Does the globe valve also have a "high in and low out" design?

2023-10-16

Which is better between "low in and high out" stop valve and "high in and low out"?

The stop valve is designed with a low inlet and a high end in order to reduce the flow resistance 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 and will not be affected by the medium pressure and temperature for a long time, which can extend the service life and reduce the chance of leakage. In addition, the packing can be replaced or added when the valve is closed, which facilitates maintenance.

Many people think that cut-off valves are all low-in and high-out, but this is not the case. Generally speaking, the stop valve has a low inlet and a high outlet. However, there are some special cases where the stop valve has a high inlet and a low outlet:

1. High pressure stop valve with diameter greater than 100mm

Due to the poor sealing performance of large-diameter valves, when the stop valve is closed using this method, the medium pressure acts on the top of the valve disc to increase the sealing performance of the valve.

2. Two stop valves connected in series on the bypass pipeline. The second stop valve requires "high inlet and low outlet"

In order to ensure the tightness of the valve within a maintenance cycle, valves that are frequently opened and closed require the installation of two stop valves in series.

For the bypass system, the installation functions of this bypass are:

① Balance the pressure before and after the main pipeline valve, making it easy to open and labor-saving, and reducing the wear of the main pipeline valve;

② Small flow pipe heating during startup;

③ On the main water supply pipe, control the water supply flow to control the boiler pressure increase speed to conduct the boiler water pressure test. The bypass stop valves are divided into primary valve and secondary valve according to the direction of medium flow. When the unit is running normally, the primary valve and secondary valve are closed, and both are in direct contact with the medium. In order to prevent the gasket between the secondary valve shell and valve cover and the packing around the valve stem from being affected by the medium and temperature for a long time, and to allow the valve packing to be replaced during operation, the required installation direction of the secondary valve is "high in, low out" ".

3. Boiler exhaust and vent stop valve

Boiler exhaust and vent stop valves are only used during the process of boiler startup and water supply. The frequency of opening and closing is small, but often causes loss of working fluid due to loose sealing. For this reason, some power plants install such stop valves in order to improve the tightness. "High in, low out".

4. Electromagnetic quick-stop valve

The function of the electromagnetic quick-stop valve is to quickly close and quickly cut off the fuel supply. The structure of the electromagnetic quick-stop valve is similar to that of the stop valve. If the working medium of the electromagnetic quick-cut valve enters from the bottom and flows out from the upper part, the force of the fuel acting on the lower part of the solenoid quick-cut valve is very large, and the weight of the electromagnetic quick-cut valve is much smaller than it.

Therefore, if the working fluid enters the quick-stop valve from the bottom, the torque generated by the weight is smaller than the torque generated by the fuel pressure, and the fuel cannot be cut off when the quick-stop valve operates, thus failing to achieve the expected purpose. If the working fluid enters from the upper part of the quick-break valve, because once the quick-break valve operates, the pressure behind the valve decreases rapidly, and the force of the fuel acting on the lower part of the valve disc quickly drops to zero, while the force of the fuel acting on the valve disc and the weight, The force caused by the gravity of the lever.

Generally, it is difficult to close the valve if low inlet and high is used under large diameter and high pressure conditions. If low inlet and high are used under high pressure and large diameter conditions, the valve stem will be easily deformed and bent under long-term water pressure, which will affect the safety and sealing of the valve; If the valve stem diameter is selected to be high and low, the diameter of the valve stem can be smaller, which will also save costs for manufacturers and users.

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