What is the difference between a globe valve and a gate valve?

Valves are control components in fluid conveyance systems, serving functions such as shutoff, regulation, flow diversion, backflow prevention, pressure stabilisation, flow diversion, or pressure relief. Valves used in fluid control systems range from the simplest shutoff valves to various types of valves employed in highly complex automated control systems, with a wide variety of types and specifications available.

Shut-off valves, gate valves, butterfly valves, check valves, and ball valves are all indispensable control components in modern piping systems. Each type of valve differs in appearance, structure, and even functional application. However, shut-off valves and gate valves share some similarities in appearance and both serve the function of interrupting flow in piping systems, leading many individuals with limited exposure to valves to confuse the two. In fact, if you observe carefully, the differences between globe valves and gate valves are quite significant.

1. Structural Differences

When selecting valves in limited installation spaces, certain considerations must be made. Gate valves rely on the pressure of the medium to tightly seal against the sealing surface, thereby achieving a leak-free effect. During opening and closing, the valve core and seat sealing surfaces remain in constant contact and friction, leading to wear on the sealing surfaces. When the gate valve is nearly closed, the pressure difference between the pipeline's upstream and downstream sides is significant, exacerbating sealing surface wear.

2. Operating Principle

When opening or closing, globe valves use a rising stem design, meaning that turning the handwheel causes the handwheel to rotate and move up or down with the valve stem. Gate valves, however, rotate the handwheel to move the valve stem up or down, while the handwheel itself remains stationary. Flow rates vary, and gate valves require full opening or full closing, whereas globe valves do not. Globe valves have specified inlet and outlet directions; gate valves have no such requirements.

Additionally, gate valves have only two states: fully open or fully closed. The travel distance of the gate plate during opening and closing is large, resulting in longer opening and closing times. The travel distance of the valve plate in a globe valve is much smaller, and the valve plate can be stopped at any position during movement for flow regulation. Gate valves are only used for shutoff and have no other functions.

Gate valves have a more complex structure than globe valves. In terms of appearance, under the same diameter, gate valves are taller than globe valves, while globe valves are longer than gate valves. Additionally, gate valves have both rising stem and non-rising stem types, while globe valves do not.

3. Performance Differences

Globe valves can be used for both shutoff and flow regulation. Globe valves have higher fluid resistance and require more effort to open and close, but due to the short distance between the valve disc and the sealing surface, the opening and closing stroke is short.

Gate valves can only be fully open or fully closed. When fully open, the fluid flow resistance within the valve body passage is almost zero, so gate valves are very easy to open and close. However, the distance between the gate disc and the sealing surface is long, resulting in a longer opening and closing time.

4. Installation and flow direction

Gate valves function equally well in both directions, with no requirements for inlet/outlet direction during installation, allowing bidirectional flow of the medium. Globe valves must be installed strictly in accordance with the arrow markings on the valve body. There is also a specific regulation regarding the inlet/outlet direction of globe valves: China's ‘Three Standardisations’ regulation stipulates that the flow direction of globe valves must always be from top to bottom.

Globe valves have a low inlet and high outlet, and from the outside, the pipes are not on the same horizontal line. Gate valves have a flow path on the same horizontal line. The travel of gate valves is greater than that of globe valves.

From the perspective of flow resistance, gate valves have lower flow resistance when fully open, while globe valves have higher flow resistance. The flow resistance coefficient of ordinary gate valves is approximately 0.08 to 0.12, with low opening and closing force, and the medium can flow in both directions. The flow resistance of ordinary globe valves is 3 to 5 times that of gate valves (WeChat Official Account: Pump Manager). When opening and closing, forced closure is required to achieve sealing. The valve core of a globe valve only contacts the sealing surface when fully closed, resulting in minimal wear on the sealing surface. For globe valves requiring an actuator due to high flow resistance, attention should be paid to adjusting the torque control mechanism.

Gate valves can be installed in two ways. One method allows the medium to enter from below the valve core. The advantage is that when the valve is closed, the packing is not under pressure, extending its service life, and packing replacement can be performed even when the upstream pipeline is pressurised. The disadvantage is that the valve's driving torque is approximately twice that of the top-entry method, resulting in significant axial force on the valve stem, which may cause bending. Therefore, this method is generally only suitable for small-diameter shut-off valves (DN50 and below). For shut-off valves with a diameter of DN200 or above, the method where the medium enters from above is selected. (Electric shut-off valves generally use the method where the medium enters from above.) The disadvantages of the method where the medium enters from above are the opposite of those of the method where it enters from below.

5. Sealing

The sealing surface of a globe valve is a small trapezoidal side of the valve plug (depending on the shape of the valve plug). Once the valve plug falls out, it effectively closes the valve (though it may not seal tightly under high pressure differentials, it still provides decent backflow prevention). Gate valves rely on the side of the valve plug gate to seal, which is less effective than globe valves. If the valve plug falls out, it does not effectively close the valve like in a globe valve.