Operators of plastic butterfly valves can control the flow of a fluid or gas by pulling a lever that opens or closes the valve. In the open position, the round disc sits perpendicular to the seal around the pipe. When the lever is pulled or rotated, however, the disc rotates around so that it fits snugly into the seal and blocks all flow. In other words, the disc has two positions, either parallel or perpendicular to the flow of water.
Butterfly valve manufacturers have created plastic valves in particular for their low product cost and flexibility. Other common materials include aluminum, for its light and flexible nature, which makes it a perfect gasket, and stainless steel for its strength and corrosion resistance. Plastic butterfly valves may be cheaper, but they are not as popular as their metal counterparts, mostly because of vulnerability to chemical corrosion. A breakdown of the valve means leaks and damage, so there are companies who do not take the risk.
Other factors besides the basic material separates one butterfly valve from another, and most of these differences can be incorporated into a plastic design as well as a metal. If the piping system is going to consist of very high pressures, then a high performance valve is used, as a pneumatic one is employed in very low pressure systems.
For companies that require the ultimate sealant guarantee, the triple offset butterfly valve should alleviate their fears. This valve is arranged in such a way that it can be turned three different positions and still contain a leak, while also allowing a safeguard against emergency shut off.
The pressure of the system, the fluids flowing through it and the variety of uses the butterfly valve must serve are all considerations a consumer must ponder before purchasing one of a thermoplastic nature or metal. Because of the advances in machining, the parts for butterfly valves as well as other tools can be precise as long as the consumer knows exactly what they need.