Why should globe valve be low in and high out?
Globe valve, also known as shut-off valve, belongs to the forced sealing valve, is a kind of cut-off valve. According to the connection mode, it can be divided into three types: flange connection, screw connection and welding connection.
The flow direction of the stop valve is from top to bottom, so the installation is directional.
This type of shut-off valve is very suitable for shut-off or regulation and throttling. Because the opening or closing stroke of the valve stem is relatively short, and it has a very reliable cut-off function, and because the change of the valve seat opening is directly proportional to the stroke of the valve disc, it is very suitable for regulating the flow.
The globe valve (stop valve) is designed for low in and high out, so as to reduce the flow resistance and save labor when opening the valve. At the same time, when the valve is closed, the packing material between the valve shell and the valve cover and the packing around the valve stem are not stressed, so they are not 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 stop valve is low in and high out, but it is not. In general, the globe valve is low in and high out, but there are some special cases in which the globe valve is high in and low out
High pressure stop valve with diameter greater than 100 mm
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In this way, the sealing performance of the valve disc is increased due to the pressure difference above the valve.
There are two shut-off valves in series on the bypass pipeline, and the second one requires “high in and low out”
In order to ensure the tightness of the valve in a maintenance cycle, the valve that is often opened and closed is required to be equipped with two stop valves in series. For the bypass system, the installation functions of the bypass are:
- ① balance the pressure before and after the main pipe valve, make it easy to open and labor-saving, reduce the wear of the main pipe valve;
- ② warm the pipe with small flow during startup;
- ③ control the feed water flow on the main feed water pipe to control the boiler pressure rise speed for boiler hydrostatic test. According to the medium flow direction, the bypass stop valves are primary valve and secondary valve respectively. During normal operation of the unit, the primary valve and secondary valve are closed, and both of them are in direct contact with the medium. In order to prevent the packing 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 replace the valve packing during operation, the installation direction of the secondary valve is “high in and low out”.
Boiler exhaust and vent stop valve
The boiler exhaust and vent stop valve is only used in the process of boiler start-up and water supply, and its opening and closing frequency is small, but it often causes the loss of working medium due to poor sealing. Therefore, in order to improve the tightness, some power plants install this kind of stop valve in the direction of “high in and low out”.
Electromagnetic quick break valve
The function of the electromagnetic quick shut-off valve is to quickly close and cut off the fuel supply. The structure of the electromagnetic quick break valve is similar to that of the stop valve. If the electromagnetic quick break valve also has working medium flowing in from the lower part and flowing out from the upper part, the force of the fuel acting on the lower part of the electromagnetic quick break valve disc is very large, and the weight of the electromagnetic quick break valve is far less than it. Therefore, if the working medium enters the quick break valve from the bottom, the torque generated by the heavy hammer is less than that generated by the fuel pressure, and the fuel can not be cut off when the quick break valve acts, so the expected purpose can not be achieved. If the working fluid enters from the upper part of the quick break valve, the pressure behind the valve will decrease rapidly once the quick break valve acts, and the force of the fuel acting on the lower part of the valve disc will soon drop to zero, while the force of the fuel acting on the valve disc and the force formed by the gravity of the hammer and lever.
Generally, it is difficult to close the valve when low in and high out are used in large diameter and high pressure conditions. If low in and high out are used in large diameter and high pressure conditions, the valve stem is easy to deform and bend under water pressure for a long time, which affects the safety and sealing of the valve. If the high in and low out position is selected, the diameter of the valve stem can be smaller, which will also save the cost for manufacturers and users.
Source: Network Arrangement – China Valve Supplier: www.epowermetals.com
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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