Globe valve is a special kind of valve, whose opening and closing member is a valve flap shaped like a plug. The sealing surface of this valve flap can be flat or tapered. Valve flap along the center line of the valve seat for linear movement, in order to achieve the valve open and close.
There are two forms of stem movement: one is the dark stem type, the stem moves inside the valve and is not directly visible; the other is the open stem type, the stem moves outside the valve and can be clearly seen lifting or rotating. No matter which form, the globe valve relies on the movement of the valve flap along the centerline of the valve seat to work.
Because of its relatively short stem opening or closing stroke and its very reliable shutoff function, the globe valve is ideally suited for regulating flow. The change in seat opening is directly proportional to the stroke of the valve, which means that by adjusting the position of the valve, the flow rate of the medium can be precisely controlled.
Globe valves are forced-sealing valves, which means that additional pressure needs to be applied to the valve flap when closing the valve to ensure that the sealing surfaces fit tightly and prevent leakage. When the medium enters the valve from underneath the valve flap, the force required to close the valve will be greater than when the valve is opened because, in addition to overcoming the friction between the valve stem and packing, the thrust generated by the pressure of the medium also needs to be overcome. Therefore, in order to prevent the stem from bending due to excessive force, the stem diameter is usually designed to be large.
However, with the emergence of self-sealing valves, globe valves, the medium flow direction has changed. Now, the medium usually enters the valve cavity from above the valve flap. In this case, the force required to close the valve decreases, while the force required to open the valve increases. The stem diameter can therefore be reduced accordingly. At the same time, due to the role of medium pressure, this form of valve sealing performance is also more reliable.
In China’s valve standardization work, it has been stipulated that the medium flow direction of the globe valve should be from top to bottom. In addition, the globe valve usually needs to be installed horizontally.
When the globe valve is open, the opening height of the valve flap reaches 25% to 30% of the nominal diameter, the flow has reached the maximum, which means that the valve is already in the fully open position. Therefore, the fully open position of the globe valve is determined by the travel of the valve flap. This feature makes the globe valve have high precision and reliability in flow regulation.
