Why is the globe valve designed to be with low inlet and high outlet openings?
The purpose is to make the flow resistance small and save effort when opening the valve. At the same time, when the valve is closed, the gasket between the valve housing and the bonnet and the packing around the valve stem are not stressed, and will not be exposed to the effects of 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 while the valve is closed for easy maintenance.
Many people think that all globe valves are with low inlet and high outlet openings, but this is not true. Sometimes the globe valve is set with high inlet and low outlet openings.
1. the high-pressure globe valve with a diameter larger than 100mm
Due to the poor sealing performance of large-diameter valves, in this method, when the globe valve is closed, the medium pressure acts on the valve flap to increase the valve's tightness.
2. When two globe valves are connected in series on the bypass pipeline, 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 requires two globe valves connected in series. For the bypass system, the installation of this bypass has the following functions:
① Balance the front and rear pressure of the main pipeline valve, make it easy to open and save effort, and reduce the wear of the main pipeline valve;
② Small flow warm pipe during startup;
③ On the main feedwater pipeline, control the feedwater flow rate and control the boiler boosting speed to carry out the boiler hydraulic pressure test. According to the medium flow direction, the bypass stop valve is a primary valve and a secondary valve. The primary valve and the secondary valve are closed during normal operation of the unit, and both are in direct contact with the medium. In order to prevent the gasket between the secondary valve housing and bonnet and the packing around the valve stem from being affected by medium and temperature for a long time, and the packing of the valve can be replaced during operation, the installation direction required for the secondary valve is "high inlet and low outlet ".
3. Exhaust the boiler and vent the globe valve
Exhausting the boiler and venting the globe valves are only used in the process of starting and feeding the boiler. The frequency of opening and closing is small, but the working fluid is often lost due to the untight seal. For this reason, in order to improve the tightness of some power plants, the installation direction of such shut-off valves is "high inlet and low outlet".
4. Electromagnetic quick-release valve
The function of the electromagnetic quick-off valve is to close quickly and cut off the fuel supply quickly. The structure of the electromagnetic quick-release valve is similar to that of the stop valve. If the electromagnetic quick-release valve also enters the working fluid from the lower part and flows out from the upper part, the force of the fuel acting on the lower part of the electromagnetic quick-release valve flap is very large, and the weight of the electromagnetic quick-release valve is much smaller than it. Therefore, if the working fluid enters the quick-disconnect valve from the lower part, the torque generated by the weight is less than the torque generated by the fuel pressure, and the fuel cannot be cut off when the quick-disconnect valve operates, thus failing to achieve the intended purpose. If the working fluid enters from the upper part of the quick-disconnect valve, once the quick-disconnect valve is actuated, the pressure behind the valve is rapidly reduced, and the force of the fuel acting on the lower part of the disc is quickly reduced to zero.
Generally, it is difficult to close the valve when it is low inlet and high outlet openings set under large diameter and high pressure. If the low inlet and high outlet is used under the condition of high pressure and large caliber, the valve stem is easily deformed and bent under water pressure for a long time, which affects the safety and sealing of the valve. Using high inlet and low outlet openings setting can make the diameter of the valve stem smaller, which also saves costs for manufacturers and users.