Mercuroid switch

Compressors are also served by high-liquid-level trips in their upstream knockout drums. These high-liquid-level trips work in the same way as the low-level boiler trips discussed above, except that the mercuroid switch is activated by a rising, rather than a falling, liquid level so as to protect the compressor from a slug of liquid. 

Designate on your flowsheet the indicators that are displayed on the control panel also show which valves are controlled from the control board. Mark all the level alarms on your flowsheet. Find the mercuroid switches or level float pots outside that activate the inside level alarms. These are located on the process vessels. With a crayon, indicate their functions. 

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