BUTTERFLY VALVES .- The butterfly valve, one type of which is shown may be used in a variety of systems aboard ship. These valves can be used effectively in lube oil, and chill water systems. The butterfly valve is light in weight, relatively small, relatively quick-acting, provides positive shut-off, and can be used for throttling.
The butterfly valve has a body, a resilient seat, a butterfly disk, a stem, packing, a notched positioning plate, and a handle. The resilient seat is under compression when it is mounted in the valve body, thus making a seal around the periphery of the disk and both upper and lower points where the stem passes through the seat. Packing is provided to form a positive seal around the stem for added protection in case the seal formed by the seat should become damaged.
To close or open a butterfly valve, turn the handle only one quarter turn to rotate the disk 90°. Some larger butterfly valves may have a hand wheel that operates through a gearing arrangement to operate the valve. This method is used especially where space limitation prevents use of a long handle.
Butterfly valves are relatively easy to maintain. The resilient seat is held in place by mechanical means, and neither bonding nor cementing is necessary. Because the seat is replaceable, the valve seat does not require lapping, grinding, or machine work.
