The globe valve can be used for cut-off and flow regulation. The fluid resistance of the globe valve is relatively large, and it is more laborious to open and close. Because the distance between the valve plate and the sealing surface is short, the opening and closing stroke is short.
Because the gate valve
can only be fully opened and fully closed, the medium flow resistance in the channel of the valve body is almost zero when it is fully opened. Therefore, the opening and closing of the gate valve is very labor-saving. However, the distance between the gate and the sealing surface is far, and the opening and closing time is long.
Differences in installation and flow directions
The flow direction effect of gate valves in both directions is the same. There are no requirements for inlet and outlet directions for installation, and the medium can flow in two directions. The globe valve should be installed in strict accordance with the direction indicated by the arrow on the valve body. There is a clear stipulation on the inlet and outlet direction of the globe valve. The flow direction of the globe valve is always from top to bottom in China.
The globe valve is low in and high out. From the appearance, it is obvious that the pipeline is not on the same horizontal line. However, the flow path of the gate valve is on a horizontal line. The stroke of gate valves is larger than that of globe valves.
As for the flow resistance, when the gate valve is fully open, the flow resistance of the load check valve is large. The flow resistance coefficient of ordinary gate valve is about 0.08 ~ 0.12. The opening and closing force is small, and the medium can flow in two directions. The flow resistance of the common cut-off valve is 3-5 times more than that of the gate valve. The valve core of the globe valve only contacts the sealing surface when it is completely closed. And the wear of the sealing surface is very small. Due to the large flow force, we should pay attention to the adjustment of torque control mechanism because the globe valve needs to be installed with actuators due to the large flow force.
There are two ways to install the globe valve. One is that the medium can enter from the lower part of the valve core. The advantage is that the packing is not under pressure when the valve is closed, which can extend the service life of the packing, and it can replace the packing when the pipe in front of the valve is under pressure. The disadvantage is that the driving torque of the valve is large, which is about 1 times more than that of the upper flow, and the axial force of the valve stem is large. The stem is easy to bend. Therefore, this method is generally only applicable to the small diameter globe valve (below DN50), and the way of medium flowing from above is selected for globe valve above DN200. ( Generally, the way of medium entering from above is adopted for the electric globe valve.) The disadvantage of media entry from the top is just the opposite of that from the bottom.
Differences in seals
The sealing surface of the globe valve is a small trapezoidal side of the valve core (depending on the shape of the valve core). Once the valve core falls off, it is equivalent to closing the valve (If the pressure difference is large, it can surely not be closed tightly. However, the check effect is good). The gate valve is sealed by the side of the valve core gate, and the sealing effect is not as good as that of the globe valve. The falling off of the valve core will not be equivalent to the closing of the valve as the globe valve.