Question 1

What is the difference between lug and wafer butterfly valves?

Accepted Answer

Wafer butterfly valves are held between two pipeline flanges by the flange bolts passing through unthreaded body lugs. They require two flanges to seal against both sides and cannot maintain pipeline pressure if one side is removed. Lug valves have threaded lugs that accept flange bolts directly, allowing installation between flanges with only one set of bolts, and can maintain seal with one side removed (dead-leg service). For Saudi Arabian HVAC and water treatment, lug design is preferred for isolation capability. For general on-off service where pipeline stays together, wafer design is more economical.

Question 2

What are triple offset butterfly valve advantages?

Accepted Answer

Triple offset butterfly valves (TOBV) overcome the seat wear issue of conventional designs through three geometric offsets: (1) center of disc offset from seat axis, (2) seat cone angle offset, (3) stem offset. This results in: (1) metal-to-metal seating with no rubber or PTFE wear elements, (2) bubble-tight shut-off (Class V leak rate per API 598), (3) bi-directional shut-off to full pressure rating, (4) maintenance-free seating for 25+ years, (5) suitable for high-temperature service up to 500°C with graphite seats. For Saudi Arabian oil pipeline PS3 stations and UAE ADNOC custody transfer applications, TOBV provides the reliability of a gate valve with the compactness of a butterfly valve.

Question 3

How to select butterfly valve for dead-leg service?

Accepted Answer

Dead-leg service occurs when a branch pipeline is isolated but not drained, creating a stagnant section. For dead-leg service, use lug-style butterfly valves (not wafer) so the branch can be fully isolated and the body can be depressurized. Select: (1) EPDM liner for water service (not NBR which degrades in stagnant water), (2) full bolt pattern (not tapped) for complete drainage, (3) 2-piece or 3-piece body for internal inspection access. For Riyadh building services with occasional dead-legs in riser branches, lug butterfly valves with drain plugs are specified. Always provide drain valves at dead-leg low points to prevent bacterial growth (Legionella) in GCC climate.

Question 4

What is the difference between centric and eccentric butterfly valve?

Accepted Answer

Centric (concentric) butterfly valves have the disc centered on the pipe axis, with seat located around the disc periphery. Simple and economical, suitable for general on-off service with clean media up to Class 150. Single eccentric (high-performance) offsets the stem from disc center, reducing seat friction and improving sealing at higher pressures (Class 150-600). Double eccentric adds stem offset from body centerline, enabling TOV design with better seating. Triple eccentric (see above) adds conical seat cone for metal-to-metal sealing. For Saudi Arabian oil terminal service, double or triple eccentric valves handle the high-pressure and fugitive emission requirements.

Parameter	Specification
Valve Type	Butterfly Valve
Material	WCB
Pressure Class	PN16
Design Standard	API / ASME / DIN Compliant

WCB Butterfly Valve PN16

Technical Specifications