power plants install such shut-off valves in a "high in and low out" direction in order to improve the tightness.
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