b'FLOATING BALL VALVES - SLFSBV01 & SLBV01 SERIESCHARACTER LINES FOR SPRING STACKS WITH SPRINGSOF THE SAME SIZE ARRANGED IN DIFFERENT ORDERN(125) 500(100) 400Force F(75) 300(50) 200(25) 100(lbf) 0 0 0.4 0.8 1.2 mm 1.6.2(1) (2) (3) (4) (5)(in x 10)Deflectionsa) Single disc b) Two discs stacked in parallel (double force at same deflection) c) Spring column with three* single springs stacked in series (triple deflection) d) Spring column with three* parallel pairs arranged in series (double force, triple deflection)* Used in very high pressures or severe service.Unless otherwise specified, 2 springs in series is used for live loaded stem seal arrangements. The springs have been designed and sized to provide the packing load required when the springs area compressed, and the series arrangement provides sufficient spring travel to ensure that a suitable compressive force remains applied as the stem seals wear, or compress. Manual lever operated valves fitted with direct mount pads are supplied with 2 Belleville springs mounted in series, to provide superior stem sealing for critical service applications and lower maintenance. The other reason is, valves fitted with direct mount pads are often utilised for direct mounting of actuators and as accessing the stem packing would require actuator removal, a live loaded packing system avoids or reduces maintenance (however, open brackets can be fitted allowing room to adjust packing). For very large sizes in higher pressure classes we often use 4 springs in series.Adding more springs in series is generally not required (a longer stroke is not needed), as in smaller sizes & lower pressure classes APV use quality 301 grade heavy gauge Bellevillesprings so even if using a direct mount actuator the 2 spring series usually requires none or very infrequent adjustment.Australian Pipeline Valve - Installation, Operation and Maintenance Manual 17'