We are developing an Automatic Top-Up Unit (ATU) for an API Plan 53B seal support system. In this case, there are two separate Plan 53B systems (DE & NDE), both requiring top-up from a single ATU equipped with a single air-operated liquid pump (AOLP). However, these two systems operate at different pressures—one at 13 barg and the other at 18 barg.
Our proposed operation is as follows:
When the pressure transmitter in either Plan 53B detects a low-pressure alarm, the Distributed Control System (DCS) will send a feedback signal to the ATU, activating the solenoid valve to start the AOLP and initiate refilling. Once the system reaches the desired operating pressure, the pressure transmitter will trigger a high-pressure alarm, prompting the DCS to close the solenoid valve and stop the refilling process.
The challenge we are facing is that both Plan 53B systems have different pressure setpoints, but we are using a single solenoid valve to control the AOLP. We need to determine whether it is possible to provide two separate signals from the DCS to a single solenoid valve and how the ATU can differentiate which Plan 53B system requires refilling
