Each flange is bolted independently to adjacent piping, eliminating the thermal expansion bolt-stretch and gasket crushing common to long through-bolts on wafer valves.

Allows full pipeline pressure retention under terminal dead-end service conditions, permitting downstream pipe dismantling for maintenance while holding full line pressure.

High-torque rack-and-pinion or heavy scotch yoke pneumatic actuators achieve 0.8-to-2.0-second full stroke speeds under standard 0.4–0.7 MPa compressed plant air.

The rigid cast ductile iron or cast steel double-flanged body resists external bending moments and ground settling loads in underground or long-span pipeline runs.

Direct-mount machining eliminates bracket deflection, ensuring precise alignment between the pneumatic drive shaft and valve stem for extended packing life.

Precision contoured disc profile minimizes turbulence and cavitation, delivering elevated Cv flow coefficients with low head loss across high-volume pumping systems.

Q1: Why are double-flanged butterfly valves preferred over wafer valves in large sizes?

Wafer valves in sizes ≥ DN300 require extremely long stud bolts spanning across the body. In plant fires or thermal excursions, long bolts expand significantly, resulting in joint decompression and hazardous external leakage. Double-flanged valves use short, independent flange bolts at each face, maintaining bolt pre-load under thermal and mechanical piping stress.

Q2: When should a Scotch Yoke actuator be selected instead of Rack & Pinion?

For valves ≥ DN350 (14 inches) or higher differential pressures, Delco equips the valve with a heavy-duty Scotch Yoke pneumatic actuator. Scotch yoke mechanisms generate an asymmetrical torque curve peaking at 0° (breakaway seating) and 90° (full open), matching the exact seating torque profile of butterfly valves and reducing actuator size and air consumption.

Q3: How does the valve perform in dead-end service?

Because each flange is bolted independently to the upstream or downstream pipeline, the downstream piping spool can be completely removed for maintenance while the valve remains securely bolted to the pressurized line, holding full bi-directional shutoff without seat extrusion.

Q4: What backup is provided for plant air failure on critical water pumping lines?

Delco configures single-acting Spring-Return (SR) actuators that automatically drive the valve to a predetermined Fail-Safe Closed (or Fail-Open) position upon pneumatic supply loss. Additionally, a sandwich-mounted declutchable manual gearbox override with handwheel allows manual operation during maintenance or power outages.