Why Should Refrigeration Shut - off Valves Have "Low - Inlet and High - Outlet" Design?

2025-02-26

Shut - off valves, also known as globe valves, belong to the forced - sealing type of valves and are a kind of cut - off valves. According to the connection methods, they are divided into three types: flange connection, threaded connection, and welded connection.

The flow direction of shut - off valves is always from top to bottom, so there is a directionality during installation.
This type of shut - off valve is very suitable for cutting off, regulating, and throttling. Since 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. Also, because the change of the valve seat opening is in direct proportion to the stroke of the valve disc, it is very suitable for flow regulation.
The shut - off valve is designed to have the medium enter from the lower part and exit from the upper part. The purpose is to reduce flow resistance and make it easier to open the valve. At the same time, when the valve is closed, the packing between the valve shell and the valve cover and the packing around the valve stem are not under stress. Thus, they are not affected by the medium pressure and temperature for a long time, which can extend the service life and reduce the probability of leakage. In addition, this allows for the replacement or addition of packing with the valve in the closed state, facilitating maintenance.
Many people think that all shut - off valves have the "low - inlet and high - outlet" design, but this is not the case. Generally, shut - off valves have the "low - inlet and high - outlet" design.

Why Should Refrigeration Shut - off Valves Have

However, there are some special cases where the shut - off valve has the "high - inlet and low - outlet" design:

High - pressure shut - off valves with a diameter larger than 100mm
Due to the poor sealing performance of large - diameter valves, when using this method, with the valve in the closed state, the medium pressure acts on the upper part of the valve disc to increase the valve's sealing performance.
Two shut - off valves in series on the bypass pipeline
The second shut - off valve is required to have the "high - inlet and low - outlet" design.
To ensure the tightness of the valve within an overhaul period, valves that are frequently opened and closed are required to be installed with two shut - off valves in series. For the bypass system, the functions of installing this bypass are as follows:
① Balance the pressure before and after the main pipeline valve, making it easier and more labor - saving to open and reducing the wear of the main pipeline valve.
② Warm the pipeline with a small flow rate during the startup process.
③ On the main feed - water pipeline, control the feed - water flow rate to control the boiler pressure - rising speed and conduct the boiler hydrostatic test.
According to the medium flow direction, the bypass shut - off valves are respectively the primary valve and the secondary valve. When the unit is operating normally, both the primary valve and the secondary valve are closed, and both are in direct contact with the medium. To prevent the packing between the valve shell 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 to enable the replacement of the valve packing during operation, the secondary valve is required to be installed with the "high - inlet and low - outlet" direction.
Vent shut - off valves
Vent shut - off valves are only used during the boiler startup and water - filling process. They have a low opening and closing frequency, but often cause working medium loss due to poor sealing. Therefore, some enterprises install this type of shut - off valve with the "high - inlet and low - outlet" direction to improve tightness.
Electromagnetic quick - break valves
The function of the electromagnetic quick - break valve is to close quickly and cut off the fuel supply rapidly. The structure of the electromagnetic quick - break valve is similar to that of the shut - off valve. If the working medium of the electromagnetic quick - break valve also enters from the lower part and exits from the upper part, the force of the fuel acting on the lower part of the valve disc of the electromagnetic quick - break valve is very large, while the weight of the heavy hammer of the electromagnetic quick - break valve is much smaller than it. Therefore, if the working medium enters the quick - break valve from the lower part, the torque generated by the heavy hammer is less than the torque generated by the fuel pressure. When the quick - break valve operates, it cannot cut off the fuel, thus failing to achieve the desired purpose. If the working medium enters the quick - break valve from the upper part, once the quick - break valve operates, the pressure behind the valve drops 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 gravity of the heavy hammer and the lever form a force.
Generally, if the "low - inlet and high - outlet" design is adopted under large - diameter and high - pressure conditions, it is more difficult to close the valve. If the "low - inlet and high - outlet" design is used under high - pressure and large - diameter conditions, the valve stem is easily deformed and bent due to long - term water pressure, affecting the safety and sealing performance of the valve. If the "high - inlet and low - outlet" design is selected, the diameter of the valve stem can be smaller, which can save costs for both manufacturers and users.