Valves such as stop valves, gate valves, butterfly valves, check valves and ball valves are all indispensable control components in various piping systems nowadays. Each type of valve has differences in appearance, structure and even function and application. However, stop valves and gate valves share some similarities in appearance, and both have the function of cutting off the pipeline. Therefore, many people who have little contact with valves confuse the two. In fact, if you observe carefully, the differences between stop valves and gate valves are quite significant.

Structurally:

When the installation space is limited, the selection should pay attention to:

Gate valves can tightly close with the sealing surface under the pressure of the medium, thus achieving no leakage. When opening or closing, the valve core and valve seat sealing surfaces are always in contact and friction with each other, so the sealing surface is prone to wear. When the gate valve is close to the closed state, the pressure difference before and after the pipeline is very large, causing more severe wear of the sealing surface.

The structure of gate valves is more complex than that of stop valves. From the appearance, under the same diameter, the gate valve is higher than the stop valve, and the stop valve is longer than the gate valve. In addition, gate valves also have exposed and concealed stem types. Stop valves do not have this.

Working principle:

When stop valves are opening or closing, it is of the rising stem type, that is, turning the handwheel will cause the handwheel to rotate and rise and fall together with the valve stem. Gate valves are turning the handwheel to make the valve stem rise and fall, and the position of the handwheel remains unchanged.

The flow rates are different. Gate valves require full opening or full closing, while stop valves do not. Stop valves have specified inlet and outlet directions, while gate valves do not have requirements for inlet and outlet directions.

In addition, gate valves have only two states of full open or full close, and the stroke of the gate plate opening and closing is very large, with a long opening and closing time. The stroke of the valve plate of stop valves is much smaller, and the valve plate of stop valves can stop at a certain position during movement for flow regulation. While gate valves can only be used for cutting off, without other functions.

Performance differences:

Stop valves can be used for both cutting off and flow regulation. The fluid resistance of stop valves is relatively large, and the opening and closing are relatively laborious. However, because the distance between the valve plate and the sealing surface is short, the opening and closing stroke is short.

Gate valves can only be fully open or fully closed. When fully opened, the medium flow resistance in the valve body channel is almost 0, so the opening and closing of gate valves is very effortless. However, the distance between the gate plate and the sealing surface is far, and the opening and closing time is long.

Installation and flow direction:

Gate valves have the same effect in both directions of flow direction. There is no requirement for inlet and outlet directions in installation, and the medium can flow in both directions. Stop valves need to be installed strictly according to the arrow direction on the valve body. There is a clear regulation for the inlet and outlet directions of stop valves. According to the "Three Modernizations" regulations of valves in China, the flow direction of stop valves should all adopt the top-down direction.

Stop valves are low-in-high-out, and from the outside, there is a clear situation where the pipeline is not on the same horizontal line. Gate valves have a flow channel on a horizontal line. The stroke of the gate plate of gate valves is larger than that of stop valves.

From the perspective of flow resistance, the flow resistance of gate valves is small when fully open, and large when stop valves are fully open. The flow resistance coefficient of ordinary gate valves is approximately 0.08 to 0.12, and the opening and closing force is small, allowing the medium to flow in both directions. The flow resistance of ordinary stop valves is 3 to 5 times that of gate valves. When opening and closing, it is necessary to forcibly close to achieve sealing. The valve core of stop valves contacts the sealing surface only when fully closed, so the wear of the sealing surface is very small. Due to the large flow force, the stop valve should pay attention to adjusting the torque control mechanism when using an actuator.

There are two installation methods for stop valves. One is that the medium can enter from the bottom of the valve core, which has the advantage that the packing does not bear pressure when the valve is closed, which can extend the service life of the packing and can perform the replacement of the packing work under the condition of the pipeline pressure before the valve. The disadvantage is that the driving torque of the valve is large, about 1 times that of the top-flowing type. The axial force on the valve stem is large, and the valve stem is prone to bending.

Therefore, this method is generally only applicable to small-diameter stop valves (with a diameter of less than DN50). For stop valves with a diameter of 200mm or larger, the medium is usually introduced from the top. (Electric stop valves usually adopt the method of the medium entering from the top.) The disadvantage of the top-entry method of the medium is exactly the opposite of the bottom-entry method.