standard valves: globe and butterfly

Introduction to Plumbing Valves

In this lesson, we will explore two specific types of plumbing valves: globe valves and butterfly valves. Understanding these valves is crucial for various plumbing applications, particularly regarding flow control.

Globe Valves

Purpose and Design

Globe valves are specifically designed for limiting the flow of a medium. They operate using a wheel and stem mechanism similar to gate valves, but with a crucial difference: the stem is connected to a washer that seals against the opening.

Structure

The design of a globe valve can be visualized as two half walls that direct the flow of water in a zig-zag pattern (denoted as a "Z pattern"). This design impacts how the valve functions when it is opened or closed.

Operation Characteristics

Globe valves open and close gradually, which helps in preventing water hammer, a common plumbing issue characterized by sudden pressure surges.

Effects on System Pressure

Due to their construction, even when fully open, globe valves do not allow for free flow of the medium, resulting in a reduction of system pressure. This reduced pressure serves to protect the valve’s internal components, making the stopper and seat less susceptible to wear and damage compared to gate valves. The primary component that does experience wear is the washer, which can be replaced when necessary.

Installation Considerations

For optimal flow efficiency, it is imperative to install a globe valve with the medium encountering the top half wall first.

Regulatory Compliance

It is important to note that the International Residential Code prohibits the use of globe valves for the main water supply shutoff or water heater shutoff applications. In these scenarios, full open valves such as ball valves or gate valves are mandatory.

Uses in Flow Control

Unlike gate valves, globe valves offer the ability to throttle or regulate the flow of a medium. The valve can be adjusted between fully open and fully shut positions, making them versatile for various uses.

Applications

  • Industrial Applications: Commonly found in wastewater treatment plants, food processing facilities, process plants, and other industrial settings.

  • Residential Applications: Can be utilized as outdoor silcocks, boiler drains, or as supply stops for lavatory tanks.

Butterfly Valves

Components and Operation

The butterfly valve consists of a disc hinged to a rod that functions to regulate flow. Various actuation methods are used, including a hand wheel, 90-degree throw handle, or an actuator that allows for quarter-turn operation of the valve disc to either open or shut the valve.

Anti-Extrusion Ring

This specific butterfly valve contains an anti-extrusion ring, which serves two essential purposes:

  1. Contaminant Prevention: Holds an elastomeric seal that prevents contaminants from entering the valve along the shaft.

  2. Leak Prevention: Prevents leaks from inside the valve along the shaft.

Bushing and Shaft

The bushing plays a role in maintaining shaft alignment, which is crucial for ensuring smooth operation of the valve.

Design Features

The butterfly valve disc is expertly designed to minimize pressure drop when the valve is fully open. The sealing area around the perimeter is polished, enhancing the seal against the seat.

Types of Butterfly Valves

There are three primary types of butterfly valves utilized in commercial applications:

  1. Lug: Suitable for specific mounting applications, allowing for easy maintenance and replacement.

  2. Wafer: Generally installed between two flanges, ideal for a low-profile installation.

  3. Offset: Designed for higher flow capacity and better sealing capabilities.

Operational Principle

Regardless of type, all butterfly valves operate based on the same core principle: the disc rotates 90 degrees to either open up flow or close to create a seal against the seat.

Applications

Butterfly valves are mainly utilized in commercial contexts and may be applied in systems handling:

  • Cooling water

  • Air

  • Gas

  • Fire protection systems
    They are capable of handling high-pressure and high-temperature applications, including water, steam, compressed air, and gas services.

Conclusion

This lesson provided an in-depth analysis of globe and butterfly valves, focusing on their design, operation, applications, and compliance standards. Understanding these components is essential for effective plumbing management and maintenance. Thank you for participating in this educational session through Interplay Learning.