When I first heard the term “globe valve”, I pictured a valve with a bulging round body. But I’ve since learned that’s not necessarily the case. Check valves and globe valves look very similar on the outside but operate very differently.
Globe valves have always been widely known as an industry standard for controlling and throttling fluids. In this post, we’ll discuss the different design variations of globe valves, their advantages, disadvantages, and best applications.
What Is a Globe Valve?
A globe valve, different from a ball valve, is a type of valve used for regulating flow in a pipeline, consisting of a movable plug or disc element and a stationary ring seat in a generally spherical body. This has an opening that forms a seat onto which a movable plug can be screwed in to close (or shut) the valve.
Globe valves are named for their spherical body shape with the two halves of the body being separated by an internal baffle. The plug is also called a disc. In globe valves, the plug is connected to a stem which is operated by screw action using a handwheel in manual valves. Typically, automated globe valves use smooth stems rather than threaded ones and are opened and closed by an actuator assembly.
Although globe valves in the past had spherical bodies which gave them their name, many modern globe valves do not have much of a spherical shape. However, the term globe valve is still often used for valves that have such an internal mechanism.
In plumbing, valves with such a mechanism are also often called stop valves since they don’t have the spherical housing, but the term stop valve may refer to valves that are used to stop flow even when they have other mechanisms or designs.
How Globe Valves Work?
A globe valve is primarily designed to stop, start and regulate flow. It is comprised of a movable disk and a stationary ring seat in a generally spherical body. The seat of a globe valve is in the middle of and parallel to the pipe, and the opening in the seat is closed off with the disk.
When the handle is turned, manually or through an actuator, a disc is lowered or raised by means of the valve stem. When the disc is fully lowered, the fluid flow is shut off. When the disc is fully raised, the fluid flow is at its maximum rate. When the disc is raised to less than the maximum level, the fluid flow is regulated with proportion to the vertical travel of the disc.
Parts Of a Globe Valve
Major Components of the globe valve are
- Valve Body: The body is the main pressure containing structure of the valve and the most easily identified as it forms the mass of the valve. It contains all of the valve’s internal parts that will come in contact with the substance being controlled by the valve. The bonnet is connected to the body and provides the containment of the fluid, gas, or slurry that is being controlled.
- Wheel and nut: For Manual/hand operated actuators use a handwheel or crank to open or close the valve. They are not automatic but offer the user the ability to position the valve as needed. The handwheel can be fixed to a stem or hammer which allows for the valve to be pounded open or closed if necessary.
- Gland Packing: Valve packing is a gasket that provides a sturdy seal between the valve’s stem and the bonnet. It is used to prevent liquid leaks in valve stems and stuffing boxes. In most valves, gland followers are tightened until the valve is leak-proof. Loose packing results in leakage; tight packing negatively affects the valve movement and may cause damage to the stem.
- Stem: The stem is part of the globe valve that connects the disk to the handwheel or the valve actuator to transmit the actuation force. Since it connects the actuator to the parts inside of the globe valve, it is considered as one of the critical globe valve parts. If the valves are controlled by actuators, the stem is smooth but for the manual valves, they are threaded.
- Bonnet: The bonnet is one of the outer globe valve parts that’s connected to the body to provide a leak-proof closure. There are different bonnet types such as bolted, screw-in, or union bonnet that are used in different globe valves. Each of these bonnet types has its own advantages.
- Disc/Valve: The plug or the disk is among the essential globe valve parts. It moves perpendicular to the seat and its movement can block or free the flow since it works as a moveable physical barrier. When the valve is closed, the plug sits against the seat to block the flow and when it sits above the seats. it enables the flow of the material.
- Valve/Disc Seat: The seat ring provides a stable, uniform and replaceable shut off surface. Seat are usually screwed in or torqued. This pushes the cage down on the lip of the seat and holds it firmly to the body of the valve. Seat may also be threaded and screwed into a thread cut in the same area of the body.
Types of Globe Valve
There are three basic globe valve body designs: Tee, Angle, and Wye.
This is the most common body type for a globe valve. The horizontal setting of the seat allows the stem and disk to travel perpendicular to the horizontal line. This design has the lowest coefficient of flow and highest pressure drop.
They’re used in severe throttling services, such as in bypass lines around a control valve. When pressure drop is not a concern and throttling is required, this globe valve design is a good solution.
The ends of this Globe valve are at a 90° angle allowing fluid to flow in a single 90° turn. This valve is used for applications that have periods of pulsating flow because of its ability to handle “the slugging effect” which naturally occurs with a pulsating flow.
This type is an alternative for the high-pressure drop commonly found in globe valves. The seat and stem are at a 45° angle which provides a straighter flow path when fully open and offers the least resistance of flow. This design is commonly used for throttling during seasonal or start-up operations.
Uses of Globe Valve
Unlike the gate valve, the globe valve can be used for regulating flow or pressures as well as complete shutoff of flow. It may also be used sometimes as a pressure relief valve or as a check valve. Compared with a gate valve or ball valve, the globe valve has considerably higher-pressure loss in the fully open position.
The following are some of the typical applications of globe valves:
- Cooling water systems.
- Fuel oil systems.
- Feedwater or chemical feed systems.
- Boiler and main steam vents and drains.
- Turbine lube oil system and others.
Advantages of Globe Valve
- Good shutoff capability
- Moderate to good throttling capability
- Shorter stroke (compared to a gate valve)
- Available in tee, wye, and angle patterns, each offering unique capabilities
- Easy to machine or resurface the seats
- With disc not attached to the stem, valve can be used as a stop-check valve
Disadvantages of Globe Valve
- Higher pressure drops (compared to a gate valve)
- Requires greater force or a larger actuator to seat the valve (with pressure under the seat)
- Throttling flow under the seat and shutoff flow over the seat.