Butterfly Valve Temperature & Pressure Ratings Explained
Pressure and temperature ratings are the two most critical specifications when selecting a butterfly valve. This guide explains how they work together and what the numbers mean.
Understanding Pressure Ratings: PN vs Class
Butterfly valves are rated using two main systems. The PN (Pressure Nominale) system is used in European and Australian standards (EN/AS), where the number represents the maximum allowable pressure in bar at 20°C. Common ratings include PN6, PN10, PN16, and PN25. The ANSI Class system is used in American standards, where Class 150 corresponds roughly to PN20 and Class 300 to PN50. TTV valves are available in both rating systems to suit Australian and international pipeline specifications.
How Temperature Affects Pressure Capacity
As temperature increases, the allowable working pressure decreases. A valve rated PN16 at 20°C may only be suitable for PN10 service at elevated temperatures, depending on body material and seat type. Metal-seated valves maintain higher pressure ratings at elevated temperatures compared to elastomer-seated designs. Always consult the manufacturer's pressure-temperature chart for the specific valve model and material combination.
DN Sizing: What the Numbers Mean
DN (Diamètre Nominal) is the metric designation for valve size, corresponding to the approximate bore diameter in millimetres. DN50 is roughly 2 inches, DN100 is 4 inches, DN300 is 12 inches, and so on. TTV butterfly valves range from DN32 (1¼ inches) up to DN3000 (120 inches) in the concentric soft-seated range, making them suitable for everything from small process lines to large trunk mains.
Seat Material Impact on Ratings
The seat material significantly affects the operating temperature range. EPDM seats handle -40°C to 120°C and are ideal for water service. NBR suits oil-based media from -20°C to 80°C. PTFE extends the range to -25°C to 200°C with excellent chemical resistance. Metal-to-metal seats push the envelope to 850°C for high-temperature applications like flue gas and steam. Selecting the right seat material is as important as selecting the right pressure rating.
Testing Standards: ISO 5208 and API 598
All TTV butterfly valves are hydrostatically tested according to ISO 5208 before leaving the factory. This standard defines test pressures and acceptable leakage rates for different tightness classes. API 598 testing provides an additional benchmark, with TTV concentric valves achieving zero leakage to API 598. These tests ensure every valve meets its rated pressure and tightness specifications before installation.