Globe valve, also known as shut-off valve, belongs to the category of forced sealing valves and is a type of shut-off valve. There are three types of connections: flange connection, threaded connection, and welded connection.
The "Three Modernizations" of valves in our country have stipulated that the flow direction of globe valves should be from top to bottom, so there is directionality during installation.
This type of shut-off valve is very suitable for cutting off, regulating, and throttling purposes. Due to the relatively short opening or closing stroke of the valve stem and its highly reliable shut-off function, as well as the proportional relationship between the change in the valve seat opening and the stroke of the valve disc, this type of valve is very suitable for regulating flow.
Many people think that shut-off valves are low inlet and high outlet, but this is not the case. Generally, globe valves have low inlet and high outlet, but there are also some special cases where globe valves have high inlet and low outlet:
1. High pressure shut-off valve with a diameter greater than 100mm
Due to the poor sealing performance of large-diameter valves, this method is used to increase the sealing performance of the valve by applying medium pressure above the valve disc when the shut-off valve is in the closed state.
2. Two shut-off valves are connected in series on the bypass pipeline, and the second shut-off valve requires "high inlet and low outlet"
To ensure the tightness of valves during a maintenance cycle, valves that frequently open and close require the installation of two series connected globe valves. For the bypass system, the installation function of this bypass is to balance the pressure before and after the main pipeline valve, making it easy and effortless to open, and reducing the wear of the main pipeline valve; ② Small flow heating pipe during start-up process; ③ On the main water supply pipeline, control the water supply flow to control the boiler pressure rise speed for boiler water pressure testing. The bypass shut-off valves according to the flow direction of the medium are the primary valve and the secondary valve. During normal operation of the unit, the primary valve and the secondary valve are closed, and both are in direct contact with the medium. To prevent the gasket between the secondary valve casing and valve cover and the packing around the valve stem from being subjected to medium and temperature for a long time, and to allow for the replacement of valve packing during operation, the installation direction required for the secondary valve is "high in, low out".
3. Boiler exhaust and vent shut-off valve
Boiler exhaust and vent shut-off valves are only used during the boiler start-up water filling process, with a low opening and closing frequency. However, they often cause loss of working fluid due to poor sealing. Therefore, some power plants install such shut-off valves in a "high in, low out" direction to improve tightness.
4. Electromagnetic quick disconnect valve
The function of the electromagnetic quick disconnect valve is to quickly close and cut off the fuel supply. The structure of an electromagnetic quick disconnect valve is similar to that of a globe valve. If the working fluid also enters from the bottom and flows out from the top, the force of the fuel acting on the lower part of the valve disc of the electromagnetic quick disconnect valve is very large, and the weight of the electromagnetic quick disconnect valve is much smaller than it. Therefore, if the working fluid enters the quick break 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 break valve is activated, thus failing to achieve the expected purpose. If the working fluid enters from the upper part of the quick stop valve, once the quick stop valve is activated, the pressure behind the valve rapidly decreases, and the force of fuel acting on the lower part of the valve disc quickly drops to zero. The force of fuel acting on the valve disc and the force formed by the weight of the hammer and lever.