It must be less than the tank's pressure capability, and also should allow some dead-band below the tank vent operating pressure to avoid interaction. Figure 2 illustrates a tank blanketed to 0.5 inch w.c. A pressure of 0.25 inch w.c. There is a dead-band of 2.1 inches w.c. The presence of an adequate dead-band will ensure stable operation and avoid unnecessary loss of blanketing gas or product going out an open tank vent.
Proper sizing is important for stable operation.
Under-sizing can result in tank pressures dropping well below the setpoint as the main flow control valve struggles to keep up with demand. Over-sizing is less critical. However, taken to an extreme, it can result in unstable operation due to exceeding setpoint. Blanket Summary A gas blanketing system will effectively contain gases within the vapor space of a tank. Such a system can contain the gas, or protect the tank contents form contact with atmospheric air.