LOOK-BACK
The IntelliSwitch switches from one bank to the other based upon the pressure supplied to the selected bank. When the volume of the liquid in the cylinder becomes low or the gas flow becomes particularly high, it is not uncommon for the pressure to drop below the switching point even if there is plenty of gas left in the cylinder.
When a typical switchover enters such a state, two undesirable situations may occur. First, the system may switch to the reserve temporarily until pressure builds on the primary enough to cause the system to switch back. This situation often leads to depleting both sides at the same time as the system rapidly alternates drawing from both sides or even draws both sides at the same time. Second, the system may permanently switch to the reserve leaving unused product in the primary and triggering a false alarm.
To avoid either of these situations, the IntelliSwitch has a Look-Back feature that allows the system to switch banks and wait 30 minutes before checking the former primary cylinder to allow it to build up more pressure. Once the pressure has recovered enough, the system will switch back to the former primary cylinder. Again, when the primary gets low it starts drawing from the secondary bank and looks back 30 minutes later. When the primary cannot stay active for more than 10 minutes, it then officially switches to the secondary bank and the local and master alarms are activated. This look-back time allows the pressure building circuit to recover and build sufficient pressure to supply the system and fully draw down the primary cylinder before an alarm is triggered indicating the cylinder is empty, allowing maximum utilization of cylinder contents.
ECONOMIZER FUNCTION
When using liquid cylinders in switchover application, it is common for the reserve cylinder to build pressure due to the vaporization of liquid within the cylinder. When this pressure reaches the set point of the relief valve on the liquid cylinder, the relief valve will open, venting gas to the atmosphere.
The IntelliSwitch constantly monitors the reserve cylinder and, at a predetermined pressure, will change the valving to allow gas from the headspace of the reserve cylinder to feed the system, thus drawing down the pressure in the reserve cylinder.
