Resilient valves are those with one or both sealing surfaces made of plastic or rubber. Table 1 shows what is acceptable in API 598. Acceptable leakage rates from valvesīoth standards accept some leakage from certain styles of valve. Two widely used leakage standards are API 598 (American Petroleum Institute) and BS 6755 (British Standard). The completely assembled valve is also required to pass leakage tests. Valves are constructed to manufacturing standards that specify performance requirements for the materials used in the valve. Figure 1 shows a variety of valve and seat sealing arrangements. In the case of manual and actuated valves, a stem sticks out of the body and has to be sealed to prevent leakage. The essence of valve operation is closing or opening a gap by moving one surface against another. Regulating valves meter the flow through the body. Isolation valves seal the fluid off on one side of the valve. The purpose of a valve is for isolation or regulation. Keywords: bubble tight, design pressure, leakage rate, fire rated, differential pressure. Consideration must be given to the nature of the process chemical, the quality of sealing and the impact of outside environmental occurrences. Valve used for isolation duties must provide secure, tight shut-off. Valves can be used to both isolate and regulate liquid and gas flow. Root Cause Analysis and the 8D Corrective Action Process course.An Introduction to Reliability Engineering.Reliability Analysis Methods online course.14 Ways to Acquire Reliability Engineering Knowledge.Reliability Engineering Management DRAFT.Innovative Thinking in Reliability and Durability.Equipment Risk and Reliability in Downhole Applications.Musings on Reliability and Maintenance Topics.Metals Engineering and Product Reliability.Product Development and Process Improvement.Rooted in Reliability: The Plant Performance Podcast.