Can globe and gate valves be mixed?
Globe valves, gate valves, butterfly valves, check valves and ball valves are essential control components in all kinds of piping systems now. Each valve is different in appearance, construction and even functional use. But globe valve and gate valve have some similarities in appearance, at the same time have the function of doing truncation in the pipeline. In fact, if you scrutinize, globe valves and gate valves are quite different.
In the case of limited installation space, should be paid attention to select the type of valve:
Gate valve can rely on the medium pressure tightly and sealing surface closed, so as to achieve the effect of leakage. When opening and closing, the sealing surface of the valve core strike with seat and rub against each other, so the sealing surface is easy to wear out. When the gate valve is close to closing, the pressure difference between front and rear of the pipeline is large, which makes the sealing surface wear more serious.
The structure of gate valve is more complex than the globe valve. under the same size, the gate valve is higher than the globe valve, globe valve is longer than the gate valve. In addition, gate valves have rising stem and non-rising stem. But globe valve haven't.
2. Operating principle
When the globe valve to open and close, is rising the stem. That is, when turn the handwheel, the handwheel will follow the stem to do rotation, up and down motion. Gate valve,When turn the handwheel, the stem to do lifting movement, but the position of handwheel keep same.
Flow varies, gate valves require full open or full closed, but globe valves do not. Globe valves have specified inlet and outlet directions, gate valves have no inlet and outlet direction requirements.
In addition, the gate valve only can be two states, fully open or fully closed. And opening and closing stroke is very large, long opening and closing time. The stroke of the globe valve is much smaller, and the wedge of the globe valve can be stopped in a certain place in the movement to do flow regulation. The gate valve only be used for truncation, without other functions.
Globe valve can be used for both truncation and flow regulation. The fluid resistance ofglobe valve is relatively large, and it is more laborious to open and close, but because the wedge is short from the sealing surface, the stroke of opening and closing is short.
Because gate valve can only be fully open and fully closed, when it is fully opened, the medium flow resistance in the valve body channel is almost 0, so the opening and closing of gate valve will be very labor-saving, but the wedge is far from the sealing surface, so the opening and closing time is long.
The effect of the flow direction for gate valve is the same in both directions, installation without inlet and outlet requirements, media can be two-way flow. Globe valves need to be installed strictly in accordance with the direction indicated by the arrow of the valve body. There is also a clear provision on the inlet and outlet direction of globe valves.
Globe valve is enter from the low and exit from high, and the pipeline is not in level line. Gate valve is in horizontal line. The travel of gate valve is larger than globe valve.
From the point of view of flow resistance, when fully open gate valve flow resistance is small, load check valve flow resistance 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. The valve core of the globe valve only touches the sealing surface when it is completely closed, so the wear of the sealing surface is very small. Due to the large flow force, the globe valve with the actuator should pay attention to the adjustment of the torque control mechanism.
There are two ways to install the globe valve. One is that the medium can enter from below the spool. The advantage is that when the valve is closed, the disc is not under pressure, which can prolong the service life of the disc and can be replaced in the case of pressure in the pipe before the valve. Disadvantage is that the driving torque of the valve is larger, is about 1 times the flow into the top, the axial force of the valve stem is large, and the valve stem is easy to bend.
Therefore, this method is generally only applicable to small size of globe valve (≤DN50), and the globe valve of DN200 or more chooses the way of medium flowing in from the top. (Electric globe valve is generally used from the top of the medium into the way.) The disadvantage of the medium coming in from above is the opposite of the medium coming in from below.
Cut-off valve sealing surface of valve core is a small trapezoidal profile (specific see the shape of the valve core), falls off once the valve core, valve closing (if the pressure difference is big, closed lax) of course, but check inverse effect is good, the gate is on the side of the heart gate to seal, the sealing effect is better than cut-off valve, valve core loss is not like a globe valve valve closed.
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