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First letter: Balanced (B) or Unbalanced (U). Second letter: single-face seal (S); pressure-free double seal (i.e., “series seal” as referred to in version 7) (T); or pressure-rated double seal (i.e., “double-face seal” as referred to in version 7) (D). Third letter: Type of sealing plate (i.e., sealing gland) (P = standard type, without throttle bushing; T = throttle bushing type, equipped with quenching, leakage liquid connection ports and/or drainage connection ports; A = auxiliary sealing device, the type of which must be specified). Fourth letter: Gasket (sealing ring) material (see Table 1). Fifth letter: End face material (see Table 2). For example, a seal coded as BSTFM is a balanced, single-face mechanical seal equipped with a sealing plate featuring a throttle bushing; the material of the static sealing gasket is fluororubber (FKM), the gasket between the dynamic sealing ring and the shaft sleeve is also fluororubber (FKM), and the material for the contact surfaces of the dynamic and static rings is tungsten carbide type 2C. Sealing materials other than those listed above shall be coded as X and specified clearly in the data sheet. Table 1: Fourth letter of the mechanical seal classification code. The fourth letter indicates the gasket between the static seal ring and the shaft sleeve, or the gasket between the dynamic seal ring and the shaft sleeve. E – Fluororubber; PTFE. F – Fluororubber. G – PTFE. H – Nitrile rubber. I – Perfluoroelastomer (FFKM). R – Graphite sheets. X – As specified. Z – Spiral wound gasket; graphite sheets. Table 2: Fifth letter of the mechanical seal classification code. The fifth letter indicates the material used for the end faces of the seal rings. Ring 1; Ring 2: L – Carbon/tungsten carbide-1; M – Carbon/tungsten carbide-2; N – Carbon silicon carbide; O – Tungsten carbide-2/silicon carbide; P – Silicon carbide/silicon carbide. X – As specified. Table 3: Temperature limits for mechanical seal gaskets and bellows. Gasket material, ambient temperature or pumping temperature: Minimum/Maximum °C°F°C°F. 1. PTFE – -75–100/200/400. 2. Nitrile rubber – -40–40/120/250. 3. Neoprene – -200/90/200. 4. Fluororubber – -20/0/200/400. 5. Metal bellows – a. 6. Perfluoroelastomer – -121/0/260/500. 7. Graphite sheets – -240–400/400b/750b. 8. PTFE filled with glass fibers – -212–350/230/450. 9. Mica/graphite – -240–400/700/1300. 10. Ethylene propylene – -57–70/180/350. Note: a: For the minimum and maximum ambient temperatures or pumping temperatures, please consult the manufacturer. b: For non-oxidizing atmospheres, the maximum temperature is 870°C (1600°F); consult the manufacturer. Formulas for converting Celsius temperature (°C) to Fahrenheit temperature (°F): Celsius temperature (°C) = (Fahrenheit temperature – 32) × 5/9. Fahrenheit temperature (°F) = Celsius temperature × 9/5 – 32. Note on mechanical seals: Unless otherwise specified, the spring material used in multi-spring seals must be Hastelloy C. The spring material for single-spring seals must be austenitic stainless steel (AISI standard 316 or equivalent). Other metal components must also be made of austenitic stainless steel (AISI standard 316 or equivalent materials) or other corrosion-resistant materials suitable for the operating conditions, with the exception of metal bellows; if metal bellows are used, their material must be recommended by the sealing manufacturer based on the operating conditions. The corrosion rate of metal bellows should be less than 50 μm (2 mils) per year. Unless otherwise specified, the sealing between the seal plate (i.e., seal gland) and the seal chamber shall be achieved using fluororubber O-rings, which are suitable for use at temperatures below 150°C. If the temperature exceeds 150°C or as specified, an austenitic stainless steel spiral gasket filled with graphite must be used. This spiral gasket must be able to withstand the full temperature of the pumped liquid (i.e., without any cooling measures). Metal sealing rings should not use spray-coated coatings as a substitute for an integrated sealing surface. If the pumping temperature exceeds 175°C, the pump manufacturer and the seal manufacturer should consult together to use a cooling flush fluid for the seal face, or to employ a cooling water chamber with continuous flow in the sealed chamber that is not open at one end. The temperature limits for mechanical seal gaskets (seals) shall comply with the provisions in Table 3.