what the difference between the displacer switch using mercury switch to actuate the pump or control loop and the float switch the float follow the level? what i know is that the float is motion balance principle to move up and down with the level and displacer use force balance principle

What considerations should i take when i want to select between these two for oil/water seperator or three phase seperator?

 

dear,
u yourself have specified that the float follows liquid level. them how come that it will follow an interface? it will always float on the lighter liquid level!!

that is why, for interface level measurement displacer is the only choice bewteen the two (i.e.float & displacer).

usually float is connected to a rod (light enough)which has a ss410 ( or similar) attractor piece, moving up & down within an austentic ss304/316 (usually!) sleevel enclosure. because float follows liquid level, it takes up the whole assemply of the float+rod+attractor piece and even minor level changes may come within an stronger magnet (differential will bemore in that case!) & it better responses to level rise/fall of liquid, than a displacer type. but at the same time, when it approached the set level, the microswitch may start chattering if there be ripples.

There is also float level switches where the floatmoves up & down between two stoppers. if the liquid conatains fine particles, the float hole may clog hampering smooth movement of the float.

hence displacer is an obvious choice in following cases:
(1) interface level switching;
(2) turbulent service;
(3) liquid contains particles.

if you have any further queries, u may email to [email protected]. but to answer u will remain my option.