Ingolf's insight: Floating ball valves are more than just floating ball valves: Part 2

摘要

Norwegian consultant and valve instructor, Ingolf Fra Holmslet continues his bimonthly series of informative articles. When floating seats are used in a floating ball valve, they can be one of two basic designs. They can either be self-relief seats, as illustrated in Figure 5, or double piston seats, as illustrated in Figure 6. Regardless of which solution is used, the main seal of the valve will be its downstream seat, just as in fixed seat valves. The difference between the valves illustrated in Figures 5 and 6 consists of the way in which the upstream seat works. The seats in both solutions are spring-loaded and seal as upstream seats when the valve cavity is depressurized. Thus, both valves can achieve double sealing in the direction of the pressure (double barrier). The fact that the seats in Figure 5 are self-relief means that the pressure inside the cavity forces the upstream seat away from the ball if the system is depressurized on the upstream side of the valve. There will always be some pressure left in the cavity; the amount of that pressure depends on the springs' resistance.