Zwick Triple offset butterfly valves are used throughout the world in process applications where guaranteed tight shut off is required.
They are designed to provide repeatable tight shut-off and efficient throttling characteristics, particularly in high-pressure and high-temperature applications.
Unlike traditional butterfly valves, which use a disc with a centred axis of rotation, triple offset butterfly valves have a unique design that incorporates three offsets:
Shaft Offset: The shaft, on which the disc is mounted, is positioned slightly off-centre from the centre of the valve’s bore. This offset helps achieve a cam-like motion during operation, reducing the friction between the disc and the seat. As a result, it enables a tight and consistent sealing performance, even under high-pressure conditions.
Laminated Seal Ring Offset: The laminated seal ring, which is responsible for providing a sealing surface, is placed at an offset to the valve’s shaft. This offset, combined with the cam-like motion of the disc provides the second offset. Zwick’s laminated seal ring has the largest surface area of any on the market, due to its unique angle. This provides better shut off reliability in service than other brands which have less seal/seat contact area.
Conical Seat: The seat, against which the seal ring makes contact, is conical and tapered in shape. The centre of the ‘cone’ is angled to be parallel with the body on one side. This is the third offset. Zwick’s unique seat angle of 25 degrees provides the frictionless sealing that makes it so durable. There is no contact between disc seal and seat until the moment of closing. This avoids the seal ‘wedging’ into the seat like other brands, eliminating wear and reducing torque.
The combination of these three offsets in a triple offset butterfly valve provides several advantages over traditional butterfly valves. These advantages include:
Improved sealing performance: The triple offset design significantly reduces leakage, even in high-pressure and high-temperature applications. This feature makes it suitable for critical processes that require tight shut-off.
Minimal wear and longer service life: The cam-like action and frictionless action between the sealing components result in less wear and tear, extending the valve’s lifespan and reducing maintenance requirements.
Lower torque requirements: The design of the triple offset valve reduces the operating torque needed for valve actuation. This feature allows for smaller and more cost-effective actuators to be used, compared to other valve types.
