Globe valves are used to start, stop, and regulate fluid flow via a disc that is moved into the fluid flow. They are frequently used in applications where fluid modulation is required and pressure drop across the valve is not a concern. In this article, you will learn about the different types of globe valves, common applications, and repair and maintenance methods.
The globe valve body attaches to a disc. A seat ring sets in the flow path. The disc mounts on a rod and attaches to a valve stem. An upward movement of the disc allows the flow to pass through the valve and a downward movement allows the disc to seat and blocks the flow. The design of globe valves makes it particularly useful for throttling applications.
Globe Valve Types
Globe valves can be categorized by the following attributes: body type, material of construction, number of seats, and actuation method.
There are three types of globe valve body types: tee, angle, and Wye.
Tee Body Style
The tee style globe valve is the most common body type. The horizontal setting of the seat allows the stem and disk to travel perpendicular to the horizontal line. This body type has the lowest coefficient of flow and highest pressure drop. The tee style is used in severe throttling services, such as in bypass lines around a control valve.
Angled Body Style
The angled design flanges into a piping system and changes direction by 90°. This type of valve is a good fit for a piping system that sees pulsating or irregular flow.
Wye Body Style
The Wye design mitigates the high-pressure drop associated with most global valves by providing a seat and a stem at a 45° angle. This allows for a straighter flow path when the valve is fully open and reduces friction and turbulence associated with the globe valve design.
Material of Construction
Globe valves’ material of construction is generally specified in three groups: the valve body, the stem, and the disc. For industrial applications, the valve body typically requires the ruggedness and mid-range price point that carbon steel provides. Cast iron can be used in less demanding applications, whereas stainless steel applications are common where pipe system specifications require additional corrosion resistance.
Globe valves provide a variety of options for disc construction. A plug type disc provides maximum erosion resistance via a long and tapered design. The composition disc provides a flat seat and a non-aero dynamic surface that makes it not a good fit for high pressure throttling. The conventional disc provide a thin contact area, allowing for good seating and moderate throttling.
Cast-iron globe valves typically see disc and seat rings made of bronze. In heavier-duty carbon steel and stainless steel valve bodies, valve trim material is usually stainless steel, which provides resistance to galling and seizure.
The typical globe valve design consists of a single seat with a disc that moves in an out of the flow path. A double-seated design with two plugs also exists. This two plug design cuts the hydraulic load on each disc in half.
In a conventional globe design, the process media directly contacts the disc. In a cage guided design, the cage isolates the plug from pressure and deflection. The cage guided design is not appropriate for viscous media as the cage can become plugged.
The globe valve stem may be manually turned or pneumatically/electrically actuated. A mechanical handle valve allows for direct operator control. Pneumatic or electrical actuators can offer fine control over flow regulation that may be required.
Because the entire system pressure exerted on the disc transfers to the valve stem, globe valves are limited to 12″ nominal pipe size. Globe valves are good fits where flow regulation is important and constant flow is not required. Common applications are cooling water, fuel oil, chemical feed, turbine, and feedwater systems.
When leak tightness and safety are major concerns, the use of a globe valve may be required. Globe valves see a high-pressure drop which may dictate the use of an actuator in smaller sizes than other valve types.
Maintenance and Repair Considerations
Globe valves are known for their ability to be easy to maintain. Regular inspection of the valve is important to ensure there is no obvious wear or valve leakage. Cycling of the valve is important to ensure the disc does not stick to the seat.