Study of the Hydrodynamic Phenomena and Fluid–Structure Interactions of a Bypass Butterfly Valve with Double Disc

Abstract

Bypass system is used to balance the pressure of the fluid between upstream and downstream of the valve before the opening of the main valve in order to achieve the rated capacity. They also reduce the fluid velocity in the early stages of operation. Conventional bypass system is made of a main valve of large diameter, a secondary valve and additional piping. Based on more than 30 years in developing and manufacturing butterfly valves from 1″ up to 150″, KSB developed a new product to integrate a bypass valve within a double disc. Main advantages are reduction of piping, joints, and tightness improvement. This study concerns the mechanical and hydraulic behaviour of a bypass butterfly valve with double disc to replace the conventional bypasses. A numerical model was performed (ANSYS CFX©) to study the flow around the double butterfly valve through hydraulic pressure loss and hydrodynamic torque coefficients. With computational fluid dynamics, it is possible to predict the hydrodynamic torque versus opening angle characteristic. One of the key parameter of butterfly valves design is to master the hydrodynamic torque that has great impact on actuator size. With this new design, actuator sizing is improved by about 30 %. This model is also used to design the configurations studied in the experimental approach. The tests carried out on the test facility of CETIM concerned the measurement of static pressure upstream and downstream of the prototype and the flow rate in order to know the pressure losses. The hydrodynamic torque measurements were performed using strain gauge inserted between the actuator and the valve neck. This experimental phase was used to validate the numerical model. It will allow KSB to size new system with virtual prototype.