Valves are control components in fluid delivery systems, with functions including shutoff, regulation, flow guidance, backflow prevention, pressure stabilization, flow splitting, or pressure relief through overflow. The types and specifications of valves used in fluid control systems, ranging from simple shutoff valves to various valves in complex automated systems, are quite extensive.
Shutoff valves, gate valves, butterfly valves, check valves, and ball valves are indispensable control components in various piping systems today. Each valve differs in appearance, structure, and even functional use. However, globe valves and gate valves share some similarities in appearance and both have the function of shutoff in pipelines, so many people unfamiliar with valves often confuse the two. Actually, if you observe carefully, the differences between globe valves and gate valves are quite significant.
1. Structural Differences
Considerations for selection when installation space is limited. Gate valves rely on media pressure to tightly close against the sealing surface, achieving a leak-proof effect. When opening and closing, the valve stem and valve seat sealing surfaces are always in contact and rubbing against each other, so the sealing surfaces are easily worn. When the gate valve is nearly closed, the pressure difference before and after the pipeline is very large, making the sealing surface wear even more severe.
2. Working Principle
When opening and closing a globe valve, it is a rising stem type, meaning that when the handwheel is turned, the handwheel rotates and rises and falls with the stem. For a gate valve, turning the handwheel causes the stem to move up and down, while the handwheel itself remains stationary. The flow rates are different; gate valves require full opening or full closing, while globe valves do not. Globe valves have specified inlet and outlet directions; gate valves do not have inlet and outlet direction requirements.
In addition, gate valves only have two states: fully open or fully closed. The gate plate's opening and closing stroke is large, and the opening and closing time is long. The valve plate movement stroke of a globe valve is much smaller, and the valve plate can stop at a certain point during movement for flow regulation. Gate valves can only be used for shutoff and have no other functions.
The structure of a gate valve is more complex than that of a globe valve. In terms of appearance, for the same diameter, a gate valve is taller than a globe valve, and a globe valve is longer than a gate valve. In addition, gate valves are divided into rising stem and non-rising stem types. Globe valves do not have this distinction.
3. Performance Differences
Globe valves can be used for shutoff and flow regulation. Globe valves have relatively large fluid resistance and are more difficult to open and close, but because the valve plate is a short distance from the sealing surface, the opening and closing stroke is short.
Because gate valves can only be fully open or fully closed, when fully open, the fluid flow resistance in the valve body passage is almost zero, so the opening and closing of the gate valve is very easy, but the distance between the gate plate and the sealing surface is far, and the opening and closing time is long.
4. Installation and Flow Direction
Gate valves have the same effect in both flow directions and do not have inlet and outlet direction requirements; the medium can flow in both directions. Globe valves must be installed strictly according to the direction indicated by the arrow on the valve body. There is a clear regulation regarding the inlet and outlet direction of globe valves; China's "Three Standardizations" regulation for valves stipulates that the flow direction of globe valves should always be from top to bottom.
Globe valves have a low inlet and high outlet; viewed externally, the pipes are clearly not on the same horizontal plane. The gate valve's flow path is on a horizontal plane. The stroke of the gate valve is larger than that of the globe valve.
From the perspective of flow resistance, when fully open, the gate valve has low flow resistance, while the globe valve has high flow resistance. The flow resistance coefficient of an ordinary gate valve is approximately 0.08~0.12, with small opening and closing force, and the medium can flow in two directions. The flow resistance of an ordinary globe valve is 3-5 times that of a gate valve (WeChat Official Account: Pump Manager). When opening and closing, forced closure is required to achieve sealing. The valve stem of a globe valve only contacts the sealing surface when it is fully closed, so the wear on the sealing surface is minimal. For globe valves requiring actuators due to high flow resistance, attention should be paid to the adjustment of the torque control mechanism.
There are two ways to install a globe valve: one is that the medium can enter from below the valve stem. The advantage is that when the valve is closed, the packing is not under pressure, which can extend the service life of the packing and allows for packing replacement while the valve's upstream pipeline is pressurized; the disadvantage is that the valve's driving torque is larger, about twice that of top-inlet flow, and the axial force on the stem is large, making the stem prone to bending. Therefore, this method is generally only suitable for small-diameter globe valves (DN50 and below), and globe valves above DN200 generally use the top-inlet flow method. (Electric globe valves generally use the top-inlet flow method.) The disadvantages of the top-inlet flow method are the opposite of the bottom-inlet flow method.
5. Sealing
The sealing surface of a globe valve is a small trapezoidal side of the valve stem (depending on the shape of the valve stem). Once the valve stem falls off, it is equivalent to the valve closing (if the pressure difference is large, it will not close tightly, but the backflow prevention effect is still good). A gate valve relies on the side of the gate plate to seal, and the sealing effect is not as good as that of a globe valve. If the valve stem falls off, it will not be equivalent to the valve closing like a globe valve.