Why is the Globe Valve Low in and High out?

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.

This type of shut-off globe valve is ideal 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 cut-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 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 installation of this bypass has the following functions: 1. Balance the front and rear pressure of the main pipeline valve, so that the opening is convenient and labor-saving, and reduces the wear of the main pipeline valve; 2. Small flow heating pipe during startup; 3. , control the flow of feed water to control the boiler pressure boost speed for 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 the loss of working fluid is often caused by poor sealing. For this reason, some power plants install such shut-off valves in order to improve the tightness. "High in and low out".

4. Electromagnetic quick-break valve

The function of the electromagnetic quick shut-off valve is to close quickly and cut off the fuel supply quickly. The structure of the electromagnetic quick-cut valve is similar to that of the globe valve. If the electromagnetic quick-cut valve also enters from the lower part and flows out from the upper part, the fuel will exert a great force on the lower part of the electromagnetic quick-cut valve disc, and the weight of the electromagnetic quick-cut valve is much smaller than it. Therefore, if the working fluid enters the quick-cut valve from the bottom, the torque generated by the heavy hammer is less than the torque generated by the fuel pressure, and the fuel cannot be cut off when the quick-cut valve acts, thus failing to achieve the expected purpose. If the working fluid enters from the upper part of the quick-cut valve, once the quick-cut valve is actuated, the pressure behind the valve decreases rapidly, the force of the fuel acting on the lower part of the valve disc quickly drops to zero, and the force of the fuel acting on the valve disc and the weight, The force created by the weight of a lever.

Generally, it is difficult to close the valve with low input and high output under large diameter and high pressure conditions. If low input and high output are used under high pressure and large diameter state, the valve stem will be 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 position, the diameter of the valve stem can be smaller, and it will save some costs for manufacturers and users.

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