Various valves are designed and used for multiple roles in process control. Linear and quarter-turn valves are two types of valves used to regulate and control fluid flow in the industry. Their design and construction reflect the intended use of the valves, with each suited to a different class of service.
All valves work by controlling the position of an internal structure that obstructs fluid passage to some extent. In general, fluid flow at the valve classifies as unrestricted (valve fully open), stopped (valve fully closed), or throttled (valve partially open). The operational requirements of the process will determine whether only two of those conditions (fully open and fully closed) or all three are required. When choosing an appropriate valve, the fluid, the process, and the surrounding environment must be considered. It is not always a simple task.
Linear valves distinguish themselves using straight-line motion to position the valve plug, disc, diaphragm, or other flow controlling elements. The linear valve trim's shape, size, and arrangement provide the operator with a flow range through the valve. The linear valve's positioning allows it to regulate fluid flow slower but more accurately. Linear motion valves include gate and fixed cone valves—linear valves best suit flow control.
Quarter turn valves move from fully open to closed by rotating a shaft connected to the controlling element 90 degrees. Their relatively simple operation allows for a rugged and compact design. The ability of quarter-turn valves to quickly reposition from open to closed positions is one of their distinguishing features. The torque required to operate the valves is typically low to moderate. Quarter turn valves include ball and butterfly valves.
Depending on the situation, linear valves and quarter-turn valves are the best choices for specific process environments. The linear valve's accuracy and ability to move in a linear fashion rather than a quarter-turn come with easy maintenance and a lower likelihood of cavitation. Both valve types are widely used and are not competing for the same application. Each excels in a specific set of applications.
