Weir Type Diaphragm Valve

Valves / Diaphragm Valve

A weir type diaphragm valve features a raised weir (saddle) in the body that the flexible diaphragm presses against to shut off flow, providing a short-stroke, low-stress sealing design ideal for corrosive, abrasive, and sanitary applications where the diaphragm isolates all wetted parts from the operating mechanism.

Working Principle

The valve body has a raised weir (saddle) across the flow passage. A flexible diaphragm (elastomer or PTFE) is clamped between the body and the bonnet. When the handwheel is turned, the compressor (a disc attached to the stem) pushes the diaphragm down onto the weir, compressing it against the raised saddle to shut off flow. The short stroke (the diaphragm only needs to travel from the open position down to the weir surface) means low diaphragm flexing and long diaphragm life. The diaphragm completely isolates the fluid from the bonnet, stem, and compressor — there is no packing to leak and no wetted moving parts other than the diaphragm itself. This makes weir type diaphragm valves the standard for corrosive, toxic, and high-purity applications.

Key Components

Body (with integral weir), diaphragm, bonnet, compressor, stem, handwheel or actuator.

Types & Variants

Type	Key Feature	Typical Use
Standard weir diaphragm	Cast body, elastomer diaphragm	Chemical processing, water treatment
PTFE-lined weir	PTFE liner + PTFE diaphragm	Strong acids, halogens
Sanitary weir	Polished 316L body, FDA diaphragm	Pharmaceutical, food & beverage
Plastic weir	PVC/CPVC/PP body	Low-cost corrosive service

Common Materials

Body: ASTM A351 CF8M (316SS) for corrosive/sanitary, ductile iron with rubber/PTFE lining for economy, PVC/CPVC/PP for low-cost chemical. Diaphragm: EPDM, NBR, Viton, or PTFE (with elastomer backing). Compressor: 316SS or coated ductile iron. Bonnet: ductile iron or 316SS.

Applicable Standards

ISO 5208 (industrial valves pressure testing)
ASME B16.34 (pressure ratings, reference)
FDA 21 CFR 177 (diaphragm material compliance)
USP Class VI (pharmaceutical diaphragm testing)
3-A Sanitary Standards (food and dairy)

Industrial Applications

Chemical manufacturing (acids, bases, solvents)
Pharmaceutical and biotech processing
Food and beverage production
Water and wastewater treatment
Semiconductor ultra-pure chemical handling
Mining and mineral processing (abrasive slurries)

Advantages & Disadvantages

Advantages

Complete fluid isolation from operating mechanism — zero emissions
No packing to leak or maintain
Short diaphragm stroke extends diaphragm life
Available in materials for virtually any corrosive service
Sanitary designs available for pharma and food

Disadvantages

Diaphragm is a wearing part — requires periodic replacement
Pressure limited to about 10-16 bar (diaphragm strength limits)
Temperature limited by diaphragm material (PTFE: ~180°C, elastomers: ~150°C)
Not suitable for high-pressure gas service (diaphragm can lift off weir)
PTFE diaphragms are stiffer and require higher operating torque

Selection Guide

For corrosive service, PTFE-lined bodies with PTFE diaphragms provide the best chemical resistance
For sanitary applications, specify 316L electro-polished bodies with FDA/USP Class VI certified diaphragms
EPDM diaphragms are standard for water and mild chemicals; Viton for hydrocarbons; PTFE for strong acids and halogens
Diaphragm life depends on stroke frequency, temperature, and pressure — schedule replacement before failure, not after
For abrasive slurries, weir type is preferred over straight type because the short stroke reduces diaphragm flexing

Practical Tips

Diaphragm failure is sudden and complete — when the diaphragm ruptures, the fluid pathway to the bonnet is open. Install a weep hole or leak detector on the bonnet to catch early failure before process fluid escapes
PTFE diaphragms typically last 2-5x longer than elastomer diaphragms in corrosive service, but they require higher torque and do not seal as tightly on low-pressure applications

FAQ

Weir type vs straight type diaphragm valve?

Weir type has a raised saddle in the body and a short diaphragm stroke, giving longer diaphragm life and lower torque. Straight type has no weir and the diaphragm must flex the full bore diameter, giving higher pressure drop but better flow characteristics for slurries. Weir type is the standard for most applications.

How often should a diaphragm be replaced?

There is no fixed interval — it depends on the service. In clean water at room temperature, diaphragms can last 5-10 years. In hot corrosive service with frequent cycling, they may need replacement every 6-12 months. Establish a replacement schedule based on the specific service conditions and inspect periodically.