Choosing the Ideal Diaphragm Valve for Performance and Longevity

A diaphragm valve is a vital component in the processing industry, designed specifically to manage the flow of both gases and liquids. The selection of an appropriate diaphragm valve tailored to your application is essential not only for optimal performance but also for extending its lifespan.

Link to LEFLOW

What is a diaphragm valve and its operational mechanism?

The operation of a diaphragm valve involves a flexible diaphragm that moves against a "lug" located within the valve body. This movement can be initiated via mechanical means using a handwheel or through pneumatic or electrical means. For the pneumatic options, there are three variants: spring closing, spring opening, or double-acting. The spring closing option is typically employed for a "fail-safe close" mechanism, while spring opening allows for a "fail-safe open" feature, ensuring that the valve self-closes or opens in situations where there is a loss of electricity or air pressure.

Globe Valve Vs Diaphragm Valve

Figure 1: A comparison between globe valves (left) and diaphragm valves (right), both crucial in industrial environments.

Globe valves and diaphragm valves play an essential role in managing fluid flow across a range of industrial applications. Although they operate under different designs and mechanisms, they can sometimes fulfill similar functions. Understanding the fundamental workings of each valve type is paramount for selecting the most suitable valve for specific applications.

Table of contents

Globe valves

Globe valves are chosen for their exceptional precision and control capabilities. The primary elements of a globe valve include a movable disk (or plug) and a stationary ring valve seat inside a roughly spherical body. The disk's motion is perpendicular to the seat, generating a variable opening that regulates the flow through the valve. Adjusting the handle or actuator causes the disk to move closer to or further from the seat, thus modifying the flow rate dynamically. This design enables precise control over fluid flow, making globe valves optimal for applications where regular flow adjustments are necessary. Common applications for globe valves include:

• Water flow regulation
• Steam service operations
• Cooling system management
• Fuel oil distribution
• Gasoline and oil systems
• Chemical injection processes
• Condenser air extraction tasks
• Boiler vent and drainage operations

Figure 2: Depiction of an open globe valve (left) versus a closed globe valve (right), highlighting components such as the stem (A), bonnet (B), plug (C), and body (D).

For further insights regarding Knife Gate Valve, reach out to us today for expert advice!

Diaphragm valves

Diaphragm valves are favored for their superior sealing and compatibility features. They control flow by raising or lowering a flexible diaphragm to either open or close the flow path. Typically, the valve body holds a weir or saddle, which the diaphragm sits upon. When the valve is in the closed position, the diaphragm presses against the weir, effectively sealing the valve and halting fluid movement. As the valve transitions to the open position, the diaphragm lifts, permitting fluid to flow through. This configuration ensures an effective seal and keeps the fluid isolated from the mechanical components of the valve, making diaphragm valves suitable for applications involving corrosive substances or slurries. The diaphragm's material can be customized according to the fluid's characteristics, enhancing compatibility across various media. Typical applications for diaphragm valves include:

• Water treatment facilities
• Chemical production sectors
• Food and beverage processing
• Pharmaceutical manufacturing
• Mining industry operations
• Pulp and paper processing
• Biotechnology uses

Figure 3: Components of a diaphragm valve are illustrated, including the handle (A), stem (B), compressor (C), diaphragm (D), bonnet (E), and valve body (F).

Choosing Between Diaphragm and Globe Valves

• Media compatibility
  • Diaphragm valve: Ideal for handling corrosive fluids, slurries, and thick materials. The material of the diaphragm (e.g., EPDM, PTFE, NBR) should be compatible with the media to prevent degradation.
  • Globe valve: Suitable for gases and liquids, including steam. Careful selection of materials for the valve body and seals (e.g., stainless steel, bronze, PTFE) is essential for compatibility.
• Temperature ratings
  • Diaphragm valve: Usually rated for temperatures ranging from -60°C to 200°C (-76°F to 392°F), depending on diaphragm material. PTFE diaphragms can withstand higher temperatures, while EPDM is suited for lower temperatures.
  • Globe valve: Typically rated for temperature ranges from -196°C (-320°F) to 600°C ( °F), making them appropriate for high-temperature applications. Specific ratings depend on the materials used in the body and trim.
• Pressure ratings
  • Diaphragm valve: Generally effective for lower pressure applications, up to around 16 bar (232 psi). The flexibility of the diaphragm restricts its capacity to manage high pressures.
  • Globe valve: Built to handle significant pressure drops, with capabilities reaching up to 400 bar ( psi). Their design facilitates improved control even under high-pressure situations.
• Flow control and regulation
  • Diaphragm valve: Excellent for on/off and throttling capabilities, especially useful for fluids that are corrosive or contain particulates. Nevertheless, they may not provide the same level of precision as globe valves.
  • Globe valve: Particularly well-suited for detailed flow control and regulation due to the linear movement of the valve stem combined with the configuration of the valve seat and disk.
• Maintenance and longevity
  • Diaphragm valve: The diaphragm functions as both a seal and a moving element, minimizing potential leak paths but necessitating replacement over time due to wear and tear.
  • Globe valve: Contains more mechanical components (such as stem, disc, and seat) that may experience wear, but they can generally be repaired or replaced with relative ease. They typically enjoy a longer lifespan in high-cycle applications. Discover more in our globe valve maintenance discussion.
• Cost considerations
  • Diaphragm valve: Often have lower initial costs, but cumulative expenses for replacement diaphragms throughout the valve's lifecycle can add up.
  • Globe valve: May demand a higher upfront investment yet can be more economical overall due to their durability and ease of repair.
• Application specifics
  • Diaphragm valve: Perfect for sterile or clean settings, especially in the food and beverage or pharmaceutical sectors.
  • Globe valve: Preferable for applications that require exact flow regulation, as seen in HVAC systems, steam distribution, and numerous process industries.

Frequently Asked Questions

What distinguishes a globe valve from a diaphragm valve?

The primary distinction lies in their operational methods; globe valves utilize a disk to interrupt flow, while diaphragm valves rely on a flexible diaphragm.

What is the operational mechanism of a globe valve?

A globe valve regulates flow by moving a disk into or away from the valve seat, thereby adjusting the size of the flow passage.

What components make up a diaphragm valve?

The main parts include the body, bonnet, diaphragm, stem, and the handwheel or actuator.

When should a diaphragm valve be preferred over a globe valve?

Opt for a diaphragm valve in scenarios that necessitate tight closures, handling corrosive fluids, or where contamination must be avoided.