Butterfly Valves

Wafer: Sandwiched between two pipe flanges using through-bolts. Cheapest, lightest, but one side must stay bolted for maintenance. Best for non-critical, dead-end not needed.
Lug: Has threaded inserts (lugs) with independent bolts. One side can be disconnected while the valve stays sealed against the other flange –ideal for dead-end service, tanks, equipment isolation.
Flanged (double-flanged): Has its own integral flanges matching pipe flanges. Strongest, supports pipe loads, best for large sizes (DN300+), buried service, and high-vibration applications.

EPDM: Best all-round for water, air, and weak chemicals up to +120°C. Most common choice.
NBR (Buna-N): Good for oils, fuels, petroleum products, aliphatic hydrocarbons. Avoid with aromatic solvents and strong oxidizers.
Viton/FKM: Excellent for acids, aromatics, and high temperatures up to +200°C. Costlier but essential for chemical processing.
PTFE: Near-universal chemical resistance. Used for corrosive acids/bases. Lower temperature limit than rubber (cold-flow concern below 0°C).
Metal seat (SS316/Inconel/Stellite): Required for steam above +180°C, high-pressure gas, and services with abrasive particles that would embed in rubber seats.

Yes –within limits. Concentric rubber-lined valves modulate reasonably well in the 20°–70° open range and are commonly used for balancing in HVAC systems. However, for precise control or high ΔP service, double-offset or triple-offset valves with characterized discs give much better linearity, less torque variation, and longer seat life under cycling conditions.

Double-offset (High-Performance): The shaft is offset behind the disc centerline and also offset from the body centerline. This causes the disc to swing away from the seat immediately upon opening, reducing friction and wear. Good for higher pressure/temperature than concentric, up to ~+230°C.
Triple-offset: Adds a geometric conical seat shape as a third offset. The metal-seated disc contacts the seat only at the fully closed position with zero rubbing during opening/closing cycle. Enables metal-to-metal ISO 5208 Rate B shutoff in steam and high-temperature gas service up to +550°C, replacing gate and globe valves at a fraction of the weight and cost.

The actuator torque must exceed the valve's breakaway (opening) torque plus a safety factor of 1.3–1.5×. Key factors: valve size (larger = more torque), pressure differential (higher ΔP = more torque), seat material (rubber has more friction than metal), and whether it's spring-return (spring force adds to required torque). Send us your valve model, size, pressure rating, and fail-position preference –we'll specify the correct actuator package pre-mounted and tested.

Rubber-lined concentric valves are nearly maintenance-free for 10–15 years in clean water service. Periodic checks: inspect seat for wear/cracks, check disc/stem for corrosion, verify actuator torque. Lug and flanged types allow in-line seat replacement. For offset valves: check seals, re-torque body bolts if needed, and lubricate the gearbox (if equipped) annually. In dirty/slurry service, plan more frequent inspections.