Let’s introduce what is the difference between a globe valve and a gate valve.
01
Structure
When the installation space is limited, pay attention to the selection:
The gate valve can rely on the medium pressure to tightly close the sealing surface, so as to achieve the effect of no leakage. When opening and closing, the valve core and the sealing surface of the valve seat are always in contact and rubbing against each other, so the sealing surface is easy to wear, and when the gate valve is close to closing, the pressure difference between the front and rear of the pipeline is very large, which makes the sealing surface wear more serious.
The structure of the gate valve will be more complex than the globe valve, from the appearance point of view, in the case of the same caliber, the gate valve is higher than the globe valve, and the globe valve is longer than the gate valve. In addition, the gate valve is divided into bright rod and dark rod. Shut-off valves do not.
How it works
When the globe valve is opened and closed, it is a rising stem, that is, when the handwheel is rotated, the handwheel will rotate and lift with the stem. The gate valve is to rotate the handwheel to make the valve stem do lifting movement, and the position of the handwheel itself remains unchanged.
Flow rates vary, with gate valves requiring full open or full closing, while globe valves do not. The globe valve has a specified inlet and outlet direction, and the gate valve has no inlet and outlet direction requirements.
In addition, the gate valve only has two states: full open or fully closed, and the stroke of opening and closing of the gate plate is very large, and the opening and closing time is long. The movement stroke of the valve plate of the globe valve is much smaller, and the valve plate of the globe valve can stop at a certain place in motion for flow adjustment. The gate valve can only be used for truncation and has no other functions.
Performance differences
The globe valve can be used for both cut-off and flow regulation. The fluid resistance of the globe valve is relatively large, and it is more laborious to open and close, but 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 closed, when it is fully opened, the medium flow resistance in the valve body channel is almost 0, so the opening and closing of the gate valve will be very labor-saving, but the gate plate is far from the sealing surface, and the opening and closing time is long.
04
Installation and flow direction
The effect of the gate valve flow direction in both directions is the same, there is no requirement for the inlet and outlet direction of installation, and the medium can flow in both directions. The globe valve needs to be installed in strict accordance with the direction marked by the arrow of the valve body, and there is a clear provision on the direction of the inlet and outlet of the globe valve, and the flow direction of the globe valve is adopted from top to bottom according to the “three transformations” of China’s valve.
The shut-off valve is low in and high out, and from the outside there is a clear pipe that is not on the level of one phase. The gate valve flow path is on a horizontal line. The stroke of the gate valve is larger than that of the globe valve.
From the perspective of flow resistance, when fully open, the flow resistance of the gate valve is small, and the flow resistance of the load stop 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 ordinary globe valves is 3-5 times that of gate valves. Opening and closing needs to be forced to close to achieve sealing, the spool of the globe valve is completely closed when it contacts the sealing surface, so the wear of the sealing surface is very small, due to the large flow of the main force to add actuator of the globe valve should pay attention to the torque control mechanism adjustment.
There are two ways to install the globe valve, one is that the medium can enter from under the spool, the advantage is that the packing is not pressurized when the valve is closed, which can extend the service life of the packing, and can replace the packing when the pipeline 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 that of the upper flow, the axial force of the valve stem is large, and the valve stem is easy to bend.
Therefore, this method is generally only suitable for small-diameter globe valves (DN50 or less), and the globe valves above DN200 use the medium flowing in from above. (Electric globe valves generally use the medium to enter from above.) The disadvantage of the media entry method from above is exactly the opposite of the lower entry method.
05
Sealing
The sealing surface of the globe valve is a small trapezoidal side of the valve core (specifically look at the shape of the valve core), once the valve core falls off, it is equivalent to the valve closing (if the pressure difference is large, of course, the closure is not strict, but the check effect is not bad), the gate valve is sealed by the side of the valve core gate plate, the sealing effect is not as good as the globe valve, and the valve core will not fall off like the globe valve equivalent to the valve closing.
Post time: Apr-08-2023