Name: Butterfly Valve DN800 PN25 Double Flange Eccentric
Brand: Supreme Valves India
SKU: BFV-DN800-PN25-DE
Availability: InStock
Rating: 4.8 (127 reviews)

Question 1

What is a double flange (double-flanged) butterfly valve?

Accepted Answer

A double flange butterfly valve (also called a 'double-ended' or 'flangeless' valve) has flanges on both the inlet and outlet sides of the valve body, making it suitable for end-of-line installations where there is no opposing flange to hold the valve in place. Unlike wafer valves that must be sandwiched between two pipeline flanges, double flange valves are bolted directly to the end of a pipe or into a dead-end header. This design is standard for DN600 and larger sizes in water transmission and irrigation, where valves are frequently installed at the end of trunk mains, at reservoir offtakes, or in pump stations where the opposite flange may not exist.

Question 2

What does 'double eccentric' (cam-centric) mean for a butterfly valve?

Accepted Answer

A 'double eccentric' (also called cam-centric or high-performance) butterfly valve has two offset features: (1) The stem is offset from the disc centerline (first eccentricity), which causes the disc to lift clear of the seat as it opens, eliminating rubbing and wear. (2) The disc seating surface is cam-shaped (second eccentricity) — meaning the disc rotates in an arc that moves it perpendicularly away from the seat as it opens. This double offset design dramatically reduces seat wear, allows the use of softer seat materials (EPDM, NBR) while maintaining tight shut-off, and extends the valve's mechanical life to 10–20× that of a conventional concentric design. Double eccentric valves are the standard specification for water transmission mains DN300 and above.

Question 3

Why is PN25 used instead of PN16 for large butterfly valves?

Accepted Answer

PN25 (25 bar) is commonly specified for DN800 butterfly valves in large water transmission projects because: (1) Large-diameter pipes in municipal water systems often operate at higher pressures than smaller pipes due to larger pumps and higher flow demands; (2) The PN25 rating provides a safety margin for pressure surge events (water hammer) which are more significant in large-diameter mains; (3) Many specifications (particularly from Middle Eastern and North African municipal utilities) require PN25 for DN600 and above to ensure the valve can handle unexpected surge pressures without failure; (4) The PN25 body can also be rated to PN16 if used with PN16 flanges — the valve body rating is independent of the flange rating in most cases. PN25 is equivalent to approximately Class 300 in ASME terminology.

Question 4

What torque is required to operate a DN800 butterfly valve at PN25?

Accepted Answer

A DN800 (32-inch) PN25 double eccentric butterfly valve requires a breakaway torque of approximately 3,500–4,500 Nm for EPDM seats due to the high seating load required for bubble-tight shut-off at 25 bar. The running torque is approximately 2,000–2,500 Nm. This requires a gear operator with a reduction ratio of approximately 50:1 or higher. Typical gear operator specifications for DN800 PN25: maximum input torque 150–200 Nm at the handwheel (requiring approximately 5–8 turns to travel 90 degrees), with an overload clutch to prevent damage. For automated systems, an electric actuator sized at 400–600 Nm output torque is required. We size all actuators with a 1.3× safety factor per ISO 5210.

Question 5

What is the face-to-face dimension of a DN800 double flange butterfly valve?

Accepted Answer

The face-to-face dimension for a DN800 PN25 double flange butterfly valve per ISO 5752 Series 14 (long pattern) is typically 450mm. Some manufacturer designs use 480mm or 500mm depending on the body geometry. The double flange design has flanges on both ends — the inlet flange is fully threaded (lugs), and the outlet flange is also fully threaded, allowing the valve to be bolted directly to a pipe end or against a blank flange. This differs from the wafer design which has clearance holes (not threads) and requires an opposing flange to hold it in place.

Question 6

What are typical applications for DN800 PN25 double eccentric butterfly valves?

Accepted Answer

DN800 PN25 double eccentric butterfly valves are typically used in: (1) Municipal water transmission trunk mains — DN800 (32-inch) is a common size for city water supply mains from treatment plants to distribution networks, (2) Large irrigation conveyance systems — canal offtakes, reservoir outlets, and main irrigation headers, (3) Power plant cooling water — circulating water intake and discharge lines at thermal and nuclear power stations, (4) Wastewater treatment plant — influent isolation, biological reactor isolation, and effluent discharge lines, (5) Desalination plant — seawater intake and brine discharge lines. The double eccentric design ensures reliable operation with minimal maintenance over the 20–30 year design life of water infrastructure.

Component	Material Specification
Body & Bonnet	Ductile Iron (ASTM A536 / EN-GJS-400-15)
Stem / Spindle	SS 410 / SS 420
Seat / Trim	EPDM / NBR / Bronze

Parameter	Specification / Standard
Manufacturing / Design Standard	EN 1171 / AWWA C509 / BS 5163
Testing Standard	API 598 / EN 12266-1
Pressure Rating	PN16 / PN25

Butterfly Valve DN80/0 PN25

Butterfly Valve — DN800 (32") PN25 — Double Flange Eccentric

Concentric vs. Double Eccentric — Why Double Eccentric?

Concentric (Standard)

Double Eccentric (Cam-Centric) — Our Design

Materials of Construction (MOC)

Technical Specifications