Globe Valves

Globe valve consists of different types of disc, as shown in the following table.

ANSI 150# SS316 Flange End Globe Valve

The valve plug is directed by the stem to keep aligned with the centerline of the valve seat. When the plug and stem are lifted from the original position, the valve is in the open position. The globe valve has two port designs, which is Standard port-guided and Double-ported.

(a) Standard Port-Guided
The seat ring is utilized as a guide for the plug to make sure the centreline of the plug and seat are aligned. The diameter size of the valve stem can be made smaller, thereby reducing sliding friction and enhancing control behavior.

(b) Double-ported
A pair of plugs and a matching pair of seats is used to throttle flow of fluid in the globe valve. The pressure difference across the fluid process between the inlet and outlet of the valve will produce a force parallel to the valve stem. There will be two opposite force vectors, one at the lower plug and the other at the upper plug. If the plug areas are approximately equal, the forces will also be approximately the same, so they are almost canceled. This makes the valve easier to start.

Globe Valves are commonly used to control fluid flow in pipeline systems for most ships and offshore. It acts as an essential role in the piping system, it is widely used in various industries such as chemical and petrochemical industries. During the operation of the valve, due to the complex geometry of the valve, various phenomena such as cavitation and flashing may occur, resulting in a high pressure drop.

The cavitation in the valve can cause issues and difficulty to the factories. If the valves in the piping system were destroyed, resulting in a costly replacement every few months. For globe valves that transport liquids, cavitation is a destructive issue during its operation, as according to Bernoulli’s equation, the pressure may drop due to changes in speed. Cavitation occurs when the partial pressure in the globe valve drops due to the increase in speed and is lower than the corresponding saturated vapor pressure of the working liquid at a certain temperature. The steam begins to form bubbles in the low-pressure area, and then bursts immediately from pressure recovery as it flows downstream, causing vibration and erosion. In addition, this will not only cause vibration of the valve body, but also high noise.

Due to cavitation, the globe valve will be damaged in a short period of time. In the petroleum industry, it is very common to replace the damaged globe valve in the pipeline system every few months. Replacing a globe valve damaged by cavitation in a factory has become a routine and costly task. At present, most valve manufacturers are trying to reduce the damage of cavitation, thereby increasing the value of the globe valve. In order to minimize the cost caused by valve cavitation, cages are used to make cavitation only come in the area adjacent to the cage itself; thus, only the cage needs to be replaced.

A study focuses on the cavitation occurrence in Globe Valve; in the research, the authors indicate that vapor emerges in the vortex inside the valve and in the downstream area of the globe valve without a cage. However, vapor does not occur in those areas of the globe valve with two cages; therefore, the vapor mainly collects at the outlet of the flow passage of the cage. The results show that the steam generation rate in the downstream area is lower than that without the cage. Therefore, it is proved that the cage cavitation mainly occurs in the area near it. This avoids cavitation damage to the valve body and downstream area.

The Gate Valves and Globe Valves are similar in terms of physical appearance. The following table shows the differences between them in terms of function, application, installation, sealing, cost, and how they work.