Globe valve is a forced sealing valve, so when the valve is closed, pressure must be applied to the valve flap to force the sealing surface not to leak. When the medium enters the valve6 from below the valve flap, the resistance needed to overcome the operating force is the frictional force of the stem and packing with the thrust generated by the pressure of the medium, the force of closing the valve is greater than the force of opening the valve, so the diameter of the stem should be large, otherwise the failure of the stem top bend will occur. In recent years, from the emergence of self-sealing valves, the media flow direction of the globe valve is changed from the top of the valve flap into the valve cavity, then under the action of media pressure, the force to close the valve is small, while the force to open the valve is large, the diameter of the valve stem can be reduced accordingly. At the same time, under the action of the medium, this form of valve is also tighter.
globe valve open, the opening height of the valve flap, 25% to 30% of the nominal diameter, the flow has reached the maximum, that the valve has reached the full open position. Therefore, the full open position of the globe valve should be determined by the stroke of the valve flap.
The globe valve has the following advantages.
Simple structure, relatively easy to manufacture and repair.
Small working stroke, short opening and closing time.
Good sealing, less friction between sealing surfaces, longer life.
Disadvantages of globe valves are as follows.
Large fluid resistance, open and close the force required.
Not suitable for the media with particles, viscosity, easy to coking.
Adjustment performance is poor.
The types of globe valves are external threaded and internal threaded according to the position of the stem thread. According to the flow direction of the medium, there are straight type, direct type and angle type. According to the sealing form, there are packing seal globe valve and bellows seal globe valve.
Installation and maintenance of globe valves should pay attention to the following matters.
Handwheel, handle-operated globe valve can be installed in any position of the pipeline.
The handwheel, handle and the Weidong mechanism are not allowed to be used for lifting.
The flow direction of the medium should be consistent with the direction of the arrow shown on the valve body.
