Cast Globe Valve

Industry Knowledge Extension

What are the characteristics of a Flanged End Cast Steel Globe Valve?

A flanged end cast steel globe valve is a type of linear motion valve designed primarily for regulating flow and providing a reliable shut-off in a pipeline. Its name is derived from the spherical shape of its body, which is typically manufactured through a casting process using carbon steel or alloy steel. This material choice offers a balance of strength and cost-effectiveness for a range of industrial applications. The defining characteristic of this valve is its flanged ends, which feature raised faces with bolt holes, allowing for robust and secure bolted connections to adjacent piping components. This design facilitates installation and maintenance.

The internal mechanism of a globe valve involves a disc or plug that moves perpendicularly to the seat, which is usually parallel to the flow line. This design creates a non-linear flow path, as the fluid is forced to change direction multiple times while passing through the valve. This characteristic results in a higher pressure drop compared to gate valves of a similar size. However, this same design provides a fine degree of control over the flow rate, making globe valves suitable for throttling duties. The seating surface is relatively large, which can contribute to a tight seal when closed. Due to the pressure drop and the forces exerted on the stem, these valves are often installed with the pressure under the disc, which helps avoid excessive effort in closing and minimizes seat wear.

What are the different types and characteristics of Cast Globe Valves?

Cast globe valves are categorized primarily by their body design and disc configuration, which influence their flow characteristics, maintenance needs, and suitability for specific services. The three main body patterns are the standard (T-pattern), the angle pattern, and the oblique (Y-pattern) globe valve.

The Standard (T-Pattern) Globe Valve is the common design. It features a Z-shaped partition inside the body, which creates the tortuous flow path that is characteristic of globe valves. This design provides good throttling and shut-off capabilities but also generates a relatively high-pressure drop. It is a general-purpose valve used in a variety of water, oil, and gas services where flow regulation is needed.

The Angle Globe Valve modifies the standard design by having the inlet and outlet ports at a 90-degree angle. This configuration eliminates the need for an elbow in the piping system, as the valve itself can change the flow direction. The flow path in an angle valve is slightly less restrictive than in a T-pattern valve, resulting in a lower pressure drop. They are often used in applications involving periodic drainage or where the line makes a right-angle turn.

The Oblique (Y-Pattern) Globe Valve is designed with the stem and seat oriented at approximately 45 degrees to the valve’s pipe axis. This design creates a much straighter flow path compared to the T-pattern, significantly reducing the pressure drop across the valve. Y-pattern globe valves are selected for services that require both throttling control and a minimal pressure loss, and they are often used in high-pressure applications or for services with erosive fluids.

What are the differences between API Full Bore Globe Valves and other standards?

The term "full bore" in valve terminology typically refers to a design where the internal diameter of the valve's opening matches the internal diameter of the connecting pipe, flow restriction. However, when discussing globe valves, the concept of a "full bore" design is less common due to the valve's inherent working principle. The primary standard for industrial steel globe valves is API 602, which covers compact forged and cast steel valves. The differences between valves built to API standards and those built to other common standards, like ASME B16.34, often relate to scope, design requirements, and testing.

API 602, titled "Gate, Globe, and Check Valves for Sizes DN 100 and Smaller for the Petroleum and Natural Gas Industries," is a specification with a distinct focus. It outlines requirements for materials, design, and testing for valves intended for refinery and pipeline service. Valves conforming to API 602 often feature additional design elements such as a flexible wedge or a plug-type disc, a backseat for live loading and stem packing replacement, and specific material trims for corrosive services. The testing requirements under API standards can be more rigorous, often including both shell and seat tests.

ASME B16.34, "Valves - Flanged, Threaded, and Welding End," is a more foundational standard that establishes pressure-temperature ratings, dimensions, and material requirements for a wider range of valves. A globe valve manufactured to ASME B16.34 will meet fundamental safety and performance criteria but may not include the specialized design features or the extensive testing protocols mandated by API 602. While an ASME valve is suitable for many general industrial applications in power, chemical, and water treatment, an API 602 valve is engineered with the specific demands of the oil and gas industry in mind, often resulting in a more robust and service-specific product. The choice between them depends on the application's specific service conditions and the end-user's specifications.