Diaphragm Valves

Diaphragm Valves in Piping Systems

Diaphragm valves are essential components in low-pressure, corrosive services, primarily serving as shutoff valves but also effective in control applications. These valves operate by moving a diaphragm up and down within the valve body, which can be either lined or unlined, depending on the fluid's corrosive properties. Certain designs even feature a plastic valve body for specialized applications.

Types of Diaphragm Valves

1. Weir Type (Saunders Type):
   The most common design, ideal for both isolation and flow control.
2. Straight-through Type:
   Designed for applications requiring minimal flow resistance.

Key Components of a Diaphragm Valve

1. Body:
   Constructed with corrosion-resistant materials such as PTFE, glass, rubber, or plastic for enhanced durability.
2. Diaphragm:
   Made from elastic materials like PTFE or rubber, ensuring a secure seal against the valve body.
3. Bonnet:
   Provides secure positioning for the diaphragm.
4. Stem:
   Facilitates diaphragm movement for valve operation.
5. Stem Bushing:
   Ensures smooth stem motion.
6. Compressor:
   Assists in diaphragm movement for effective functioning.
7. Hand Wheel:
   Manual operation for opening and closing the valve.
8. Bonnet Bolting:
   Keeps the bonnet and diaphragm securely in place.

Construction and Specifications

• Material Selection:
  The valve body and bonnet are typically cast, with materials chosen to match service conditions.
• Operating Pressure:
  These valves are generally suitable for pressures between 7-10 kg/cm². Frequent maintenance is required due to diaphragm wear.
• Connection Types:
  Flanged, threaded, or welded connections are available. Flanged ends are standard for lined valves to ensure proper sealing of the lining material.

Stem Designs

1. Indicating Type:
   The stem position visibly shows the valve's port opening.
2. Non-Indicating Type:
   The stem position does not display the valve's status.

Standards

While diaphragm valves are not governed by API or ANSI standards, they adhere to British Standards and MSS-SP specifications, ensuring reliability and quality.