Normally, quarter-turn or rotary valves are used as EBVs. Ball and high-performance butterfly valves are frequently selected for typical process applications. For special applications, globe, plug, and gate valves are used as EBVs.
Plants and projects have a piping specification which define piping classes for each service. Each piping class lists standard block valves and provides a direct reference to a purchase order description that includes a make and model number of a recommended valve. Follow these recommendations unless there is a good reason to upgrade the EBV.
In the Corporation Piping Classification, GB-135169, only a few of the piping classifications list quarter-turn valves that can be adapted to standard actuators. Every classification includes a gate valve, and many include plug valves. To obtain a complete description of a ball or butterfly valve, either check the ERTC Piping Item Description Catalog or contact the Piping Systems engineer of ERTC’s Materials and Equipment Engineering Unit.
Piping item numbers for butterfly and ball valves found in piping classifications are listed in Figure 1300-12 for the most common process classes: E1, H1, L1, and N1. Confirm these item numbers and their corresponding descriptions with the plant’s mechanical design group. ERTC’s Quality Assurance Group keeps an up-to-date list of acceptable valve manufacturers.
High-performance butterfly valves require smaller actuators than other types of quarter-turn valves. Their disadvantages are that they:
• Block part of the fluid path.
• May cause a pressure drop in the line.
• May not have a bubble-tight shutoff unless adjusted and maintained properly.
Flangeless valves (wafer style) are not acceptable, even when metal shields are installed around the exposed bolts. Ball valves must be flanged, and butterfly valves must be lugged.
Orbit ball valves are listed as block valves in many of the classifications in the Corporation Piping Specification. These ball valves are not standard quarter-turn valves, but they can be actuated with special thrust actuators made by Orbit.
Gate valves do not accommodate on-off service readily for several reasons:
• Actuators in thrust service become extremely large and heavy and are very expensive.
• Required actuator thrust is highly dependent on the shutoff pressure drop. Increased pressure drop may prevent the valve from closing in an emergency.
• In many process services, gate valves do not maintain adequate shut-off capabilities after being in service.
• Thermal expansion may impose moment loads on the valve body and cause the valve to stick when closing.
• In the future, it may be more difficult for gate valves to pass the new, fugitive emission standards.
Electric and air motors may be used to operate gate and globe valves, but they do not have fail-safe capabilities and must be energized to work. Consequently, both types of motors must be protected against loss of utilities and fire. Consider redundant electrical power, backup nitrogen sources, reserve tanks, fireproofed electrical cables, and fireproofing on the motor actuator.