China Tricentric Butterfly Valve Factory & Exporter

While double-offset valves offset the shaft along the axis of flow (Offset 1) and laterally from the pipe centerline (Offset 2), their sealing geometry remains circular, meaning the disc edge rubs against the seat during the final 10° to 15° of closure. This rubbing contact causes elastomeric or polymer seat wear over repetitive cycles.

A Tricentric (triple offset) valve introduces an angular third offset: the conical seat axis is tilted away from the pipe axis. This geometric orientation creates an elliptical cone sealing interface. Sealing is achieved purely by mechanical wedging torque at 0° shutoff rather than rotational interference, eliminating rubbing across 100% of the travel arc. This allows the use of hard, resilient metal-to-metal seating materials that handle abrasive, high-pressure, and high-temperature service without galling.

Yes, ZFA engineered triple offset butterfly valves deliver true bi-directional bubble-tight shutoff compliant with API 598 Rate A in both flow directions. However, the physical mechanics differ depending on flow orientation:

Shaft Downstream (Preferred Direction): Pipeline pressure acts directly on the back of the disc, naturally pushing the disc seal ring tighter into the body seat cone. This creates a pressure-assisted seal, reducing required seating actuator torque.

Shaft Upstream (Reverse Direction): Process pressure acts to lift the disc away from the seat. To maintain zero leakage, the actuator must provide sufficient torque to overcome line pressure. Our engineering datasheets provide precise "Reverse Delta-P Torque Curves" to ensure electric or pneumatic actuators are sized with appropriate safety margins (typically 25% to 35%).

Laminated Seal Ring (SS316 + Flexible Graphite): Consists of alternating laminations of stainless steel sheets and high-purity graphite. The graphite provides microscopic resilience to fill irregularities in the seat face, providing zero bubble leakage at lower actuator torques. Ideal for temperatures from -50°C to +450°C in clean hydrocarbons, steam, and water.

Solid Metal Seal Ring: Built entirely from solid hardened alloys (e.g., Inconel 718, Monel, or solid Stellite). While requiring higher seating torque, solid metal seats are mandatory for abrasive media containing catalyst fines, slurry lines, high-velocity throttling, and ultra-high temperatures up to +815°C where graphite would oxidize or wash out.

Quality begins with base casting integrity. Castings undergo positive material identification (PMI), chemical ladle analysis, and non-destructive examination (RT/UT). For cryogenic service down to -196°C, valves feature an extended column bonnet to keep the packing warm, pass liquid nitrogen (-196°C) cryogenic seat leak testing per BS 6364, and receive Charpy V-notch impact testing on austenitic grades.

For high-temperature service, thermal elongation calculations guide shaft-to-bearing clearance machining, utilizing cobalt-based Stellite sleeve bearings and self-lubricating high-temperature graphite bushings to prevent seizing under extreme thermal expansion.

Yes. Tricentric valves can be installed in vertical, horizontal, or inclined pipelines. However, in lines carrying slurries, solids, or steam condensate, we strongly advise installing the shaft horizontally so that opening the lower portion of the disc sweeps pipeline debris away from the bottom shaft bearing cavity, preventing particulate accumulation.