API - Leser

Accessories and OptionsBalanced bellows – Subassembly item 15LESER is able to provide a balanced bellows design throughthe use of stainless steel bellows.A BBalanced bellows are generally used for two applications:- to compensate for back pressure- to seal off the bonnet from the outlet chamberCompensation for back pressureThe back pressure acts on the reverse side of the disc, creating a forcein the closing direction (F c ) of the safety valve. The magnitude of this forcedepends on the seat area and the level of the back pressure. The balancedbellows constitute an opposite area with the same area like the seat. Theback pressure acts on, thereby reducing or eliminating the closing force. Thisreduction of the force in the closing direction can be viewed as a compensatingforce acting in the opening directon (F o ).p aA SF OF CA quantitative representation is shown in the table below:Actual area Back pressure Actual force Direction of force Compensation criteriaSeat area = A S p a F C = p a x A S closing A S = A BBellows area = A B p a F O = p a x A B opening F C = F OSealing the bonnet from the outlet chamberLESER‘s balanced bellows reliably seal the bonnet from the outlet chamber; protecting the guide,moving parts and the spring from problems associated with the fluid, such as dirt, corrosion, impurities of temperature.Operating conditionsOptionsTemperature limits [°C] up to 550 °C[°F] up to 1000 °FMinimum set pressure Orifice Steam /Air Water[bar] [psig] [bar] [psig]D 3,5 50,8 3,5 50,8E 3,5 50,8 3,5 50,8F 0,6 8,7 2,0 29G 3,2 46,4 2,8 40,6H 2,8 40,6 2,8 40,6J 3,5 50,8 5,0 72,5K 2,2 31,9 2,5 36,3L 3,5 50,8 3,5 50,8M 2,6 37,7 2,2 31,9N 1,8 26,1 1,8 26,1P 2,2 31,9 2,2 31,9Q 1,3 18,8 2,3 33,5R 1,0 14,5 1,4 20,3T 1,2 17,4 2,5 36,399/12 LWN 480.01-E