Triple Offset Butterfly Valves
Triple offset butterfly valves are mechanisms that control the flow of fluids in pipes while being eccentric in three places. Butterfly valves consist of a seal around the wall of a pipe, a round or elliptical disc and a control lever. These valves are quarter turn valves meaning that the control lever must only be rotated 90° in order to close off the pipe.
Triple offset butterfly valves may be made of stainless steel, cast iron, plastic and other materials. The diameter of these valves range from a few inches to a few feet because they are used in a variety of situations. There are different kinds of butterfly valves that have been modified for different fluids, pressures and usages.
Triple offset valves are generally used in high pressure environments because the disc is a conical cross section; it is elliptical and positioned slightly differently within the pipe. It provides a tight seal while experiencing less wear. These valves also do not use a rubber seal like other butterfly valves do, which means that the seal makes metal-to-metal contact.
Butterfly valves can be classified as hydraulic valves and are used in water distribution, chemical services, ventilation applications and other situations involving a liquid or gas where fast pipe shutoff is beneficial or necessary. High performance butterfly valves are typically double offset, a similar design to the triple offset butterfly valve.
A triple offset butterfly valve is closed when the disc is upright in the seat, the actual place where the valve creates a seal. The control lever is connected to the valve through the outer enclosure so when the lever rotates, the disc or vane does too. The disc’s outer perimeter is machined to form an elliptical.
The disc is not centered in the pipe as other butterfly valves are designed to be; instead, it is slightly off-center and is made to have three offsets, or non-centered positions, that allow different rates of flow for the gas or liquid that is flowing through the pipes. The first offset is that the stem, which connects the disc to the rest of the valve, is not centered vertically.
The disc is not flat but has sides that slope to a rounded point so the disc appears off-balance. The second offset is that it is not centered vertically within the thickness from the flat side of the disc to the rounded tip. The third offset is related to the engagement angle when the disc moves on its diagonal axis. Triple offset butterfly valves generally have a lower maximum capacity than flat disc valves that are centered.