Why should the globe valve be low in and high out? Long knowledge!

The globe valve, also known as the gate valve, belongs to the forced sealing valve and is a kind of cut-off valve. According to the connection method, it can be divided into three types: flange connection, screw connection and welding connection. Chinese valves“Sanhuagi”It has been stipulated that the flow direction of the stop valve should be top-down, so there is directionality during installation. This type of shut-off globe valve is very suitable for cutting or regulating and throttling. Because the opening or closing stroke of the valve stem of this type of valve is relatively short, and it has a very reliable cut-off function, and because the change of the valve seat opening is proportional to the stroke of the valve disc, it is very suitable for flow adjustment. The cut-off valve is designed with low inlet and high outlet, 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 medium pressure and temperature for a long time, which can prolong the service life and reduce the chance of leakage. In addition, it is also possible to replace or add packing when the valve is closed, which is convenient for maintenance. Many people think that globe valves have low entry and high exit, but this is not the case. Under normal circumstances, the cut-off valve is low in and high out, but there are some special cases in which the cut-off valve is high in and low out: 1. The high-pressure cut-off valve with a diameter greater than 100mm has poor sealing performance due to the large diameter valve. Under normal conditions, the medium pressure acts on the disc to increase the sealing performance of the valve. 2. Two cut-off valves connected in series on the bypass pipeline, the second cut-off valve requires“high in low out”In order to ensure the tightness of the valve within a maintenance cycle, two shut-off valves in series are required for valves that are frequently opened and closed. For the bypass system, the functions of this bypass installation are as follows: ① Balance the front and rear pressure of the main pipeline valve, make the opening convenient and labor-saving, and reduce the wear of the main pipeline valve; ② Warm the small flow pipe during startup; , Control the feed water flow to control the boiler pressure increase speed for boiler hydrostatic test. According to the flow direction of the medium, the bypass cut-off valves are divided into primary valve and secondary valve. When the unit is in normal operation, the primary valve and secondary valve are closed, and both of them are in direct contact with the medium. In order to prevent the gasket between the valve casing and bonnet of the secondary valve and the packing around the valve stem from being affected by the medium and temperature for a long time, and to replace the packing of the valve during operation, the required installation direction of the secondary valve is“high in low out”. 3. Boiler exhaust and vent cut-off valve Boiler exhaust and vent shut-off valves are only used in the process of boiler start-up and water supply. The frequency of opening and closing is small, but it often causes loss of working fluid due to poor sealing. For this reason, some power plants have to improve The tightness of the installation direction of this type of globe valve“high in low out”. 4. Electromagnetic quick-break valve The function of the electromagnetic quick-break valve is to close quickly and cut off the fuel supply quickly. The structure of the electromagnetic quick-break valve is similar to that of the stop valve. If the working medium enters from the bottom and flows out from the top of the electromagnetic quick-break valve, the force of the fuel acting on the lower part of the electromagnetic quick-break valve disc is very large, and the weight of the electromagnetic quick-break valve is much smaller than that of the stop valve. it. Therefore, if the working medium enters the quick-break valve from the lower part, the torque generated by the weight is smaller than that produced by the fuel pressure, and the fuel cannot be cut off when the quick-break valve operates, thus failing to achieve the desired purpose. If the working fluid enters from the upper part of the quick-break valve, since the pressure behind the valve drops rapidly once the quick-break valve operates, the force of fuel acting on the lower part of the valve disc will quickly drop to zero, while the force of fuel acting on the valve disc and the weight, hammer, The force exerted by the weight of the lever. Generally, it is difficult to close the valve with low inlet and high outlet under high pressure and high pressure conditions. If low inlet and high outlet are used under high pressure and large diameter, the valve stem is easily deformed and bent under water pressure for a long time, which will affect the safety and sealing of the valve; If you choose a high inlet and a low location, the diameter of the valve stem can be smaller, and it will also save some costs for manufacturers and users.