4100 HLAS High Level Alarm Switch

The 4100 HLAS High Level Alarm Switch is the most reliable redundant displacer switch (warning device) used for overfill prevention. For more information on Overfill Prevention, see API 2350.

Theory of Operation

The GSI 4100 HLAS is a mechanically activated displacer switch. As the product level increases to the set point level, the displacer is either lifted by an external or internal floating roof, or gains buoyancy within the product. When the weight of the displacer is reduced, a spring lifts the rod on which the displacers are attached. The spring rod has a magnet attached to the rod, thus, when the rod lifts it moves the magnet past the reed switch to activate the status contact / alarm.

The 4100 HLAS is available in the following configurations:

• One activation point (high-high level) with one reed switch
• One activation point (high-high level) with two reed switches (redundant)
• Two activation points (high and high-high level) with one reed switch each
• Two activation points (high and high-high level) with two reed switches each (redundant)

When the HLAS is equipped with redundant reed switches, it provides both redundancy and self-checking capability.

The HLAS comes with an optional Checker Assembly that allows for the testing of the switch locally at the tank (ground level or on top) prior to an incoming transfer into the tank. The Checker Assembly is a pull cable that physically lifts the displacer independently of the spring rod. This allows for the testing of the spring and the reed switches.

Applications

• Overfill Prevention