Why is the globe valve designed with low inlet and high outlet?

The globe valve is designed for low inlet and high outlet, with the aim of reducing flow resistance and saving effort when opening the valve. When the valve is closed at the same time, the gasket between the valve shell and valve cover and the packing around the valve stem are not subjected to force, which can prolong the service life and reduce the probability of leakage by not being subjected to medium pressure and temperature for a long time. In addition, this can also replace or add packing when the valve is closed, making maintenance easier.

Many people believe that globe valves are low in and high out, but in fact, there are also some special situations where globe valves are high in and low out:

1. High pressure globe valve with a diameter greater than 100mm

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

2. Two globe valves connected in series on the bypass pipeline, with the second globe valve requiring "high inlet and low outlet"

To ensure the tightness of the valve within a maintenance cycle, valves that frequently open and close require the installation of two series globe valves. For the bypass system, the installation functions of this bypass include:

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 Warm up pipes with small and medium flow during startup;

③ On the main water supply pipeline, control the water flow to control the boiler pressure increase speed for boiler water pressure test. The bypass globe valves are divided into primary and secondary valves according to the direction of medium flow. During normal operation of the unit, the primary and secondary valves are closed and both come into direct contact with the medium. To prevent the gasket between the secondary valve shell and valve cover, as well as the packing around the valve stem from being subjected to medium and temperature effects for a long time, and to replace the valve packing during operation, the installation direction required for the secondary valve is "high in and low out".

3. Boiler exhaust and vent globe valves

The boiler exhaust and vent globe valves are only used during the water supply process during boiler startup, with a small opening and closing frequency. However, they often cause fluid loss due to poor sealing. Therefore, some power plants have installed these globe valves in a "high inlet and low outlet" direction to improve their tightness.

It is generally difficult to close the valve when using low inlet and high outlet methods under large caliber and high-pressure conditions. If low inlet and high outlet are used under high pressure and large diameter conditions, the valve stem is prone to deformation and bending under long-term water pressure, which affects the safety and sealing of the valve. Choosing a high inlet and low outlet can reduce the diameter of the valve stem, which will also save some costs for manufacturers and users.