What is a globe valve?
A globe valve is intended to start and stop flow like most valves and is also good for throttling fluids and changing pressure. Another benefit of a globe valve is its ability to prevent backflow. It can be visually recognized by its round body. Globe valves do not pass fluids straight through like a gate valve does. Instead, fluid travels in a non-linear direction through a globe valve which reduces fluid pressure in the line after passing through the valve. Most globe valves are intended to have an inflow of fluid with less than 300 PSI. Because a globe valve is a slow-closing valve, stopping flow is unlikely to result in fluid hammer.
Typically, the nominal pipe size when dealing with a globe valve should not exceed 12 inches, but specialized globe valves do exist to meet larger requirements. Make sure to consider your pressure requirements and make adjustments to meet your sizing needs, and choose valve trim wisely to reduce corrosion. All globe valves have a body, disc, bonnet, and stem. Each of these parts have variations to meet the requirements for a valve’s intended purpose.
Valve body type is the most distinguishing feature of a globe valve. Things to consider when choosing a body type are the pressure that will be flowing into the valve, pressure needed for fluid exiting the valve, and how consistent the pressure flowing into the valve will be. These factors will help you decide the material you need to use for the body and the trim as well as the actual configuration of the body. As a note, you may notice some different types of bonnets, but globe valves are usually union weld or bolt bonnet.
The body design used most commonly in marine applications is a, “T-style” globe valve. The Pima B122E Bronze globe valve in the image to the left is an example of a T-style globe valve. The body of this globe valve looks like an upside-down capital, “T.” However, the flow of the fluid passing through moves in a zig-zag or, “Z-shaped,” direction. This internal layout reduces the pressure of the fluid passing through it even when the valve is in the open position.
Another common body style for globe valves is the angle globe. This body style is a 90-degree bend and is used when fluid may need to be restricted or stopped before changing directions. This type of valve is commonly used when fluid may have pulsating or irregular flow patterns, which means that the trim of the valve needs to be durable. Often, the trim of choice is monel.
The third and final style we will be highlighting in this article is the Y-globe. This globe valve is a little different because the flow direction is not changed as much as with other globe valves. The result is less pressure drop than with a T-globe or angle valve. In a Y-globe, the stem presses the disc against the flow of fluid at a 45 degree angle.
Globe valve discs can come in different shapes and are used for different amounts of flow control. Flat-faced discs are fairly common. It is pressed against the opening in the valve by rotating the stem giving a positive shut off of flow. Another type of disk is the needle disk. This is a narrower and usually cone-shaped disk that gives a more precise throttling of flow. While there are other variations of these two, these are the most basic types of globe-valve disks.
Stems on globe valves can be either rising or non-rising, though in the marine industry rising is the more common design. The stem is the long, thin, threaded component with a handle on the end. By spinning it, the disc is moved into or away from the flow of fluid. Rising stems will extend away from the valve as it is turned counter-clockwise and retract into the valve when turned clockwise. Non-rising stems will not extend at all, which is great for situations of limited space. They may have an indicator on the stem to show when the valve is opened or closed. One thing to keep in mind is that the force of the fluid is transferred directly on the stem, so you want it to be sturdy. This is why globe valve stems are often sturdy materials such as monel.
When you are ready to replace your old globe valves, make sure to connect with the Marine Valve Experts at Tork Systems, Inc!