There are many types of valves used to isolate process flow. Each valve type has its own ability when it is fully closed and in isolation mode. The degree of tightness varies with valve type, make, media, differential pressure, temperature, and time in service. Some valve types or special preparations have unequal isolating abilities depending on the flow direction while isolating.

Understanding how valves isolate, especially with challenging applications, can help one choose the appropriate valve technology. All isolation valves are bidirectional, that is, they can seal from either flow direction. However, bidirectionality can add some isolation wrinkles and thus needs further explanation.

Many valves cannot isolate equally from either direction. Think of a car; it can go backward and forwards, just not equally well. Isolation ability, the ‘tightness’ of the closure, is a misunderstood subject in the valve industry. It has been made more complicated due to the valve’s ability to handle bidirectional flow at…